B sampling The process of obtaining a sequence of discrete digital values from a continuous sequence of analog data. SAR See synthetic aperture radar SAR SAT Search and Rescue Tracking System carried on NOAA polar-orbiting satellites that receives emergency signals from persons in distress. The satellites transmit these signals to ground receiving stations in the U.S. and overseas. Signals are forwarded to the nearest rescue coordination center which computes the location from which the emergency signals came and provides the coordinates of the emergency site to a rescue team. See Search and Rescue. satellite A free-flying object that orbits the Earth, another planet, or the sun. satellite dish (aka parabolic reflectorj Bowl shaped antennas that collect and focus the signals that a satellite beams down to Earth. The dish reflects the incoming radio frequency energy to a focal point where it can be picked up by a feedhorn antenna to transfer the RF energy to a transmission line. The bigger the dish, the greater will be the intercepted RE energy and hence, the gain. For example, a satellite dish is used to receive GOES WEFAX imagery Satellite Operations Control Center (SOCC) NOAA National Environmental Satellite Data and Information Service (NESDIS) Satellite Operations Control Center located in Suitland, Maryland. A principal operating feature of the NOAA system is the centralized remote control of the satellite through command and data acquisition (CDA) stations. The CDA stations transmit command programs to the satellite, and acquire and record meteorological and engineering data from the satellite. Data is transmitted from CDA to Suitland NESDIS Data Processing Services Subsystem (DPSS). DPSS is responsible for data processing and timely generation of meteorological products and distribution of these products. satellite orbital elements See Keplerian elements. satellite positioning A procedure by which satellites are used to locate precise objects or particular points on Earth. satellite revolution The time from one perigee (the point of an elliptical orbit path where a satellite is closest to Earth) to the next. perigee > S-Band One of the segments or bands into which the radio frequency spectrum above 1000 MHz is divided, designated by letters. Signals from GOES and other geostationary spacecraft transmitting on or near 1 691 MHz are transmitting on S-Band. scanner A system that optically scans its detector(s) across a scene and records or stores the data in a two-dimensional format to form an image. scanning radiometer An imaging system consisting of lenses, moving mirrors, and solid-state image sensors used to obtain observations of the Earth and its atmosphere. Scanning radiometers, which are the sole imaging systems on all current operational weather satellites, have far better long4erm performance than the vidicon IV camera tubes used with earlier spacecraft. scattering The process by which electromagnetic radiation interacts with and is redirected by the molecules of the atmosphere, ocean, or land surface. The term is frequently applied to the interaction of the atmosphere on sunlight, which causes the sky to appear blue (since light near the blue end of the spectrum is scattered much more than light near the red end). screaming eagles Cloud pattern so named because some observers maintain they can see the head of an eagle facing west in these cloud patterns. The pattern is similar to a comma, only the pattern is disorganized and not solid. Weather associated with screaming eagles consists of rain showers and gusty surface winds up to about 25 knots. The eagles can intensifv and enlarge when moving into areas east of troughs; in that case, intense thundeF storms can develop. Screaming eagles are common in the Pacific Ocean between Hawaii and the equator and are uncommon in the western Atlantic. sea breeze Local coastal wind that blows from the ocean to land. Sea breezes usually occur during the day because the heating differences of land and sea cause pressure differences. Cooler heavier air from the sea moves in to replace rising warm air on the coastline. See land breeze. sea level The datum against which land elevation and sea depth are measured. Mean sea level is the average of high and low tides. Search and Rescue International satellite-aided search and rescue project. COSPASI SARSAT satellites monitor the entire surface of the Earth, and transmit distress signals to special ground receiving stations. The receiving stations compute the location of the signal, and notifv the nearest rescue coordination center. Satellite search has cut recovery time from days to hours, and has aided downed airplanes, capsized boats, and persons in other emergencies. SEM See Space Environment Monitor TIROS. semi-major axis (aka aJ One of the six Keplerian elements, it indicates the size of an orbit. The semi-major axis is one half of the longest diameter of an orbital ellipse, e.g., one-half of the distance between the apogee and perigee of an Earth orbit. (The semi-major axis is related to the orbital period and mean motion by Kepler's third law. See Kepler's three laws of motion.) See Keplerian elements for diagram. sensor Device that produces an output (usually electrical) in response to stimulus such as incident radiation. Sensors aboard satellites obtain information about features and objects on Earth by detecting radiation reflected or emitted in different bands of the electromagnetic spectrum. Analyzing the transmitted data provides valuable scientific information about Earth. Weather satellites commonly carry radiometers, which measure radiation from snow, ice, clouds, and bodies of water Spaceborne radars are used for Earth observations, bouncing radar waves off land and ocean surfaces to study sea-surface conditions, ice thickness, and land surface features. A wind scatterometer is a special type of radar designed to measure ocean surface winds indirectly by bouncing signals off the water and measuring them from various angles. Infrared (IR) detectors measure heat generated by Earth features in the IR band of the spectrum. Photographic reconnaissance sensors in their simplest form are large telescope-camera systems used to view objects on Earth's surface. The bigger the lens, the smaller the object that can be detected. Camera-telescope systems now incorporate all sorts of sophisticated electronics to produce better images, but even these systems need cloudless skies, excellent lighting, and good color contrast between objects and their surroundings to detect objects the size of a basketball. Some of the satellites produce film images that must be returned to Earth, but a more convenient method is to record the image as a series of digital code numbers, then reconstruct the image from the electronic code using a computer at a ground station. sensor calibration The relationship between input and output for a given measurement. signal Electrical impulses, sound or picture elements, etc., received or transmitted. Signals can exist in many different forms and media (electrical/wires, acoustic/air light/transparent fibers, etc.), but all signals will vary with time. The signal shape plotted as a function of time is called the waveshape or waveform. Some waveforms are repetitive or periodic, that is, a small segment of the waveform repeats itself regularly. Other waveforms, such as noise, are nonperiodic or aperiodic. All waveforms can be distilled into the combination of pure waves called sine waves. The frequency of a sine wave is the rate at which the fundamental shape repeats itself. Most signals occupy a limited range of frequencies between a lower limit and an upper limit. This range or band of frequencies occupied by a signal is called the bandwidth of the signal. Communication medium or channel can pass only a specific range or band of frequencies, which is called the bandwidth of the channel. The bandwidths of the channel and the signal determine the number and types of signals that can be transmitted by a particular communication channel. Signals often are too small and need to be made larger through a process called amplification. The amount of amplification is measured in decibels. However amplification is an imperfect process, and inadvertently introduces various distortions, noise, and bandwidth limitations. Often, multiple signals must share the same medium. One way the sharing can be accomplished is to place each signal in its own band of frequencies within the total band of the medium. The combining of a number of signals to share a medium by dividing it into different frequency bands for each signal is called frequency-division multiplexing. Frequency-division multiplexing requires the ability to move signals around so that each multiplexed signal occupies its own band. This is accomplished through a process called modulation, in which a high-frequency sine wave carries the signal into the specified band. Either the amplitude or the frequency of the carrier wave can be varied, or modulated, in synchrony with the information-bearing signal. These methods are called amplitude modulation (AM) and frequency modulation (FM). FM is the more complex process of the two, and the bandwidth of the FM carrier can be many times that of the modulating signal. The process of demodulating a frequency-modulated signal eliminates much of the deleterious effects of additional noise. (The trade-off between bandwidth and noise immunity characterizes most communication systems. Both are analog modulation schemes for multiplexing signals in the frequency spectrum.) Digitizing a signal requires a number of steps and results in a binary digital signal that takes on one of two discrete values. This process results in considerable immunity to additive noise, but requires a considerable increase in bandwidth. signal~to-noise ratio (SNR) In decibels (dB), the difference between the amplitude of a desired radio frequency (RF) signal and the internal or external RF noise level in a system. A negative SNR indicates the signal is below the system noise level and unusable. The greater the positive SNR, the less effect noise will have on the final quality. SNR of at least + 1 2dB is necessary to produce imagery with minimal noise effects. sine wave A smoothly varying wave that repeats itself; its frequency is the rate at which the fundamental shape repeats itself. Any waveform can be distilled into a combination of pure sine waves of varying frequencies and amplitudes. sink The process of providing storage for a substance. For example, plants-through photosynthesis~transform carbon dioxide in the air into organic matter which either stays in the plants or is stored in the soils. The plants are a sink for carbon dioxide. Skylab The first U.S. space station, launched unmanned in May 1 973 and soon after occupied in succession by three crews through November 1973. SNR See signal-to-noise ratio. SOCC See Satellite Operations Control Center software The programs, data, or routines used by a computer distinguished from the physical components (e.g., hardware). solar backscatter ultraviolet radiometer (SBUVJ Instrument that measures the vertical distribution and total ozone in the Earth's atmosphere. Data is used for the continuous monitoring of ozone distribution to estimate long-term trends. SBUV instruments are flown on NO4~ polar-orbiting satellites. solar constant Aka total solar irradiance. The constant expressing the amount of solar radiation reaching the Earth from the sun, approximately 1 370 watts per square meter It is not, in fact, truly constant and variations are detectable. solar cycle Eleven-year cycle of sunspots and solar flares that affects other solar indexes such as the solar output of ultraviolet radiation and the solar wind. The Earth's magnetic {ield, temperature, and ozone levels are affected by this cycle. solar radiation Energy received from the sun is solar radiation. The energy comes in many forms, such as visible light (that which we can see with our eyes). Other forms of radiation include radio waves, heat (infrared), ultraviolet waves, and x-rays. These forms are categorized within the electromagnetic spectrum. solar wind A continuous plasma stream expanding into interplanetary space from the sun's corona. The solar wind is present continuously in interplanetary space. After escaping from the gravi tational field of the sun, this gas flows outward at a typical speed of 400 km per second to distances known to be beyond the orbit of Pluto. Besides affecting Earth's weather solar activity gives rise to a dramatic visual phenomena in our atmosphere. The streams of charged particles from the Sun interact the Earth's magnetic field like a generator to create current systems with electric potentials of as much as 1 00,000 volts. Charged electrons are energized by this process, sent along the magnetic field lines towards Earth's upper atmosphere, excite the gases present in the upper atmosphere and cause them to emit light which we call the auroras. The auroras are the northern (aurora borealis) and southern (aurora Australis) lights. bow shock Earth sounder A special kind of radiometer that measures changes in atmospheric temperature with height, as well as the content of various chemical species in the atmosphere at various levels. The High Resolution Infrared Radiation Sounder (HIRS), found on NOAA polar-orbiting satellites, is a passive instrument. See passive system. Space Environment Monitor (SEMJ Instrument that measures the condition of the Earth's magnetic field and the solar activity and radiation around the spacecraft, and transmits these data to a central processing facility. NOAA polaForbiting and geostationary satellites both carry SEMs. See TIROS. Spacelab A manned laboratory module built by the European Space Agency (ESA) that accommodates dozens of experiments on each flight, mainly in the categories of materials science and life science. Spacelink NASA electronic database for educators, with information stored on a computer at the Marshall Space Flight Center. Via computer educators communicate with NASA education specialists and access the following menus: current NASA news, aeronautics research, U.S. Space Program historical information, aerospace research in the 1 980s and beyond, overviews of NASA and its Centers, NASA educational services, classroom materials, and space program spin-offs. The computer access number is 205-895-0028, the data word format is 8 data bits, no parity, and 1 stop bit300, 1 200, or 2400 baud modem required. Callers with Internet access may reach NASA Spacelink at: spacelink.msfc.nasa.gov. space physics Scientific study of magnetic and electric phenomena that occur in outer space, in the upper atmosphere of the planets, and on the sun. Space Shuttle NASAs manned, recoverable spacecraft designed to be used as a launch vehicle for Earth-orbiting experiments and as a short-term research platform. spectral band A finite segment of wavelengths in the electromagnetic spectrum. spectrum I. The series of colored bands diffracted and arranged in the order of their respective wave lengths by the passage of white light through a prism or other diffracting medium and shading continuously from red (produced by the longest visible wave) to violet (produced by the shortest visible wave). 2. Any of various arrangements of colored bands or lines, together with invisible components at both ends of the spectrum, similarly formed by light from incandescent gases or other sources of radiant energy, which can be studied by a spectrograph. 3. In radio, the range of wave lengths of radio waves, from 3 centimeters to 30,000 meters, or of frequencies of radio waves, from 1 0 to 1 0,000,000 kilocycles. Also radio spectrum. 4. The entire range of radiant energies. See electromagnetic spectrum. SPOT Systeme Pour 'Observation de Ia Terre. French, polar-orbiting Earth observation satellite(s) with ground resolution of 1 0 meters. SPOT images are available commercially and are intended for such purposes as environmental research and monitoring, ecology management, and for use by the media, environmentalists, legislators, etc. SPOT Image Company that markets data gathered by the SPOT satellite worldwide. start tone Five seconds of 300 Hz black to white square wave modulation of the WEFAX subcarrier signaling the start of a frame transmission (the beginning of a direct readout image). stop tone Five seconds of 450 Hz black to white square wave modulation of the WEFAKsubcarrier signaling the stop of a frame transmission (end of a direct readout image). stratosphere Region of the atmosphere between the troposphere and mesosphere, having a lower boundary of approximately 8 km at the poles to 1 5 km at the equator and an upper boundary of approximately 50 km. Depending upon latitude and season, the temperature in the lower stratosphere can increase, be isothermal, or even decrease with altitude, but the temperature in the upper stratosphere generally increases with height due to absorption of solar radiation by ozone. subcarrier The 2400 Hz audio tone transmitted by APT and WEFA,t' spacecraft. Amplitude modulation of this tone is used to convey video information. subsatellite point Point where a straight line drawn from a satellite to the center of the Earth intersects the Earth's surface. subsatellite track See ground track. subsystem 1. A subunit of either the physical climate system (e.g., ocean dynamics) or the biogeochemical cycles (e.g., terrestrial ecosystems). 2. A subunit of a spacecraft, e.g., the telemetry subsystem, the power subsystem, the sensor subsystem, etc. sun The closest star to Earth (149,599,000 km away on average). The sun dwarfs the other bodies in the solar system, representing approximately 99.86 percent of all the mass in the solar system. One hundred and nine Earths would be required to fit across the Sun's disk, its interior could hold over 1.3 million Earths. The source of the Sun's energy is the nuclear reactions that occur in its core. There, at temperatures of 1 5 million degrees Celsius (27 million degrees Fahrenheit) hydrogen atom nuclei, called protons, are fused and become helium atom nuclei. The energy produced through fusion at the core moves outward, first in the form of electromagnetic radiation called photons. Next, energy moves upward in photon heated solar gas-this type of energy transport is called convection. Convective motions within the solar interior generate magnetic fields that emerge at the surface as sunspots and loops of hot gas called prominences. Most solar energy finally escapes from a thin layer of the Sun's atmosphere called the photosphere-the part of the Sun observable to the naked eye. The sun appears to have been active for 4.6 billion years and has enough fuel for another 5 billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow Earth. After a billion years as a "red giant" it will suddenly collapse into a "white dwarf." It may take a trillion years to cool off completely sun-synchronous Describes the orbit of a satellite that provides consistent lighting of the Earth-scan view. The satellite passes the equator and each latitude at the same time each day. For example, a satellite's sun-synchronous orbit might cross the equator twelve times a day each time at 3:00 p.m. local time. The orbital plane of a sun-synchronous orbit must also precess (rotate) approximately one degree each day, eastward, to keep pace with the Earth's revolution around the sun. survey mode Refers to observational emphasis upon frequent global coverage, usually with restricted spatial and spectral resolution, aimed at developing a consistent, long-term data product for later interpretation. swath The area observed by a satellite as it orbits the Earth. synoptic chart Chart showing meteorological conditions over a region at a given time; weather map. synoptic view The ability to see large areas at the same time. synthetic aperture radar (SARJ A high-resolution ground-mapping technique that effectively synthesizes a large receiving antenna by processing the phase of the reflected radar return. The along4rack resolution is obtained by timing the radar return (tim~gating) as for ordinary radar The crosstrack (azimuthal) resolution is obtained by processing the Doppler phase of the radar return. The cross4rack "dimension" of the antenna is a function of the length of time over which the Doppler phase is collected. See Doppler effect. D TDRSS See Tracking and Data Relay Satellite System. telemetry 1. Telecommunications transmission to a distance of measured magnitude by radio or telephony with suitably coded modulation, e.g., amplitude, frequency phase, pulse. 2. Transmission of data collected at a remote location over communications channels to a central station. 3. Surveying measurement of linear distances by use of tellurometer-a device that uses microwaves to measure distance. telephony Used to transmit sounds between widely removed points with or without connecting wires. Television and Infrared Observation Satellite (TIROSJ A series of NASA and NOAA satellites launched to monitor Earths' weather from outer space. The era of the meteorological satellites began with the launch of TIROS- I on April 1, 1 960. For the first time, it was possible to monitor weather conditions over most of the world regularly from space. A series of these satellites were launched throughout the 1 960s, those funded by NASA for research and development were called TIROS, and those funded by the Environmental Science Services Administration (ESSA, the predecessor of NO~) for the operational system were called ESSA. A second generation of lTOS/NO~* environmental satellites was initiated by the launch of ITOS- 1 in 1 970, followed by a number of NOAA satellites. The third generation of TIROSN/NOAA environmental satellites was initiated by the launch of TIROS-N in 1 978. * Pairs of acronyms such as ITOS/NOAA arise because NASA funds and names its prototype satellites and then the operating agency funds and names the rest of the series. TIROS TIROS-NINOAA satellites NOAA satellites that continuously orbit the Earth from North to South Pole (hence, polar orbiting) at an altitude of approximately 470 nautical miles (870.44 km or 540.86 statute miles). These environmental satellites collect visible and infrared imagery and provide atmospheric-sounding data and meteorological data relay and collection. A primary mission of TIROS-N/NOAA is to monitor the 70 percent of the globe covered by water-where weather data is sparse and provide continuous data to the National Weather Service for use in numerical forecast modeling. Each TIROSN/NOAA carries six primary systems: 1. The Advanced Very High Resolution Scanning Radiometer (AVH R R ( senses clouds over both ocean and land, using the visible and infrared parts of the spectrum. It stores measurements on tape, and later plays them back to NOAAs command and data acquisition stations. The satellites also broadcast in real time, and the broadcasts can be received around the world by anyone equipped with a direct readout receiving station. 2. The TIROS Operational Vertical Sounder (TOVS) is a 3-part TIROS system to measure: ˇ Temperature profile of the Earth's atmosphere from the surface to 1 0 millibars; ˇ Water content of the Earth's atmosphere; ˇ Total ozone content of the Earth's atmosphere; 3. The ARGOS Data Collection and Platform Location System (DCSJ collects data from sensors placed on fixed and moving platforms, including ships, buoys, and weather balloons, and transmits data to a ground station antenna. Because ARGOS also determines the precise location of these moving sensors, it can serve wildlife managers by monitoring and tracking the transmitters placed on birds and animals. 4. The Space Environment Monitor ~SEM) measures energetic particles emitted by the sun over essentially the full range of energies and magnetic field variations in the Earth's near-space environment. Readings made by these instruments are invaluable in measuring the sun's radiation activity. 5. Search and Rescue Tracking (COSPAS/SARSAT) equipment receives emergency signals from persons in distress. The satellites transmit the signals to ground receiving stations. The signals then are forwarded to rescue coordination centers. The rescue centers compute the location of the signals and provide the coordinates of the emergency site (usually within a few miles). 6. Earth Radiation Budget Experiment (ERBE) is a radiometer flown on NOAA 9 and 1 0, designed to measure all radiation striking and leaving the Earth. This enables scientists to measure the loss or gain of terrestrial energy to space. Shifts in this energy "budget" affect the Earth's average temperatures. Even slight changes can affect climatic patterns. temperature Measure of the energy in a substance. The more heat energy in the substance, the higher the temperature. The Earth receives only one twobillionth of the energy the sun produces. Much of the energy that hits the Earth is reflected back into space. Most of the energy that isn't reflected is absorbed by the Earth's surface. As the surface warms, it also warms the air above it. terabit A trillion (1 0 2) bits. thematic mapper (TM) A Landsat multispectral scanner designed to acquire data to categorize the Earth's surface. Particular emphasis was placed on agricultural applications and identification of land use. The scanner continuously scans the surface of the Earth, simultaneously acquiring data in seven spectral channels. Overlaying two or more bands produces a false color image. The ground resolution of the six visible and shortwave bands of the Thematic Mapper is 30 meters, and the resolution of the thermal infrared band is 1 20 meters. Thematic mappers have been flown on Landsats-4 and -5. thermal infrared Electromagnetic radiation with wavelengths between about 3 and 25 micrometers. thunder The sound that results from lightning. Lightning bolts (static electricity) produce intense heat. This burst of heat makes the air around the bolt expand explosively producing the sound we hear as thunder. Since light travels faster than sound, we see the lightning before we hear the thunder. thunderstorm Local storm resulting from warm humid air rising in an unstable environment. Air may start moving upward because of unequal surface heating, the lifting of warm air along a frontal zone, or diverging upper-level winds (these diverging winds draw air up beneath them). The scattered thunderstorms that develop in the summer are called airmass thunderstorms because they form in warm, maritime tropical air masses away from other weather fronts. More violent severe thunderstorms form in areas with a strong vertical wind shear that forces the updraft into the mature stage, the most intense stage of the thunderstorm. Severe thunderstorms can produce large hail, forceful winds, flash floods, and tornadoes. TIROS See Television and Infrared Observation Satellite. TM See thematic mapper TNL Thermal Noise Level. TOGA See Tropical Ocean Global Atmosphere Program. TOMS See Total Ozone Mapping Spectrometer TOPEXIPOSEIDON Ocean Topography Experiment, United States (NASA)/France (CNES). Launched in 1 992, the mission carries a radar sensor-called an altimeter-to measure the ocean's surface topography with unprecedented precision. TOPEX/POSEIDON is a core element of the international World Ocean Circulation Experiment (WOCE) and the Tropical Ocean Global Atmosphere (TOGA) seagoing measurements program. Mission objectives are to: ˇ Study ocean circulation and its interaction with the atmosphere to understand climate change better; ˇ Improve our knowledge of heat transport in the ocean; ˇ Model global ocean tides; ˇ Study the marine gravity field; ˇ Calculate sea-level variations on both global and local scales. tornado A twisting, spinning funnel of low pressure air. The most unpredictable weather event, tornadoes are created during powerful thunderstorms. As a column of warm air rises, air rushes in at ground level and begins to spin. If the storm gathers energy a twisting, spinning funnel develops. Because of the funnel's cloud and rain composition and the dust, soil, and debris it draws up, the funnel appears blackish in color. The most energetic storms result in the funnel touching the ground. In these tornadoes, the roaring winds in the funnel can reach 300 mph, the strongest winds on Earth. Funnels usually travel at 20 to 40 mph, moving toward the northeast. When tornadoes form over lakes or oceans they suck water into the funnel cloud and are called waterspouts. Total Ozone Mapping Spectrometer (TOMS) Flown on NASAs Nimbus-7 satellite, its primary goal is to continue the high-resolution global mapping of total ozone on a daily basis. The Nimbus-7 launch in 1 978 enabled TOMS to begin delivering data in 1 979 and continue providing information until 1 993. TOMS has mapped the total amount of ozone between the ground and the top of the atmosphere, provided the first maps of the ozone hole, and continues to monitor this phenomenon. Because of its longevity, TOMS also has obtained information on the more subtle trends in ozone outside the ozone hole region. This results from development of a powerful new calibration technique that removes the instrument measurement drift that developed over the years. With this technique applied to the TOMS 1 4.5-year data record, a global ozone decrease of 2.69 percent per decade was detected. To ensure that ozone data will be available through the next decade, NASA will continue the TOMS program using U.S. and foreign launches. In 1 99 1, the former Soviet Union launched a Meteor-3 satellite carrying a TOMS instrument provided by NASA. A third TOMS will be launched onboard a NASA Earth probe satellite in 1 994, and the japanese Advanced Earth Observations Satellite (ADEOS) will carry a fourth TOMS when it launches in 1 996. TOVS TIROS Operational Vertical Sounder. See Television Infrared Operational Satellite (TIROS). Tracking and Data Relay Satellite System (TDRSS) An orbiting communications satellite, developed by NASA, used to relay data from satellite sensors to ground stations and to track the satellites in orbit. trade winds Surface air from the horse latitudes that moves back toward the equator and is deflected by the Coriolis Force, causing the winds to blow from the Northeast in the Northern Hemisphere and from the Southeast in the Southern Hemisphere. These steady winds are called trade winds because they provided trade ships with an ocean route to the New World. See wind. TRMM See Tropical Rainfall Measuring Mission. Tropical Ocean-Global Atmosphere (TOGAJ TOGA is a program jointly sponsored by the United Nations World Meteorological Organization (WMO); the International Council of Scientific Unions (ICSU); the United Nations Educational, Scientific, and Cultural Organization (UNESCO) Intergovernmental Oceanographic Commission (bC); and the ICSU Scientific Committee on Oceanic Research (SCOR). TOGA has four major objectives: ˇ To collect and catalog observations of the tropical atmosphere and ocean; ˇ To assess the evolution of the tropical atmosphere/ocean system in real time; ˇ To promote the development of short-term climate-prediction computer models for the tropics; ˇ To study the influence of the tropical atmosphere/ocean system on the climate at higher latitudes. Tropical Rainfall Measuring Mission (TRMMJ Ajoint NASA/NASDA mission planned for launch in 1997. The goal of TRMM is to obtain a minimum of 3 years of climatologically significant observations of rainfall in the tropics. Because rainfall is such a variable phenome non, adequate sampling is a difficult problem. By averaging the instantaneous rainfall rates for 30 days over a 50 by 50 grid, TRMM will obtain observations that meet climatological requirements. TRMM measurements, used together with cloud models, also will provide accurate estimates of vertical distributions of latent heating in the atmosphere. The present uncertainty about the quantity and distribution of precipitation, especially in the tropics, prohibits definition of the mass and energy exchange between the tropical ocean and atmosphere. Since the tropical atmosphere and oceans are closely coupled, cloud radiation and rainfall are likely to have significant effects on ocean circulation and marine biomass. TRMM data will play a significant role in global change studies, especially in developing an interdisciplinary understanding of atmospheric circulation, ocean-atmospheric coupling. and tropical biology TRMM data on tropical clouds, evaporation, and heat transfer will be used to understand the larger scale coupling of the atmosphere to oceans. See Earth Probes. tropical storm formation Tropical storms generally form in the eastern portion of tropical oceans and track westward. Hurricanes, typhoons, and willywuhes all start out as weak low pressure areas that form over warm tropical waters (e.g., surface water temperature of at least 80 0F). Initially winds and cloud formations over the warm tropical waters are minimal. Both intensifv with time. Formation of tropical storms also requires a significant Coriolis effect to induce proper spin in the wind formation. As the storm begins to organize itself into a coherent pattern, it will experience increased activity and intensity. When a storm develops a clearly recognizable pattern, it is referred to as a tropical depression. When wind speeds reach 35 knots (40.3 mph), it is called a tropical storm and is given a name. When wind speed equals or exceeds 74 mph, the storm is called a hurricane. In the western Pacific, a hurricane is referred to as a typhoon. In waters around Australia it is called a cyclone or willy-willy Hurricanes intensifv when moving over areas of increased water temperatures, and weaken over colder water surfaces. Upper atmosphere wind shear (different wind direction and speeds at different elevations) will frequently prevent or slow intensification of tropical storms by "spreading out" the storm horizontally and preventing the formation of strong updrafts of warm, humid air. Movement over a land-mass will weaken hurricane winds but will result in large-scale rain that can result in large-scale flooding. When encountering a strong frontal system (such as a polar front) the hurricane will curve and track along the leading edge of the front or become implanted in it. Satellite infrared imagery can identifv surface water temperatures that will foster tropical storm development. tropics The area between 23.5 degrees north and south of the equator. This region has small daily and seasonal changes in temperature, but great seasonal changes in precipitation. troposphere The lower atmosphere, to a height of 8-1 5 km above Earth, where temperature generally decreases with altitude, clouds form, precipitation occurs, and convection currents are active. See atmosphere. tropospheric emission spectrometer A high-resolution infrared spectrometer for monitoring the minor components of the lower atmosphere. trough Elongated area of low atmospheric pressure, either at the surface or in the upper atmosphere. true anomaly (aka J) One of six Keplerian elements, it locates a satellite on an orbit. True anomaly is the true angular distance of a satellite (planet) from its perigee (perihelion) as seen from the center of the Earth (sun). See Keplerian elements. typhoon Hurricanes in the Western Pacific Ocean. w ultraviolet radiation The energy rangejust beyond the violet end of the visible spectrum. Although ultraviolet radiation constitutes only about 5 percent of the total energy emitted from the sun, it is the major energy source for the stratosphere and mesosphere, playing a dominant role in both energy balance and chemical composition. Most ultraviolet radiation is blocked by Earth's atmosphere, but some solar ultraviolet penetrates and aids in plant photosynthesis and helps produce vitamin D in humans. Too much ultraviolet radiation can burn the skin, cause skin cancer and cataracts, and damage vegetation. UARS See Upper Atmosphere Research Satellite United States Geological Survey (USGSJ A bureau of the Department of the Interior USGS was established in 1 879 following several Federally-sponsored independent natural resource surveys of the West and Midwest. The Department of the Interior has responsibility for most of our nationally owned public lands and natural resources. The USGS monitors resources such as energy minerals, water land, agriculture, and irrigation. The resulting scientific information contributes to environmental-policy decision making and public safety. For example, USGS identifies flood- and landslide-prone areas and maintains maps of the United States. United States Global Change Research Program (USGCRPJ The USGCRP addresses significant uncertainties concerning the natural and human-induced changes to Earth's environment. The USGCRP has a comprehensive and multidisciplinary scientific research agenda. See Global Change Research Program. Upper Atmosphere Research Satellite (UARSJ UARS is part of a long-term, international program of space research into global atmospheric change. Beginning in 1 991, NASAs UARS program began to carry out the first systematic, detailed satellite study of the Earth's stratosphere, mesosphere, and lower thermosphere; establish the comprehensive data base needed for an understanding of stratospheric ozone depletion; and bring together scientists and governments around the world to assess the role of human activities in atmospheric change. Launched on September 1 2, 1 991, UARS became the first official space component of Mission to Planet Earth. USGCRP See United States Global Change Research Program. UTC See Coordinated Universal Time. UV Ultraviolet. See ultraviolet radiation. w Van Allen belts or Van Allen Radiation belts Doughnut-shaped regions encircling Earth and containing high energy electrons and ions trapped in the Earth's magnetic field (the magnetic field has definite boundaries, and is distorted into a tear-drop shape by the solar wind). Explorer I, launched by NASA in 1958, discovered this intense radiation zone. These regions are called the inner and outer Van Allen radiation belts, named after the scientist who first observed them. See magnetosphere. vernal equinox The beginning of spring in the Northern Hemisphere. The time/day that the sun crosses the equatorial plane going from south to north. Very High Frequency (VHFJ Referring to the 50-400 MHz portion of the radio frequency spectrum. Polar-orbiting satellite transmissions (APT) are made in the 136-138 MHz range using FM modulation. video A signal containing information on the brightness levels of different portions of an image along with information on line and frame synchronization. In the case of satellite signals, the video information is transmitted in the form of an AM modulated subcarrier visible That part of the electromagnetic spectrum to which the human eye is sensitive, between about 0.4 and 0.7 micrometers. See spectrum. Visiblellnfrared Spin Scan Radiometer (VISSRJ High-resolution, multi-spectral imaging system flown on the pre-GOES-8 geostationary GOES spacecraft. Similar systems are flown on the METEOSAT and GMS spacecraft. volcano A naturally occurring vent or fissure at the Earth's surface through which erupt molten, solid, and gaseous materials. Volcanic eruptions inject large quantities of dust, gas, and aerosols into the atmosphere. A major component of volcanic clouds is sulfur dioxide, a strong absorber of ultraviolet radiation. Chemical interactions between sulfur dioxide and water cause sulfuric acid aerosols which can scatter some of the incident solar radiation back to space, thus causing a global cooling effect. For exampIe, Mt. Pinatubo in the Philippines erupted in June 1 99 I, and in the following year the global surface temperature was observed to decrease by about 0.30 C. volt The unit of electromotive force, or difference of potential, which will cause a current of one ampere to flow through a resistance of one ohm. Named for Italian physicist Alessandro Volta (1745-1827). W Degrees west longitude, referenced to the Greenwich (prime) meridian. water vapor (aka moisture) Water in a gaseous form. wave 1. In electricity a periodic variation of an electric current or voltage. 2. In physics, any of the series of advancing impulses set up by a vibration, pulsation, or disturbance in air or some other medium, as in the transmission of heat light sound, etc. one wavelength wavelength Physical distance of one period (wave repeat) weather Atmospheric condition at any given time or place. Compare with climate. Weather Facsimile (WEFAX) A system for transmitting visual reproductions of weather forecast maps, temperature summaries, cloud analyses, etc. via radio waves. WEFAX transmissions are relayed by NOAAs geostationary GOES spacecraft. weather symbols Some commonly used symbols are illustrated in the chart on the right. weather terms Clear: Sky cloud-free to 30 percent covered. ˇ Sunny: Sunshine 70-100 percent of the day ˇ Partly sunny and partly cloudy: Both terms refer to 40 to 70 percent cloud cover. Partly sunny is used in the day; partly cloudy is used at night. ˇ Fog: A cloud on the ground. Fog is composed of billions of tiny water droplets floating in the air. ˇ Snow: Precipitation of ice crystals. ˇ Snow flurries: Intermittent snowfall that may result in little accumulation. ˇ Sleet: Pellets of ice that form when rain or melting snowflakes freeze while falling. (Occurs in cold weather; hail usually occurs in summer.) ˇ Freezing rain: Rain that turns to ice on impact with the surface. ˇ Rain: Extended period of precipitation. Associated with large storm systems rather than single clouds or thunder storms ˇ Showers: Brief interval of rain that does not affect a large area Weather Symbols p> cold front clear sky, no clouds &mIŁ warm front 2/10 3/10 cloudy ______________ occluded front half the sky covered with clouds stationary front thunderstorm completely overcast ˇ ** * moderate rain moderate snow ˇ Squall: Fast-moving thunderstorm or line of thunderstorms that often can produce damaging winds, hail, and tornadoes. ˇ Hail: Pieces of ice that fall from thunderstorms. Hail often is composed of concentric rings of ice that form as the particle moves through "wet" and "dry" areas of the thunderstorm. Weather watch Statement about a particularly dangerous weather system that may occur at some specified time in the future. Weather warning Statement that dangerous weather is likely or is occurring. Take action. WEFAX See weather facsimile. willy-willy Australian term for tropical cyclone, hurricane. wind A natural motion of the air; especially a noticeable current of air moving in the atmosphere parallel to the Earths' surface. Winds are caused by unequal heating and cooling of North Pole northeasterlies 600 ~ 300 horse northeast trades low pressure 0o southeast trades~ preiffi_~g~ latitudes 300 horse westerlies southeasterlies 60~ South Pole Earth's large-scale wind belts leaves rustle; 4-7 2 slight breeze small wavelets 8-12 3 gentle breeze leaves & twigs in motion; large wavelets moderate small branches move; 13-18 4 breeze small waves 2-4 feet tall fresh small trees sway; 19-24 5 breeze whitecaps 4-8 feet tall 25-31 6 strong large branches sway; breeze whitecaps 8-13 feet tall whole trees in motion; 32-38 7 near gale waves 13 feet tall 39-46 8 gale twigs break oft trees; waves up to 16 feet tall branches break; 47-54 9 strong gale waves up to 21 feet trees blown over; 55-63 10 whole gale waves up to 26 feet 64-73 11 storm widespread damage; waves up to 35 feet tall 74-up 12 hurricane widespread damage; large ships sink * Beaufort Number the Earth and atmosphere due to absorbed, incoming solar radiation and infrared radiation lost to space-as modified by such effects as the Coriolis force, the condensation of water vapor; the formation of clouds, the interaction of air masses and frontal systems, friction over land and water; etc. The chart above is an abbreviated version of the Beaufort Wind Scale, named for the British admiral who invented it in 1 805. wind chill The wind can reduce significantly the amount of heat your body retains. The following wind chill chart does not take into account such variables as type of clothing worn, amount of exposed flesh, and physical condition, all of which would alter body heat. wind speed (mph) 35 30 25 20 15 10 15 16 9 2 -5 -11 -18 20 12 4 -3 -10 -17 -24 25 8 1 -7 -15 -22 -29 30 6 -2 -10 -18 -25 -33 35 4 -4 -12 -20 -27 35 40 3 -5 -13 -21 -29 -37 45 2 -6 -14 -22 -30 -38 WIND CHILL ( degrees F) simple wind-chill equation Tw = TA - .5 x VA Tw = wind chill TA = air temperature VA = wind speed For example, if the temperature is 200 and the wind 20 mph: Tw 20 - 1.5 x 20 Tw = 20 - 30 Tw =-100F wind vane An instrument used to indicate wind direction. wind vector Arrow representing wind velocity. The arrow points in the direction of the wind. The length of the arrow is proportional to wind speed. wind velocity Vector term that includes both wind speed and wind direction. window Term used to denote a region of the electromagnetic spectrum where the atmosphere does not absorb radiation strongly. WOCE See World Ocean Circulation ExperimenL workstation A "smart" computer terminal that serves as a primary scientific research tool, offering direct access to experimental apparatus, information files, internal computers, and output devices, usually connected to an external communications network. World Ocean Circulation Experiment (WOCE) A study of the general global circulation of the oceans. It emphasizes the measurements and understanding needed to describe and understand the circulation, to simulate it, and to predict its changes in response to climatic changes. WWW World Weather Watch. a yagi A type of receiving antenna that has several rod elements mounted on a beam. Its directional pattern of sensitivity and ease of construction make it ideal for APT direct readout stations See antenna. B zephyr A Mediterranean term for any soft, gentle breeze