RESEAR w phi alioni lechnolog) Satellite SMS/GOES lot Swuhronous MeteoroloKical Satellite iihe \\»\ designation) and GOES lot Geostationary Operational Environmental satellite I the NOAA designation) IMI refers to the international Magnetospheric Uplorer. Mother Daughter to twool the s.it, -lines m this system S"lot S-t ubed) designates the Small St lemlfli Satellite designed spet ifli all) to Investigate the, cause ol geomagneth storms .,n,i substonra NOAA satellites (also called ITOS, for Improved TIROS Operational System) are operational polai orbiting environmental spacecraft. TIROS, an acronym for Television infrared Obser- vational satellite i nniinue- to evolve, with IIROS N a third generation operational satellite planned lor the NOAA series. geostationary altitudes (6.6 earth radii) in order to trigger naturally occurring magnetospheric plasma instabilities. The result of such stimulation would be the scattering of the surrounding energetic trapped particle population down the field line into the ionosphere. The resulting ionospheric disturbance should be easily detected by ground instrumen- tation and could result in a visible aurora. Such active modification projects, as op- posed to the present program of passive observation, are considered necessary tests of theoretical models. Research in ionospheric physics in the Space Environment Laboratory is con- cerned with developing an understand- ing of the boundary conditions to the ionosphere, and the resulting dynamic behavior of the ionosphere and its in- teractions with the upper, neutral at- mosphere. These programs investigate spatial and temporal irregularities in the ionosphere, interactions between the ionosphere and the magnetosphere, and the response of the ionosphere to natural and artificial transient energy in- puts. Much of the effort is concerned with models and theoretical studies. A theoretical model of the equatorial F- region — the highest layer of the ionosphere — has been developed that accounts for the anomalous distribution of electron density near the equator. Other modeling efforts here include the modification of one developed at Stan- ford Research Institute, that predicts ionospheric scintillation effects which perturb satellite communication systems, and a "standard" solar flux model for moderate solar conditions in the 1,000 to 3,000 Angstrom range. Another describes the increases and decreases of electron densities during a magnetic storm. This model is based on a point heat-source located on the noon point of the auroral oval, from which the disturbance emanates. In this imaginary system, the earth's rotation causes the source to move faster than the distur- bance, setting up a "wake" which sweeps across the planet. A "storm front" is established along the envelope at which disturbances are focused, while ahead of the front, a wind is set up which lifts the plasma to levels of low electron loss, giving rise to the positive phase. At and behind the front a change of chemical composition occurs, causing enhanced electron loss and so producing the negative phase. The lower thermosphere — the region from 80 to 150 kilometers' altitude — is also the subject of theoretical study. Pre- sent investigations here are evaluating the major sources and sinks of ther- mospheric energy, and their variations with season, latitude, and other factors. Operational space environment monitors are continually being im- proved, as more sophisticated in- struments are placed aboard the new generations of environmental satellites. A Space Environment Monitoring (SEM) subsystem in the SMS/GOES series is designed to provide data on energetic particles, solar X-rays, and the earth's magnetic field at geostationary altitudes. Working closely with the NASA program office, the laboratory provides liaison and guidance to space agency contrac- tors responsible for the SEM portion of the SMS/GOES system. It also designed a telemetry receiving system and on-line data-processing and display system for SEM data. Experimental ionospheric observations are made using a modern digital ionosonde. lonosonde measurements will be compared to the in situ measurements of the Atmosphere Ex- plorer satellite in a cooperative program with NASA. The ionospheric physics area provides the principal investigator for the ATS-F satellite radio beacon experi- ment which will be in a data collection stage in 1974 and 1975. A comprehensive particle-monitoring subsystem has been specified for the TIROS N and follow-on operational satellites in that series. This flight in- strumentation is being developed inter- nally by the Space Environment Laboratory, working with contractors in other laboratories and in industry. Support for the ATS-F project consists of ■ evaluating and checking the assembled experiments — one flight unit and one flight spare — prior to the 1974 launch of this satellite. It also involves development of basic specifications for the satellite radio beacon transmitter, liaison with NASA, and contractor liaison during construction of the unit. A com- prehensive receiver for beacon transmissions is being constructed and checked out under the ground sector of the program funded by the ATS-F pro- ject. The receiver and data-acquisition system will use a minicomputer both for receiver control and calibration and data acquisition. IME experiment support has included production of major portions of the proposed technical and management sections and project liaison with NASA during initial program definition. The opportunity for this experiment, which involves placing a satelliteborne solid- state detector aboard the spacecraft, is provided under the joint sponsorship of NASA and ESRO, the European Satellite Research Organization, program to launch three satellites, the first two of which are scheduled for a January 1977 launch. Work is also underway to develop several new on-board techniques for data-processing, including multidimen- sional pulse-height analysis. In addition, it is intended that several integrated cir- cuit modules will be developed within this program to improve system perfor- mance for certain critical pulse-analog and pulse-height-discriminator portions of the experiment. Time-of-fiight measurement techniques are being in- vestigated as a possible means of im- proving heavy ion species identification. A project funded by the Department of Defense aims at developing systems for measuring the inplace elec- tromagnetic properites of rocks and soil at MegaHertz frequencies. One byproduct of this instrumentation effort has been the development of a program- mable, calculator-controlled network- analyzer system. Instrument development to improve sounding rocket payloads is also un- derway. Experiments made in coopera- tion with the Norwegian Government used sensors for four auroral research flights. In the mid-1970's, a complete Javelin payload will be integrated with sensors from the Space Environment Laboratory and other research organizations to use in the sounding rocket program. Understanding how energy and matter are exchanged in the highly interacting magnetosphere and ionosphere is a critical element of the Space Environment Laboratory investigation. These curves show typical heating-rate profiles for most of the major heating sources in the 80-to-l 50-kilometer region. The sun and man photograph was taken in hydrogen alpha light by NOAA's solar observatory in Boulder, Colo. Molecular Thermal Conduction \ ('D) Deactivation^ Direct Solar Heating Recombination \s Abji c °2 Tidal Waves 30 Heating Rate. °K per Day The Solar Watch and Warning rimitive societies are untouched by events on the sun — as long as this star produces the daily ration of light, heat, and beneficial radiation; as long as its ecliptic steers the seasons, there is no need tor non-technical man to give it much attention. But for our complex, high-technology culture, there is nothing remote about the distant storms that sweep the sun. In fact, the solar'in- fluence grows year by year, and deepens as we learn more about environmental interactions in this sun-dominated cor- ner of the galaxy. The sun goes through approximate 11- year cycles of alternately increased and diminished activity. During the several years around the time of peak activity, flares occur that may cover an area on the sun many times the total surface of the earth. These great outbursts of energy in the solar "atmosphere" (chromosphere) are usually associated with groups of sunspots, and both spots and flares appear to be closely linked to changing magnetic field polarities on the sun. The Space Environment Services Center, the forecasting and warning arm of the Space Environment Laboratory, monitors the solar surface continuously, providing real-time information on con- ditions in the space environment to civil and military managers of sun-sensitive activites. When solar activity increases, the Center issues timely reports and forecasts of possible future activity and probable geophysical effects. These can be profound. The prompt X- rays strike into the upper atmosphere, altering conditions along sun-facing ionospheric paths used for some types of radio communications. Solar particles — energetic protons and electrons — reach the earth environment several days later, interacting with the upper atmosphere over the polar regions to produce auroral displays. At the same time, strong, irregular electrical currents flow in the magnetosphere and polar ionosphere, changing the magnetic field at the earth's surface. Electrical power systems in northern latitudes of the United States are sometimes interrupted during geomagnetic storms, which may induce strong currents in long electrical transmission and communications lines, tripping circuit breakers and burning out transformers. In the past, geomagnetic storms have been responsible for power blackouts in large cities as well as exten- sive interruption of long-distance telephone communications. As power and communication nets become in- tricate and more heavily laden, unex- pected geomagnetic storms may very well increase the incidence of power dis- ruptions, especially during the "brown- outs" which have become routine in the northeastern United States. Utilities and telephone companies have joined the ranks of solar forecast clientele, and have begun research aimed at explaining the causes and effects of their unique and critical relationship with the sun. Communications problems caused by solar disturbances helped create the pre- sent forecasting service, and continue to be a prime concern at the Space Environ- ment Services Center, for military and civilian programs require real-time reports and forecasts concerning solar effects on high-latitude radio com- munications. A Memorandum of Agree- ment is in effect between the Commerce Department and the Department of the Air Force for cooperative space en- vironmental support activities between NOAA's Environmental Research Laboratories and the Air Force Global Weather Central at Offutt Air Force Base, Nebraska, and the Aerospace En- vironmental Support Center, at Ent Air Force Base, Colorado (both of the Air Weather Service). Cooperative activities under this agreement include joint Air Weather Service-NOAA staffing of the Space Environment Services Center at Boulder and of the laboratory's High- Latitude Monitoring Station at Anchor- age, Alaska, sharing of data and data- transmission facilities, joint observing programs, and operation of the global network of "solar patrol" observatories. Extensive communication forecast and monitoring services are also provided to such northland users as the Federal Avia- tion Administration, Federal Com- munications Commission, Federal Bureau of Investigation, State of Alaska Communications System, Bureau of In- dian Affairs, the oil industry, and various fisheries interests. A literal "space weather service," the Space Environment Services, Center monitors conditions on the sun and the geophysical effects of increased solar activity. Manned space missions like Skylab, at left, are among the Center's major clients. Very energetic solar particles, arriving as soon as 20 minutes after a flare, can penetrate the polar atmosphere to heights at which supersonic transports fly. At times of great flares, such particles may pose a radiation hazard to passengers aboard these aircraft. Ac- cordingly, regular monitoring and forecasts of energetic particle events are supplied to the Concorde supersonic transport program, to permit aircraft to take evasive action in the event of a hazardous solar flare. Human vulnerability to the stream of energy from an active sun increases greatly outside the atmospheric shield, and providing timely data to the National Aeronautics and Space Administration in support of manned space missions has been one of the Space Environment Ser- vices Center's primary reasons for being. Over the early years of space explora- tion, the NOAA facility has helped keep the solar radiation hazard to manned space missions to a minimum through forecasts of these events and accurate predictions of the intensity of the flare- produced proton streams. These forecasts will be of still greater value as manned missions last longer, and the ex- posure of astrocrews increases. The Center has also helped the space program achieve certain research goals. For example, the observation schedules for the Apollo Telescope Mount — an array of six solar telescopes — aboard Skylab were developed from data fur- nished by the Space Environment Serv- ices Center and cooperating observ- atories, permitting maximum use of this unique solar observatory circling outside the atmosphere. A real-time data service is a crucial ele- ment in this solar monitoring and forecasting activity, and includes the High-Latitude Monitoring Station in Anchorage, where various ground-based radio experiments provide information on the state of the Arctic ionosphere and geomagnetic field; and the data display systems in the Services Center and an observatory at Table Mountain, near Boulder. Data received at Anchorage and Table Mountain are processed in real time by small computers and relayed to the forecaster. In addition, solar proton and magnetic data (through the courtesy of Dr. G. Paulikas, Aerospace Corporation, and Dr. P. Coleman, UCLA, respectively) are received from a satel- lite in geostationary orbit over the Pacif- ic Ocean, and solar radio and ionospheric radio experiment data come in from the Table Mountain observatory, as do solar proton, solar X-ray, and magnetic data from the GOES spacecraft. The Space Environment Services Center Maintains a real-time solar geophysical data base in a time-share computer accessible to users via telephone and teletype. Included in this system are data collected from a global network of radio and optical solar telescopes; data from satellites (including the Pioneers, VELA, ATS-1, GOES, NOAA) providing information on solar X-rays, solar protons, the solar wind, and the magnetic field; geomagnetic, ionospheric, cosmic ray, and neutron data from ground observ- atories; and three-day forecasts of the level of solar activity, including percen- tage probabilities of large flares, geomagnetic conditions, and average solar radio flux. Other data products available from the Center include brief resumes of data ex- cerpted from the data base, alerts and warnings concerning major solar geo- physical events, and weekly data sum- maries with hydrogen alpha photo- graphs and other graphic material. Pub- lications include special reports on such significant events as the August 1972 solar flares and their geophysical effects. Recent benefits obtained from operations-oriented research include an enhanced ability to predict geo- magnetic storm activity from direct ob- servations of interplanetary magnetic- field sector boundaries by space probes, and indirectly, from observations of the f;eomagnetic field at high and polar-cap atitudes. Synoptic maps of the large- scale magnetic fields of the sun are being constructed, based on the chromo- speric structures photographed in hy- drogen alpha light by the solar patrol ob- servatories. These maps, which can be updated in real time, provide important information on the evolution of solar ac- tivity, and definite clues to the possi- bility of major flares and the propa- gation of solar disturbances to the earth. Observing the sun at different wavelengths emphasizes different features on the solar surface. The three solar discs shown here were photographed simultaneously in (from left) white, hydrogen alpha, and calcium light. .■$:- r ' S i wmm Collisions and Thin Chemistries or the space Environment Laboratory the processes which concern researchers begin in the sun and reach out through interplanetary space to the environment of earth, and the activities of men. The work of the Aeronomy Laboratory, on the other hand, tends to be more planet-centered, dealing mainly with the thin outer shells of meager gases and electrified particles which mark the region in which atmosphere diminishes and finally vanishes into the virtual vacuum of space. The chemistry and dynamics of this nebulous region, the meteorology of the high upper at- mosphere, and the relationships between events there and man's ability to communicate over distance are cen- tral figures in this laboratory's programs. Theoretical solar-terrestrial and plasma physics studies occupy part of the Aeronomy Laboratory's effort, and deal mainly with the regions of interaction between the ionosphere and the outer reaches of the earth's magnetosphere, and with how energy and matter are transmitted, exchanged, and transformed in the ionosphere. Recent experimental and theoretical studies have shown that the ionosphere plays a major role in governing the interaction between the solar wind and the earth's atmosphere, leading to the dramatic phenomenon of the aurora and the attendant disruptive effects on radio communications and power lines. A model that incorporates this coupling between the ionosphere and the outer reaches of the magnetosphere is under development, and promises to explain the events leading up to major auroral disturbances in a quantitative way. The D-region of the ionosphere — the lowest ionized layer — provides the basis for the propagation of the low- frequency radio waves used for worldwide oceanic navigation systems, and is also responsible for absorption of the higher frequency radio waves used for radio and marine communications. The laboratory is working on a model that simulates this important ionospheric region under both natural and perturbed conditions, and that will eventually in- clude a detailed set of the influential chemical and dynamic factors operating there. Plasma turbulence has a direct effect upon telecommunications, radar, and the distribution of both natural and ar- tificially produced (e.g., radioactive) ionization in the atmosphere. Such tur- bulence can enhance radio com- munications between points on earth by scatter propagation; but it can also seriously degrade radio communications between the surface and space vehicles. Accordingly, a general theory has been developed to answer questions concern- ing atmospheric plasma turbulence. Physically, this theory is based on the effect of turbulent electric fields on the perturbed trajectories of diffusing par- ticles; the spectrum of turbulence is then determined by these perturbed trajec- tories. Detailed theoretical studies have also been made of modifications of the ionosphere by intense radio transmis- sion. A model has been developed that predicts large increases in resistivity and temperature following such trans- missions, and changes of the electron distribution of the ionosphere during modification. Such changes, observed in experiments conducted by the Aeronomy Laboratory, the Space En- vironment Laboratory, and the Institute for Telecommunication Sciences (of the Commerce Department's Office of Tele- communications), are of great interest for telecommunications and defense purposes. Experience with the ionosphere is be- ing "exported" to lower levels of the at- mosphere, and applied to the problem of air quality. Turbulent eddy diffusion is a dominant process in pollution disper- sal, and this research will attempt to predict and model pollution-dispersing processes and interactions. Aeronomy Laboratory researchers are also exploring how techniques developed to predict the behavior of thin, charged gases can be applied to the urgent problems of air quality in the atmospheric zone of life. Research on atmospheric processes and composition in the Aeronomy Laboratory focuses on the region where The interaction of the electrically charged ionosphere and the neutral (uncharged) atmosphere are simulated in the Aeronomy Laboratory's flowing afterglow facility, in which ionized and neutral gases are mixed and their reaction-rate constants are determined as functions of temperature and other parameters. » «. JKJ lifer • 9 ' W • **. 5. * \] atmosphere and ionosphere mix, in- teract, and are mutually transforming. This work studies the collisions and chemical reactions of ionized and neutral elements in the high upper at- mosphere and lower portions of the ionized D-region, the concentration and variability of atmospheric gases above the stratosphere, and the fundamental particle wave processes — and improved methods of measuring them — of this at- mospheric region. Experimental and theoretical basic research on atomic and molecular processes in the earth's atmosphere emphasizes measurement of ionospheric ion-neutral reaction rate constants. The complex reaction schemes which con- vert positively charged molecular oxygen (O2) and nitric oxide (NO 4 ) ions to hydrated hydronium ions in moist at- mospheres have been studied in great detail and are being extended. These studies have been applied to an analysis of D-region positive ion chemistry. Stratospheric and tropospheric positive ion reaction schemes, including the im- Eortant effects of ammonia, have also een measured. Detailed negative ion reaction schemes have been determined in this laboratory and are forming the basis for analyzing the first in situ D-region negative-ion composition measure- ments. The flowing afterglow technique has been extended to measurements of electron-attachment rate-constants and applied to studies of electron attach- ment to several metal oxides. This work is important for understanding the behavior of ionization in the wake of space vehicles re-entering the at- mosphere. Tropospheric negative-ion reaction schemes have been studied, in- cluding the effects of trace sulphur diox- ide (SO2) on the ion composition. A large amount of basic molecular data has been derived from the ion-molecule reaction studies, including bond In order to investigate the major gases, an occultation technique is being employed where atmospheric absorp- tion is obtained by viewing the sun through the atmosphere at twilight with satellite-borne instruments. Data from the Naval Research Laboratory satellite energies, electron affinities, ionization potentials, and equilibrium constants. The electron binding energies of the im- portant D-region species NO 2 and NO - (nitrogen dioxide and nitrogen trioxide) have been precisely measured. A new program of atmospheric neutral reaction kinetics is under development. Using sophisticated laser techniques developed in the adjoining National Bureau of Standards laboratory, sensitive methods of detection of the radicals OH and HO2 and also HCO are now being used to study reaction kinetics involving these species. This work is being carried out in collaboration with a National Bureau of Standards group. In the laboratory's atmospheric com- position studies, research includes the measurement of chemically active neutral constituents in the mesosphere and lower thermosphere, and the deter- mination of the variability of the major thermospheric gases. An experimental technique to measure atomic oxygen has been developed which takes advantage of the oxidizing potential of atomic oxy- gen. A thin film of silver, used as a resistive element in an electric circuit, is exposed to the atmosphere and the change in resistance due to oxidation is related to the ambient atomic oxygen density. Data from several rocket flights with this instrument have shown sub- stantial latitudinal variations in the oxy- gen density. SOLRAD 8 show substantial day-to-day and large seasonal variations in molecular oxygen in the lower ther- mosphere. Data from SOLRAD 10 and OSO 6 are being analyzed and data from Skylab will be analyzed as it becomes available. The chemistry and physics giving rise to the vertical and global distributions of the various gases are also being studied. Emphasis in the past has been on photochemistry: however, increasing ef- fort is being placed on understanding the transport processes. Because the dis- tributions of the gases depend on the temperature structure, some future ef- fort will be placed on understanding the thermal balance in the atmosphere. Studies are carried on by the Aeronomy Laboratory of particle and wave processes, especially the fun- damental particle and wave processes that are important to atmospheric phenomena such as aerosol physics, wave propagation, collision processes, and wave-particle interactions. The development and use of measurement techniques for determining atmospheric properties is part of this work. A systematic development of the kinetic theory of gases in the transition regime where the mean-free-path between collisions is neither large nor small has been started. There is no such systematic development available at pre- sent, although this regime is important in the upper atmosphere for vehicles in- teracting with the atmosphere, and in the lower atmosphere for particulate matter such as aerosols. A method for dealing with trace constituents in a gas under transition-regime conditions has been developed and is being applied to the calculation of airglow line profiles in the upper atmosphere. Instruments at Fritz Peak, Colo., observatory are used to monitor airglow and other sky phenomena at altitudes of interest to Aeronomy Laboratory scientists. The scanning photometer at left and the photometer below are used to monitor airglow, sensing different colors as different filters are used. The atomic oxygen sensor shown on the facing page was developed to obtain data at auroral altitudes. Structure in the radio-frequency resonances observed by radio sounders on satellites near the plasma frequency has been shown to depend on electron temperature and provides a new method of measuring it. Interest in this explana- tion and in the geophysical use of resonances has led to the development of an advanced sounder, which was launched on a rocket to an altitude of 650 kilometers and obtained enough data to show that the resonances behaved consistently with predictions. A more sophisticated sounder planned for an equatorial launch should provide a more conclusive validation of the theory: it will also test the use of such observations as a measurement tech- nique for electron density and tempera- ture (both along and across the field) along with drifts and magnetic field strength. Laboratory studies are being carried out on the effect of the plasma parametric decay instability on the beating of plasma by strong radio- frequency fields. The instability has been positively identified and the threshold electric field required to excite the in- stability has been measured. This helps to explain the large observed heating rates of ionospheric plasma when the F region is irradiated by intense radio waves. A discrepancy between two different techniques of measuring ionospheric ion temperatures has been resolved. Laboratory work and theoretical calculations show that non-uniformities in the grid plane of retarding potential analyzers have led to inferred ion temperatures that have been high by as much as 30 percent compared to radar backscatter measurements. A theory for taking into account the effect of satellite electrical potential on inferred ion and electron densities in the exosphere has been developed and applied to satellite data obtained through the plasmapause. Previous ion densities obtained without taking this effect into account have been incorrect at times by as much as an order of magnitude. Optical observations of ionospheric phenomena apply a variety of sensitive and specialized detection methods to problems concerned with the energy balance, composition, and dynamics of the upper atmosphere. Although major emphasis is placed upon observation and interpretation of naturally occurring op- tical emission from the atmosphere, the program also includes detection of emis- sion induced by artificial heating of the ionosphere by radar, and laboratory studies in photochemistry when re- quired for interpretation of field measurements. In addition to a major program of measurements at the Fritz Peak Observ- atory, Colorado, infrared studies of aurora and airglow are performed on an Air Force jet, and infrared studies bear- ing on the Martian ozone abundance are planned in conjunction with the Smithsonian Observatory in Arizona. In almost every line of investigation the im- portant problems demand instruments of great sensitivity and spectral purity which cannot be commercially obtained — they must be designed and developed within the program itself. Variations in molecular oxygen in the thermosphere (the region of increasing temperatures from about 80 to 200 kilometers' altitude) and ozone abun- dance in the mesosphere (50-80 kilometers) as reflected in twilight emis- sion features from atomic and molecular oxygen are under study here. The large seasonal and geomagnetic variations observed seem to reflect changes in the turbulent transport rate near 100 kilometers, a quantity which plays a fun- damental role in determining upper at- mospheric composition and thermal balance. Thermospheric neutral winds and temperature are being monitored directly by studying the shape and wavelength shift in airglow emission lines with high-resolution inter- ferometers. These two fundamental quantities, which can be determined in both the 100- and 300-kilometer altitude regions separately, are basic to an under- standing of thermospheric dynamics and thermal structure, and are of great sig- nificance in ionospheric dynamics. Optical studies, both separately, and in combination with incoherent radar backscatter studies, reveal major changes in thermospheric composition in geomagnetically disturbed periods. In- frared auroral studies based on aircraft observations show major emission not directly resulting from particle bombard- ment. This may reflect a significant alteration in the composition and chemistry at auroral altitudes. Related studies of subauroral red (SAR) arcs yield information on the morphology and energy flow from the outer plasma- sphere under disturbed conditions. Radar studies are being conducted of ionospheric irregularity structure in the equatorial and auroral E regions, and the equatorial Spread F. The equatorial in- vestigations have been conducted primarily at the Jicamarca Radar Observ- atory in Peru, while the auroral observ- ations are made at field sites in Alaska. Many of these experiments use a port- able radar system developed within the laboratory. The investigations are concerned primarily with the physical processes that produce ionospheric irregularities, while additional emphasis has been given to using the results to obtain a better insight into ionospheric coupling with both the magnetosphere and atmosphere. These same techniques have also been applied to obtain the "radar spectral signature" of various species of birds as an aid in their identification on airport radar systems. Study of the physical processes in the ionospheric F region is carried out using ionospheric and nightglow data ob- tained at Jicamarca and near Boulder. Special attention is given to the physics of processes of recombination and nightglow excitation. A new radar in a canyon at Sunset, ten miles west of Boulder, is being used to study motions in the troposphere, stratosphere, and mesosphere, using a technique developed at Jicamarca. ««■ ■*#«/\ Weather and the HaircN>f Man Only the alchemist's dream of transmuting base metals into gold equals the perennial ambition of those who would comprehend the processes we call weather — comprehend them, predict them, even change them. For the alchemist the search continues. But atmospheric scientists have pushed their disciplines to within a generation of realizing the largest of their ''impossible" objectives. Much of this progress has come in the efforts of science to understand and mitigate the atmosphere's more violent offspring — the turbulent cumuli of tropical skies; squall lines and their destructive cavalries of lightning, thunderstorms, and tornadoes; hurricanes; and the great cyclonic systems that sweep the continent with entire families of lesser, but violent events. Investigators in what are now NOAA's Environmental Research Laboratories have helped with this pioneering work. The Atmospheric Physics and Chemistry Laboratory, in Boulder, has done much to define the roles and populations of atmospheric constituents and to apply lessons learned in earlier weather modification projects to the modification of large-scale storm systems. It has also developed methitlsjp'hich may be able to suppress*dfestru#tively intense lightning discharee^%f The Experimental Meteorology Laboratory in Miami has brought tropical cumulus cloud-seeding techniques to a point where they have been applied quasi-operationally in a series of drought- breaking storms, and where research has begun to focus on the fundamental causal relationships in cloud seeding and cloud modification. The National Hurricane Research Laboratory, also in Miami, has led the development of methods of hurricane modification — aimed at the reduction of destructively high winds and storm surge, not the total suppression of hurricanes — to the threshold of operational utility. The National Severe Storms Laboratory in Norman, Oklahoma, is learning to read the extremely well-kept secrets of the tornado and its havoc- playing parent, the severe thunderstorm. Airborne, instrumented platforms are required to enter the rugged laboratory of the atmosphere. The Research Flight Facility, based at Miami International Airport, provides the squadron of research aircraft and their uniquely experienced crews, while a Boulder-based effort seeks to arm the new generation of NOAA aircraft with the best airborne data systems available from present technology. Art Into Science T here was A time in the United States when the business of altering the weather was best known for its early practitioners, the fast-talking rain- makers whose bizarre apparatus and or- nate wagons roll through American lore and literature. That view has given way before the mid-century advances of weather modification as a science. To- day, there is consensus among the dis- tinguished scientists and engineers who have been attracted to this field that few meteorological developments would be so generally beneficial. There is also general recognition that the art of weather modification has, over the past generation, become a science, although not yet an exact one. What seemed insurmountable problems a relatively few years ago have now been either solved or greatly simplified. In the sense that scientists know approximately what their weather modification project will do, most of the broad technical problems have been resolved. There is such a thing as operational weather modification today, most of it in the growing band of private weather-modifying organizations. There are still many unknowns. It is one thing to know what is going to happen in a general way, and quite another to know precisely what will happen, when, where — and why. So that the trend and tone of such research in NOAA changed in the early 1970's as objectives evolved from trying to get a little more rain or a lighter kind of snow or smaller hailstones, to learning the detailed causes and effects behind these results and their broad geophysical im- plications. Also in this period of change, NOAA scientists began extending the weather modification expertise gained at one scale of time and motion, in one geographic location, to processes at other scales and latitudes. Most present-day weather modifica- tion projects use generally similar techniques of cloud seeding to achieve different results. The principle of cloud seeding is that water tends to remain in supercooled liquid state at temperatures far below freezing, unless it has a suitable "platform" to coalesce around — a sub- limation nucleus. To freeze supercooled water, an agent introduced into the cloud must either lower temperatures sufficiently for water to freeze spon- taneously (dry ice does this) or provide an ice-like, crystalline nucleus (like silver iodide). The latter is the seeding agent used in most of NOAA's work, dispensed by a slow-burning solid pyrotechnic whose exhaust product is a silver-iodide cloud. An attendant effect of seeding is to reach into the stored heat energy carried by water in the atmosphere. Water ab- sorbs or releases relatively large amounts of heat energy as it changes state — it ab- sorbs heat as it changes from solid to li- quid to vapor, and releases heat chang- ing from vapor to liquid to solid. Thus, inducing supercooled water to freeze liberates significant amounts of this "la- tent heat," causing additional buoyancy and greater development of the cloud. This means that weather modification researchers can not only induce ad- ditional precipitation by causing super- cooled water to freeze (and fall), but can also manipulate the distribution of heat energy to enhance or destroy the various equilibria of the system. In the weather modification work of NOAA's En- vironmental Research Laboratories, cloud seeding is used both to enhance and alter precipitation and to redistribute the energy fields of weather systems. Another common feature of these ef- forts is that they deal principally with the turbulent creatures of the atmosphere, ranging from cumulus clouds, whose vertical motion (convection) makes them basic weather factories, to continent- sized extratropical storms. The broad objective is not to add to snowpack or in- crease rainfall, but to make the violent phenomena of the atmosphere accom- modate themselves a little more to man. It is work that becomes less experimental season by season. In the atmospheric physics and chemistry laboratory the emphasis in weather modification has shifted from obtaining specific short-term precipita- tion effects to the broader question of modifying entire cyclonic systems (see page 17), and to comprehending the in- teractions of seeding nuclei with the natural populations of nuclei and water in the atmosphere. Much of the impetus behind the search for more fundamental knowledge of the forms and functions of at- mospheric nuclei comes from the laboratory's experience in modifying winter storms over the Great Lakes. From 1968 to 1972, the laboratory conducted annual experiments over Lake Erie to determine whether the heavy downwind-shore snows experienced there could be beneficially redistributed. Theoretically, the introduction of silver iodide into the water-logged storm An intensive study of ice nucleation in the Atmospheric Physics and Chemistry Laboratory is helping explain the poorly understood process by which ice crystals form around natural and man-introduced microscopic nuclei. At left, microscopic views of a typical ice crystal are shown with an X-ray analysis of their chemical composition across the nucleus. At right, filters from a western United States benchmark network are providing NOAA scientists with a regional ice-nuclei climatology, essential to understanding natural and artifical precipitation processes. 11 clouds over the lake would increase the number of freezing nuclei and produce large numbers of smaller snow crystals rather than the larger, naturally formed crystals. The smaller crystals would fall from the cloud more slowly and so be distributed over a wider area. Subse- quent numerical modeling of the Lake Erie storms suggested that, by 'judicious seeding of the storms which move along the lake's long axis it should be possible to drop the major portion of precipita- tion back into the lake rather than on shore — that is, to use the techniques of weather modification as a water resource management tool. The laboratory has also been conduc- ting radiometric cloud physics missions before and after seeding attempts over the Great Lakes and the High Plains. Radiation budget observations and calculations were made of pre- and post- seeded cloud decks. Investigators found definite indications that strong local in- frared cooling at the cloud top prior to seeding and the resulting overturning were a primary mechanism in sustaining the cloud deck in the absence of orographic (mountain) effects. Results obtained after seeding were less clear cut and displayed widely differing infrared cooling rates in the glaciated areas, directly related to interface temperature effects. Observations and calculations showed cooling rates (from cloudless conditions) in the glaciated area which resulted in additional cumulus develop- ment; in some missions, where seeded areas drifted over a warmer land surface, increased convection from below result- ed in small cumulus development at altitudes between one and three kilometers. This research effort is in- creasing with the objective of deter- mining the radiative budget effects caused by artificial cloud development or suppression, as part of the study of ex- tratropical cyclone modification. It is also helping to explain the important ques- tion of areal and downwind develop- ment of seeded areas. A strong effort in nucleation chemistry conducted by the laboratory seeks to ex- plain the microscopically small parts and players behind the larger drama of weather modification effects. Here the objectives are to establish source and sink relationships and spatial dis- tributions of nuclei in the atmosphere, develop criteria for distinguishing man- made from natural nuclei, and improve the fundamental understanding of how water vapor is converted into drops and ice crystals. In the experimental portion of this program, methods have been developed to identify ice nuclei shape and com- position using scanning electron-micro- scopy in conjunction with energy- dispersive X-ray analysis. An ice-nuclei network consisting of 24 sampling stations in the 17 western states (including Hawaii and Alaska) provides the specimens used for these measurements. These techniques should help explain the role of natural nuclei, and provide some indication of cloud seeding efficiency as expressed by the amount and distribution of seeding agent found in the sampled nuclei pop- ulation. Measurements made in Hawaii have established that the islands produce a variety of "artificial" nuclei, which affect Hawaiian weather and climate. Cane field fires are a source of ice nuclei, probably through the action of copper sulfide derived from the high copper content of the plants. Volcanic fumeroles produce cloud condensation nuclei through the action of hygroscopic sul- furic acid and sulfate aerosols. Even island vegetation is a source of aerosols, in this case a volatile organic one produced through photolytic polymeri- zation of isoprenes (rubbery nydro- carbons) emmitted by ferus and ohia- leua trees. Gas chromatographic and mass spec- trometric analyses made by the laboratory indicate that organic matter distributed in ocean water affects maritime cloud development and dynamics. As this organic material is carried into the atmosphere during the bursting-bubble process, it is polymer- ized into an aerosol by ultraviolet light, which retards the condensation efficien- cy of sea salt particles and so affects cloud condensation nuclei populations in the maritime atmosphere. The laboratory has also developed, and applied to automobile exhaust, a laser ^spectroscopic particle analyzer which characterizes aerosol systems by measuring the specific absorption and emission of electromagnetic radiation near the aerosol source. Development of 12 » this instrument will eventually result in a computerized data retrieval system in which spectroscopic aerosol characteristics will be related to the presence in various aerosol systems of Aitken, condensation, and freezing nuclei. The data will also provide infor- mation about the infrared absorptivity of aerosols and so permit a better evalua- tion of how they affect weather and climate through their interference with sun and sky radiation. Other studies attempt to develop a better understanding of how ice nuclei act on water vapor, and of the effect of water vapor and temperature on the crystal structures of snowflakes develop- ing from frozen droplets. These researchers are also trying to refine their evaluations of the effect of aerosols on climate, relating the aerosol effect to at- mospheric residence time, a critical value in determining long-term effects. Measurements are also being made of the effects of stratospheric aerosols on the amplitude and phase of seasonally periodic variations in the amount of solar radiation received at NOAA's Mauna Loa Observatory, in Hawaii. From this study, a climatology of nuclei is being developed by the Atmospheric Physics and Chemistry Laboratory with the eventual goal of providing at- mospheric nuclei inventories at local, regional, and global scales. This informa- tion will permit an assessment of the contribution of human activities to the atmospheric nuclei budget. At the same time, investigators here are looking into the efficiency of nuclei-generating techniques used in weather modification projects, how well these nuclei succeed in glaciating clouds (that is, inducing supercooled water to freeze), and how long they remain suspended in the at- mosphere. These studies are also cover- ing the effect of the nucleating action of silver iodide on light quanta, water vapor, and atmospheric trace con- stituents. The experimental meteorology labora- tory has been concerned with in- vestigating the physics and dynamics of convective clouds, from the scale of in- dividual cumulus elements to the mesoscale systems influencing the southern Florida peninsula. Of particular interest is the interrelationship between cloud microphysics and dynamics and the processes which govern precipita- tion-formation within the clouds. The laboratory has uniquely applied cloud-seeding technology toward |f RNM1NT P*