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 NOAA Technical Report ERL 412-PMEL 33 
 
 Circulation in the Strait of 
 Juan de Fuca: 
 
 Recent Oceanographic Observations 
 in the Eastern Basin 
 
 J. R. Holbrook, R. D. Muench, 
 D. G. Kachel, and C. Wright 
 
 April 1980 
 
 U. S. DEPARTMENT OF COMMERCE 
 
 National Oceanic and Atmospheric Administration 
 Environmental Research Laboratories 
 
NOAA Technical Report ERL 412-PMEL 33 
 
 
 ''*«*&, £^* 
 
 ,<p 
 
 Circulation in the Strait of 
 Juan de Fuca: 
 
 Recent Oceanographic Observations 
 in the Eastern Basin 
 
 J. R. Holbrook, R. D. Muench, 
 D. G. Kachel, and C. Wright 
 
 Pacific Marine Environmental Laboratory 
 Seattle, Washington 
 
 April 1980 
 
 U. S. DEPARTMENT OF COMMERCE 
 
 Philip M. Klutznick, Secretary 
 
 National Oceanic and Atmospheric Administration 
 Richard A. Frank, Administrator 
 
 Environmental Research Laboratories 
 
 Boulder, Colorado 
 Wilmot N. Hess, Director 
 
NOTICE 
 
 Mention of a commercial company or product does not constitute 
 an endorsement by NOAA Environmental Research Laboratories . 
 Use for publicity or advertising purposes of information from 
 this publication concerning proprietary products or the tests 
 of such products is not authorized. 
 
 u 
 
CONTENTS 
 
 Page 
 
 ABSTRACT 1 
 
 1 . INTRODUCTION 1 
 
 1 . 1 Physical Oceanography 2 
 
 1 . 2 Geography 2 
 
 1 . 3 Meteorology 2 
 
 1 . 4 Precipitation and Runoff 6 
 
 2. CURRENTS IN THE EASTERN STRAIT OF JUAN DE FUCA 7 
 
 2 . 1 Observations and Measurements 7 
 
 2 . 2 Energy Distribution 10 
 
 2 . 3 Mean Flow 14 
 
 2 . 4 Tidal Currents 21 
 
 2 . 5 Subtidal Fluctuating Flow 23 
 
 2.5.1 Subtidal current observations 26 
 
 2.5.2 Wind observations 28 
 
 2.5.3 Local wind forcing 30 
 
 2.5.4 Nonlocal meteorological forcing 30 
 
 2 . 6 Freshwater Effects on Currents 37 
 
 3 . CONTINUING STUDIES 38 
 
 4. SUMMARY AND CONCLUSIONS 39 
 
 5 . ACKNOWLEDGMENTS 40 
 
 6 . REFERENCES 40 
 
 ui 
 
Digitized by the Internet Archive 
 
 in 2013 
 
 
 http://archive.org/details/circulationinstrOOholb 
 
CIRCULATION IN THE STRAIT OF JUAN DE FUCA: 
 
 RECENT OCEANOGRAPHIC OBSERVATIONS 
 
 IN THE EASTERN BASIN 1 
 
 J. R. Holbrook, R. D. Muench, 2 D. G. Kachel, and C. Wright 
 
 ABSTRACT. In two field experiments conducted in the eastern Strait of 
 Juan de Fuca during winter 1977-78 and summer 1978, 3-mo time series 
 measurements of currents, over-the-water winds, shore winds, and water 
 properties were obtained. From these data sets, the principal water mo- 
 tions are identified and described. Over time scales of 4 to 25 h, tidal 
 currents dominate the current fluctuations and account for 58% to 99% of 
 the current variance. Mean flow is characterized by an estuarine circu- 
 lation that consists of a vigorous two-layer pattern with near-surface 
 velocities directed seaward at 20 to 40 cm/s and deep layer velocities 
 directed landward at 10 cm/s. Although local winds play a minor role 
 in modifying near- surface circulation, coastal storms dramatically affect 
 circulation in the eastern basin. During the winter experiment seven 
 current reversals (up- strait subtidal flow) were observed for periods 
 of 2 to 6 days and had eastward maximum velocities of 20 cm/s . The 
 extent to which coastal winds affect flow in the eastern basin depends 
 on their strength, duration, and direction. The reversals that propa- 
 gated up-strait at speeds of 20 to 30 cm/s were observed as far as New 
 Dungeness Spit, 135 km east of Cape Flattery. Coastal Ocean Dynamics 
 Applications Radar (CODAR) surface drifter and current measurements 
 during an intensive 4-day study period further delineate the spatial 
 characteristics of a single coastally generated reversal. Although the 
 long-term average near-surface flow is seaward, the effects of tidal 
 currents and coastal storms and the resultant complex pattern of eddies , 
 fronts, and shore- directed currents lead to a regime in which surface 
 pollutants could impact the shore as far east as Whidbey Island. 
 
 1. INTRODUCTION 
 
 The Strait of Juan de Fuca is the principal channel connecting the inland waters of Puget 
 Sound and the Strait of Georgia with the North Pacific Ocean. It is the main shipping route to 
 major northwest Canadian and U.S. population centers , and accounts for most of the water 
 exchange between the populous inland waterways and the open ocean. Since these waterways, 
 including the Strait, are used for both industry and recreation, a working knowledge of the 
 marine environment is needed on which to base management decisions . 
 
 In 1975 the Pacific. Marine Environmental Laboratory (PMEL) of NOAA began studies on 
 several oceanographic aspects of the Strait, emphasizing water circulation. Investigations 
 during the first 2 yr resulted in a comprehensive report (Cannon, 1978) that summarized exist- 
 ing knowledge and discussed results of field work in the western Strait. Our report presents 
 the results of field work in 1977-1978 in the eastern portion of the Strait of Juan de Fuca and 
 synthesizes these results with those presented in Cannon's report. Together these two papers 
 constitute the final report for the program and provide a comprehensive description of ocean- 
 ographic circulation in the Strait of Juan de Fuca. While emphasizing water movement in the 
 eastern Strait, this report describes net and fluctuating flows, seasonal variability, and 
 driving mechanisms. No attempt is made to relate this work to ecosystem studies. 
 
 1 Contribution #440 from the NOAA/ERL Pacific Marine Environmental Laboratory. 
 2 Science Applications, Inc., NW, 13400B Northrup Way #36, Bellevue, Washington 98005. 
 
1.1 Physical Oceanography 
 
 Estuarine systems are defined as regions where terrestrial runoff and marine waters mix 
 (Pritchard, 1967). They are generally, but not necessarily, stratified in salinity and density. 
 Consequently , maximum vertical density stratification can be expected during periods of large 
 freshwater input, such as spring snowmelt or autumn and winter storms, and minimum strati- 
 fication occurs during periods of small freshwater input. 
 
 The Strait of Juan de Fuca may be considered a weakly stratified, partially mixed estuary 
 with strong tidal currents (100 to 150 cm/s), a 3- to 4-m spring tide height range, and a 
 surface-to-bottom salinity differential of 2°/ 00 to 3°/ 00 (Herlinveaux and Tully, 1961; Rattray, 
 1967). Freshwater runoff primarily enters the Strait of Georgia (via the Fraser River) and 
 Puget Sound where the circulation is a fjord type. Before entering the eastern Strait of Juan 
 de Fuca, these diluted source waters are tidaUy mixed in the passages leading through the San 
 Juan Archipelago and across Admiralty Inlet. Although there are important cross-channel varia- 
 tions, the along-strait mean flow may be characterized by the classic estuarine circulation 
 with out-strait (westward) transport near the surface and in-strait (eastward) transport near 
 the bottom. This circulation is maintained by fresh water that enters the system and sets up a 
 longitudinal sea-surface slope and internal density gradients. 
 
 The significance of low-frequency current fluctuations in estuarine systems has only 
 recently been recognized, aided by the availability of extended time series current observa- 
 tions . Observational studies of these processes in other estuaries have been described by 
 Elliott (1978), Wang (1979), Wang and Elliott (1978), Muench and Heggie (1978), Svendsen 
 (1977), and others. Low-frequency fluctuations in the Strait of Juan de Fuca have been ana- 
 lyzed by Holbrook and Halpern (1977, 1980) and Holbrook et al. (1980). These studies have 
 revealed that the low-frequency fluctuations can be driven either by local winds or by off- 
 shore forcing that causes coastal sea level fluctuations. In the deeper, partially mixed 
 estuaries, offshore forcing appears to be dominant. 
 
 In addition, descriptive data analyses for the Strait of Juan de Fuca have been presented 
 by Cannon and Laird (1978), Fissel (1976), Fissel and Huggett (1976), Herlinveaux and Tully 
 (1961), Hugget et al. (1976), and Thomson (1975). The scope of these studies has been 
 limited by the availability of data, but they provided useful input for Cannon's 1978 synthesis 
 of oceanographic conditions in the Strait. 
 
 1.2 Geography 
 
 The Strait of Juan de Fuca is a glacially formed submarine valley intruding landward from 
 the Pacific Ocean. At its eastern end it bifurcates to form the channels of the San Juan 
 Archipelago, connecting to the Strait of Georgia to the north, and Admiralty Inlet leading 
 southward to Puget Sound (fig. 1). It is bounded on the south by the 1,800-m-high Olympic 
 Range and to the north by the Seymour Range on Vancouver Island, where elevations reach 
 1,200 m. An effective 60-m-deep sill projects southward off Victoria and separates the Strait 
 into western and eastern basins where depths exceed 100 m (54 km) (fig. 2). The western ba- 
 sin is approximately 20 km wide and 90 km long. Cross-channel bottom topography is generally 
 U-shaped with center-channel depths gradually increasing seaward from 170 m off Port Angeles 
 to 240 m near the mouth north of Neah Bay. Depths of more than 200 m continue along the 
 axis of Juan de Fuca Canyon, which crosses the entire continental shelf. Bottom topography 
 in the eastern basin is more complex; deep channels separate numerous banks and shoals. The 
 deepest channel exiting the eastern basin runs northward through Haro Strait across a 90-m 
 sill into the Strait of Georgia. Sill depths of 45 and 64 m are found in Rosario Strait and 
 Admiralty Inlet, respectively. Ediz Hook and New Dungeness Spit are major landforms that 
 developed along the southern shore of the Strait as a result of eastward littoral drift of 
 glacial deposits from the Elwha River, 5 nmi west of Port Angeles, and nearby cliffs. 
 
 1.3 Meteorology 
 
 The meteorology of western Washington is influenced by the atmospheric high pressure 
 region that normally overlies the eastern Pacific Ocean with its center at about 30°N, 145 °W. 
 Much of the coastal wind field can be attributed to a combination of circulation around this 
 
122° _ 
 
 -48°V- 
 
 Figure 1. — Strait of Juan de 
 Fuca, with nearby features 
 and connecting waterways. 
 
 124°W 
 
 Figure 2. — Topography of the Strait of Juan de Fuca. An effective 60-m-deep sill pro- 
 jects southward from Victoria and separates the Strait into eastern and western basins. 
 Positions of selected surface (A) and subsurface (9) current meter mooring sites are 
 shown. (See also fig. 6.) Locations where coastal winds were computed by Bakun (1977) 
 are indicated (O) • 
 
137 136 135 134 133 i 32 131 130 129 128 \?7 126 125 124 123 122 121 120 119 118 117 116 115 114 113 112 111 
 
 COLUMBIA RIVER 
 
 SURFACE WIND STRESS 
 
 LONG TERM MEAN 
 
 (1858-1972) 
 
 FOR 
 
 JUNE 
 
 STRE55 IN DTK£ Ctl-2 
 
 137 136 135 1 34 133 13? 131 133 129 128 127 126 125 [24 123 122 121 120 119 118 117 116 115 1U 113 112 111 
 
 13 7 136 135 1 3d 133 132 131 130 129 126 127 126 125 124 123 122 121 120 119 118 117 116 115 111 113 112 111 
 
 U ; \ **&*_ ' vfiNCC 
 
 COLUMBIA RIVER 
 
 SURFACE WIND STRESS 
 
 LONG TERM MEAN 
 
 (1858-1972) 
 
 FOR 
 
 DECEMBER 
 
 CAPE rtNDOCIND 
 
 5mE5S IK OTNE Cn-2 
 
 137 136 135 134 133 132 131 130 123 128 127 126 125 124 123 122 121 120 119 118 117 116 115 114 113 112 111 
 
 Figure 3. — Monthly mean (1858-1972) surface wind stress off Washington- 
 Oregon coast during June and December . Values were computed from ship 
 observations. (Adapted from Nelson, 1977.) 
 
 semipermanent high and the passage of migrating low pressure cells. In summer the high is 
 better developed and shifts northward toward the Gulf of Alaska (35°-40°N, 150°W), so that 
 resulting summer winds along the Pacific coast are predominantly northwest. In winter, there 
 is a southward migration and general weakening of the anticyclone. Simultaneously, the semi- 
 permanent Aleutian low pressure cell intensifies and causes a reversal of the winds along the 
 Pacific coast. Coastal winds in autumn and early winter are generally southeast, then shift to 
 south- southwest by late winter. Figure 3 shows representative surface wind stress vectors for 
 June and December (Nelson, 1977). These wind stress fields are based on historical surface 
 marine wind observations and illustrate the seasonal variability of the coastal wind field. 
 
 Winter weather is dominated by cyclonic storms that migrate across or north of the region 
 and are interspersed occasionally with periods of high pressure. Gale force (17 to 24 m/s) or 
 higher winds occur frequently along the coast near Tatoosh Island. Such gales are southerly, 
 persist for 2 or 3 days, and are accompanied by high sea and swell. From an analysis of 731 
 weather maps, Maunder (1968) has identified and categorized seven anticyclonic and nine cy- 
 clonic weather patterns characteristic of the region. The two most common low pressure pat- 
 
terns are those having centers near Vancouver Island and those with centers farther northwest 
 in the Gulf of Alaska. In the first of these patterns, disturbances form in the central 
 Pacific between the Aleutian low and Central Pacific high, traverse the Pacific commonly on 
 an east-northeasterly trajectory, and reach land over Vancouver Island. In the second type, 
 frontal systems spin off from the quasi-stationary low pressure area in the Gulf of Alaska and 
 move rapidly across the Pacific. Such cold fronts frequently stall and dissipate offshore 
 before moving inland. Maunder found that in winter approximately 74% of the patterns could be 
 classified as having low pressure. Occasionally, however, an upper level, high pressure ridge 
 develops over northwest Canada and leads to clear skies, near freezing temperatures, and 
 northeast winds . 
 
 Winds over the Strait of Juan de Fuca are strongly influenced by orographic effects . In 
 channels and passageways where continental topography interrupts geostrophic flow of air, 
 winds tend to be directed along-axis from high to low pressure regions . The western Strait 
 of Juan de Fuca is such an orographic channel. For example, when a low pressure system lies 
 off the Washington coast the resultant westward pressure gradient causes westward airflow that 
 accelerates through the Strait with low speeds at Port Angeles and higher speeds at Tatoosh 
 Island. Such an airflow was first described as a "gap wind" by Reed (1931). As storm fronts 
 migrate eastward, the resulting along-strait pressure gradient reverses and generates west 
 winds in the Strait. The unpredictable movement and timing of such frontal systems make 
 forecasting difficult in this region. In general, seaward or easterly winds occur more fre- 
 quently in winter, whereas landward or westerly winds predominate in summer (Harris and 
 Rattray, 1954). 
 
 During summer, northwest coastal winds are funneled up-strait and enhanced by an up- 
 strait atmospheric pressure gradient. More than 75% of all winds at Port Angeles during sum- 
 mer are from the western quadrant. A strong diurnal oscillation or sea breeze, driven by the 
 flow of coastal air that replaces inland air masses that ascend because of daily heating, is 
 superposed on the eastward mean flow. 
 
 The three most prevalent regional wind patterns as modeled by Overland et al. (1979) 
 result from (1) an inland high pressure system, (2) a low pressure system passing to the 
 north, and (3) an offshore east Pacific high pressure ridge (fig. 4). The first pattern typi- 
 
 OFFSHORE EAST PACIFIC 
 
 HIGH PRESSURE SYSTEM 
 
 (SUMMER) 
 
 LOW PRESSURE SYSTEM 
 
 PASSING TO NORTH 
 
 (WINTER) 
 
 Figure 4. — Examples of regional surface 
 wind patterns induced by an inland high 
 pressure system, a low pressure system 
 passing to the north, and an offshore 
 east Pacific high pressure system. 
 (Adapted from Overland et al., 1969; 
 Pease et al . , 1979.) 
 
1976 1977 1978 
 
 J FMAMJ JflSONO J F M A M J J A S N D |j F MAM J J A S QND 
 
 _, - 30 
 
 TOTAL WIND VARIANCE 
 
 COASTAL /BAKUN 
 
 SURFACE MOORING DEPLOYMENTS 
 
 SUBSURFACE MOORiNG DEPLOYMENTS 
 □ □...□ 
 
 J UT. 
 
 JFMAMJJASONDJFMAMJJASONDJFMAMJJASOND 
 1976 1977 1978 
 
 Figure 5. — Fraser River discharge, total 
 wind variance , and monthly mean winds 
 during mooring deployments. During 
 winter, discharge was low and wind 
 variance was high with northward coastal 
 winds and variable along-strait winds 
 associated with eastward propagating low 
 pressure systems. During summer, river 
 discharge was high and wind variance was 
 low with southward coastal winds and 
 eastward along-strait winds modulated by 
 a local sea breeze effect. 
 
 fies the winds most frequently observed from December through March. Net westward winds 
 increase in strength with distance seaward, particularly in the western Strait. Eastward 
 winds can occur in the Strait year-round during frontal passages, and are caused by the sec- 
 ond wind pattern. This pattern accounts for many of the strong westerlies observed during 
 the winter experiment in the eastern Strait. Of interest in this second pattern is the complex 
 wind circulation in the eastern Strait, where southerly winds from Puget Sound converge with 
 westerly winds directed up-strait. Summer months are characterized by persistent westerlies 
 that funnel up-strait and are coherent throughout the length of the Strait. This regional 
 wind situation reflects the third large-scale pressure pattern. 
 
 1.4 Precipitation and Runoff 
 
 Maritime air along the Washington coast is moist and approximately at thermal equilibrium 
 with the ocean surface. During fall and winter, orographic lifting and cooling of inland- 
 moving air masses result in widespread precipitation over the Strait of Juan de Fuca region . 
 The driest section of the region is directly on the northeast side of the Olympic Mountains, 
 and precipitation east of the Olympic Mountains and Vancouver Island is generally much lower 
 than that on the open Pacific coast. The average precipitation at Neah Bay at the entrance of 
 the Strait is 272 cm/yr; at Port Angeles it is 69.5 cm/yr; in the southern San Juan Islands 
 it is 49 cm/yr. 
 
 The drainage area into the Strait includes the southern part of the Strait of Georgia 
 (Herlinveaux and Tully, 1961), Puget Sound, and the many smaller seaways. It also includes 
 the San Juan and adjacent islands, the southeastern coastal slopes of Vancouver Island, the 
 coastal slopes of the adjacent mainland, and the Fraser River, which extends inland for about 
 2,500 km. Most of the terrestrial drainage areas are high mountainous regions, so winter snow 
 storage plays a major part in regulating runoff. The snow cover advances to near sea level in 
 January and retreats to the permanent snow level at about 1,400-m altitude by September. The 
 precipitation is greatest at high altitudes , but drainage does not occur until the spring 
 thaws . Rivers draining the high levels therefore commence to rise in late March and attain 
 maximum discharge in June. This pattern is particularly true for the Fraser River, which 
 supplies up to 70% to 75% of the fresh water discharging into the the Strait (Herlinveaux and 
 Tully, 1961), with the larger proportion probably in June and the smaller in January. Dur- 
 ing the winter field experiments in the eastern Strait, the Fraser River discharge was near 
 normal; however, peak discharge was below normal in 1977 and 1978 (fig. 5). 
 
2. CURRENTS IN THE EASTERN STRAIT OF JUAN DE FUCA 
 
 2.1 Observations and Measurements 
 
 Data used to describe circulation processes in the Strait of Juan de Fuca were gathered 
 from remote recording current meters, wind recorders, and tide gages, and shipboard CTD sys- 
 tems. Locations of moored current meters are shown in fig. 6. Table 1 lists depth and period 
 of operation for the meters at each station. Two types of current meters were deployed. 
 Aanderaa RCM-4 current meters were used on taut wire moorings with an anchor and acoustic 
 release at the bottom and a 1,000-lb subsurface buoyancy float above the top current meter 
 (fig. 7). The second type of mooring contained vector- averaging current meters (VACM) sus- 
 pended below a surface toroidal float (fig. 8); mounted on the buoy tower was a vector- 
 averaging wind recorder (VAWR). 
 
 The VACM continuously measures current speed using a Savonius rotor and almost contin- 
 uously measures direction with a small- vane/vane- follower assembly and magnetic compass. 
 In every 45° of a rotor revolution, a unit vector, with direction computed by adding discrete 
 compass and vane orientations, is internally converted to Cartesian coordinates. These north- 
 south and east-west components are internally summed during the instrument averaging period. 
 The number of data samples or unit vectors used in each vector average is a function of cur- 
 rent speed; e.g., a 100-cm/s current would generate approximately 12,000 vector additions over 
 a 7.5-min recording cycle. Such a sampling scheme reduces contamination of the current spec- 
 trum by surface wave noise (Halpern and Pillsbury, 1976; Saunders, 1976). Consequently, 
 these meters were considered the most suitable for use on a surface-following mooring subject 
 to wave noise. During data processing, the north-south and east- west sums are converted to 
 current velocity components using calibration formulae given by McCullough (1975). Halpern 
 (1980) has shown that the AMF VACM can yield near-surface current measurements in the open 
 ocean with an accuracy of about 2 cm/s . 
 
 The Aanderaa meters, unlike the VACM's, record speed continuously over a preset inter- 
 val, generally 10, 15, or 20 min, and provide a mean value of speed and an instantaneous 
 direction for each recording interval. They are therefore susceptible to biasing by wave- 
 induced noise from rotor pumping, and were used only below depths of about 30 m on the sub- 
 surface moorings. 
 
 Data from the Aanderaa meters were resolved into north and east components and low-pass 
 filtered to remove high-frequency noise. Two new data series were then produced using a 
 Lanczos filter (Krancus et al. , 1978). The first series was filtered so that more than 99% of 
 the amplitude was passed at periods greater than 5 h, 50% at 2.86 h, and less than 0.5% at 2 h. 
 The second series, filtered to remove most of the tidal energy, passed more than 99% of the 
 amplitude at periods of more than 55 h, 50% at 35 h, and less than 0.5% at 25 h. This series 
 was then resampled at 6-h intervals and used for examining nontidal circulation . 
 
 The wind recorders used in this project were mounted on surface buoys (see fig. 8). 
 These VAWR's are modified versions of the VACM operating in an inverted position. In this 
 design wind speed is measured by a Climet three-cup anemometer, and direction is measured 
 by a small balanced vane. These sensors are interfaced to the VACM electronics so that 
 two vector computations are made for each anemometer revolution. Pre- and post-experiment 
 wind tunnel calibrations indicate that wind speeds are accurate to about 0.2 m/s . 
 
 Temperature and salinity data were collected by two separate but similar types of CTD 
 systems. A Plessey model 9040, combined with a model 8400 data logger, sampled twice per 
 second for simultaneous values of conductivity, temperature, and depth. Data were recorded 
 during the down cast using a lowering rate of 30 m/min. Nansen bottle samples were taken at 
 each station to assist in temperature and salinity calibration. The data were averaged to 
 provide 1-m mean temperature, salinity, and sigma-t values. In the other CTD system, a 
 Plessey model 9400 coupled with a model 8400 data logger operated with a sampling frequency 
 of 0.2 s. Nansen bottle calibration samples were taken about every third station. Data from 
 both systems were processed in the same manner. Cruises during which CTD data were ob- 
 tained are summarized in table 2. 
 
Figure 6. — Positions of surface and subsurface moorings and shore-based wind recorders 
 during winter and summer experiments in the eastern Strait of Juan de Fuca. 
 
Table 1. — Summary of mooring deployments 
 
 Mooring 
 
 Depth 
 
 
 
 Recording 
 
 
 T 
 
 Latitude 
 
 Longitude 
 
 
 (m) 
 
 
 
 inte 
 
 rval 
 
 
 (days) 
 
 (N) 
 
 (W) 
 
 ST-8 
 
 4 
 
 2 
 
 Jan 
 
 78 - 
 
 14 Feb 
 
 78 
 
 44 
 
 48°14.6' 
 
 123°15.4 
 
 
 10 
 
 2 
 
 Jan 
 
 78 - 
 
 14 Feb 
 
 78 
 
 44 
 
 
 
 
 10 
 
 19 
 
 Dec 
 
 77 - 
 
 26 Feb 
 
 78 
 
 70 
 
 
 
 
 20 
 
 19 
 
 Dec 
 
 77 - 
 
 26 Feb 
 
 78 
 
 70 
 
 
 
 
 20 
 
 19 
 
 Dec 
 
 77 - 
 
 16 Apr 
 
 78 
 
 119 
 
 
 
 ST-9 
 
 4 
 
 19 
 
 Dec 
 
 77 - 
 
 6 Apr 
 
 78 
 
 109 
 
 48°23.3' 
 
 123°01.5' 
 
 
 4 
 
 19 
 
 Jan 
 
 78 - 
 
 5 Mar 
 
 78 
 
 46 
 
 
 
 
 10 
 
 19 
 
 Jan 
 
 78 - 
 
 5 Mar 
 
 78 
 
 46 
 
 
 
 
 4 
 
 19 
 
 Dec 
 
 77 - 
 
 24 Feb 
 
 78 
 
 68 
 
 
 
 
 20 
 
 19 
 
 Dec 
 
 77 - 
 
 24 Feb 
 
 78 
 
 68 
 
 
 
 ST- 10 
 
 4 
 
 19 
 
 Dec 
 
 77 - 
 
 16 Apr 
 
 78 
 
 119 
 
 48°13.0' 
 
 122°57.2' 
 
 
 10 
 
 19 
 
 Dec 
 
 77 - 
 
 16 Apr 
 
 78 
 
 119 
 
 
 
 
 20 
 
 19 
 
 Dec 
 
 77 - 
 
 5 Mar 
 
 78 
 
 77 
 
 
 
 ST-11 
 
 4 
 
 16 
 
 Jul 
 
 78 - 
 
 25 Aug 
 
 78 
 
 41 
 
 48°14.4' 
 
 123°05.5' 
 
 
 10 
 
 16 
 
 Jul 
 
 78 - 
 
 25 Aug 
 
 78 
 
 41 
 
 
 
 
 20 
 
 16 
 
 Jul 
 
 78 - 
 
 25 Aug 
 
 78 
 
 41 
 
 
 
 
 20 
 
 16 
 
 Jul 
 
 78 - 
 
 14 Sep 
 
 78 
 
 61 
 
 
 
 ST- 12 
 
 4 
 
 16 
 
 Jul 
 
 78 - 
 
 23 Aug 
 
 78 
 
 39 
 
 48°20.6' 
 
 122°56.5' 
 
 
 10 
 
 16 
 
 Jul 
 
 78 - 
 
 23 Aug 
 
 78 
 
 39 
 
 
 
 
 20 
 
 16 
 
 Jul 
 
 78 - 
 
 23 Aug 
 
 78 
 
 39 
 
 
 
 
 4 
 
 4 
 
 Sep 
 
 78 - 
 
 29 Oct 
 
 78 
 
 56 
 
 
 
 
 20 
 
 4 
 
 Sep 
 
 78 - 
 
 29 Oct 
 
 78 
 
 56 
 
 
 
 
 20 
 
 16 
 
 Jul 
 
 78 - 
 
 29 Oct 
 
 78 
 
 106 
 
 
 
 ST-13 
 
 4 
 
 16 
 
 Jul 
 
 78 - 
 
 17 Oct 
 
 78 
 
 94 
 
 48°14.1' 
 
 122°57.4' 
 
 
 10 
 
 16 
 
 Jul 
 
 78 - 
 
 17 Oct 
 
 78 
 
 94 
 
 
 
 
 20 
 
 16 
 
 Jul 
 
 78 - 
 
 17 Oct 
 
 78 
 
 94 
 
 
 
 
 10 
 
 16 
 
 Jul 
 
 78 - 
 
 29 Oct 
 
 78 
 
 106 
 
 
 
 
 20 
 
 16 
 
 Jul 
 
 78 - 
 
 29 Oct 
 
 78 
 
 106 
 
 
 
 JDF-40 
 
 31 
 
 18 
 
 Dec 
 
 77 - 
 
 3 Feb 
 
 78 
 
 122 
 
 48°23.3' 
 
 123°03.2' 
 
 
 61 
 
 19 
 
 Dec 
 
 77 - 
 
 12 Feb 
 
 78 
 
 56 
 
 
 
 
 131 
 
 18 
 
 Dec 
 
 77 - 
 
 18 Apr 
 
 78 
 
 122 
 
 
 
 JDF-41 
 
 29 
 
 18 
 
 Dec 
 
 77 - 
 
 18 Apr 
 
 78 
 
 122 
 
 48°23.0' 
 
 122°46.6" 
 
 
 59 
 
 18 
 
 Dec 
 
 77 - 
 
 18 Apr 
 
 78 
 
 122 
 
 
 
 JDF-42 
 
 30 
 
 18 
 
 Dec 
 
 77 - 
 
 18 Apr 
 
 78 
 
 122 
 
 48°13.8 
 
 122°58.3' 
 
 
 60 
 
 18 
 
 Dec 
 
 77 - 
 
 18 Apr 
 
 78 
 
 122 
 
 
 
 
 120 
 
 18 
 
 Dec 
 
 77 - 
 
 18 Apr 
 
 78 
 
 122 
 
 
 
 JDF-43 
 
 28 
 
 17 
 
 Dec 
 
 77 - 
 
 26 Mar 
 
 78 
 
 101 
 
 48°08.7' 
 
 122°42.4' 
 
 
 43 
 
 17 
 
 Dec 
 
 77 - 
 
 26 Mar 
 
 78 
 
 100 
 
 
 
 
 68 
 
 17 
 
 Dec 
 
 77 - 
 
 16 Feb 
 
 78 
 
 63 
 
 
 
 JDF-48 
 
 23 
 
 17 
 
 Dec 
 
 77 - 
 
 17 Apr 
 
 78 
 
 123 
 
 48°11.6' 
 
 123°31..r 
 
 
 53 
 
 17 
 
 Dec 
 
 77 - 
 
 17 Apr 
 
 78 
 
 122 
 
 
 
 
 93 
 
 17 
 
 Dec 
 
 77 - 
 
 23 Jan 
 
 78 
 
 38 
 
 
 
 
 136 
 
 17 
 
 Dec 
 
 77 - 
 
 17 Apr 
 
 78 
 
 123 
 
 
 
 JDF-49 
 
 32 
 
 17 
 
 Dec 
 
 77 - 
 
 17 Apr 
 
 78 
 
 122 
 
 48°15.0' 
 
 123°16.5' 
 
 
 62 
 
 17 
 
 Dec 
 
 77 - 
 
 17 Apr 
 
 78 
 
 122 
 
 
 
 
 112 
 
 17 
 
 Dec 
 
 77 - 
 
 12 Jan 
 
 78 
 
 27 
 
 
 
 JDF-51 
 
 30 
 
 11 
 
 Jul 
 
 78 - 
 
 3 Oct 
 
 78 
 
 85 
 
 48°22.9' 
 
 122°46.8' 
 
 
 60 
 
 12 
 
 Jul 
 
 78 - 
 
 18 Sep 
 
 78 
 
 69 
 
 
 
 JDF-52 
 
 30 
 
 13 
 
 Jul 
 
 78 - 
 
 4 Oct 
 
 78 
 
 84 
 
 48°14.6' 
 
 122°58.9' 
 
 
 60 
 
 13 
 
 Jul 
 
 78 - 
 
 4 Oct 
 
 78 
 
 84 
 
 
 
 JDF-53 
 
 45 
 
 11 
 
 Jul 
 
 78 - 
 
 30 Sep 
 
 78 
 
 82 
 
 48°08.7' 
 
 122°42.3' 
 
 
 60 
 
 11 
 
 Jul 
 
 78 - 
 
 20 Sep 
 
 78 
 
 72 
 
 
 
SURFACE 
 
 SUBSURFACE FLOAT 
 26m 
 
 AANDERAA 
 RCM-4 30m 
 
 AANDERAA 
 RCM-4 50m 
 
 AANDERAA 
 RCM-4 90m 
 
 AANDERAA 
 RCM-4 130m 
 
 AMF RELEASE 
 139m 
 
 3 000** 
 ANCHOR 
 
 iii/i) TTTfrm >//// 
 
 BOTTOM 
 JDF 49 
 
 //'/>))))/ 
 
 143 m 
 
 Figure 7. — Typical subsurface mooring 
 containing Aanderaa current meters 
 suspended below a 1,000-lb subsurface 
 float. 
 
 2.2 Energy Distribution 
 
 Currents in the Strait of Juan de Fuca were found to be highly time dependent. Current 
 fluctuations were measured over a broad range of time scales, from 15 min to 100 days. Across 
 this band of motions, current energy fell naturally into three principal categories: long-term 
 mean circulation, tidal oscillations, and long-period subtidal fluctuations. The division of 
 fluctuating energy can be seen clearly in representative east-west (solid line) and north-south 
 (dashed line) power density spectra of currents at 4-m depth for mooring sites A and G 
 (fig. 9). Black horizontal bars at the top identify the subtidal (<0.025 cph), diurnal (0.033- 
 0.043 cph), and semidiurnal (0.076-0.085 cph) frequency bands that contained most of the cur- 
 rent variance. At 4-m depth, at sites A and G, 86% and 83%, respectively, of the total current 
 variance were contained in these three bands . Table 3 summarizes the variances in other selec- 
 ted current records from the eastern Strait. 
 
 The vertical distribution of variance in these bands is illustrated in fig. 10 for sites A 
 and G during winter and summer conditions. Subtidal current variance was greatest near the 
 surface and decreased rapidly with increasing depth in the upper 30 to 40 m of the water 
 column. In the lower layer, subtidal variance represented only a small fraction of total 
 variance. The distribution of tidal variance was more constant with depth and represented 
 most of the total current variance. 
 
 Characteristic power density spectra of computed winds off the Washington coast (Bakun, 
 1977, personal communication) and measured shore winds in the Strait at Race Rocks for winter 
 
 10 
 
4 m 
 
 10m 
 
 20 m 
 
 Miller Swivel 
 VACM 0418 
 |/2" Galvanized Chain 
 
 VACM 0368 
 
 85 m 
 
 ^I35m 
 
 VACM 0374 T 
 
 1/2" Galvanized Chain 
 
 Miller Swive 
 
 Acoustic Release 0113 
 
 I 1/8" Chain 
 
 Anchor 3050 lb 
 
 Figure 8. — Typical surface mooring containing vector-averaging current meters 
 (VACM' s) suspended below a toroidal surface float. Mounted on the surface 
 buoy tower was a vector-averaging wind recorder (VAWR) . 
 
 and summer conditions are shown in fig. 11. The spectra are red, with 85% to 95% of the vari- 
 ance energy at frequencies below 0.025 cph. At Race Rocks, the total wind variance was 
 nearly the same during winter and summer; however, during winter, it was divided approxi- 
 mately 2:1 between the east-west and north-south components, whereas during summer nearly 
 all the wind variance was contained in the east-west component. Off the coast, wind vari- 
 ance was 88% greater during winter than summer and was divided about equally between com- 
 ponents . Although all spectra had an energy peak at time scales of 3 to 6 days , the peak 
 was generally not significant at the 95% level. During summer the east- west components of 
 both coastal and Strait winds had a significant peak at the diurnal frequency, reflecting the 
 influence of the sea breeze effect. 
 
 11 
 
Table 2. — Summary of cruises on which CTD data were collected 
 
 Cruise 
 
 Vessel 
 
 Dates 
 
 No. of 
 stations 
 
 0PR509MA76 
 
 PR509MA76E 
 
 Strait-DI 
 
 Snow Goose 
 
 Strait-DI 
 
 Strait-DI 
 
 Strait- SG 
 
 SG-2 
 
 Strait-OC 
 
 Strait-OC 
 
 Snow Goose 
 
 Strait-SG 
 
 Strait-DI 
 
 Strait-SG 
 
 Strait-SG 
 
 Strait-MC 
 
 MacArth 
 MacArth 
 Discove 
 Snow Go 
 Discove 
 Discove 
 Snow Go 
 Snow Go 
 Oceanog 
 Oceanog 
 Snow Go 
 Snow Go 
 Discove 
 Snow Go 
 Snow Go 
 MacArth 
 
 ur 
 
 ur 
 
 rer 
 
 ose 
 
 rer 
 
 rer 
 
 ose 
 
 ose 
 
 rapher 
 
 rapher 
 
 ose 
 
 ose 
 
 rer 
 
 ose 
 
 ose 
 
 ur 
 
 23 
 
 Feb - : 
 
 L5 Apr 76 
 
 28- 
 
 •29 
 
 Oct 
 
 76 
 
 3- 
 
 •4 
 
 Nov 
 
 76 
 
 17- 
 
 •19 
 
 Nov 
 
 76 
 
 15- 
 
 ■17 
 
 Feb 
 
 77 
 
 18- 
 
 ■21 
 
 Jun 
 
 77 
 
 19- 
 
 -22 
 
 Jul 
 
 77 
 
 23- 
 
 ■26 
 
 Auq 
 
 77 
 
 22- 
 
 -29 
 
 Sep 
 
 77 
 
 16- 
 
 ■19 
 
 Dec 
 
 77 
 
 16- 
 
 -20 
 
 Dec 
 
 77 
 
 12- 
 
 -17 
 
 Jan 
 
 78 
 
 19- 
 
 •21 
 
 Mar 
 
 78 
 
 11- 
 
 -15 
 
 Apr 
 
 78 
 
 20- 
 
 ■23 
 
 Auq 
 
 78 
 
 31 
 
 Oct - : 
 
 L Nov 78 
 
 141 
 16 
 33 
 34 
 39 
 53 
 65 
 73 
 
 163 
 35 
 89 
 
 133 
 28 
 48 
 42 
 15 
 
 1000 
 
 io 5 
 
 10' -■ 
 
 10' - 
 
 10 z 
 
 10' 
 
 10° 
 
 PERIOD (HOURS) 
 100 10 1 
 
 U 
 
 — v 
 
 SITE A/4m 
 (5Nov-l4Feb77) 
 
 95 PERCENT 
 
 4J, 
 
 .001 
 
 .01 .1 1 
 
 FREQUENCY (CYCLES/HOUR) 
 
 10 
 
 1000 
 
 PERIOD (HOURS) 
 100 10 1 
 
 10*- 
 
 10 4 - 
 
 
 -;: io*. 
 
 UJ 
 
 to 
 
 10'- 
 
 10* 
 
 10' - — 95 PERCENT 
 
 U 
 
 — V 
 
 SITE G/4m 
 (16 Jul-I70ct78) 
 
 -IX 
 
 .001 .01 .1 1 
 
 FREQUENCY (CYCLES/HOUR) 
 
 10 
 
 Figure 9. — Density spectra of east-west (U, ) and north-south (V , J 
 
 current components at 4-m depth for sites A and C. Black horizontal 
 bars at top identify subtidal (< 0.025 cph) , diurnal (0.033-0.043 
 cph) , and semidiurnal (0.076-0 .085 cph) frequency bands. 
 
 12 
 
Table 3. — Summary of variances in selected current records 
 
 Mooring 
 
 Depth 
 (m) 
 
 Record 
 length 
 (days) 
 
 
 Total variance (cm 2 /s 2 ) 
 
 
 
 
 Low-freq. 
 (<0.025 cph) 
 
 Diurnal 
 (0.033-0.043 cph) 
 
 Semidiurnal 
 (0.076-0.085 cph) 
 
 Remainder 
 
 Total 
 
 ST-8 
 
 4 
 
 44 
 
 109 
 
 725 
 
 2124 
 
 185 
 
 3143 
 
 
 10 
 
 70 
 
 105 
 
 694 
 
 1954 
 
 251 
 
 3004 
 
 
 20 
 
 119 
 
 61 
 
 510 
 
 1882 
 
 181 
 
 2634 
 
 ST- 9 
 
 4 
 
 109 
 
 114 
 
 334 
 
 691 
 
 269 
 
 1408 
 
 
 10 
 
 46 
 
 101 
 
 300 
 
 738 
 
 \39 
 
 1278 
 
 
 20 
 
 68 
 
 101 
 
 369 
 
 688 
 
 181 
 
 1339 
 
 ST-10 
 
 4 
 
 119 
 
 158 
 
 236 
 
 1070 
 
 307 
 
 1771 
 
 
 10 
 
 119 
 
 112 
 
 226 
 
 1054 
 
 223 
 
 1615 
 
 
 20 
 
 77 
 
 75 
 
 248 
 
 873 
 
 146 
 
 1342 
 
 ST-11 
 
 4 
 
 41 
 
 134 
 
 576 
 
 1452 
 
 467 
 
 2629 
 
 
 10 
 
 41 
 
 88 
 
 537 
 
 1545 
 
 441 
 
 2611 
 
 
 20 
 
 41 
 
 54 
 
 440 
 
 1474 
 
 293 
 
 2261 
 
 ST- 12 
 
 4 
 
 39 
 
 63 
 
 223 
 
 1642 
 
 256 
 
 2184 
 
 
 10 
 
 39 
 
 55 
 
 232 
 
 1562 
 
 225 
 
 2074 
 
 
 20 
 
 106 
 
 41 
 
 153 
 
 1124 
 
 183 
 
 1501 
 
 ST-13 
 
 4 
 
 94 
 
 160 
 
 353 
 
 1381 
 
 577 
 
 2212 
 
 
 10 
 
 94 
 
 95 
 
 318 
 
 1331 
 
 269 
 
 2013 
 
 
 20 
 
 94 
 
 45 
 
 268 
 
 1209 
 
 186 
 
 1708 
 
 JDF-40 
 
 31 
 
 46 
 
 43 
 
 443 
 
 680 
 
 66 
 
 1232 
 
 
 61 
 
 55 
 
 26 
 
 581 
 
 665 
 
 57 
 
 1329 
 
 
 131 
 
 120 
 
 64 
 
 285 
 
 621 
 
 161 
 
 1131 
 
 JDF-41 
 
 29 
 
 121 
 
 27 
 
 267 
 
 540 
 
 145 
 
 979 
 
 
 59 
 
 121 
 
 28 
 
 225 
 
 639 
 
 106 
 
 998 
 
 JDF-42 
 
 30 
 
 121 
 
 28 
 
 208 
 
 698 
 
 50 
 
 984 
 
 
 60 
 
 121 
 
 19 
 
 207 
 
 666 
 
 47 
 
 939 
 
 
 120 
 
 121 
 
 19 
 
 219 
 
 607 
 
 104 
 
 949 
 
 JDF-43 
 
 43 
 
 98 
 
 67 
 
 1863 
 
 9718 
 
 265 
 
 11913 
 
 
 68 
 
 60 
 
 191 
 
 1231 
 
 3633 
 
 374 
 
 8795 
 
 JDF-48 
 
 23 
 
 121 
 
 155 
 
 993 
 
 2504 
 
 155 
 
 3807 
 
 
 53 
 
 121 
 
 44 
 
 1005 
 
 3012 
 
 77 
 
 4138 
 
 
 93 
 
 36 
 
 29 
 
 1626 
 
 2887 
 
 72 
 
 4614 
 
 
 136 
 
 121 
 
 30 
 
 814 
 
 1825 
 
 213 
 
 2882 
 
 JDF-49 
 
 32 
 
 121 
 
 23 
 
 763 
 
 2720 
 
 11 
 
 3517 
 
 
 62 
 
 121 
 
 18 
 
 690 
 
 2495 
 
 69 
 
 3272 
 
 
 112 
 
 26 
 
 92 
 
 422 
 
 1052 
 
 498 
 
 2064 
 
 13 
 
VARIANCE (cm 2 /s 2 ) 
 
 500 1000 1500 2000 2500 3000 3500 500 1000 1500 2000 2500 
 
 100 
 
 200 
 
 £ 250 
 
 1 
 
 -* 1 i__ — »i 
 
 1 
 
 — 102 l02 
 
 "A 
 
 /SUBTIDAL 
 
 \ 
 /diurnal 
 
 ♦ f 44 
 
 SITE A 
 WINTER 
 
 
 SEMIDIURNAL] 
 
 \ 
 
 
 - 
 
 / 
 
 /TOTAL 
 
 
 1 
 
 X 
 
 «44 
 
 
 I / 
 i / 
 • • 
 
 
 
 
 uii iii i ii mil inn n / / 1/ ii/i/ii /////////// 
 
 250 
 
 rf^42 
 
 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I I I 1 1 1 1 1 I 1 1 1 1 1 / 
 
 150 
 
 200 
 
 1 1 1 1 I I I I I I 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 / 
 
 500 1000 1500 2000 2500 
 
 100 
 
 150 
 
 200 " 
 
 250 
 
 SITE G 
 SUMMER 
 
 U 1 1 1 1 1 1 1 / 1 / 1 / 1 1 1 1 1 / 
 
 Figure 10. --Vertical distribution of variance in subtidal , diurnal, 
 and semidiurnal frequency bands at sites A and G during winter and 
 summer conditions _, 
 
 2.3 Mean Flow 
 
 Mean flow in the eastern Strait of Juan de Fuca is driven by several forces: 
 
 The pressure gradient field maintained by freshwater input from continental runoff, 
 resulting in seaward flow in the upper layer and landward flow in the deep layer. 
 This results in the classic two-layer estuarine circulation. 
 
 Nonlinear interaction of tidal currents with local bottom and lateral topography such 
 that, at the completion of a tidal cycle, a residual flow has occurred. 
 
 Wind stress in a given direction over a period of time, resulting in net wind-driven 
 flow. 
 
 The observed total mean flow reflects interaction of these separate modes. Cannon (1978) 
 showed that the two-layer estuarine flow component constitutes a significant portion of total 
 mean circulation in the western Strait of Juan de Fuca. 
 
 Observations from current meters at 4-, 10-, 20- and 30-m depths at moorings 49, 40, and 
 42 (winter) and mooring 52 (summer) indicate that motions in the upper 30 m were vertically 
 highly coherent. Therefore the 30-m records are assumed to represent upper layer flow and 
 are used in the following discussion of flow patterns . It must be noted that net speeds 
 rapidly decreased with depth in the upper layer as a result of the vertical shear maintained by 
 the density field. Table 4 lists vector mean speeds and directions from those moorings in the 
 upper layer where vertical comparison between records was possible. Vertical profiles of net 
 currents near the Strait entrance at site A and in the eastern Strait at site G illustrate the 
 strong two-layer estuarine flow throughout the system (fig. 12). 
 
 14 
 
10000 
 10 4 
 
 PERI00 (HOURS) 
 1000 100 10 
 
 10» 
 
 10« 
 
 x 
 & 
 
 £ 10' -j 
 
 o 
 
 UJ 
 
 to 
 
 \ 
 
 z: 
 
 ior -J 
 
 lo-*- 
 
 io- 
 
 .0001 
 
 Computed 
 
 Coastal Winds 
 
 at 48°N, I25°W 
 
 Winter 
 
 (19 Dec-l6Apr78) 
 
 95 PERCENT 
 
 ■ . M .l , 
 
 .001 .01 .1 
 FREQUENCY (CYCLES/HOUR) 
 
 10000 
 10 4 +— 
 
 10'- 
 
 10' 
 
 X 
 
 £ 10' : 
 
 
 10° 
 
 10" 1 - 
 
 lff 4 
 
 PERIOD (HOURS) 
 1000 100 10 
 
 ' I'l l 
 
 .0001 
 
 Race Rocks Winds 
 
 Winter 
 
 (19 Dec-16 Apr 78) 
 
 95 PERCENT 
 
 J.I.I. , ■ ■ 
 
 .001 .01 .1 
 FREQUENCY (CYCLES/HOUR) 
 
 10000 
 10 4 
 
 10* 
 
 10' 
 
 V 10' 
 
 10° 
 
 10' • 
 
 Iff* 
 
 PER 1 00 (HOURS) 
 1000 100 10 
 
 Computed 
 
 Coastal Winds 
 
 at 48°N, I25°W 
 
 Summer 
 
 (16 Jul-29 Oct 78) 
 
 — 95 PERCENT 
 
 -LU^ 
 
 .0001 .001 .01 .1 
 FREQUENCY (CYCLES/HOUR) 
 
 10000 
 10 4 
 
 10'- 
 
 10* 
 
 X 
 Q- 
 C-J 
 
 -„ 10' 
 
 10° - 
 
 io- 
 
 io- 
 
 PERIOD (HOURS) 
 1000 100 10 
 
 Race Rocks Winds 
 
 Summer 
 
 (16 Jul-29 Oct 78) 
 
 — 95 PERCENT 
 
 J.J.I,, 
 
 .0001 
 
 .001 .01 -1 
 
 FREQUENCY (CYCLES/HOUR) 
 
 Figure 11. — Density spectra of east-west (U , ) and north-south (V, ) 
 
 wind spectra at 48°N, 125°W, computed by Bakun (1977) and at Race 
 Rocks during winter and summer conditions. 
 
 15 
 
Table 4. — Vector mean speed and direction for currents in near-surface layer 
 
 Mooring Depth 
 (m) 
 
 Recording Record length Latitude Longitude Vector mean 
 
 interval (days) (N) (W) Speed (cm/s) Dir.(°T) 
 
 ST-9 4 12/19/77 - 4/ 6/78 
 10 1/19/78 - 3/ 5/78 
 20 12/19/77 - 2/24/78 
 
 109 
 46 
 68 
 
 48°23.3' 
 
 123°01.5' 
 
 15.3 
 14.4 
 13.4 
 
 324 
 329 
 331 
 
 JDF-40 
 
 31 
 
 12/18/77 - 2/ 3/78 
 
 47 
 
 48°23.2' 123°03.2' 
 
 7.9 
 
 013 
 
 ST-8 
 
 4 
 10 
 20 
 
 1/ 2/78 
 12/19/77 
 12/19/77 
 
 2/14/78 
 2/26/78 
 4/16/78 
 
 44 48°14.6' 123°15.4' 20.1 
 
 70 19.9 
 
 119 19.1 
 
 243 
 251 
 246 
 
 JDF-49 
 ST-10 
 
 32 
 
 4 
 
 10 
 20 
 
 12/17/77 - 4/17/78 
 
 12/19/77 
 12/19/77 
 12/19/77 
 
 4/16/78 
 4/16/78 
 3/ 5/78 
 
 122 48°15.0' 123°16.5' 12.5 
 
 119 48°13.0' 122°57.2' 22.1 
 
 119 19.4 
 
 77 12.5 
 
 240 
 
 319 
 317 
 315 
 
 JDF-42 30 12/18/77 - 4/18/78 
 
 ST- 13 4 7/16/78 - 10/17/78 
 
 10 7/16/78 - 10/29/78 
 
 20 7/16/78 - 10/29/78 
 
 122 
 
 48°13.8' 122°58.3' 
 
 2.1 
 
 309 
 
 94 
 
 48°14.1' 
 
 122°57.4' 
 
 26.7 
 
 296 
 
 106 
 
 
 
 25.8 
 
 295 
 
 106 
 
 
 
 19.9 
 
 299 
 
 JDF-52 
 
 30 
 
 7/13/78 - 10/ 4/78 
 
 84 
 
 48°14.6' 122°58.9' 
 
 6.4 
 
 298 
 
 The flow during winter is illustrated by 35-h filtered currents (figs. 13-15) that show 
 upper (30-m) and lower (130-m) layer flow was well developed along the axis of the eastern 
 Strait, particularly at moorings 48, 49, and 42. Numbers around roses indicate percent of 
 observations in that direction, and the length indicates the mean. At moorings 48 and 49, 
 upper layer flow was seaward 60% to 70% of the time at about 15 cm/s. At mooring 42 to the 
 east the seaward flow tendency had decreased to about 50% of the observations, and speeds 
 had slowed to about 5 cm/s. The mid-depth (60-m) records at these three moorings showed a 
 confused pattern because the level of no net flow was near that depth. Consequently, the 
 60-m mean speeds were smaller than those nearer the surface at moorings 48 and 49 (5-10 cm/s) 
 and also showed a southerly cross-channel trend not present in the upper layer. At mooring 
 42 the 10 to 15 cm/s mean flow at 60 m was primarily landward (eastward) rather than seaward. 
 Apparently the depth of no net flow was shallower than 60 m at that mooring, whereas it was 
 deeper than or near that depth at moorings 48 and 49. The 130-m depth records indicated 
 landward flow. Mean speeds were about 5 cm/s at mooring 48 and were greater (20 cm/s) to 
 the east at mooring 49. At mooring 42, mean speeds were about 10 cm/s. The record from 48, 
 the westernmost mooring, showed the most directional scatter. From these observations we 
 conclude that the central eastern Strait of Juan de Fuca was characterized during winter by 
 a two-layer mean flow regime with a level of no net motion at about 50 m, which became 
 slightly shallower toward the east. 
 
 16 
 
21 22 23 24 25 26 27 
 
 SIOBB-T 
 
 21 22 23 24 25 26 27 
 
 sionn-T 
 
 NET CURRENTS 
 (cm/s) 
 
 NET CURRENTS 
 (cm/s) FLOOD 
 
 Figure 12. — Vertical distribution of mean along-strait currents and density at 
 sites A and G during winter and summer conditions . Near-shore mean currents 
 at 4-m depth measured from surface moorings are shown at top. 
 
 Moorings 40 and 41, situated off the entrances to Haro and Rosario Straits, respectively, 
 showed the influence of flow through those channels . Flow at mooring 40 was northward into 
 Haro Strait at 30 m and had mean speeds of about 10 cm/s. At 60 and 130 m, flow was more 
 variable and had a marked easterly rather than northerly component. Mean speeds at 60 m 
 were about 5 cm/s, whereas at 130 m mean speeds were about 10 cm/s or comparable to the 
 upper layer values. The observations from mooring 41 off Rosario Strait indicated a weak 
 (5 cm/s) southerly flow in the upper layer and a great deal of directional variability. The 
 60-m record indicated a primarily eastward flow at about 10 cm/s. The flow patterns at these 
 two locations were markedly different from those observed farther south along the axis at the 
 Strait of Juan de Fuca. The two-layer flow regime was not well defined, and, presumably, the 
 circulation in this region is more complicated because of large-scale eddies, bottom topog- 
 raphy, and residual tidal flows. The horizontal mooring spacing was not sufficient to resolve 
 large-scale features, and therefore the details of circulation in the northern portion of the 
 eastern Strait are unknown at this time. 
 
 The northerly upper layer flow just off Haro Strait was unexpected since freshwater input 
 from sources to the north (the Fraser River) should drive a mean two-layer circulation in Haro 
 Strait. Recent current measurements by Canadian investigators show a well developed two-layer 
 circulation with out-strait flow near the surface in Haro Strait (Webster, 1977). Southerly 
 upper layer flow off Rosario Strait, however, agreed qualitatively with such a pattern. We 
 hypothesize that northward flow into Haro Strait at the mooring sites reflects a tidally driven 
 residual flow caused by flood (northward) tidal currents (see section 2.4). These measurements 
 illustrate that local effects near the mouths of connecting straits may cause complex and often 
 confusing circulation patterns . 
 
 17 
 
Figure 13. — Current roses for 35-h filtered 
 data at 30-m depth during winter. 
 
 Figure 14., — Current roses for 35-h filtered 
 data at 60-m depth during winter. 
 
 24' 18' 12' 06' 123° 54' 48' 42' 
 
 48 42 
 
 Figure 15. — Current roses for 35-h filtered 
 data at 130-m depth during winter. 
 
 Figure 16. — Record-averaged currents at 
 30-m depth during winter. 
 
 18 
 
Figure 17. — Current roses for 35-h filtered 
 data at 30-m depth during summer. 
 
 Figure 18. — Current roses for 35-h filtered 
 data at 60-m depth during summer. 
 
 The tendency for mid-depth and deep currents to have easterly or cross-channel flow 
 components was apparently due to a clockwise circulation cell in the eastern Strait, particu- 
 larly well shown at 30 m during winter 1977-78 (fig. 16). This rotational flow tendency was 
 present at moorings 42, 40, and 41 throughout the water column, and also during the summer at 
 stations 50 and 51 (see current roses in figs. 17 and 18); no data were obtained from station 
 52. The constancy of this pattern with depth and season suggests that it may be driven by the 
 tides, a mechanism that would tend to force a barotropic, seasonally independent flow. The 
 regional topography is such that ebbing tidal currents from Rosario Strait would tend to form a 
 strait- wide clockwise eddy in the eastern Strait, which might be further abetted by ebb tides 
 from Admiralty Inlet. This eddy would tend to disintegrate during flood tides, but the net 
 effect over several tidal cycles would be a mean clockwise circulation . A test of this hypoth- 
 esis awaits further analyses of the tidal model developed by Crean (1978). 
 
 Currents at the single mooring in Admiralty Inlet, mooring 43, were heavily influenced by 
 the waters of the Puget Sound system to the south (figs. 13, 14, and 18). Strong cross- 
 channel flow at 30 m reflected local topographic influences, whereas a 20 cm/s inward flow at 
 60 m reflected the estuarine flow regime driven by freshwater input into the Puget Sound sys- 
 tem. Because of high peak current speeds (2 to 3 m/s) encountered during ebb and flood tides 
 in Admiralty Inlet, the mooring was subject to considerable drag and consequent heeling. 
 Therefore the middle and upper layer observations are probably not as reliable as the deep 
 layer observations. The upper layer record, moreover, was shorter than the deep layer record 
 because of upper current meter malfunction. Continuity arguments dictate that mean upper and 
 lower layer transports should be similiar since net precipitation (including runoff) minus 
 evaporation was much smaller by comparison. Thus, a mean outflow would be expected in the 
 upper layer, but none was apparent from our records. 
 
 Summer current records from the eastern Strait of Juan de Fuca were far less complete 
 than the winter records because of instrument malfunctions and gill net fouling. The 35-h 
 filtered current roses constructed from available summer data indicate the same qualitative 
 flow patterns at 30 and 60 m in the eastern Strait as observed during winter (figs. 17 and 18). 
 There was no statistical difference between winter and summer current speeds . This contrasted 
 
 19 
 
w 
 
 *£*• -,.\\^ 
 
 %:■ Vrt-'* 
 
 
 
 nSSo? /fVJ- 
 
 \\ V.. SITE #11 
 
 
 \ X --X CARDS 050 1-0600 ^}f/ .'. + 5 £':'■ 
 
 \ Y" LAT. 48- 16.0 N 
 
 
 \ y LON. 123-03. 8W 
 
 
 \ %.:.■ DATE 14 APRIL 
 
 976 V/^ iS^S C? 
 
 \ V:: RETURNED 49% 
 
 £^kM 
 
 
 
 \%.t ■•'••'' 
 
 
 Figure 19. — Examples of drift card recoveries for cards deployed in the eastern Strait 
 (from Pashinski and Charnell , 1979) . 
 
 with the western extreme of the Strait where the mean two-layer flow showed summer speeds 
 about double the winter speeds (Holbrook et al. , 1979), a result of coastal forcing (see 
 section 2.5.4). 
 
 Further evidence for minimal seasonal variation in surface flow in the eastern Strait is 
 provided by results of a drift card study conducted in 1976 and 1977 (Pashinski and Charnell, 
 1979). These results are in agreement with basic estuarine circulation in the Puget Sound- 
 Strait of Juan de Fuca system as defined by our current observations. The cards released in 
 the eastern basin show the greatest dispersion and on the average were in the water for 3 days 
 or longer before going aground (see fig. 19). However, since winds are the dominant factor in 
 distribution, most cards can be grounded in a short time by very strong winds. Therefore, 
 effective prediction depends on knowing forcing factors in near-real time. 
 
 The two-layer estuarine flow is driven by freshwater input, which is reflected in the 
 salinity distribution. Salinities and temperatures recorded during CTD cruises in February, 
 April, October, and November 1976, and in December 1977, were examined for along- strait var- 
 iations . A consistent change in the horizontal salinity and temperature fields occurred near 
 the sill zone south of Victoria. Separate averages were made for the water masses lying east 
 and west of this natural division. 
 
 Most average salinity values in the east were lower than those in the west. Two excep- 
 tions were February 1976 and December 1977, when water in the top 100 m in the western 
 Strait had a lower average salinity than water at comparable depths in the eastern Strait. 
 Salinity in the water column increased from top to bottom throughout the system. Surface- 
 to-bottom differences in average values were smaller in the eastern Strait than in the western 
 Strait. For example, in December 1977, the average value in the western Strait was 5.0°/ oo , 
 whereas in the eastern Strait it was 1.8°/ 00 . 
 
 Horizontal variations in temperature from west to east were typically 1° to 2°C. In the 
 eastern Strait the lowest average temperatures occurred in February and increased throughout 
 the year to December when the highest values were reached. As might be expected, tempera- 
 ture decreased from top to bottom, but even this variation was minimal. In December and 
 February, the differences in temperature between the surface and water at 150 m were 0.13°C 
 and 0.17°C, respectively. In April and November, the difference was less than 0.5°C. 
 
 20 
 
124°W 
 
 Figure 20. — M 2 tidal current ellipses at 10- to 30-m depth. 
 
 2.4 Tidal Currents 
 
 Tidal currents in the Strait of Juan de Fuca constitute both a navigational hazard and a 
 primary mechanism for dispersal of spilled pollutants . A summary of existing information on 
 tidal heights and currents in the Strait, along with a brief analysis of tidal wave behavior, 
 has been presented by Parker (1977). In his analysis, he used the results of an intensive 
 current and sea level monitoring program carried out from 1973-75 by the National Ocean 
 Survey of NOAA and included previously available data. Crean (1978) numerically treated 
 the problem of barotropic tidal behavior in the Strait, and his results give considerable 
 insight into this complex system. 
 
 Our current observations substantiate the results of earlier analyses. Tides in the 
 Strait of Juan de Fuca behave as a progressive wave that propagates eastward from the open 
 ocean and whose interactions lead to semidiurnal mixed tidal currents in the eastern Strait. 
 We present tidal currents in the form of ellipses for the entire Strait to illustrate west-east 
 continuity (figs. 20-23). Only the major semidiurnal and diurnal components, M 2 and K x , are 
 shown because they contain the most energy and behave similarly to the other components . A 
 tabulation of the five major components, M 2 , K 1; S 2 , N 2 , and 1} is presented for comparison 
 (table 5). The constituents were computed using the first 29 days of each record listed, so 
 they represent only the first portion of the series. Analysis of selected records in the 
 eastern Strait has revealed that the tidal characteristics vary slightly with time over the 
 duration of the mooring, and the values given may therefore be considered representative. 
 
 The ellipses provide a summary of tidal characteristics. We also present graphs depicting 
 major axis amplitudes and phases for the major constituents as a function of distance landward 
 from the mouth of the Strait (fig. 24). The M 2 currents were generally about 10 to 20 cm/s 
 stronger than the K 1 currents throughout the entire Strait. The difference was greatest at the 
 constriction just south of Victoria, where M 2 current speeds were about 60 cm/s and K x speeds 
 were about 40 cm/s. Speeds for four major constituents were about the same at the inner and 
 outer ends of the Strait. The highest speeds observed occurred in Admiralty Inlet (not shown) 
 where the M 2 component had an amplitude of about 120 cm/s. High speeds at that location are 
 caused by the constricted channel, which must feed a large tidal prism to the Puget Sound 
 system to the south, and actual instantaneous current speeds at that location have been ob- 
 served as high as ~300 cm/s. Throughout the region, the elongate nature of the tidal ellipses 
 reflects the constraining influence of the lateral boundaries; in several instances the cross- 
 channel components represented by the minor ellipse axes were of the same order as noise in 
 
 21 
 
124°W 
 
 Figure 21. — M 2 tidal current ellipses at 120- to 170-m depth. 
 
 the current records . The only instance of appreciable rotary motion was in the near-bottom 
 M 2 constituent south of Victoria. The increase in phase of the M 2 and K x constituents with 
 distance up-strait demonstrates the progressive nature of the tidal wave (fig. 24). Tidal 
 constituent amplitude increased with distance up-strait to approximately Race Rocks and de- 
 creased further eastward. 
 
 Our observed tidal currents compare favorably with those that Crean (1978) obtained with 
 his numerical model (fig. 25). His streamlines aid in interpreting the ellipses presented 
 
 SAN V JUAN^ A / \ 
 
 124°W 
 
 Figure 22. — iCj tidal current ellipses at 10- to 30-m depth. 
 
 22 
 
Figure 23. — Ki tidal current ellipses at 120- to 170-m depth. 
 
 earlier by providing better spatial resolution. For example, the on-offshore orientation of 
 the M 2 and K x ellipses just south of the San Juan Islands at Strait-9 (shown in figs. 20-23) 
 occurs just before the streamlines curve sharply and enter Haro Strait. Of particular interest 
 is the formation of eddies south of Victoria, at the entrance to Haro Strait, and east of New 
 Dungeness Spit. 
 
 Ebbesmeyer et al. (1979) have summarized the historical oceanographic data in Port 
 Angeles Harbor. Results from this study and hydraulic tidal model runs demonstrate the im- 
 portance of forcing by exterior flows and local wind. Their combined effects yielded a resi- 
 dence time of several days to a week for near-surface water in the harbor. Net near-shore 
 flow between New Dungeness Spit and Ediz Hook was shown to be consistently eastward or up- 
 s trait. 
 
 2.5 Subtidal Fluctuating Flow 
 
 Estuarine circulation is composed of both tidal and nontidal currents. Gravitational 
 convection, an aspect of the nontidal portion, has been a topic of extensive research during 
 past decades, since it drives the two-layer mean flow normally associated with an estuary 
 (Officer, 1976). Between the quasi-steady-state gravitational convection and the tidal oscilla- 
 tions exists a broad range of time scales over which energetic motions may also occur. For 
 this report, subtidal flow is considered to encompass current fluctuations with periods of 2 to 
 100 days. 
 
 Studies in other estuaries have shown that winds, atmospheric pressure, and river runoff 
 can cause these intermediate scales of estuarine motion. For example, in Narragansett Bay, 
 longitudinal currents with periods of 2 to 3 days were highly coherent with longitudinal winds , 
 with currents lagging the winds by 3 h (Weisberg and Sturges, 1976). In contrast, forcing of 
 subtidal currents in Chesapeake Bay was relatively complex (Elliott, 1978; Wang and Elliott, 
 1978; Wang, 1979). For time scales longer than 10 days, a significant proportion of the fluc- 
 tuations was generated at the Bay mouth by along-shore coastal winds. At time scales of 4 
 to 10 days, both coastal and local lateral winds were important; at time scales shorter than 
 4 days, a longitudinal seiche motion was thought to occur. Elliott et al. (1978) found that 
 flow near the head of Chesapeake Bay was determined by the size of the Susquehanna River 
 discharge. 
 
 23 
 
Table 5. — Mi, S2, #2' ^1 / ^1 constituents for current records 
 
 
 Latitude 
 (N) 
 
 Longitude 
 (W) 
 
 Approx. 
 
 water 
 
 depth 
 
 (m) 
 
 Current 
 
 meter 
 
 depth 
 
 (m) 
 
 Series 
 length 
 (days) 
 
 Beginning 
 of series 
 
 Samples 
 
 per 
 
 h 
 
 Type 
 
 current 
 meter 
 
 
 
 M 2 
 
 
 
 S 2 
 
 Station 
 
 no. 
 
 Major 
 dir. 
 (°) 
 
 Speed 
 
 (cm/s) 
 
 Greenwich 
 phase 
 
 Rot. 
 
 Major 
 dir. 
 (°) 
 
 Major 
 
 Minor 
 
 JDF 1A S 
 
 48°11.4' 
 
 123°39.8' 
 
 126.2 
 
 12 
 
 42 
 
 2-25-76 
 
 6 
 
 A 
 
 -84.1 
 
 59.05 
 
 2.60 
 
 'l26.6 
 
 C 
 
 -89.5 
 
 JDF 2A M 
 
 48°14.6' 
 
 123°39.1' 
 
 166.4 
 
 15 
 
 41 
 
 2-26-76 
 
 6 
 
 A 
 
 -80.9 
 
 67.69 
 
 9.04 
 
 131.8 
 
 C 
 
 -80.7 
 
 JDF 3A N 
 
 48°18.0' 
 
 123°38.5' 
 
 184.0 
 
 15 
 
 41 
 
 2-26-76 
 
 6 
 
 A 
 
 -68.0 
 
 63.53 
 
 9.34 
 
 122.5 
 
 C 
 
 -61.9 
 
 JDF 13 
 
 48°19.5' 
 
 124°12.0' 
 
 205.6 
 
 40 
 
 47 
 
 10-29-76 
 
 3 
 
 A 
 
 -60.7 
 
 44.66 
 
 0.31 
 
 114.5 
 
 C 
 
 -59.5 
 
 JDF 1A S 
 
 48°11.4' 
 
 123°39.8' 
 
 126.2 
 
 121 
 
 42 
 
 2-25-76 
 
 6 
 
 A 
 
 -86.7 
 
 44.26 
 
 13.66 
 
 93.5 
 
 CC 
 
 -68.4 
 
 JDF 2A M 
 
 48°14.6' 
 
 123°39.1' 
 
 166.4 
 
 161 
 
 41 
 
 2-26-76 
 
 6 
 
 A 
 
 -80.0 
 
 38.95 
 
 18.82 
 
 105.0 
 
 CC 
 
 -55.3 
 
 JDF 3A N 
 
 48°18.0' 
 
 122°38.5' 
 
 184.0 
 
 179 
 
 41 
 
 2-26-76 
 
 6 
 
 A 
 
 -94.9 
 
 40.20 
 
 14.58 
 
 105.8 
 
 CC 
 
 -95.8 
 
 JDF 11 
 
 48°26.0' 
 
 124°30.9' 
 
 235.9 
 
 170 
 
 44 
 
 12-14-76 
 
 3 
 
 A 
 
 113.8 
 
 45.51 
 
 3.57 
 
 59.2 
 
 C 
 
 111.7 
 
 ST-1 
 
 48°14.4' 
 
 123°40.8' 
 
 170.0 
 
 10 
 
 81 
 
 2-13-76 
 
 8 
 
 V 
 
 -73.5 
 
 58.94 
 
 4.04 
 
 124.6 
 
 C 
 
 -62.4 
 
 ST-2 
 
 48°15.0' 
 
 123°44.4' 
 
 170.0 
 
 10 
 
 101 
 
 11-06-76 
 
 8 
 
 V 
 
 -78.8 
 
 59.93 
 
 7.25 
 
 115.7 
 
 C 
 
 -79.1 
 
 ST-3 
 
 48°26.4' 
 
 124°33.0' 
 
 250.0 
 
 10 
 
 101 
 
 11-06-76 
 
 8 
 
 V 
 
 -62.5 
 
 41.89 
 
 2.74 
 
 105.8 
 
 CC 
 
 -46.1 
 
 ST-4 
 
 48°19.8' 
 
 124°09.6' 
 
 190.0 
 
 4 
 
 101 
 
 11-06-76 
 
 8 
 
 V 
 
 -58.7 
 
 51.89 
 
 4.54 
 
 107.0 
 
 C 
 
 -71.3 
 
 MESA W 
 
 48°25.9' 
 
 124°31.2' 
 
 237.7 
 
 76 
 
 45 
 
 6-18-77 
 
 3 
 
 A 
 
 -71.9 
 
 45.93 
 
 2.06 
 
 137.7 
 
 C 
 
 -74.2 
 
 MESA S 
 
 48°18.4' 
 
 124° 14.1' 
 
 191.0 
 
 159 
 
 45 
 
 6-20-77 
 
 3 
 
 A 
 
 -65.7 
 
 40.71 
 
 2.51 
 
 109.5 
 
 CC 
 
 -75.2 
 
 MESA E 
 
 48°14.8' 
 
 123°44.0' 
 
 169.0 
 
 157 
 
 44 
 
 6-21-77 
 
 3 
 
 A 
 
 -78.5 
 
 39.36 
 
 16.36 
 
 100.0 
 
 CC 
 
 -50.3 
 
 MESA W 
 
 48°25.9' 
 
 124°31.2' 
 
 237.7 
 
 11 
 
 45 
 
 6-19-77 
 
 3 
 
 A 
 
 -55.4 
 
 45.11 
 
 0.68 
 
 104.1 
 
 C 
 
 -45.9 
 
 MESA S 
 
 48°18.4' 
 
 124°14.r 
 
 191.0 
 
 13 
 
 45 
 
 6-20-77 
 
 6 
 
 Plessey 
 
 -60.9 
 
 44.16 
 
 2.93 
 
 115.2 
 
 C 
 
 -48.1 
 
 MESA N 
 
 48°22.4' 
 
 124°09.4' 
 
 165.0 
 
 30 
 
 45 
 
 6-20-77 
 
 3 
 
 A 
 
 -64.2 
 
 17.60 
 
 0.63 
 
 102.9 
 
 C 
 
 -70.5 
 
 MESA E 
 
 48°14.8' 
 
 123°44.0' 
 
 169.0 
 
 12 
 
 42 
 
 6-21-77 
 
 3 
 
 A 
 
 -77.8 
 
 9.54 
 
 0.16 
 
 42.8 
 
 CC 
 
 114.7 
 
 ST-5 
 
 48°15.0' 
 
 123°46.6' 
 
 170.0 
 
 10 
 
 97 
 
 6-21-77 
 
 8 
 
 V 
 
 -72.7 
 
 62.75 
 
 16.54 
 
 114.6 
 
 C 
 
 -70.4 
 
 ST-6 
 
 48°26.4' 
 
 124°33.6' 
 
 250.0 
 
 10 
 
 73 
 
 6-21-77 
 
 8 
 
 V 
 
 -53.5 
 
 42.30 
 
 1.04 
 
 96.1 
 
 C 
 
 -41.2 
 
 ST- 7 
 
 48°20.4' 
 
 124°13.2' 
 
 210.0 
 
 10 
 
 97 
 
 6-21-77 
 
 8 
 
 V 
 
 -58.2 
 
 29.15 
 
 0.91 
 
 100.8 
 
 c 
 
 -49.6 
 
 JDF 40 
 
 48°23.2' 
 
 123°03.2' 
 
 144.0 
 
 131 
 
 122 
 
 12-18-77 
 
 3 
 
 A 
 
 -123.5 
 
 30.32 
 
 3.84 
 
 122.5 
 
 CC 
 
 42.5 
 
 JDF 41 
 
 48°23.0' 
 
 122°46.6' 
 
 80.5 
 
 59 
 
 122 
 
 12-18-77 
 
 3 
 
 A 
 
 -100.1 
 
 28.47 
 
 1.18 
 
 115.3 
 
 CC 
 
 -3.7 
 
 JDF 42 
 
 48°13.8' 
 
 122°58.3' 
 
 133.0 
 
 120 
 
 122 
 
 12-18-77 
 
 3 
 
 A 
 
 -86.8 
 
 32.53 
 
 0.31 
 
 107.7 
 
 CC 
 
 -74.1 
 
 JDF 43 
 
 48°08.7' 
 
 122°42.4' 
 
 79.0 
 
 68 
 
 63 
 
 12-17-77 
 
 3 
 
 A 
 
 -56.1 
 
 36.63 
 
 0.60 
 
 117.8 
 
 CC 
 
 -53.9 
 
 JDF 48 
 
 48°11.6' 
 
 123°31.1' 
 
 146.3 
 
 136 
 
 123 
 
 12-17-77 
 
 3 
 
 A 
 
 -84.1 
 
 51.19 
 
 11.87 
 
 118.3 
 
 CC 
 
 -97.5 
 
 JDF 49 
 
 48°15.0' 
 
 123°16.5' 
 
 125.0 
 
 62 
 
 122 
 
 12-17-77 
 
 3 
 
 A 
 
 -93.0 
 
 63.35 
 
 2.57 
 
 127.1 
 
 C 
 
 -94.7 
 
 JDF 40 
 
 48°23.2' 
 
 123°03.2' 
 
 144.0 
 
 31 
 
 122 
 
 12-18-77 
 
 3 
 
 A 
 
 34.7 
 
 33.99 
 
 1.31 
 
 -42.5 
 
 CC 
 
 38.5 
 
 JDF 41 
 
 48°23.0' 
 
 122°46.6' 
 
 80.5 
 
 29 
 
 122 
 
 12-18-77 
 
 3 
 
 A 
 
 -135.9 
 
 27.63 
 
 2.09 
 
 129.4 
 
 CC 
 
 25.6 
 
 JDF 42 
 
 48°13.8' 
 
 122°58.3' 
 
 133.0 
 
 30 
 
 122 
 
 12-18-77 
 
 3 
 
 A 
 
 -87.9 
 
 33.75 
 
 3.82 
 
 129.6 
 
 c 
 
 -81.3 
 
 JDF 43 
 
 48°08.7' 
 
 122°42.4' 
 
 79.0 
 
 28 
 
 101 
 
 12-17-77 
 
 3 
 
 A 
 
 -47.5 
 
 121.97 
 
 3.50 
 
 119.2 
 
 c 
 
 -43.6 
 
 JDF 48 
 
 48°11.6' 
 
 123°31.1' 
 
 146.3 
 
 23 
 
 123 
 
 12-17-77 
 
 3 
 
 A 
 
 -88.3 
 
 64.75 
 
 2.52 
 
 125.0 
 
 c 
 
 -97.4 
 
 JDF 49 
 
 48°15.0' 
 
 123°16.5' 
 
 125.0 
 
 32 
 
 122 
 
 12-17-77 
 
 3 
 
 A 
 
 -95.0 
 
 65.64 
 
 1.70 
 
 127.8 
 
 c 
 
 -94.0 
 
 ST-8 
 
 48°14.4' 
 
 123°15.6' 
 
 130.0 
 
 10 
 
 119 
 
 12-19-77 
 
 8 
 
 V 
 
 -102.0 
 
 57.41 
 
 1.17 
 
 116.9 
 
 CC 
 
 -101.2 
 
 ST-9 
 
 48°23.4' 
 
 123°01.8' 
 
 150.0 
 
 10 
 
 23 
 
 12-19-77 
 
 8 
 
 V 
 
 37.4 
 
 34.32 
 
 3.77 
 
 -51.2 
 
 c 
 
 42.8 
 
 ST-10 
 
 48°13.2' 
 
 122°57.0' 
 
 120.0 
 
 10 
 
 119 
 
 12-19-77 
 
 8 
 
 V 
 
 -91.1 
 
 40.48 
 
 5.54 
 
 116.5 
 
 c 
 
 -97.3 
 
 JDF 51 
 
 48°22.9' 
 
 122°46.8' 
 
 84.0 
 
 30 
 
 85 
 
 7-11-78 
 
 6 
 
 A 
 
 52.3 
 
 37.55 
 
 1.-61 
 
 -30.3 
 
 CC 
 
 50.4 
 
 JDF 52 
 
 48°14.6' 
 
 122°58.9' 
 
 133.5 
 
 30 
 
 84 
 
 7-13-78 
 
 6 
 
 A 
 
 -85.7 
 
 40.74 
 
 3.64 
 
 124.0 
 
 c 
 
 -75.4 
 
 JDF 53 
 
 48°08.7' 
 
 122°42.3' 
 
 77.0 
 
 45 
 
 82 
 
 7-11-78 
 
 6 
 
 A 
 
 -47.4 
 
 71.44 
 
 1.16 
 
 135.4 
 
 c 
 
 -50.7 
 
 ST-11 
 
 48°13.2' 
 
 123°05.4' 
 
 130.0 
 
 10 
 
 41 
 
 7-16-78 
 
 8 
 
 V 
 
 -74.8 
 
 46.30 
 
 1.28 
 
 110.2 
 
 c 
 
 -86.0 
 
 ST- 12 
 
 48°20.4' 
 
 122°58.2' 
 
 110.0 
 
 10 
 
 39 
 
 7-16-78 
 
 8 
 
 V 
 
 -114.2 
 
 45.08 
 
 19.27 
 
 117.1 
 
 c 
 
 -110.1 
 
 ST-13 
 
 48°14.4' 
 
 122°57.6' 
 
 140.0 
 
 10 
 
 106 
 
 7-16-78 
 
 8 
 
 V 
 
 -83.3 
 
 41.74 
 
 8.65 
 
 113.5 
 
 c 
 
 -74.0 
 
 JDF 51 
 
 48°22.9' 
 
 122°46.8' 
 
 84.0 
 
 60 
 
 69 
 
 7-12-78 
 
 6 
 
 A 
 
 -85.1 
 
 30.70 
 
 2.03 
 
 93.3 
 
 c 
 
 50.1 
 
 JDF 52 
 
 48°14.6' 
 
 122°58.9' 
 
 133.5 
 
 60 
 
 84 
 
 7-13-78 
 
 6 
 
 A 
 
 -84.4 
 
 36.12 
 
 2.59 
 
 126.5 
 
 CC 
 
 -88.2 
 
 JDF 53 
 
 48°08.7' 
 
 122°42.3' 
 
 77.0 
 
 60 
 
 72 
 
 7-11-78 
 
 6 
 
 A 
 
 -52.2 
 
 55.73 
 
 3.29 
 
 132.1 
 
 c 
 
 -52.5 
 
 24 
 
Table 5. — M^, S^, N 2 , K\ , 0\ constituents for current records (continued) 
 
 S 2 (cont.) N 2 K x Oj 
 
 Speed (cm/s) Greenwich Rot. Major Speed (cm/s) Greenwich Rot. Major Speed (cm/s) Greenwich Rot. Major Speed (cm/s) Greenwich Rot. 
 
 phase dir. phase dir. phase dir. phase 
 
 Major Minor (°) Major Minor (°) Major Minor (°) Major Minor 
 
 13.75 
 
 2.91 
 
 143.6 
 
 C 
 
 -103.0 
 
 15.62 
 
 4.25 
 
 116.6 
 
 CC 
 
 -83.7 
 
 46.73 
 
 4.08 
 
 17.5 
 
 CC 
 
 88.2 
 
 18.64 
 
 0.76 
 
 177.2 
 
 CC 
 
 17.05 
 
 1.79 
 
 155.5 
 
 C 
 
 -76.8 
 
 20.11 
 
 0.73 
 
 104.6 
 
 c 
 
 -80.8 
 
 43.80 
 
 3.55 
 
 30.0 
 
 C 
 
 -81.7 
 
 23.39 
 
 0.42 
 
 16.9 
 
 CC 
 
 18.70 
 
 0.51 
 
 132.2 
 
 cc 
 
 -32.8 
 
 13.86 
 
 0.39 
 
 103.7 
 
 cc 
 
 -78.9 
 
 32.70 
 
 3.76 
 
 50.0 
 
 C 
 
 -73.2 
 
 26.52 
 
 2.38 
 
 30.0 
 
 CC 
 
 11.39 
 
 0.82 
 
 149.2 
 
 c 
 
 -45.2 
 
 4.24 
 
 0.22 
 
 78.8 
 
 cc 
 
 -64.5 
 
 30.00 
 
 1.19 
 
 13.3 
 
 C 
 
 -64.0 
 
 17.18 
 
 1.37 
 
 -4.3 
 
 C 
 
 11.35 
 
 4.94 
 
 114.3 
 
 cc 
 
 -45.4 
 
 6.59 
 
 1.32 
 
 61.7 
 
 c 
 
 -89.4 
 
 27.28 
 
 0.31 
 
 16.1 
 
 CC 
 
 45.2 
 
 12.75 
 
 0.79 
 
 154.6 
 
 C 
 
 8.88 
 
 6.98 
 
 108.9 
 
 cc 
 
 -73.2 
 
 7.42 
 
 3.69 
 
 58.1 
 
 cc 
 
 -99.4 
 
 33.03 
 
 3.17 
 
 22.2 
 
 CC 
 
 84.8 
 
 18.80 
 
 1.57 
 
 160.3 
 
 CC 
 
 9.56 
 
 3.79 
 
 138.3 
 
 cc 
 
 -84.5 
 
 6.55 
 
 1.52 
 
 65.9 
 
 cc 
 
 78.3 
 
 36.57 
 
 7.24 
 
 187.2 
 
 CC 
 
 85.6 
 
 20.50 
 
 3.32 
 
 145.8 
 
 cc 
 
 14.36 
 
 1.71 
 
 88.0 
 
 c 
 
 -65.0 
 
 13.76 
 
 0.89 
 
 -19.3 
 
 c 
 
 -63.1 
 
 26.42 
 
 2.62 
 
 112.5 
 
 C 
 
 -61.8 
 
 17.68 
 
 1.68 
 
 7.5 
 
 c 
 
 15.55 
 
 1.58 
 
 129.9 
 
 cc 
 
 -54.1 
 
 16.14 
 
 1.53 
 
 73.1 
 
 cc 
 
 -82.4 
 
 38.60 
 
 2.41 
 
 25.7 
 
 C 
 
 -86.6 
 
 23.05 
 
 5.53 
 
 20.1 
 
 c 
 
 12.27 
 
 1.91 
 
 151.9 
 
 c 
 
 -58.7 
 
 14.99 
 
 0.95 
 
 81.8 
 
 c 
 
 -75.9 
 
 38.71 
 
 3.41 
 
 17.1 
 
 C 
 
 -75.5 
 
 18.43 
 
 2.36 
 
 4.8 
 
 cc 
 
 8.57 
 
 1.95 
 
 136.2 
 
 c 
 
 -107.2 
 
 5.26 
 
 4.31 
 
 116.7 
 
 cc 
 
 -66.2 
 
 31.86 
 
 0.18 
 
 11.6 
 
 C 
 
 -65.1 
 
 16.96 
 
 0.00 
 
 -10.2 
 
 cc 
 
 9.63 
 
 1.09 
 
 136.4 
 
 c 
 
 -43.8 
 
 10.63 
 
 0.10 
 
 82.8 
 
 cc 
 
 -68.7 
 
 33.59 
 
 2.71 
 
 8.6 
 
 C 
 
 -59.0 
 
 20.02 
 
 5.85 
 
 -9.1 
 
 c 
 
 11.86 
 
 1.89 
 
 149.1 
 
 c 
 
 -79.1 
 
 9.86 
 
 0.15 
 
 126.5 
 
 c 
 
 -64.4 
 
 28.68 
 
 1.74 
 
 14.6 
 
 C 
 
 -65.7 
 
 16.76 
 
 2.79 
 
 25.8 
 
 c 
 
 10.28 
 
 0.01 
 
 137.4 
 
 cc 
 
 -64.0 
 
 7.44 
 
 0.10 
 
 73.7 
 
 cc 
 
 -68.1 
 
 24.76 
 
 0.18 
 
 12.5 
 
 CC 
 
 -63.7 
 
 12.69 
 
 0.31 
 
 -7.1 
 
 cc 
 
 8.78 
 
 4.41 
 
 95.8 
 
 cc 
 
 -93.9 
 
 7.01 
 
 3.93 
 
 81.1 
 
 cc 
 
 -87.3 
 
 27.28 
 
 2.61 
 
 12.4 
 
 CC 
 
 100.2 
 
 15.34 
 
 3.81 
 
 162.0 
 
 cc 
 
 12.80 
 
 2.92 
 
 124.6 
 
 c 
 
 -44.3 
 
 9.27 
 
 0.51 
 
 70.6 
 
 c 
 
 -66.9 
 
 26.63 
 
 1.34 
 
 15.0 
 
 CC 
 
 -57.3 
 
 11.76 
 
 3.98 
 
 -4.1 
 
 cc 
 
 8.97 
 
 0.27 
 
 137.8 
 
 cc 
 
 -61.3 
 
 8.77 
 
 1.68 
 
 73.0 
 
 c 
 
 -65.7 
 
 26.95 
 
 0.30 
 
 18.8 
 
 c 
 
 -60.6 
 
 17.79 
 
 1.78 
 
 -10.2 
 
 c 
 
 4.93 
 
 1.36 
 
 -18.8 
 
 c 
 
 -63.2 
 
 14.80 
 
 0.68 
 
 137.7 
 
 c 
 
 -70.4 
 
 10.68 
 
 0.09 
 
 10.5 
 
 c 
 
 -59.2 
 
 4.80 
 
 0.19 
 
 21.7 
 
 cc 
 
 28.94 
 
 6.95 
 
 41.8 
 
 c 
 
 -74.8 
 
 6.12 
 
 2.96 
 
 95.7 
 
 c 
 
 111.5 
 
 6.29 
 
 1.38 
 
 108.0 
 
 cc 
 
 98.1 
 
 8.01 
 
 2.91 
 
 43.4 
 
 cc 
 
 16.72 
 
 6.60 
 
 139.8 
 
 c 
 
 -69.5 
 
 12.23 
 
 5.33 
 
 89.7 
 
 c 
 
 -64.9 
 
 34.86 
 
 6.87 
 
 18.0 
 
 c 
 
 -83.3 
 
 20.32 
 
 1.55 
 
 24.8 
 
 c 
 
 10.76 
 
 1.45 
 
 127.2 
 
 c 
 
 -51.6 
 
 8.40 
 
 0.66 
 
 60.5 
 
 c 
 
 -65.0 
 
 24.10 
 
 1.86 
 
 5.7 
 
 cc 
 
 -60.9 
 
 11.72 
 
 3.05 
 
 -25.0 
 
 cc 
 
 2.14 
 
 1.31 
 
 189.9 
 
 cc 
 
 -56.0 
 
 9.98 
 
 0.08 
 
 100.3 
 
 c 
 
 -64.0 
 
 17.18 
 
 0.22 
 
 8.9 
 
 cc 
 
 -49.0 
 
 10.40 
 
 2.15 
 
 16.8 
 
 c 
 
 9.76 
 
 2.62 
 
 -14.0 
 
 cc 
 
 -164.2 
 
 5.18 
 
 0.45 
 
 82.6 
 
 c 
 
 54.7 
 
 20.91 
 
 0.68 
 
 191.6 
 
 cc 
 
 26.8 
 
 12.90 
 
 6.28 
 
 147.9 
 
 c 
 
 4.96 
 
 1.34 
 
 29.2 
 
 cc 
 
 -107.6 
 
 6.72 
 
 1.18 
 
 98.7 
 
 c 
 
 62.7 
 
 18.90 
 
 1.34 
 
 194.5 
 
 cc 
 
 54.0 
 
 12.53 
 
 2.00 
 
 156.1 
 
 c 
 
 10.76 
 
 2.51 
 
 128.4 
 
 c 
 
 -94.2 
 
 7.90 
 
 1.94 
 
 79.1 
 
 cc 
 
 -84.4 
 
 18.40 
 
 0.98 
 
 1.6 
 
 c 
 
 93.7 
 
 12.58 
 
 0.80 
 
 155.8 
 
 cc 
 
 42.06 
 
 1.28 
 
 143.9 
 
 c 
 
 122.5 
 
 35.64 
 
 2.47 
 
 133.2 
 
 c 
 
 -54.1 
 
 20.73 
 
 1.28 
 
 -24.6 
 
 c 
 
 -46.4 
 
 14.13 
 
 1.90 
 
 2.9 
 
 c 
 
 12.03 
 
 1.84 
 
 146.3 
 
 cc 
 
 -85.2 
 
 11.02 
 
 0.02 
 
 82.8 
 
 c 
 
 -97.0 
 
 37.60 
 
 2.67 
 
 13.5 
 
 cc 
 
 82.8 
 
 22.32 
 
 2.64 
 
 174.3 
 
 c 
 
 16.48 
 
 0.25 
 
 155.6 
 
 cc 
 
 -96.9 
 
 12.84 
 
 0.76 
 
 91.5 
 
 c 
 
 -88.9 
 
 36.94 
 
 2.27 
 
 18.1 
 
 c 
 
 -83.7 
 
 16.69 
 
 0.55 
 
 -0.3 
 
 c 
 
 7.03 
 
 1.55 
 
 -21.1 
 
 cc 
 
 -140.8 
 
 7.48 
 
 2.48 
 
 113.8 
 
 cc 
 
 37.9 
 
 25.14 
 
 1.60 
 
 213.9 
 
 cc 
 
 23.8 
 
 11.59 
 
 2.30 
 
 207.6 
 
 cc 
 
 7.17 
 
 2.49 
 
 -20.8 
 
 c 
 
 -130.0 
 
 6.11 
 
 1.22 
 
 105.2 
 
 cc 
 
 66.4 
 
 22.04 
 
 1.38 
 
 189.4 
 
 cc 
 
 93.0 
 
 12.27 
 
 5.55 
 
 139.9 
 
 cc 
 
 6.65 
 
 1.15 
 
 163.6 
 
 c 
 
 -93.4 
 
 5.43 
 
 0.44 
 
 89.2 
 
 c 
 
 -82.3 
 
 19.16 
 
 3.73 
 
 34.9 
 
 c 
 
 -87.1 
 
 12.06 
 
 1.23 
 
 28.9 
 
 cc 
 
 44.26 
 
 3.56 
 
 113.0 
 
 c 
 
 -45.3 
 
 20.07 
 
 1.65 
 
 137.8 
 
 cc 
 
 -44.9 
 
 57.05 
 
 4.07 
 
 10.0 
 
 cc 
 
 -35.2 
 
 35.71 
 
 8.50 
 
 -3.0 
 
 cc 
 
 17.63 
 
 0.68 
 
 162.0 
 
 cc 
 
 -92.5 
 
 13.63 
 
 0.08 
 
 91.8 
 
 cc 
 
 -87.1 
 
 43.97 
 
 2.90 
 
 29.6 
 
 c 
 
 -85.2 
 
 27.29 
 
 1.05 
 
 4.7 
 
 c 
 
 16.85 
 
 0.04 
 
 152.1 
 
 cc 
 
 -101.3 
 
 15.10 
 
 1.01 
 
 94.7 
 
 c 
 
 -96.0 
 
 39.46 
 
 0.04 
 
 25.7 
 
 cc 
 
 -95.3 
 
 19.55 
 
 1.38 
 
 7.4 
 
 cc 
 
 16.96 
 
 1.15 
 
 146.4 
 
 c 
 
 -119.9 
 
 12.78 
 
 0.32 
 
 86.4 
 
 cc 
 
 -107.2 
 
 33.05 
 
 2.52 
 
 19.3 
 
 cc 
 
 71.7 
 
 15.79 
 
 4.91 
 
 173.3 
 
 cc 
 
 9.80 
 
 0.63 
 
 190.6 
 
 cc 
 
 26.7 
 
 7.61 
 
 0.69 
 
 -61.9 
 
 cc 
 
 48.7 
 
 22.50 
 
 3.24 
 
 204.6 
 
 cc 
 
 49.8 
 
 11.87 
 
 0.11 
 
 183.8 
 
 cc 
 
 7.95 
 
 1.50 
 
 152.1 
 
 c 
 
 -81.3 
 
 6.95 
 
 1.40 
 
 107.3 
 
 c 
 
 -89.1 
 
 18.97 
 
 1.32 
 
 24.9 
 
 c 
 
 -74.2 
 
 13.96 
 
 3.07 
 
 17.1 
 
 c 
 
 8.77 
 
 1.28 
 
 -0.4 
 
 c 
 
 -113.9 
 
 5.95 
 
 0.80 
 
 120.0 
 
 c 
 
 66.3 
 
 26.06 
 
 3.60 
 
 188.7 
 
 cc 
 
 84.7 
 
 15.02 
 
 5.32 
 
 177.5 
 
 cc 
 
 10.61 
 
 2.06 
 
 144.3 
 
 c 
 
 -83.0 
 
 7.37 
 
 0.57 
 
 99.3 
 
 c 
 
 -85.9 
 
 19.39 
 
 2.47 
 
 24.8 
 
 c 
 
 -89.1 
 
 9.87 
 
 1.46 
 
 19.7 
 
 c 
 
 20.27 
 
 1.44 
 
 137.8 
 
 c 
 
 -48.8 
 
 13.09 
 
 0.16 
 
 114.3 
 
 cc 
 
 -46.9 
 
 29.50 
 
 0.56 
 
 9.3 
 
 cc 
 
 -42.6 
 
 15.15 
 
 1.70 
 
 20.7 
 
 c 
 
 13.02 
 
 2.30 
 
 146.8 
 
 cc 
 
 -76.8 
 
 10.30 
 
 1.57 
 
 78.3 
 
 cc 
 
 -93.6 
 
 28.84 
 
 2.34 
 
 25.1 
 
 c 
 
 -85.2 
 
 17.63 
 
 0.64 
 
 4.7 
 
 cc 
 
 11.30 
 
 3.30 
 
 151.0 
 
 c 
 
 -108.8 
 
 11.15 
 
 4.57 
 
 89.4 
 
 c 
 
 -91.1 
 
 15.68 
 
 4.93 
 
 27.6 
 
 c 
 
 61.5 
 
 13.26 
 
 2.64 
 
 180.8 
 
 c 
 
 16.26 
 
 2.12 
 
 157.2 
 
 c 
 
 -80.3 
 
 8.99 
 
 0.84 
 
 84.3 
 
 c 
 
 -80.1 
 
 25.54 
 
 7.95 
 
 31.6 
 
 c 
 
 -82.8 
 
 14.69 
 
 0.56 
 
 0.2 
 
 cc 
 
 8.13 
 
 1.65 
 
 -35.2 
 
 c 
 
 -97.5 
 
 4.59 
 
 0.73 
 
 57.4 
 
 cc 
 
 70.4 
 
 16.16 
 
 4.29 
 
 178.4 
 
 cc 
 
 55.1 
 
 11.65 
 
 2.40 
 
 138.0 
 
 c 
 
 7.80 
 
 0.56 
 
 137.9 
 
 cc 
 
 -83.0 
 
 7.37 
 
 0.57 
 
 99.3 
 
 c 
 
 -85.9 
 
 19.39 
 
 2.47 
 
 24.8 
 
 c 
 
 -89.1 
 
 9.87 
 
 1.46 
 
 19.7 
 
 c 
 
 16.73 
 
 0.28 
 
 139.4 
 
 cc 
 
 -47.5 
 
 9.17 
 
 0.44 
 
 113.9 
 
 c 
 
 -45.9 
 
 25.71 
 
 0.58 
 
 16.4 
 
 c 
 
 -44.3 
 
 11.29 
 
 0.52 
 
 28.1 
 
 cc 
 
 25 
 
60 - 
 
 50 
 
 < 40 
 
 o 
 
 ^ 30 
 
 u. 
 
 o 
 
 Q 20 
 
 SURFACE MOORING ID 
 4 5 2-1 
 
 _| U_J 
 
 11 10,13 
 
 LEGEND 
 o — o WINTER 
 d-d SUMMER 
 J I I 
 
 20 
 
 80 
 
 1 00 
 
 I20 
 
 I40 
 
 I40 
 
 I20 
 
 I00 
 
 40 
 
 20 
 
 / 
 
 I60 ^ 
 I20 E 
 
 „„ Ld 
 
 80 oo 
 < 
 o-|40 x 
 
 20 
 
 40 
 DISTA 
 
 60 80 I00 
 
 NCE UP-STRAIT ( km) 
 
 I20 
 
 I40 
 
 Figure 24. — K-± tidal current amplitudes 
 (M 2 , K\, 0\, N 2 ) and phases (M 2 , K L ) for 
 the major constituents (as computed from 
 selected current records) as a function 
 of distance landward from the mouth of 
 the Strait. 
 
 Results in this section demonstrate the importance of coastal wind forcing and the rela- 
 tive lack of influence by local winds and river runoff in the Strait of Juan de Fuca. One of 
 Cannon's (1978) principal findings was that large- amplitude, long-period current flucuations 
 occurred in the western Strait particularly in winter. These motions caused the net seaward 
 estuarine flow in the surface layer to reverse for periods up to 10 days, causing eastward 
 intrusions of coastal ocean water as far as 90 km from the mouth and retention of surface water 
 within the system,. These events were related to coastal storms and followed periods of strong 
 southwesterly winds off the Washington coast (Holbrook and Halpern, 1977; Holbrook et al. , 
 1980). They penetrated the eastern basin to an undetermined extent. 
 
 2.5.1 Subtidal current observations 
 
 In the eastern Strait, the spatial distribution of subtidal current variance did not vary 
 appreciably with season in contrast to the vast difference in subtidal variance between winter 
 and summer measured in the western Strait (Holbrook et al. , 1980). The vertical and horizon- 
 tal distribution of subtidal current fluctuations can best be seen by examining currents 
 measured at locations A and G (see fig. 2). Examples of subtidal along-strait current fluc- 
 tuations during winter and summer at sites A and G are contrasted in fig. 26. Throughout 
 this section, tidal and higher frequency fluctuations have been removed by applying a 
 A|s A 2 4 Godin low-pass filter (Godin, 1973), which has a half-amplitude frequency of 
 0.0143 cph. The largest current fluctuations occurred at 4-m depth at site A near the mouth 
 
 26 
 
Figure 25. — Typical flood and ebb currents computed from barotropic tidal model, showing 
 locations of surface current moorings . 
 
 of the Strait during winter, where subtidal current reversals accounted for 35% of the fil- 
 tered record, lasted from 3 to 10 days, and had maximum up-strait speeds of 25 to 55 cm/s. 
 During winter 1977-78 at site G, three periods of up-strait flow were measured that lasted 
 from 2 to 7 days and had maximum up-strait speeds of 5 to 30 cm/s. Between June and August 
 at site A, the along-strait components of near surface and lower layer currents exhibited 
 less variability than during fall, winter, and spring. No reversals occurred at sites A or 
 G during these months. During September at site A, quasi-steady-state summer conditions 
 ended, and three reversals occurred. The longer period fluctuations were generally 180° 
 out of phase between the surface and deep layers. The amplitude of the deep layer currents 
 was much smaller than that of the near- surface currents. 
 
 The longitudinal distribution of subtidal current variance in the near- surface and deep 
 layer is shown in fig. 27. Subtidal variance decreased with depth in the near-surface layer, 
 especially in the western Strait during winter when the variance was primarily confined to the 
 upper 40 m of the water column. During summer in the western Strait and throughout the year 
 in the eastern Strait, subtidal variance below 50-m depth was less than 50 cm 2 /s 2 . Thus, the 
 estimated subtidal rms amplitude about the mean estuarine flow in the deep layer was less than 
 7 cm/s throughout the system. Fluctuations in the surface layer were larger and were related 
 to meteorological events (see discussion of wind forcing in this section). 
 
 Horizontal coherence between mooring sites in the eastern Strait was weak. For example, 
 coherence squared estimates over the most energetic region of the spectrum (centered at 
 0.00323 cph) between 4-m currents at ST-8 and ST-9 and at ST-8 and ST- 10 were 0.57 and 
 0.55, respectively. Over the entire subtidal frequency range approximately 19% and 18%, 
 respectively, of the variance was coherent between these pairs, with all the coherent vari- 
 ance occurring in the east- west component; no estimate for the north- south components was 
 significant at the 95% level. In contrast, over the tidal frequencies, 85% and 95% of the 
 variance were coherent. 
 
 Vertical coherence was much higher than horizontal coherence at all mooring sites, with 
 85% to 95% of the subtidal variance significantly coherent in the upper layer. For example, 
 coherence estimates over the most energetic region of the spectrum (centered at 0.00323 cph) 
 between 4 and 20 m at ST-9 and ST- 10 were 0.93 and 0.94, respectively. 
 
 In summary, the distribution of subtidal variance in the eastern Strait may be character- 
 ized as less intense than in the western Strait, with weak horizontal and strong vertical 
 
 27 
 
-30 
 
 e: 
 
 LOWER- LAYERU59m) 
 
 SITE A SUMMER CURRENTS 
 
 FLOOD 
 
 21 25 301 5 
 JUN JUL 
 
 77 77 
 
 10 15 20 25 30 1 5 
 RUG 
 77 
 
 10 15 20 25 30 1 5 
 SEP 
 77 
 
 10 15 20 25 
 
 E 
 
 130 25 30 1 5 
 
 DEC JHN 
 
 77 78 
 
 10 15 20. 25 30 1 5 
 FEB 
 78 
 
 10 15 20 25 1 5 
 MAR 
 78 
 
 10 15 20 25 30 1 5 
 APR 
 78 
 
 60 
 
 30 
 
 : - 
 
 -30 - 
 
 -60 
 
 NEAR-SURFACE (4m) 
 
 L0WER-LAYER(60m 
 
 SITE G SUMMER CURRENTS 
 
 16 20 25 30 1 5 
 JUL AUG 
 
 78 * 78 
 
 10 15 20 25 30 1 5 
 SEP 
 78 
 
 10 15 20 25 301 5 
 OCT 
 78 
 
 EBB 
 
 FLOOD 
 
 10 15 
 
 Figure 26. — Along-strait subtidal currents at sites A and G during winter and 
 Tidal and higher frequency fluctuations have been removed by applying an A\ 
 Godin (1973) low-pass filter. Up-strait flow is negative. 
 
 summer . 
 5 A 2k 
 
 coherence in the near- surface layer. The low level of horizontal coherence is not necessarily 
 surprising, since bottom and lateral topographic features are extremely irregular. Also, the 
 appropriate horizontal scale for internal motions as defined by the internal Rossby radius of 
 deformation was estimated to be between 2 and 10 km, which was less than the horizontal spa- 
 cing of the moorings . 
 
 2.5.2 Wind observations 
 
 Over-the-water and coastal wind measurements were made during winter 1977-78 and 
 summer 1978 in conjunction with current observations in the eastern basin of the Strait. 
 Over-the-water winds were measured and recorded by vector-averaging wind recorders 4 m 
 above the water from surface buoys located at sites 8 through 13 (fig. 6). Winds were 
 measured and recorded onshore by Aanderaa wind recorders at Smith Island, New Dungeness 
 Spit, and Tatoosh Island. Winds measured at permanent weather stations operated by the 
 U.S. National Weather Service and Environment Canada were used to supplement the time 
 series data. The coastal wind field was estimated from a 3° by 3° atmospheric pressure 
 grid centered at 48°N, 125°W, 25 km off the Washington coast (Bakun, 1978, personal com- 
 munication). Surface frictional effects were approximated by rotating the wind vectors 
 15° counterclockwise and reducing speeds by 30%. 
 
 28 
 
TISOm 
 
 20 
 
 40 60 80 100 120 
 
 DISTANCE UP- STRAIT(km) 
 
 1000 
 
 800 
 
 600 
 
 400 
 
 200 - 
 
 ■ JUN-AUG 77 ■ 
 
 JUL-AUG 78- 
 
 SUMMER 
 
 UPPER LAYER 
 4m l0m 
 
 Figure 27. — Longitudinal distribution of 
 subtidal variance during winter and 
 summer. Subtidal variance was pri- 
 marily confined to the upper 40 m of 
 the water column. 
 
 20 
 
 40 60 80 100 
 
 DISTANCE UP- STRAIT (km) 
 
 120 
 
 140 
 
 During the winter experiment, winds along the Washington coast were predominantly south- 
 easterly, reflecting offshore cyclonic activity. The maximum computed wind was 24.7 m/s to- 
 ward 333° TN on 9 February 1978. Winds measured at the buoy sites and shore stations in the 
 Strait were easterly, with the exception of brief periods of strong westerlies associated 
 with frontal passages. The strongest winds were recorded on 5 January, with maximum shore 
 wind speeds of 21.9, 19.1, and 14.4 m/s at Race Rocks, New Dungeness, and Smith Island, re- 
 spectively. Coincident maximum over-the-water winds were 19.8, 17.9, and 17.3 m/s at ST-8, 
 9, and 10, respectively. During this storm, a winter 1977-78 maximum atmospheric pressure 
 difference of 8 mb was observed between Bellingham and Quillayute airports . In the eastern 
 Strait, westerly winds generally decreased in strength with distance eastward as a result of 
 orographic effects . In the regions east of the buoy sites , southerly winds from Puget Sound 
 influenced the local wind field. 
 
 During the summer experiment, coastal winds were northwesterly, reflecting the offshore 
 Pacific high. Winds in the Strait were westerly and had an additional superposed 5 to 10 m/s 
 afternoon sea breeze on most days . The amplitude of the sea breeze was least in the eastern 
 Strait. By late August storm activity had increased, and between 23 and 26 August a low 
 pressure system centered 500 km off the Washington coast generated southerly winds of more 
 than 13 m/s for several days. This storm occurred during a 4-day study period when surface 
 currents were intensively monitored (see section 2.5). 
 
 Statistical comparisons between winds measured at the buoy sites and at the National 
 Weather Service remote shore locations revealed that winds throughout the region were similar 
 at any given time. Over-the-water winds were significantly correlated with coastal winds at 
 the 95% level, with east- west components having higher correlation coefficients (R = 0.6 to 
 0.8) than north-south components (R = 0.4 to 0.6). Over-the-water wind speeds were weaker, 
 
 29 
 
typically 60% to 80% of the coastal wind speeds. Uncorrelated fluctuating wind components had 
 root-mean-square amplitudes of 2 to 3 m/s . The correlations between over-the-water winds and 
 different nearby coastal winds were similar. For example, correlation coefficients between the 
 east-west components of winds measured at ST-8 and New Dungeness and Port Angeles were 
 0.62 and 0.56, respectively. 
 
 2.5.3 Local wind forcing 
 
 The near- surface current response to the local wind field was weak but statistically 
 significant at the 95% level. The squared coherence between the over-the-water winds and the 
 near-surface currents (at 4-, 10-, 20-m depth) at ST-8 was 0.46 at periods longer than 8 days 
 for east-west winds and currents and between 0.52 and 0.72 at periods of 1.4 to 2.9 days for 
 east-west winds and north-south currents. In all, 18% of the subtidal current fluctuations at 
 ST-8 at 4-m depth were related to the local winds . Poorer coherences were computed for ST-9 
 and ST- 10 during winter. Although the current response nearer the surface was undoubtedly 
 more dramatic, measurements in this study showed a weak relationship between the local winds 
 and near-surface currents. The strongest local winds of the winter occurred on 5 January, 
 when westerly wind speeds exceeded 15 m/s for several hours. These winds caused the verti- 
 cal mean shear between 4 and 10 m at ST-8 and ST- 10 to decrease from 1 cm/s/m to approxi- 
 mately zero. However, the net flow remained westward at all measured depths in the near- 
 surface layer. Similar fluctuations in the vertical shear were recorded during other strong 
 westerlies. This response decreased with depth, and the vertical shear change between 10- 
 and 20-m depths was smaller. This lack of local wind forcing may be due in part to the 
 limited duration (usually a few hours) of strong winds in the Strait. 
 
 2.5.4 Nonlocal meteorological forcing 
 
 A principal result of experiments conducted in the western Strait was the finding that 
 the near-surface and deeper subtidal current fluctuations were highly coherent with coastal 
 winds (Cannon, 1978; Holbrook and Halpern, 1977; Holbrook et al. , 1980). This relationship 
 can be reviewed by examining time series of coastal winds and along- strait currents in the 
 western Strait during winter, as shown in fig. 28. Vertical lines are drawn at times of maxi- 
 mum near-surface up-strait current reversal at site A. Maximum near-surface current rever- 
 sals at site C lagged those at site A by 47 h, indicating an up-strait propagation velocity of 
 37 cm/s . Periods of deceleration in the along- strait flow before maximum reversal are coinci- 
 dent with south-southwesterly coastal winds and rising sea level near the Strait entrance at 
 Neah Bay and Port Renfrew. These data suggest that an Ekman flux mechanism was responsible 
 for the generation of these reversals, which then slowly propagated up-strait. Maximum up- 
 strait reversals were accompanied by a reversal in the vertical current shear making them 
 near-surface baroclinic phenomena. No phasing was observed in the deeper layer, which also 
 responded to coastal winds, suggesting that the barotropic response in the near-surface 
 layer was masked by the larger amplitude baroclinic response. 
 
 An important characteristic of coastal forcing is the directionality of the offshore winds, 
 which generates the response. Figure 29 shows squared coherence spectra between computed 
 coastal winds and along-strait currents at sites A and C. Contours of squared coherence are 
 drawn as a function of wind direction (positive axis represents direction toward which wind 
 blows). Maximum squared coherence was found over the most energetic portion of the spectrum 
 (periods of 12 days) when the winds were along a 020° to 200° TN axis. The squared coher- 
 ence estimates (95% confidence interval) were 0.90 (0.70 to 0.96) at site A and 0.73 (0.34 to 
 0.88) at site C. The current response lagged (±95% confidence interval) the coastal winds by 
 39 (±6) h at site A and by 91 (±23) h at site C. Totals of 71% and 44% of the along-strait 
 subtidal variability at sites A and C, respectively, were attributed to coastal winds along 
 an 020° to 200° TN axis. Table 6 summarizes other statistics between the records shown in 
 fig. 28. It is noteworthy that coastal winds from the southeast (toward 350° to 300° TN) did 
 not generate a strong current response in the Strait over the long-period time scales. 
 
 Although the impact of coastal forcing on circulation was less dramatic in the eastern 
 Strait than in the western Strait, it still represented a principal driving force of subtidal 
 current reversals. As in the western Strait, the frequency and strength of up-strait flow 
 reversals in the eastern Strait decreased with distance eastward. Representative time series 
 of near-surface currents in the eastern Strait at sites D (JDF48) and G (ST-10) as well as 
 
 30 
 
 
' 'lb 15 ' ' ?0 25 30 5 10 15 20 25 30 1 5 10 IS 20 25 30 1 5 10 15 
 
 JJ 
 
 £ 
 
 SITE A\ 
 
 aI ALONG-STRAIT VERTICAL SHEAR /U(4tn) 
 
 -unomi A 
 
 , 
 
 
 ii\ a rr\ L a ft\ 
 
 / 
 
 )\ £*fl 
 
 \_/-SITE C^ N_^sy- |, 
 
 
 
 
 5 10 15 20 25 301 5 10 15 20 25 30 1 5 10 15 20 25 30 1 5 10 
 
 wnu nFr JHN ~s-P 
 
 CORRECTED SEA LEVEL 
 
 PORT RENFREW 
 
 JD 1010 
 E 
 
 I ** .LOW-PASS FILTERED | 
 
 ^UNFILTERED 
 
 
 
 ATMOSPHERIC PRESSURE AT OUILLAYUTE 
 
 
 
 5 10 15 20 25 3q 5 10 15 20 25 30 1 5 10 15 20 25 30 1 5 
 NOV DEC JHN F|B 
 
 76 76 77 77 
 
 5 10 15 20 25 301 5 10 15 20 25 30 1 5 10 15 20 25 30 1 5 10 15 
 NOV DEC JRN FEB 
 
 76 76 77 77 
 
 Figure 28. — Low-pass filtered time series of local winds, near- 
 surface and deep currents, vertical current shear between 4 
 and 10 m, computed geostrophic coastal winds, corrected sea 
 level at Port Renfrew and Neah Bay, and atmospheric pressure 
 at various sites. Vertical lines indicate times of maximum 
 up-strait (negative) current flow at site A. Periods of 
 deceleration in the along-strait direction, before maximum 
 current reversal, are coincident with SSW coastal winds and 
 rising corrected sea level at Port Renfrew and Neah Bay. 
 
 31 
 
PERIOD (H) 
 
 PERIOD (H) 
 
 002 03 04 
 
 FREQUENCY (CPH) 
 
 02 003 
 
 FREQUENCY (CPHI 
 
 Figure 29. — Squared coherence spectra (above) for 6-h values of computed geostrophic 
 coastal winds (Bakun, 1977) and 6-h average along-strait currents and density 
 spectra (below) at sites A and C. Maximum subtidal coherence occurred with 
 coastal winds directed along a 020° -200° axis. 
 
 local and computed coastal winds are shown in fig. 30. Vertical lines are drawn at times of 
 maximum up-strait reversal at site D. Seven periods of reversed currents at 23-m depth at site 
 D accounted for 16% of the subtidal record, lasted from 2 to 4 days, and had maximum speeds 
 of 6 to 18 cm/s. At 4-m depth at site G, 44 km up-strait, three reversals accounted for 14% 
 of the subtidal record, lasted from 4 to 6 days, and had maximum speeds of 6 to 27 cm/s. 
 
 Although all seven reversals at site D occurred after periods of southerly coastal winds , 
 the direction and duration of these winds played an important role in both reversal strength 
 and up-strait penetration distance. As seen in fig. 29, the response to southeasterly coastal 
 winds was weak whereas south-southwesterly winds generated the largest coherencies. During 
 winter 1977-78, coastal winds were predominantly southeasterly with only brief periods of 
 southwesterly flow. Consequently, reversals in the eastern Strait were not as large as might 
 be expected during other winters . Three reversals at site G followed periods of south- 
 southwesterly winds . Although some of the strongest southeasterly winds occurred on 7-8 
 January, the induced reversal was not measured at site G, despite the additive effects of a 
 strong up-strait wind stress. One of the clearest examples of coastal forcing occurred in 
 March, when southerly coastal winds of more than 15 m/s blew for several days (6-8 March) 
 and were preceded and followed by periods of relative calm. The maximum reversal was meas- 
 ured at site D on 10 March, nearly 4 days after commencement of southerly coastal winds. 
 The relative effects of wind strength are seen during periods of southerly winds that vary in 
 strength on 15-17 and 23-27 March. 
 
 Although coastal low pressure systems with southwesterly winds occur more frequently and 
 persist longer during winter than during summer, occasionally a low pressure system will sit 
 
 32 
 
Table 6. — Squared coherence and phase between local and coastal winds, currents , vertical 
 current shear, corrected sea level, and atmospheric pressure shown in fig. 28 
 
 
 
 Along-strait currents 
 (cm/s) 
 
 
 Current 
 (cm/ 
 
 shear 
 
 5) 
 
 Corrected 
 
 sea level 
 
 (cm) 
 
 Atmospheric 
 
 pressure 
 
 (mb) 
 
 
 A/4 m 
 
 A/181 
 
 m 
 
 B/4 m 
 
 B/178 m 
 
 C/4 m 
 
 A 
 (4-10 
 
 m) 
 
 C 
 (4-10 m) 
 
 Port 
 Renfrew 
 
 QA 
 
 BA-QA 
 
 Record length (days) 
 
 102 
 
 41 
 
 
 51 
 
 42 
 
 102 
 
 102 
 
 
 102 
 
 102 
 
 102 
 
 102 
 
 Computed coastal 
 wind along 020°-200° 
 at 48°N, 125°W (Bakun) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Variance 1 
 % total 2 
 Phase lag 3 (h) 
 95% conf. 
 
 553 
 
 71 
 
 39 
 
 6 
 
 41 
 
 70 
 
 
 
 20 
 
 
 5 
 2 
 1 
 4 
 
 41 
 
 78 
 
 -3 
 
 9 
 
 207 
 
 44 
 91 
 23 
 
 8.0 
 40 
 29 
 30 
 
 
 5.3 
 36 
 88 
 29 
 
 5.1 
 
 15 
 
 -12 
 
 13 
 
 3.0 
 7 
 
 O 6 
 2 
 
 0.48 
 
 27 
 
 12 
 
 3 
 
 Along-strait local 
 wind at site B 
 
 Variance 1 
 % total 2 
 Phase lag 3 
 95% conf. 
 
 (h) 
 
 121 
 
 11 
 
 124 
 
 11 
 
 52 
 
 9.2 
 
 16 
 
 21 
 
 56 
 
 22 
 
 11 
 
 46 
 
 -3 
 
 8 4 
 
 -34 
 
 -5 4 
 
 -28 
 
 21 
 
 10 
 
 3 
 
 13 
 
 5 
 
 15 
 
 39 
 
 7.7 
 52 
 
 -33 
 27 
 
 6 
 
 3 5 
 
 2 
 
 1.7 
 
 4 
 
 13 
 
 2 
 
 1.7 
 
 94 
 
 -9 
 5 
 
 1 Subtidal variance (cm 2 /s 2 , cm 2 , mb 2 ) coherent at 95% level. 
 
 Percent of total subtidal variance coherent at 95% level. 
 
 Phase lag (with 95% confidence interval) of estimate containing most coherent variance. 
 
 Positive phase means winds lead coherent series. 
 
 Up-strait winds lead maximum out-strait currents in lower layer by indicated phase lag. 
 
 Up-strait winds lead high water at Port Renfrew by 3 h. 
 
 Northward coastal winds occur at the same time as low pressure at Quillayute. 
 
 off the coast long enough during summer to generate a response in the Strait. Such a system 
 was observed during 20-27 August 1978 (fig. 31). South- southwesterly winds associated with 
 this system generated a near- surface, up-strait current reversal that was observed 4 to 6 days 
 later in the eastern Strait. In fig. 32 a vertical line is drawn at the time of arrival of the 
 maximum reversal at site D to illustrate the phase lag of this response relative to the coastal 
 winds and currents farther up-strait. The reversal was measured at site F 39 h later than at 
 site D, giving an up-strait phase velocity of 21 cm/s in the eastern Strait. The currents at 
 site G did not reverse (Holbrook et al. , 1980). 
 
 Before and during up-strait propagation of the storm-induced reversal, an intensive 4-day 
 study period was carried out, during which surface currents were monitored using the Coastal 
 Ocean Dynamics Analysis Radar (CODAR) and surface drifters. In this study NOAA, Environ- 
 ment Canada, and MESA-contracted scientists investigated in greater detail the near-surface 
 circulation in the Strait to provide an intercomparison of direct and remote sensing techniques 
 for measuring near-shore currents, and to provide observational data for testing the Puget 
 Sound surface circulation model. 
 
 The CODAR system, which consisted of two shore-based, transportable HF Doppler radars, 
 remotely mapped hourly surface currents over a 900-km 2 area with a spatial resolution of 
 1.2 km (Barrick et al. , 1977). Measurements were made between Point Wilson and New 
 Dungeness for 3 days and between New Dungeness and Port Angeles for 1 day. Although 
 analysis of this data set is continuing, preliminary comparisons between the near- surface 
 currents measured by VACM's at the three surface mooring sites and the CODAR data show 
 good agreement for both the mean and tidal flows. The 3-day average (23-25 August) flow 
 (fig. 33) showed net seaward velocities of 20 to 40 cm/s throughout the eastern Strait. 
 Examples of typical flood and ebb surface currents as measured by the CODAR system are 
 shown in fig. 34; because of the additive effects of estuarine circulation, the ebbs are 
 stronger and floods weaker than those computed from Crean's model (fig. 25). This pattern 
 was consistent with most of the near-surface current data during this period. The sub- 
 
 33 
 
Figure 30. — Low-pass filtered time series of near-surface currents at sites D and G, and 
 unfiltered local and coastal winds during winter. Vertical lines are drawn at times of 
 maximum up-strait reversal at site D. Extent to which coastal winds affected flow in 
 eastern basin depended on their strength, duration, and direction. 
 
 sequent 24-h average CODAR current map in fig. 35 corresponded to the time of arrival of 
 the reversal between Port Angeles and New Dungeness 3 days later. The core of the east- 
 ward flow was located near mid- strait, with shoreward components on either side. In the 
 convergence zone near the reversal front, the seaward estuarine flow was diverted southward 
 with an eastward recirculation north of New Dungeness Spit. This CODAR map dramatically 
 illustrates the complexity of current reversals and suggests their potential effect on the 
 movement of foreign material transported by surface currents . 
 
 Surface drifter trajectories tracked by Canadian investigators (Ages, personal communica- 
 tion, 1979) also showed a net seaward drift before the storm's effects and a landward (east- 
 ward) drift as the reversal propagated through the western Strait (fig. 36). Up-strait 
 excursions of more than 35 km over a 24-h period were observed. Other surface drifter studies 
 (Cox et al. , 1978) showed an intensification of the flood tidal flow north of the New Dungeness 
 Spit on 26 August, which was associated with the reversal. 
 
 In summary, the field observations demonstrated the role of nonlocal meteorological 
 forcing in modifying circulation in an estuary opening onto the Pacific continental shelf. 
 Winds conducive to coastal downwelling (southwesterlies) generated a current response in the 
 Strait that was larger than the net gravitational circulation and led to current reversals that 
 
 34 
 
Figure 31. — Surface pressure maps showing stationary low pres- 
 sure system centered 300-400 km off the Washington coast 
 between 23 and 25 August 1978. 
 
 propagated up- strait. Although the current variance associated with coastal wind forcing de- 
 creased with distance up-strait and with depth, the effects of coastal storms were observed as 
 far as 135 km up-strait. Since southerly coastal winds occurred with lower frequency and 
 intensity during summer, subtidal current reversals were rare between June and August. In 
 contrast, local along-strait winds were weakly coherent with subtidal current fluctuations and 
 can be considered secondary to coastal forcing in modifying the near-surface circulation. It 
 should be noted that the moored current measurements were not made at depths shallower than 
 4 m, and therefore the effects of local winds on surface currents may be greater. 
 
 35 
 
COMPUTED COASTAL WINDS AT , 48° N. 125° W (BAKUN) 
 
 NORTH 
 
 I 
 
 "^fPf ^"WW^W ^'"^^ 
 
 ^ 
 
 fajkJfiAL 
 
 ' WS W 
 
 16 20 25 30 1 5 10 15 20 25 30 1 5 10 15 20 25 301 5 10 15 
 JUL AUG SEP OCT 
 
 78 78 78 78 
 
 60 
 
 ALONG- STRAIT CURRENTS/ SITE D 
 
 I 
 
 EBB 
 
 FLOOD 
 
 ALONG -STRAIT CURRENTS /SITE F 
 
 I 
 
 FLOOD 
 
 60 
 
 ALONG- STRAIT CURRENTS /SITE G 
 
 EBB 
 
 Figure 32. — SSW coastal winds associated with the offshore low-pressure 
 system (fig. 31) generated an along-strait current reversal at sites D 
 and F. A vertical line is drawn at the time of arrival of the reversal 
 at site D and illustrates the phase lag of this response relative to 
 coastal winds and currents farther up-strait. 
 
 3- DAY 
 
 NET CURRENTS 
 
 23-25AUG 1978 
 
 Figure 33. — Three-day averaged surface 
 currents as measured by CODAR. Aster- 
 isks mark locations of the two shore- 
 based HF Doppler radar units. The 
 pattern of new seaward velocities of 
 20-40 cm/s was consistent with near- 
 surface current measurements. 
 
 36 
 
"^ FLOOD 
 
 1400 23AUG78 
 
 123° 00 
 
 Figure 34. — Typical flood and ebb surface current maps as measured by the CODAR. 
 
 2.6 Freshwater Effects on Currents 
 
 Although freshwater runoff from the Fraser River (which was assumed to represent the 
 regional river discharge) varied widely with season (fig. 6), the induced net circulation 
 varied little between summer and winter. As an example, the vertical distributions of mean 
 currents at site G (shown in fig. 12) were nearly identical in winter and summer. Nearer the 
 coast at site A, the upper layer outflow reflected the additional effects of coastal forcing 
 discussed earlier in this section. This lack of direct response to variation in river runoff 
 can be addressed by applying steady-state gravitational circulation theory (Hansen and Rattray, 
 1965; Officer, 1976). Holbrook and Halpern (1980) have used this theory to show that the 
 
 123° 00' 
 
 24 -HOUR AVERAGED 
 
 NET CURRENT 
 
 26 AUG 1978 
 
 I23°00 
 
 Figure 35. — Twenty-four hour averaged 
 surface currents on 26 August measured 
 by CODAR. This period corresponds to 
 time of arrival of current reversal 
 shown in fig. 32 in this area. The 
 core of the reversal (eastward flow) 
 was located near mid-strait with 
 shoreward components on either side. 
 In the convergence zone near the re- 
 versal front, the seaward estuarine 
 flow was diverted southward with an 
 eastward recirculation north of 
 New Dungeness Spit. 
 
 37 
 
Figure 36. — Surface drifter trajectories tracked by Canadian investigators during the 
 period following the coastal storm shown in fig. 31. 
 
 direct effects of river runoff on the sea surface slope are insignificant (~10 " 2 smaller) when 
 compared with the indirect effects of runoff on the salinity distribution and therefore, the 
 longitudinal density gradients. Thus, only the indirect effects of fresh water on the internal 
 mass field are important. Efforts to measure seasonal changes in the longitudinal density 
 field using CTD survey data and to relate them to subtidal current fluctuations were not 
 successful, due in part to tidal aliasing and the limited number of cruises. In general, 
 gradients were larger during summer than winter; however, the statistical confidence limits 
 were too large to allow meaningful conclusions . 
 
 
 3. CONTINUING STUDIES 
 
 A major result of the study described by Cannon (1978) and this report (section 2.5) was 
 the discovery of large amplitude (25 to 55 cm/s), low-frequency current fluctuations that over- 
 shadowed the net circulation in the Strait during much of the year. These low-frequency 
 motions were manifested in the near-surface layer by prolonged reversals in the estuarine 
 circulation, during which intrusions of coastal oceanic waters propagated eastward at 20 to 
 30 cm/s throughout the Strait. The intruded waters were relatively warmer and fresher during 
 fall and winter months and contained coastal species of zooplankton and phy toplankton . These 
 current fluctuations are well correlated to coastal atmospheric forcing off the Washington 
 coast (see section 2.5.4). Our knowledge concerning spatial and seasonal distribution of 
 the reversals is limited by the relatively short records (compared with the observed 10- to 
 100- day oscillations) that have been collected near midchannel and by the lack of any near- 
 shore time series current measurements. Historical wave and tide height records also suggest 
 that our moorings in the western Strait were deployed during an atypical winter when storm 
 activity was unusually quiet, and therefore, the magnitude and extent of the reversals may be 
 much greater during normal seasons. It is unknown whether the coastal winds directly force 
 the along-strait, low-frequency fluctuations through an Ekman flux mechanism near the mouth 
 or indirectly through coastal sea level fluctuations induced by either (1) Ekman dynamics on 
 the continental shelf, i.e., downswelling; (2) partial blockage by Vancouver Island of the 
 northward flowing Davidson Current; or (3) northward propagating free and/or forced conti- 
 nental shelf waves . Concurrent coastal and Strait time series measurements are necessary 
 to examine and sort out these generating mechanisms. 
 
 38 
 
In early 1979, scientists from the Institute of Ocean Sciences (IOS) at Patricia Bay, 
 Vancouver Island, began an extensive oceanographic study off the west coast of Vancouver 
 Island. Three lines of current moorings are being maintained normal to the coast to contin- 
 uously monitor the upper, middle, and bottom layer currents for a period of 1 to lh yr. This 
 is the first major current survey conducted off the Canadian west coast. Physical oceanogra- 
 phic features that will be studied include the following: (1) continental shelf waves, (2) inter- 
 nal baroclinic tides, (3) prevailing ocean currents, (4) surface tidal currents, (5) water pro- 
 perties and oceanic fronts, and (6) ocean turbulence. B. Hickey, University of Washington, 
 also investigated atmospheric forcing of continental shelf circulation along the Washington 
 coast. 
 
 In "concert with the Canadian and University of Washington studies, PMEL (with MESA 
 support) began in March 1979 a 15-mo cooperative experiment to examine the seasonal and spa- 
 tial distribution of the low-frequency, near-surface currents in the western Strait of Juan de 
 Fuca, and to relate them to continental shelf circulation along Vancouver Island and the Wash- 
 ington coast and to sea level and sea level gradient fluctuations within the Strait. Portions 
 of this study will be conducted jointly with scientists from IOS and will take advantage of the 
 extensive set of concurrent oceanographic measurements from the continental shelf. 
 
 Analysis of the CODAR data set is continuing, in conjunction with the other physical 
 measurements obtained in August 1978. Expected analyses include (1) a comparison between 
 near-surface currents measured by the CODAR system, current meters, and surface drifters, 
 (2) a spatial analysis of tidal currents, and (3) a study of the effects of local wind forcing 
 on surface currents . 
 
 4. SUMMARY AND CONCLUSIONS 
 
 Cannon (1978) summarized research results accumulated during the past 15 yr for the 
 Strait of Juan de Fuca. His discussion primarily focused on the western basin, the region 
 where most measurements had been made up to that time. Winter and summer experiments were 
 subsequently conducted during 1977-78 in the eastern basin. This report describes the 
 principal water motions that were identified and observed. 
 
 It was found that over time scales of 4 to 25 h, tidal currents dominated water motions 
 throughout the Strait of Juan de Fuca. From 58% to 99% of the current variability can be 
 explained by tidal oscillations in the Strait. The four principal tidal components in the 
 eastern basin were M 2 , K x , O l5 and N 2 . Amplitudes varied from 40 to 60, 20 to 35, 15 to 20, 
 and 8 to 14 cm/s, respectively (fig. 24). Canadian numerical tidal model studies have shown 
 the complexity of these currents as they flow across the irregular bottom topography and 
 through confined passages (fig. 25). The tidal currents can exceed 200 to 250 cm/s (4 to 
 5 kn) in the more restricted passages of the San Juan Islands and in Admiralty Inlet. Around 
 near- shore and over- shoal regions, eddies and tidal fronts can become locally important; how- 
 ever, they have received little study, and circulation details remain undetermined. 
 
 Superposed on the tidal motions are the estuarine and wind-driven currents which, over 
 time scales longer than 1 day, play a principal role in transporting surface trapped and sus- 
 pended pollutants . The effects of these motions in modifying the tidal ebb and flood currents 
 are apparent when outputs from Crean's barotropic tidal model and the CODAR surface current 
 maps are compared. The estuarine circulation consisted of a well developed two-layer pattern, 
 with near- surface velocities directed seaward at 20 to 40 cm/s and deep layer velocities di- 
 rected landward at 10 cm/s. The level of no net motion varied between 40- and 60-m depth. 
 The surface manifestation of this estuarine pattern was a broad westward transport of surface 
 water, which supports the commonly held concept that surface trapped material should move 
 seaward. However, the daily ebbing and flooding tidal currents greatly complicate this pic- 
 ture. Eddies, fronts, and complex recirculation patterns make the prediction of trajectories 
 difficult and limited in accuracy. Results from drift card studies illustrate this, since 
 landings are distributed on beaches peripherally throughout the entire eastern Strait. 
 
 Local winds had a minimal role in generating near-surface currents. Although the winds 
 were coherent with and helped to maintain the vertical current shear, only a small percentage 
 of the current fluctuations at 4-m depth were directly related to measured, over-the-water 
 winds. The surface currents are undoubtedly affected to a greater degree, but moored cur- 
 rent measurements in this study do not allow a simple extrapolation to the surface. 
 
 39 
 
One of the most significant findings of this study was the effect of coastal storms on 
 circulation in the eastern basin. Moored current meter observations during winter 1977-78 
 showed that seven current reversals leading to up-strait subtidal surface flow occurred for 
 2- to 6-day periods, with maximum speeds of 20 cm/s. These reversals occurred subsequent 
 to south- southwesterly storm winds along the coast and were associated with rising sea level 
 at the mouth of the Strait. The extent to which coastal winds affected flow in the eastern 
 basin depended on their strength, direction, and duration. Reversals were observed as far as 
 135 km from the Strait entrance at site G . 
 
 Although coastal low pressure systems with southwesterly winds occurred more frequently 
 and persisted longer during winter than summer, occasionally a low pressure system dominated 
 the coast long enough during summer to generate a response in the Strait. Such a system was 
 present between 23 and 25 August 1978, during an intensive study period. South- southwesterly 
 coastal winds generated a near-surface current reversal that was observed 4 to 6 days later in 
 the eastern Strait. The 24-h averaged CODAR current map corresponding to the time of arrival 
 of the reversal between Port Angeles and New Dungeness dramatically showed the reversal of 
 normal seaward flow of surface water. Complexity near the reversal front was evidenced by the 
 diverted southward estuarine flow that appeared to recirculate eastward off New Dungeness Spit. 
 Surface drifters showed first a net seaward drift before the storm's effects, and then a land- 
 ward (eastward) drift as the reversal propagated through the western Strait and into the east- 
 ern Strait . These field observations demonstrate the major role that nonlocal meteorological 
 forcing can play in modifying circulation in an estuary opening onto the Pacific continental 
 shelf. 
 
 Observations presented in this report imply that a spill resulting from a tanker accident 
 within the Strait could impact the ecologically sensitive near-shore zone and beaches before 
 flushing into the coastal ocean . Intrusions of coastal water generated by coastal winds are 
 common during winter and have been observed year-round; therefore, an oil slick could have 
 an eastward trajectory well into the eastern basin region. Because of the complex pattern 
 of eddies, fronts, and shore- directed current components, the potential for oil slick beaching 
 increases with eastward distance into the system. 
 
 5. ACKNOWLEDGMENTS 
 
 Funding for a majority of these studies was provided by the U.S. Environmental Protection 
 Agency to NOAA and managed by NOAA's Puget Sound Project Office of the Marine Ecosystems 
 Analysis (MESA) program. This support is gratefully acknowledged. In addition, these funds 
 were supplemented by the Pacific Marine Environmental Laboratory (PMEL) . The National Ocean 
 Survey (NOS) provided ship support for many of the PMEL field activities, and assistance by 
 the officers and crews was invaluable. 
 
 Special thanks are due Patrick B. Crean, Richard E. Thomson, and W. Stan Hugget of 
 Environment Canada's Institute of Ocean Sciences of Patricia Bay, and Donald. E. Barrick 
 and A. Shelby Frisch of NOAA's Wave Propagation Laboratory at Boulder, and Andrew Bakun 
 of NOAA's Pacific Environmental Group at Monterey. Many discussions of their work as well 
 as assistance in the field have greatly aided us in our efforts. 
 
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 40 
 
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