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Storm Team Weather Glossary

Acid Deposition
Atmospheric Pressure
Carbon cycle
Carbon dioxide
Chlorofluorocarbons (CFCs)
Climate Sensitivity
Condensation Nuclei
Developing Countries
Dew Point
Dobson Units
Earth Observing System
El Ninõ
El Ninõ-Southern Oscillation
Electromagnetic Spectrum
Environmental refugees
Food Chain
Fossil Fuels
Gaia Hypothesis
General Circulation Models
Geographic Information System
Geothermal Energy
Global Change
Global Warming
Green Revolution
Greenhouse Effect
Greenhouse Gases
Ground Truth
Gulf Stream
Hydrologic Cycle
Ice Age
Image resolution
In Situ
Milankovitch Theory
Montreal Protocol
Multispectral Scanner
Ozone Depletion
Ozone Hole
Passive Solar Design
Photochemical Smog
Plate Tectonics
Radiation Budget
Rain Gauge
Remote Sensing
Renewable Energy
Solar Constant
Solar Radiation
Spectral Band
Sustainable Development
Thematic Mapper
Total Ozone Mapping Spectrometer
Trade Winds
Tropical Cyclone
Tropospheric Ozone
Ultraviolet radiation
Volatile Organic Compounds
Water vapor
Wind Shear
Younger Dryas

Acid Deposition is precipitation (rain, snow, etc.) made acidic by the addition of sulfur dioxide and nitrogen oxides into the atmosphere as a result of fossil fuel burning. Automobile exhaust and emissions from coal-fired power plants are two significant causes of acid deposition. In severe cases, acid precipitation kills fish and other aquatic life and damages and/or destroys trees and crops. In some instances, it has rendered entire lakes and forests nearly lifeless. Index

Advection is horizontal transport of any property, such as heat or humidity. Index

Aerosol is a gaseous suspension of fine solid particles. Index

Albedo is the fraction of light reflected by a surface, often expressed as a percentage. Light colored surfaces, such as snow and ice, have a high albedo, while dark, light-absorbing surfaces have a low albedo. Index

Anthropogenic means caused or created by human beings. For example, anthropogenic carbon dioxide emissions are those caused by human activities such as burning fossil fuels. Index

Atmosphere is the envelope of gases that surrounds a planet. Earth's atmosphere is one of five interrelated components that make up the Earth system. The other four are the biosphere, hydrosphere, cryosphere, and pedosphere, which are defined below. Index

Atmospheric Pressure is the force exerted by the air on each unit of area of a surface, essentially equivalent to the weight of the overlying atmosphere. High atmospheric pressure generally leads to stable weather conditions while low pressure can result in storms. Index

Atom is the smallest unit of a chemical element that can take part in a chemical reaction. An atom is composed of a nucleus containing protons and neutrons, and is surrounded by electrons. Index

AVHRR stands for Advanced Very High Resolution Radiometer, the imagery produced by NOAA (National Oceanographic and Atmospheric Administration) satellites. Pixel size is 1km x 1km for local area coverage (LAC) and 2km x 2km for global area coverage (GAC). Index

Barometer is an instrument used to measure atmospheric pressure. Index

Biodiversity refers to the total number of biological species in a particular area. Index

Biomass is the total dry weight of living material in a particular area. Index

Biome is a distinctive ecological system, characterized primarily by the nature of its vegetation. Index

Biosphere refers to the region on land, in the oceans and in the atmosphere inhabited by living things. Index

Biota refers to all living things, including animal and plant life. Index

Blizzard is snow falling with winds faster than 35 miles per hour and visibility of a quarter mile or less over an extended time period. Index

Business-as-usual, in the context of global climate change, refers to a scenario for future world patterns of energy use and greenhouse gas emission which assumes that there will be no significant change in people's attitudes and priorities. Index

Carbon cycle is the exchange of carbon between land, atmosphere and oceans. About one quarter of the total carbon (in the form of carbon dioxide) in the atmosphere is cycled in and out each year; half of this is exchanged with the land biota, and the other half, through physical and chemical processes, across the ocean's surface. Index

Carbon dioxide (CO2) is one of the major greenhouse gases. Anthropogenic CO2 results mainly from burning fossil fuels (coal, oil, gas) and from deforestation. Index

Celsius is a temperature scale, also called the Centigrade scale. Its fixed points are the freezing point of water (0.C) and the boiling point of water (100.C). To convert from Celsius to Fahrenheit, multiply the Celsius temperature by 1.8 and add 32. Index

Chlorofluorocarbons (CFCs) are synthetic compounds which destroy stratospheric ozone and are also greenhouse gases. The primary use of CFCs today is as a coolant in refrigerators and air conditioners. CFCs are also used as solvents, foam blowing agents and aerosol propellants, though the use of CFCs in aerosol cans in the U.S. was outlawed 15 years ago. Substitutes for CFCs are under development, and some are already available. The Montreal Protocol for the Protection of the Ozone Layer is an international agreement that requires that parties to the convention in developed nations phase out CFCs by 1996. Index

Climate refers to the temperature, humidity, precipitation, winds, radiation, and other meteorological conditions characteristic of a locality or region over an extended period of time. Compared to weather, climate involves longer times and deals not only with the atmosphere, but also with oceans, land and biosphere. Index

Climate Sensitivity refers to the size of the climate change expected to result from a change in external influences. One description of climate sensitivity is the global average temperature rise expected to result from a doubling of carbon dioxide in the atmosphere. Index

Cloud is a visible mass of condensed water vapor (liquid or ice) particles. Index

Compound is a substance formed from two or more elements chemically combined in fixed proportions. Index

Condensation is the process of changing state from gas to liquid. Index

Condensation Nuclei are small particles in the air that attract water and encourage condensation. Index

Convection generally refers to vertical motion in the atmosphere or ocean generated by temperature difference and resulting in the transfer of heat. Index

Cryosphere is one of the five interrelated components of the Earth system. It is that portion of the Earth's surface with average temperatures below the freezing point of water. The bulk of the cryosphere is at or near the poles, but cryospheric regions also exist atop high mountain ranges on all continents. The cryosphere is composed of snow, permanently frozen ground (permafrost), floating ice, and glaciers. Index

Deforestation is destruction of forests, usually by cutting or burning. Deforestation enhances the greenhouse effect in two ways. First, when wood is burned or decomposes, it releases carbon dioxide. Second, trees which are destroyed can no longer serve their function of removing carbon dioxide from the atmosphere in the process of photosynthesis. Index

Demography is the study of the nature and structure of human populations including their distribution, age structure, composition, life styles, and change. Index

Desertification is degradation of land characterized by reduced soil moisture and vegetation including crops, and by soil erosion. Like deforestation, desertification can affect climate in several ways, including by altering the water cycle. Index

Developing Countries, sometimes called less developed countries (LDCs) or "Third World," generally means low-income nations, usually with little industrialization, often accompanied by high rates of illiteracy and poor public health. Most developing countries are in the southern hemisphere. Index

Dew Point is a measure of humidity, given in terms of the air temperature at which dew begins to form, as water vapor condenses into liquid. Index

Dobson Units (DU) is the standard way to express ozone amounts. Ozone varies with latitude and season, typically ranging from about 250 to 460 Dobson units. Dobson was a researcher at Oxford University who, in the late 1920s, built the first instrument, now called the Dobson meter, for measuring total ozone from the ground. Index

Drought is a period of abnormal dryness for a particular region. Index

Drylands are areas of the world where precipitation is low and where rainfall consists of small, erratic, short, high-intensity storms. Index

Ecology is the science that deals with the study of the interrelationships between living organisms and their environments. Index

Ecosystem refers to a distinct system of interdependent plants and animals, along with their physical environment. An ecosystem may be as large as the entire Earth, or as small as a pond. Index

Earth Observing System (EOS) refers to a series of small- to intermediate-sized spacecraft that is the centerpiece of NASA's Mission to Planet Earth. Planned for launch beginning in 1998, each of the EOS spacecraft will carry a suite of instruments designed to study global change. Index

El Ninõ is a warming of the surface waters of the eastern equatorial Pacific that occurs at irregular intervals of 2 to 7 years, usually lasting 1 to 2 years, which has a significant influence on regional and global climate. El Ninõ has been linked to colder, wetter winters in parts of the U.S., drier hotter summers in South America and Europe, and drought in Africa, as well as reduced numbers of fish in South American coastal waters. Index

El Ninõ-Southern Oscillation (ENSO) refers to the combined effects of El Ninõ (see above) and a global-scale shift in atmospheric pressure called the Southern Oscillation. In the warm phase of ENSO, El Ninõ warming extends over much of the tropical Pacific and becomes clearly linked to the SO pattern. Many of the countries most affected by ENSO events are developing countries with economies that are largely dependent upon their agricultural and fishery sectors as a major source of food supply, employment and foreign exchange. New capabilities to predict the onset of ENSO events can thus have important human impacts. While ENSO is a natural part of Earth's climate variability, whether its intensity or frequency may change as a result of global warming is a concern. Index

Electromagnetic Spectrum is a continuum of all kinds of electric, magnetic, and visible radiation. [insert diagram of spectrum with wavelengths and sections] Index

Electron is a negatively charged component of an atom. Index

Element refers to any substance that cannot be separated by chemical means into two or more simpler substances. Index

Endemic means naturally occurring only in a certain region, as in a species that is endemic to a particular place. Index

Environment is the complex of physical, chemical and biological factors in which a living organism or community exists. Index

Environmental refugees are people obliged to leave their traditional or established homelands due to environmental problems (deforestation, desertification, floods, drought, sea-level rise, nuclear plant accidents), on a permanent or semi-permanent basis, with little or no hope of ever returning. Though no formal accounting has been taken, there may currently be about 25 million environmental refugees in the world, according to one estimate. Index

Equator is an imaginary circle around the Earth that is equally distant from the North and South Poles and defines the latitude 0. Index

Eutrophication is the process by which a body of water becomes rich in dissolved nutrients through human-created or chemical processes (such as runoff laden with chemical fertilizers used in agriculture). This often results in a deficiency of dissolved oxygen, producing an environment that favors plant over animal life.

Evaporation is the process of changing state from liquid to gas. Index

Evapotransporation is the discharge of water from Earth's surface to the atmosphere by evaporation from bodies of water, or other surfaces, and by transpiration (the process by which water is taken up by roots and released as water vapor by leaves) from plants. Index

Exotic means originating outside of an area, such as an exotic species. Index

Fahrenheit is a temperature scale based on water freezing at 32.F and boiling at 212.F under standard atmospheric pressure. To convert from Fahrenheit to Centigrade, subtract 32. from the Fahrenheit temperature and divide the resulting quantity by 1.8. Index

Feedback refers to a sequence of interactions in which the final interaction influences the original one. In such a sequence, a cause produces a result, and the result then in turn influences its cause. For example, by one estimate, global warming is expected to increase air conditioner use in the U.S. enough to require 86 additional power plants by the year 2010. The burning of fossil fuels in those power plants would in turn cause more global warming, causing more air conditioner use, causing more warming, and so on, in a positive feedback loop. As a system changes, it may generate processes that affect the original change. If one of these processes amplifies the change (such as increasing global warming in the above example) we call it a positive feedback. If it dampens the change, we call it a negative feedback. Index

Food Chain refers to a series of plants and animals that depend upon each other as food sources (i.e., a plant is eaten by a small fish, which is eaten by a larger fish, which is eaten by a bird, and so on). Index

Fossil is the hardened remains or traces of plant or animal life from a previous geological period preserved in the Earth's crust. Index

Fossil Fuels such as coal, oil, and natural gas are created by the decomposition of ancient animal and plant remains. They are finite (limited) resources, and release carbon dioxide and other gases when burned. [insert graph of the fossil fuel age spike] Index

Gaia Hypothesis is the idea, developed by James Lovelock, that Earth's systems behave as a single living entity striving to maintain health and stability conducive to the existence of life. Index

General Circulation Models (GCMs) are computer models of Earth's climate that are used to improve our understanding of factors that influence climate and enhance our ability to forecast future climate patterns. One reason GCMs are so useful is that they allow researchers to turn individual variables on and off and observe the results, isolating factors in a way that is not possible in the physical world. Index

Geoengineering refers to artificial modification of Earth systems to counteract anthropogenic effects such as global warming or stratospheric ozone depletion. An example of geoengineering aimed at reducing global warming is the "iron hypothesis," which suggests that adding iron to the oceans could stimulate the growth of algae which would photosynthesize, thus taking carbon dioxide from the atmosphere. In general, geoengineering proposals would be costly and logistically difficult, and before they were undertaken, it would be prudent to be certain that unanticipated adverse consequences would not occur. Index

Geographic Information System (GIS) uses computers to combine remote sensing data with other information (e.g., topographic, political, cultural, economic, ground truth). In essence, a GIS is a way of managing Earth science data to bring out geographical interrelationships. Index

Geosphere refers to the physical elements of the Earth's surface, crust and interior. Index

Geostationary or geosynchronous describes an orbit in which a satellite is always in the same position with respect to the Earth. The satellite travels around the Earth, in the same direction and at the same speed as the Earth's rotation, completing one orbit in a 24-hour period. All geostationary satellites are directly above Earth's equator and are at the same altitude. Index

Geothermal Energy is energy obtained by the transfer of heat to Earth's surface from its depths. A natural hot spring is one such example. Index

Glacier is a multi-year accumulation of snowfall in excess of snow melt on land, resulting in a mass of ice covering at least a tenth of a square kilometer, that shows some evidence of movement in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to the oceans as the largest reservoir of total water. Glaciers are fo anund on every continent except Australia. Index

Global Change refers to change to the Earth system which is either a global phenomenon or that occurs regionally, but strongly enough and often enough to be of global significance. The leading current global change issues include climate change due to an enhanced greenhouse effect, stratospheric ozone depletion, acid precipitation, urban air pollution, and loss of biodiversity. Index

Global Warming is a term used to describe a predicted warming of Earth's climate due to increased concentrations of greenhouse gases in the atmosphere. The Intergovernmental Panel on Climate Change (IPCC), composed of many of the world's leading authorities on the subject, estimates that if atmospheric CO2 doubled, global average temperature would eventually increase by 1.5. to 4.5.C (about 3.-8.F) with a "best guess" of 2.5.C (4.F). The IPCC also estimates that about half of this warming will have occurred by the year 2030. Index

Green Revolution refers to a dramatic increase in food production, primarily as a result of the development of new strains of crops. Index

Greenhouse Effect is the natural process whereby gases in Earth's atmosphere act like the glass in greenhouse, letting the Sun's energy in, but keeping some of it from going back out. Were it not for this natural effect, Earth's climate would be about 33. C (60. F) colder, and life as we know it would not exist. The "enhanced greenhouse effect" refers to an increase in this natural heat-trapping phenomena caused by anthropogenic emissions of greenhouse gases. Index

Greenhouse Gases are water vapor, carbon dioxide, methane, tropospheric ozone, nitrous oxide, CFCs, and other gases which absorb some of the long wave thermal radiation emitted from Earth's surface, thereby warming the atmosphere. With the exception of water vapor, these are also called "trace gases" since they total less than 1% of the atmosphere. Index

Ground Truth is the collecting of information on Earth's surface at the same place and time as a remote sensor gathers data. Ground truth information is used to interpret and calibrate remotely sensed data from satellites. Index

Gulf Stream is a warm, swift ocean current that flows from the Gulf of Mexico, along the coast of the Eastern U.S., across the Atlantic to the European coast, and makes Ireland, Great Britain and the Scandinavian countries warmer than they would be otherwise. Index

GWP stands for Global Warming Potential, and is the ratio of how much a gas contributes, molecule for molecule, to enhancing the greenhouse effect compared to carbon dioxide. Index

Habitat refers to the environment in which an individual or population occurs. Index

Hail is precipitation composed of lumps of ice. Hail is produced when large frozen raindrops or other particles in cumulonimbus clouds, grow by accumulating supercooled liquid droplets. Violent updrafts in the cloud carry the particles up through the freezing air, allowing the frozen core to accumulate more ice. When the piece of hail becomes too heavy to be carried by rising air currents, it falls to the ground. Index

Halocarbons are halons, chlorofluorocarbons, hydrochlorofluorocarbons, and other chemicals that deplete the stratospheric ozone layer. The term halocarbons is used in the Montreal Protocol on Substances that Deplete the Ozone Layer. Index

Humidity is the amount of water vapor in the air. The higher the temperature, the greater the number of water molecules the air can hold. "Relative humidity" describes the amount of water in the air compared with how much the air can hold at the current temperature. For example, 50% relative humidity means the air holds half the water vapor it is capable of holding. Index

Hurricane is a severe tropical storm whose winds exceed 74 miles per hour. Hurricanes originate over the tropical and subtropical North Atlantic and North Pacific oceans, because high sea surface temperatures are essential to their formation. Index

Hydrochlorofluorocarbons (HCFCs) are replacements for chlorofluorocarbons (CFCs) which are less ozone-depleting than CFCs but not totally ozone-safe. HCFCs are also greenhouse gases, contributing to global warming. Index

Hydrologic Cycle refers to the natural sequence through which water evaporates from the ocean, land surface, and plants into the atmosphere as water vapor, falls to Earth as precipitation, and largely returns to the ocean through pathways including rivers and ground water. Index

Hydrosphere is one of the five interrelated components of the Earth system and consists of all of Earth's waters including the oceans, fresh waters, and water vapor in the atmosphere. Index

Ice Age is a geological time period during which sheets of ice cover extensive parts of the Earth. Index

Image resolution has to do with the level of detail in an image and is determined by the area represented by each pixel (picture element). The smaller the area represented by a pixel, the more detailed the image. For example, if a U.S. map and a world map are printed on the same size paper, one square inch on the U.S. map will represent far less area and provide far more detail than one square inch of the world map. The U.S. map would thus be said to have higher resolution. Index

Indigenous means naturally occurring in an area, such as an indigenous species. Index

In Situ is Latin for "in original place" and usually refers to data collected at the actual location of the object or material measured, as opposed to remote sensing. Index

Insolation is the solar radiation falling upon a particular horizontal surface on or above Earth's surface. Index

Ion is an atom or molecule that has acquired an electric charge by the loss or gain of one or more electrons. Index

Isothermal means of or indicating equality of temperature. Isotherms are lines connecting points of equal temperature on a weather map. Index

Kilometer is a metric unit of distance equal to 3,280.8 feet or 0.621 miles. Index

Landsat is the name for a group of five satellites dedicated to applying remote sensing techniques to the inventory, monitoring, and management of Earth's natural resources. The Landsat system currently uses two sensors: multispectral scanner (MSS) and thematic mapper (TM). Index

Lightning is a discharge of atmospheric electricity accompanied by a vivid flash of light. During thunderstorms, static electricity builds up in clouds. A positive charge builds in the upper part of the cloud, while a negative charge builds in the lower portion. When the difference between the charges becomes great, the charge jumps from one area to another, creating a lightning bolt. Most lightning bolts strike from one cloud to another but they can also strike the ground. Such bolts occur when positive charges build up on the ground. A negative charge or "leader" flows from the cloud toward the ground and then a positively charged leader (called the return stroke) runs from the ground to the cloud. What appears as a lightning bolt is actually a series of downward and upward strokes, all taking place in less than a second. Index

Magnetosphere is the region surrounding a celestial body where its magnetic field controls the motions or charged particles. Earth's magnetosphere is dipolar, meaning it behaves as if it were produced by a giant magnet located near the center of the planet with its north pole tilted several degrees from Earth's geographic north pole. Index

Mean is the scientific term for average as in "global mean temperature." Index

Milankovitch Theory states that major ice ages of the past may be triggered by regular variations in Earth's orbit around the Sun, leading to changes in incoming solar radiation. Index

Modeling is an investigative technique which uses a mathematical or physical representation of a system or theory to test for effects that changes in system components may have on the overall functioning of the system. Mathematical modeling using computers plays a major role in climate research, by simulating how Earth's climate will respond to changes in atmospheric concentrations of greenhouse gases. Index

Molecule means two or more atoms of one or more elements chemically combined in fixed proportions. For example, atoms of the elements carbon and oxygen, chemically bonded in a 1:2 proportion, create molecules of the compound carbon dioxide (CO2). Molecules can also be formed of a single element, as in ozone (O3). Index

Monsoon refers to a particular seasonal weather pattern in sub-tropical regions, especially when characterized by periods of heavy winds and rainfall. Monsoons are caused by a pronounced seasonal change in wind direction. Winds usually blow from land to sea in winter, while in the summer, this reverses, bringing precipitation. Monsoons are most typical in India and southern Asia. Index

Montreal Protocol on Substances that Deplete the Ozone Layer is an international agreement that prescribes a timetable for ending the production of chlorofluorocarbons (CFCs) and related compounds. Begun in 1987, this unprecedented international treaty is a unique example of scientists and industry working with governments to seek a global solution to the human-caused environmental challenge of ozone depletion. After the original agreement was signed, new evidence arose proving that deeper cuts in CFC production were necessary to protect the ozone layer. The 1990 London amendments and the 1992 Copenhagen amendments sped up the halocarbon phase out and controlled several other chemicals that were not in the original agreement: methyl chloroform, carbon tetrachloride, methyl bromide, and HCFCs. The revised agreement now calls for the phaseout of CFCs to be complete by 1996. The treaty also attempts to make the phaseouts fair to developing countries by setting up a fund, paid for by developed nations, to assist developing countries in making the switch to ozone-safe chemicals. Index

Multispectral Scanner (MSS) is a sensor system carried on Landsat satellites. Index

Neutron is a component of most atomic nuclei, without electric charge, and of approximately the same mass as the proton (positively charged component). Index

Orbit is the path of a body, such as a planet or satellite, in its periodic revolution around another body in space. For example, satellites which orbit Earth near latitude 0. are said to have equatorial orbits, since they remain above the equator. Satellites with inclinations near 90. are said to be in polar orbits because they cross over or near Earth's north and south poles as they revolve around the planet. Index

Ozone is a gaseous molecule consisting of three atoms of oxygen (O3). Ozone in Earth's stratosphere forms a protective layer that shields Earth's inhabitants from damaging ultraviolet radiation from the Sun. Ozone in the troposphere, near Earth's surface, on the other hand, is a harmful pollutant resulting from the interaction of anthropogenic emissions of nitrogen oxides and volatile organic compounds and sunlight. Index

Ozone Depletion refers to the thinning of the stratospheric ozone layer which protects life on Earth from excess ultraviolet radiation from the sun. Human-made halocarbons are primarily responsible for this reduction in the amount of ozone in the stratosphere. Index

Ozone Hole refers to a region of the atmosphere over Antarctica where, during springtime in the Southern Hemisphere, up to three quarters of the stratospheric ozone disappears. Anthropogenic halocarbons are the primary cause of this phenomenon. Index

Paleoclimatology is the reconstruction of ancient climates by using evidence such as tree rings and air trapped in ice cores. Researchers use such evidence to understand natural climatic shifts which can help us in understanding and eventually predicting future climate trends. Index

Passive Solar Design refers to designing buildings to maximize the use of solar radiation to warm and light the interior. Passive solar design criteria include properly siting the building, using energy efficient windows, and providing for both appropriate levels of insulation and thermal mass (material in the walls or floors of the building which stores heat and thereby helps to moderate temperature variations). Index

Pedosphere is one of the five interrelated components of the Earth System, and consists of the solid portion of the Earth. The pedosphere rides on continental structures that evolve over millions of years as a consequence of the tectonic motions of Earth's land masses. Index

pH is a measure of the acidity or alkalinity of a solution. A value of 7 is neutral, values less than 7 are acid, and values over 7 are alkaline or basic. A change of one unit on the pH scale represents a factor of ten in acidity. For example, a solution with a pH of five is ten times as acid as one with a pH of six. Index

Phenology is the science dealing with the relationships between climate and periodic biological phenomena that are related to or caused by climatic conditions, such as the seasonal budding of trees and migration of birds. Index

Photochemical Smog, present in many large cities, is formed by chemical reactions involving nitrogen oxides and hydrocarbons (from human activities including automobile use) taking place in the presence of sunlight. The principle component of photochemical smog is tropospheric or ground-level ozone. Index

Photosynthesis is the series of chemical reactions by which plants use the sun's energy, carbon dioxide and water vapor to form materials for growth, and release oxygen. Index

Phytoplankton are minute forms of plant life in the oceans at the base of the marine food chain. Index

Pixel is the smallest element of an electronically-coded image. Pixel is a contraction of the words "picture element." See image resolution. Index

Plate Tectonics is the concept that Earth's crust is composed of rigid plates that move over a less rigid interior. The movements of these plates cause geological events such as earthquakes and continental drift, and over long periods of time, can cause significant shifts in Earth's land masses. Index

ppbv stands for parts per billion by volume, a measure of concentration Index

ppmv stands for parts per million by volume, a measure of concentration Index

Precipitation is moisture that falls from clouds. Raindrops form around particles of salt or dust. Water or ice droplets stick to these particles, the drops attract more water and continue to grow until they are large enough to fall out of the cloud. Index

PV stands for photovoltaic. A photovoltaic or solar cell is a device, often made of silicon, which converts solar radiation directly into electricity. Index

Radiation Budget is an accounting of the radiation which enters and leaves a planet's atmosphere. The quantity of solar radiation entering the atmosphere from space should be balanced by the thermal radiation leaving the Earth's surface and atmosphere. Index

Rainforest is an evergreen woodland of the tropics distinguished by a continuous leaf canopy and an average rainfall of about 100 inches per year. Rainforests play an important role in the global environment for several reasons. They are the most biologically diverse biome on the planet, encompassing just 6-7% of Earth's land, but thought to house nearly half of its species. Rainforests also take up carbon dioxide, helping to balance anthropogenic emissions. When rainforests are cut or burned, the opposite occurs: they release stored carbon dioxide, adding to the greenhouse effect. Index

Rain Gauge is a calibrated container that measures the amount of rainfall occurring during a specific period of time. Index

Remote Sensing is the process of obtaining information from a distance, especially from aircraft and satellites. Modern remote sensing technology has greatly expanded our ability to see and understand the Earth and its systems and to observe changes. Remote sensing has become a critical tool in activities ranging from the verification of arms control treaties to the provision of emergency aid to disaster-stricken regions. Through remote sensing we learn about problems such as droughts, famines, and floods; we obtain information about agricultural practices, weather conditions, transportation systems, river flows, and terrain changes. We use remote sensing to locate Earth's natural resources and can then use that information to exploit or protect them. Index

Renewable Energy refers to energy from sources which are not depleted by use. Examples include using passive solar energy to heat buildings, solar thermal energy to heat water or turn turbines to produce electricity, photovoltaic cells to convert sunlight directly to electricity, wind power, and hydroelectric energy. Index

Sequestration is removal and storage, as when carbon dioxide is sequestered from the atmosphere by plants via photosynthesis. Index

Sink is a scientific term for storage or removal of a substance. For example, plants, through photosynthesis, transform carbon dioxide from the air into organic matter which is then "stored" in the plant or in the soil. Plants are thus said to be sinks" for carbon. One of the key uncertainties regarding climate is that the quantity of carbon held in the various sinks and the rates of exchange between them are not well known. Index

Solar Constant is the average total radiation reaching the top of Earth's atmosphere from the sun. The number used for this constant, about 1370 watts per square meter, is not, in fact, truly constant; variations of about a tenth of a percent have been measured during the last two decades. Index

Solar Radiation is energy from the sun. It is the main energy source for Earth's climate system, heating the surface and driving currents in the oceans and winds in the atmosphere. Ordinary visible sunlight is the most obvious form of solar radiation, but other forms are significant too. For example, see ultraviolet radiation. Index

Sonde is a device sent up into the air, typically borne on a balloon, to obtain information about atmospheric conditions. Radiosondes, for example, measure temperature, pressure and humidity and then "radio" or transmit these data to Earth. Index

Spectral Band is a segment of wavelengths within the electromagnetic spectrum. Index

Stratosphere is the region of the atmosphere between the troposphere and mesosphere, having a lower boundary approximately 8 kilometers above Earth's surface at the poles and 15 km at the equator and an upper boundary of approximately 50 km. This is the region that houses the stratospheric ozone layer which protects Earth from ultraviolet solar radiation. [insert diagram] Index

Sustainable Development is development which meets the needs of the present without compromising the ability of future generations to meet their own needs. Some people also believe that the concept of sustainable development should include preserving the environment for other species as well as for people. Index

Synoptic means simultaneous. For example, a synoptic weather map displays meteorological conditions observed in different places at a single time. Synoptic also refers to a large or general view of something. For example, an aerial photograph provides a "synoptic," or "bird's eye view" of an area. Index

Terrestrial means pertaining to the Earth, as distinct from other planets (as in extraterrestrial life). It also means pertaining to the land, as distinct from the water or air (as in a terrestrial, as opposed to aquatic, ecosystem). Index

Thematic Mapper (TM) is one of the sensor systems carried on Landsat 4 and 5 satellites. The TM acquires surface reflectance (brightness) data in 6 visible and infrared bands, at a pixel size of 30m. A simple thermal band acquires data in 60m pixels. In GLOBE, we will not be using any of the thermal data. Index

Thunder is the sound that results from lightning. A lightning bolt produces an intense burst of heat which makes the air around it expand explosively, producing the sound we hear as thunder. Since light travels faster than sound, we see the lightning before we hear the thunder. The difference in time between the two can tell us how far away the clouds producing the lightning and thunder are. Index

Thunderstorm is a local storm resulting from rising warm humid air, which produces lightning and therefore thunder, usually accompanied by rain or hail, gusty winds, and strong vertical air motion. Index

Tornado is a strong, rotating column of air extending from the base of a cumulonimbus cloud to the ground. These twisting, spinning funnels of low pressure air are the most unpredictable weather event, created during powerful thunderstorms. Index

Total Ozone Mapping Spectrometer (TOMS) is an instrument, first flown on NASA's Nimbus-7 satellite, whose primary function is to monitor global ozone. TOMS has been delivering ozone data since 1979, providing high-resolution mapping of total ozone, from the ground to the top of the atmosphere, on a daily basis. TOMS provided the first maps of the ozone hole and continues to monitor this phenomenon. Index

Trade Winds are global-scale winds in the tropics that blow generally toward to west in both hemispheres (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 a sailing route to the "New World," America. Index

Transpiration is the transfer of water from plants to the atmosphere; water is taken up by the roots of plants and released as water vapor by the leaves. Index

Tropical Cyclone is a low-pressure weather system in the tropics in which the central core is warmer than the surrounding atmosphere. A tropical storm is a tropical cyclone with winds from 39 to 74 miles per hour. When winds exceed 74 miles per hour, the cyclone is called a hurricane. Index

Tropics refers to the region of Earth from latitude 23.5. north (the Tropic of Cancer) southward across the equator to latitude 23.5. south (the Tropic of Capricorn). This region has relatively small daily and seasonal changes in temperature, but great seasonal changes in precipitation. Index

Tropospheric Ozone refers to ozone (O3) in the region of the atmosphere that extends from Earth's surface to about 7 miles up. As opposed to stratospheric ozone (the "good ozone" that protects us from excess ultraviolet (UV) radiation from the sun), tropospheric ozone or "bad ozone," results from the interaction of nitrogen oxides (NOx), volatile organic compounds (VOCs), and sunlight. Most of the pollutants which lead to the formation of tropospheric ozone come from automobiles, power plants, and other human activities. In many cities, ozone is a significant health problem; 98 U.S. cities have higher concentrations of ozone than the U.S. Environmental Protection Agency finds acceptable. Ozone also causes $3 to 5 billion a year in lost crop production and significant losses in forest products. Tropospheric ozone is also a significant greenhouse gas. Index

Typhoon is a tropical cyclone with winds 75 miles per hour or greater in the northwest Pacific ocean. In other parts of the world, such storms have different names, such as hurricanes. Index

Ultraviolet radiation (UV) is the energy range just beyond the violet end of the visible spectrum. Most UV is blocked by earth's atmosphere (particularly the stratospheric ozone layer) but some solar UV penetrates and aids in plant photosynthesis and the production of Vitamin D in humans. Too much UV can burn the skin, cause skin cancer and cataracts, and damage vegetation. Index

Volatile Organic Compounds (VOCs) are precursors of tropospheric ozone and photochemical smog. They are produced by human activities including the use of dry cleaning solvents. Index

Volcano is a naturally occurring vent or fissure at Earth's surface through which erupt molten, solid, and gaseous materials. Volcanic eruptions inject large quantities of dust, gas, and aerosols into the atmosphere and can thus cause temporary climatic cooling. Index

Watershed is a catch basin that guides all precipitation and runoff (water, sediment, and dissolved materials) to a common watercourse or body of water. Index

Water vapor is the invisible, gaseous form of water. Index

Wind is a natural motion of the air, especially a noticeable current of air moving in the atmosphere parallel to Earth's surface. Winds are caused by uneven heating and cooling of the Earth and atmosphere. Index

Wind Shear is a sudden change in wind speed or direction. Index

Younger Dryas is the name for a cold climatic event lasting about 1500 years which interrupted the warming of the Earth after the last ice age. Index

Zooplankton are minute forms of animal life in the ocean which feed on phytoplankton (minute plant life). Index

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