A UNITED STATES DEPARTMENT OF COMMERCE PUBLICATION SESC The Space Environment Services Center fi ft Knr^^^^i K.- U.S.I Department of v Commerce National Oceanic and Atmospheric Administration 4fo ,1373 /re tf> vV . £ ^ Environmental Research Laboratories k energy — everything about it — is on the grand scale, by earth standards. Even the space en- vironment through which our planet sweeps is dominated by this middling star 92,900,000 miles (150 million kilometers away, and pro- foundly influenced by the solar stream of light and heat and other forms of energy. The fer billionths of the sun's output that we receiv is enough to provide the equivalent of nearly five million horsepower for each square mile (2.6 square kilometers) of our outer atmos- phere — and enough to pervade and sustain all life on earth, drive the earth's weather systems, and influence global currents in the sea. Solar energy is also responsible for the existence of- the ionosphere, the ionized por- tion of the earth's atmosphere above about 60 miles (100 kilometers) height, and so affects the- ways in which we communicate over global distances. NOAA, the U.S. Commerce fs National Oceanic and Atmos- linistration, and its Environmental boratories are concerned with the hich human life and prospects are by events in the physical environ- ment. Where this environment means the - —ind and the influence of upon geomagnetic and at- mospheric processes, this concern is focused in the Space Environ seeks to describe, con predict the ships of eaiui .u sun. ine laoo casting arm, the Space Environn Center (SESC), is an important part of this . nuiwiiaifmi August 1972 solar disc and flare closeups, in hydrogen alpha hydrogen beta The SESC continuously monitors solar activity from observatories in Boulder, Colorado, and at key loca- tions around the world, and through data received from satellites. Using this stream of data the Boulder facility makes periodic reports of current and expected solar activity to some 50 concerned government and private organizations. This reporting and forecasting service helps managers of spaceflight programs, civil and military communications networks, electrical utili- ties, and other sun-sensitive activities accommodate their operations to the solar mood. The SESC is mainly concerned with the occasional extremes in solar activity. Although always incredibly stormy by earth standards, the sun goes through ap- proximately 11-year-long cycles of alternately increased and diminished activity. During the several years around the period of peak activity, flares occur which may cover an area on the sun several times the total surface of the earth. These enormous eruptions of energy in the chromosphere (the thin, layer of solar atmosphere above the visible solar surface, or photos- phere, characterized by increasing temperature with height) are usually associated with sunspot groups. Both sunspots and flares appear to be intimately re- lated to changing patterns of magnetic field polarities. The earth is enveloped by the solar wind, a flow of charged particles and imbedded magnetic fields from the sun that shapes the planet's magnetosphere and influences the Van Allen radiation belts and even the ionosphere. This energetic flow is greatly modified by solar flares, which send bursts of high-energy protons, low-energy protons, X-radiation and radio waves, and a plasma (ionized gas) cloud earthward. Electromag- netic radiation arrives here in about eight minutes, high-energy protons in about 20 minutes, low-energy protons in as much as 40 hours, and the plasma cloud in one to three days. The terrestrial effects of the flares include perturbations of the Van Allen belts of trapped radiation, the initiation of great displays of the aurorae, interruptions of some types of radio telecommunica- tion, and a radiation hazard to life outside the atmos- pheric shield. Forecasters at the SESC report and predict of solar activity and its probable geophysical effects. Bursts of increased solar radiation — visible, X-rays, radio waves, energetic protons and electrons — stream outward from the large flares. These emissions are monitored and analyzed by SESC, cooperating observa- tories, and robot sensors on satellites. Warnings that a major flare has occurred are issued, and predictions are made about the arrival at earth of the slower particles, and the expected geophysical effects. Such effects can be profound. The prompt X-rays strike deep into the upper atmosphere, radically chang- ing conditions along sunlit ionospheric paths used for some types of radio communications — causing, for ex- ample, some frequencies to be absorved instead of reflected. Solar particles arriving one to three days later interact with the upper atmosphere over the polar regions, producing magnificent displays of aurorae. At the same time, strong but irregular electrical currents flow in the magnetiosphere and polar ionosphere, changing the magnetic field at the surface of the earth. During these magnetic storms, strong currents may be induced in long electrical transmission and communi- cation lines, disrupting service. Very energetic solar particles, arriving as soon as 20 minutes after the flare, can penetrate the polar at- mosphere to heights at which supersonic transports fly. At times of very great flares, such particles may pose a radiation hazard to passengers on such aircraft. Particles from solar flares are always a potential hazard to astronauts outside of the shield afforded by the atmosphere, and the low-latitude, low-altitude mag- netic field of the earth. In fact, one of SESC's most i important jobs is to provide timely data to the National Aeronautics and Space Administration, which partially supports the activity, to ensure that the solar hazard to manned space missions is kept to a minimum through timely forecasts of these events and accurate predic- tions of the intensity of the flare-produced proton stream. The work at SESC is the operational precursor to STEM, the Solar-Terrestrial Environment Model, an am- bitious modeling program being worked on in the Space Environment Laboratory using research results obtained by researchers here and abroad. Consisting of six "sub-models" — models which numerically simulate the solar flare, propagation, interplanetary medium, energy transfer into the magnetosphere, the magnetos- phere itself, and ionospheric interactions — STEM should provide a unique and valuable tool to those who, like the solar forecasters at SESC, seek to comprehend the influences of the sun upon our planetary home. FILAMENTS (CALLED QUIESCENT a SOLAR PROMINENCE ON LIMB) QUIESCENT SOLAR PROMINENCE ACTIVE SOLAR PROMINENCE tude + 4.69, .1 C2 star in the main sequence. Although its mean density is only about one-fifth that of the earth, the sun is some 333,000 times more massive - acceleration jfue to gravity (which is a function of mass) at the apparent surface of the sun is nearly 280 times greater than our familiar 32 feet (98 centimeters) per second. Jhe gaseous ball of the sun rotates, but not rigidly. A point in the middle latitudes of the sun rotates at about 4,i00 miles 17,200 kilometers) per hour, completing a full turn every 27 days, faster than hich takes a little more than 28 days. Temperatures in the solar furnace range from some 6,000 degrees Celsius at the surface to r degrees in the interior, where hydrogen <■,. transformed into helium atoms. The tenuous corona far above the photosphere is again very hot — over 1 million degrees. The composite sun displayed here is a NOAA hydrogen-alpha photo bordered by a photo- graph of the corona obtained by the coronagraph at the University of Hawaii's Haleakala Observatory PENN STATE UNIVERSITY LIBRARIES NOAA's Environmental Research Laboratories, head- quartered in Boulder, Colorado, conduct broad inves- tigations of man's physical environment at facilities around the country. Besides the Space Environment Laboratory, these include major oceanographic facili- ties in Miami and Seattle; centers for experimental meteorology, weather modification, and atmospheric research in Boulder, Miami, and Norman, Oklahoma; air-pollution research laboratories at various locations nationwide; a Boulder laboratory developing electro- magnetic and acoustic sensors for environmental ob- servation; tsunami research and climate-monitoring facilities in Hawaii; an atmosphere- and ocean-simu- lating computer laboratory in Princeton, New Jersey; and a squadron of research aircraft in Miami. Studies of solar and interplanetary phenomena are con- ducted by the Aeronomy Laboratory as well as the Space Environment Laboratory, and much of the data from these activities is stored and disseminated by NOAA's Environmental Data Service and its Boulder-based National Geophysi- cal and Solar-Terrestrial Data Center. Visitors are welcome at SESC, but it helps to arrange the visit in advance. Write: SESC, NOAA Environmen- tal Research Laboratories, Boulder, Colo. 80302. The telephone num- NOAA/PA 72034 ber is (303) 499-1000, ext. 3204. 1973 4^E~