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GLOSSARY

Our comprehensive earth science glossary is available to assist in your understanding of the MY NASA DATA microsets, lesson plans and computer tools. Please select the first letter of the word you wish to check for a definition and further information.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
All definitions
A
accretion:
the growth of ice crystals or snowflakes by collision with supercooled cloud droplets that freeze upon contact.  
A
aerosol:
small liquid or solid particles dispersed in the atmosphere. Large quantities are often regarded as pollutants in the form of haze and smoke.   NASA Fact Sheet on Aerosols
A
aggregation:
the process by which snowflakes clump together or collide as they fall, especially snowflakes in the shape of dendrites.  
A
air mass:
a body of air that has relatively uniform temperature and humidity based on the surface characteristics of its source region.   Continental polar air mass formed over Canada
Image courtesy University of Illinois WW2010 Project
A
air quality:
a measure of the degree to which air is free from harmful pollution. In the US, the Environmental Protection Agency identifies and regulates the harmful compounds in air, particularly those that harm human health, damage crops, or cause harm to building, roads, and other structures (for example, acid rain). Scientists study the sources of air pollutants, how pollution changes as air moves around the planet, and how the chemistry in the atmosphere removes air pollutants..   Clean Air Primer
A
albedo:
a measure of reflectivity; the planetary albedo of the Earth averages about 0.31, meaning that on average about 31 percent of the light from the Sun is reflected back to space. The value at any given time is dependent on cloud cover and ground cover (snow, ice).  
A
algorithm:
A precise rule (or set of rules) specifying how to solve some problem, or do a calculation.  
A
altitude:
the vertical distance or height measured from sea level.  
A
anomaly:
the difference from the average, or climatological, value. Anomalies are often used in climate science, as they make small changes in variables much easier to see.  
A
Aqua:
The second spacecraft of NASA\'s Earth Observing System (EOS). Aqua is collecting global data sets for research on the Earth System, with a particular emphasis on the water cycle.   The Aqua website
A
ASDC:
acronym for Atmospheric Science Data Center. ASDC is located at NASA Langley Research Center in Hampton, Virginia. ASDC processes, archives and distributes NASA satellite data relating to clouds, aerosols, radiation budget and tropospheric chemistry.   The ASDC website
A
atmosphere:
the mixture of gases that surrounds the Earth and some other planets. The concentrations of the gaseous constituents of Earth's atmosphere are determined by biogeochemical processes, including manmade effects.  
A
atmospheric column:
a vertical pillar defined by a unit area on Earth's surface and bounded by the top of the atmosphere that is used to quantify an atmospheric parameter such as pressure, ozone or precipitable water. See image illustrating atmospheric pressure.  
A
atmospheric haze:
Fine dust or water vapor causing a reduction in visibility.   IMPROVE website - click Loop under the picture to see the effect of haze
A
atmospheric pressure:
the weight of the column of the atmosphere above a surface. On average, the atmospheric pressure at sea level is 1013.25 millibars (mb), but it can be relatively higher or lower than this value based on air temperature and humidity. Changes in atmospheric pressure at a given location often indicate changing weather.   More about atmospheric pressure Explanation of atmospheric pressure
Image courtesy University of Illinois WW2010 Project
A
AVHRR:
the Advanced Very High Resolution Radiometer is the primary sensor on NOAA polar orbiting satellites. It detects cloud cover and surface temperatures of cloud layers, land and water.   Satellite Observations of the Gulf Stream Temperature
B
biomass:
The total mass of organic matter including living or dead plant material, vegetation, or agricultural waste.  
B
biomass burning:
refers to the burning of vegetation whether by wildfire or manmade causes; agricultural fields are often cleared by setting prescribed fires.   NASA Fact Sheet on biomass burning Red dots represent California wildfires on October 27, 2003
Image courtesy MODIS Rapid Response Team
B
blackbody:
A theoretically perfect absorber of all incident radiation, which then emits radiation as a function only of its own temperature. Pictured to the right is a blackbody used to calibrate the ERBE and CERES instruments.   Tool to explore blackbody emission spectrum A blackbody used to calibrate the ERBE and CERES instruments.
Image courtesy NASA
C
carbon dioxide:
A colorless, odorless gas that is a major greenhouse gas. Commercially, carbon dioxide is used as a refrigerant (dry ice), in beverage carbonation, and in fire extinguishers. It is also produced from the burning of fossil fuels and organic matter. It is composed of a single carbon atom and two oxygen atoms.  
C
carbon monoxide:
A clear odorless gas formed from the incomplete combustion of carbon-based fuels. Carbon monoxide is a short lived gas in the lower layer of the atmosphere. Sources of carbon monoxide include: cigarette smoke, blocked fireplaces and gas stoves, idling cars.   MOPITT images showing a global view of carbon monoxide
C
Celsius:
A scale for the measurement of temperature named after Anders Celsius, a Swedish astronomer, who invented it. Water freezes at 0 degrees C and boils at 100 degrees C.   Temperature conversion tool Fahrenheit, Celsius and Kelvin temperature scales
Image courtesy NASAexplores
C
centimeter:
A unit measuring distance or height. It is used as a unit for precipitable water in the LAS. This is the height of the layer of water that would exist if all the water vapor in the atmospheric column were condensed to liquid at the Earth's surface.  
C
CERES:
The Clouds and the Earth's Radiant Energy System is one of the scientific satellite instruments developed for NASA's Earth Observing System (EOS).   The CERES Web Site Reflected Solar Radiation for July 2000
Image courtesy CERES Science Team
C
chlorofluorocarbon:
Gas made of chlorine, fluorine, and carbon, abbreviated CFC. In the troposphere, a CFC molecule does not normally react with other substances. However, in the stratosphere, ultraviolet radiation from the Sun breaks apart the CFC molecule. This releases a chlorine atom which serves as a catalyst to destroy many ozone molecules through a series of chemical reactions.  
C
chlorophyll:
a green pigment found in plants, algae and some bacteria that absorbs the energy in light for photosynthesis.  
C
climate:
the long-term weather conditions for a region, generally determined by 30 or more years of records.  
C
climatic diagram:
also called climogram, climatograph, climograph, climagram, climagraph, climatogram, hythergraph. A graph that represents annual climatological information for a particular location. Pictured to the right, monthly average values of precipitation and temperature are displayed throughout the year.   example of a climatic diagram
C
climatology:
This term has two meanings. The basic meaning is the science or study of the climate. The second meaning, which is used within the MY NASA DATA project, is a long-term average of a variable in the Earth system. For weather-related information, at least a 30-year average is preferred. For most satellite datasets, one is lucky to find a 5-year climatology, because the data have not been measured for much longer than that.  
C
cloud:
collections of water (in liquid or ice phase) in the atmosphere that are often classified by their shape and height.   Cloud Classification Chart from the S'COOL Project
C
cloud coverage:
Cloud coverage, also called cloud fraction, or cloud cover, describes the amount of cloud in the sky. It can be measured as a percentage (0-100) or as a fraction (0-1.0).  
C
cloud fraction:
See cloud coverage.  
C
cloud opacity:
a parameter that characterizes the reduction of light or energy through a cloud due to interactions with its water, ice or particle content. See definition for optical depth.  
C
cloud pressure:
a measure of the location (altitude) of a cloud layer. Since pressure decreases in a smooth manner with height in the atmosphere, this gives the same information as cloud top altitude above mean sea level. Cloud pressure values are greater for low clouds and smaller for high clouds (so they vary in the opposite direction from the cloud altitude for these clouds).  
C
cloud temperature:
The cloud temperature is, as it sounds, the temperature of a cloud. However, what this means exactly depends on how the measurement is made. Most of the time we do not put a thermometer in the cloud, but instead determine this by remote sensing. And most clouds are not at a single temperature, but are generally colder at the top and warmer at the bottom. The temperature measured by remote sensing is often called a cloud effective temperature. It measures the temperature of the cloud mass within about 1 optical depth of the edge (where optical depth varies with wavelength, so that the measured temperature depends on the sensor being used, at least to some extent). Measurements made from orbit, then, will generally measure a lower temperature than those made from the ground (unless the cloud is thin).   Clouds in Infrared Imagery
C
cloud water (liquid or ice):
This parameter tells how much water - either in the form of liquid drops or of ice crystals - that a cloud contains. It typically is measured over some finite region, not for a single cloud.  
C
CMAP:
National Oceanic and Atmospheric Administration (NOAA) Climate Diagnostics Center (CDC) Climate Merged Analysis of Precipitation. Data containing monthly averaged precipitation rate values. Values are obtained from five kinds of satellite estimates..   CMAP Web site NOAA Climate Diagnostics Center
Image courtesy NOAA Climate Diagnostics Center, Boulder, Colo
C
column number density:
A unit often used in remote sensing. The number of something (particles, atoms, molecules, ...) in an atmospheric column over an area. The area could be a square centimeter, square meter, square kilometer, etc... This provides information about the total amount of that substance in the column, but does not provide any information about how it is distributed: uniformly mixed in the atmosphere (i.e., CO2), vs concentrated near the surface (i.e. pollution), vs concentrated at some other level (i.e., the ozone layer). Because the number of atoms or molecules is usually large, scientific notation is used. For example: 1.e15 NO2 molecules in a column over one square centimeter of the surface (1,000,000,000,000,000 NO2 molecules in an atmospheric column)..     Related MY NASA DATA Activity:  Parts Per Billion Activity (PowerPoint) Illustration of molecules within an atmospheric column
Image courtesy MY NASA DATA Team
C
combustion:
A rapid chemical change, the process of burning.  
C
concentration:
the strength of a solution or mixture, or the amount of a substance in a liquid or gas. Units of measurement will vary depending upon the substance and medium (e.g. milligrams per meter cubed, parts per billion volume, etc.).  
C
condensation:
the phase change of water from vapor to liquid by cooling, releasing latent heat energy to the atmosphere, or, when water changes from a gas state to a liquid state.  
C
conduction:
the transfer of energy through a medium from molecule to molecule due to a gradient in temperature or electric potential.  
C
contrail:
condensation trail; cloud formed due to the exhaust of jet aircraft.   GLOBE Contrail Education Web Site Image of persistent contrails, newer (left) to older (right)
Image courtesy Carol Clark, Oregon
C
convection:
the transfer of heat energy vertically through a medium. In the atmosphere, convection may be seen visibly by cloud formation and thunderstorm development.  
C
convergence:
the inflow of air horizontally into an area; if occurring at the surface, the air must rise and may cause cloud formation.   Illustration of convergence
C
coordinates:
a set of numbers that specify a position in reference to a set of axes. A pair of coordinates may be used to describe an exact location on a map. See definition of x-axis or y-axis, latitude or longitude.  
C
Coriolis force:
an apparent force resulting from Earth's rotation that causes deflection of mass to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.   More information Illustration of the Coriolis effect
Image courtesy Univ. of Illinois WW2010
C
correlation:
the extent to which two or more variables are related and change together, often shown graphically using a scatter plot or time plot.   Using scatter plots to show correlations scatter plot showing a correlation
D
day length:
the daily period of time of insolation for a given location, meaning, how long the Sun is above the horizon.  
D
degree:
a standard unit of measure for several purposes to include temperature on a scale such as Celsius, Fahrenheit or Kelvin, latitude or longitude to locate or designate places on Earth, and planar angles equal to a 360th of a circle.   Fahrenheit, Celsius and Kelvin temperature scales
Image courtesy NASA explores
D
dependent variable:
a variable that changes in response to the independent variable. On a simple X-Y coordinate graph the dependent variable is usually on the Y-axis.   Example of dependent variable
D
desert dust:
Aerosols comprising of minerals from arid and semi-arid regions that absorb sunlight as well as scatter sunlight. Through absorption of sunlight, the dust particles warm the layer of the atmosphere where they reside. This warmer air is believed to inhibit the formation of storm clouds. Desert dust is also a source of nutrients for many remote regions.   Earth Observatory article on aerosols
D
dew point:
the temperature to which an air mass must be cooled in order for the air mass to become saturated (relative humidity equals 100 percent), assuming constant pressure and moisture content. Additional moisture would condense into water droplets.  
D
difference plot:
a plot showing the difference between two sets of data (graphed value = data value 1 - data value 2). A zero measurement means that both sets of data are identical, whereas a high number indicates values are far apart. The difference can be positive or negative depending on which variable has the greater value and the order of subtraction. If creating a difference plot between two different variables, the units of measurement must match.  
D
divergence:
the horizontal outflow of air from a particular area; if at the surface, causes sinking vertical motion in the atmosphere.   Illustration of divergence
D
dobson unit:
a standard unit measure for ozone in a column of air.   Graphical explanation
E
Earth's Energy Budget:
The balance between the energy coming into a system compared to the energy going out of that system.   Earth's Energy Budget(PDF) Earths Energy Budget
Image courtesy Loeb et al., 2009
E
Earth tilt:
The angle at which the Earth's rotation axis is tilted relative to the plane of its orb it around the Sun.   The Earth's Rotation (from Windows to the Universe) Earth's rotation axis is tilted
Image courtesy NASA Explorer News
E
EBAF:
The Energy Balanced and Filled (EBAF) product is a special product from the CERES Terra dataset. It provides monthly mean top-of-atmosphere (TOA) radiative fluxes constrained such that the five-year average global net TOA flux is consistent with the CERES Science Team's best estimate of heat storage in the Earth-atmosphere system (a net gain of 0.85 Watts per meter squared per year). CERES EBAF is primarily intended for studies that use Earth Radiation Budget (ERB) data for climate model evaluation, estimating the Earth's annual global mean energy budget, and in studies of heat transports from the Equator to the poles.   EBAF Energy Budget
Image courtesy NASA
E
electromagnetic energy:
Type of energy distinct from chemical energy, kinetic energy, etc. Visible light and radio waves are both forms of electromagnetic energy. See also Radiation.   Imagine the Universe
E
electromagnetic radiation:
Radiation consisting of waves of energy associated with electric and magnetic fields. See electromagnetic energy.  
E
electromagnetic spectrum:
The full range of frequencies, from radio waves to gamma rays, that characterizes electromagnetic energy.   Illustration of the spectrum The Electromagnetic Spectrum
Image courtesy NASA
E
elevation:
the height of a location on Earth's surface above or below sea level, usually measured in meters or feet.  
E
El Nino:
the term used to identify the irregular development of warmer ocean surface water off the coast of Equador and Peru when the Trade Winds weaken and the usual upwelling of cold, nutrient-rich water reduces.   NOAA El Nino Education Page El Nino SST Nov 1997
E
emit:
To give off or send out energy. The Earth emits longwave radiation after absorbing shortwave radiation from the Sun.   Tool to explore blackbody emission spectrum
E
ENSO:
an acronym meaning El Nino - Southern Oscillation. The Southern Oscillation is the reversal of the atmospheric circulation in the Equatorial Pacific region which causes the onset of El Nino conditions. See definition for El Nino.  
E
EOS:
acronym for Earth Observing System. A major international science program to monitor climate and environmental change.   The Earth Observing System website
E
Equator:
the line circling the Earth at 0 degrees latitude, dividing the North and South hemispheres.   Location of the Equator
Image courtesy NASA Mission to Planet Earth
E
equinox:
the condition when solar declination is 0 degrees, or when the sun is directly over the Equator. This occurs twice yearly on March 21 (vernal equinox) and September 21 (autumnal equinox).   Diagram of the seasons and equinox
Image courtesy NOAA
E
equivalent water thickness:
a measurement of change in mass on the Earth. For example, 1 cm of water thickness change means mass change equivalent to a 1 cm layer of water. The changes in mass may be due to surface and deep currents in the ocean, runoff and ground water storage on land masses, exchanges between ice sheets or glaciers and the oceans.   The GRACE mission
E
ERBE:
acronym for Earth Radiation Budget Experiment.   ERBE Website
E
ERBS:
acronym for Earth Radiation Budget Satellite. A NASA satellite carrying instruments used in the ERBE experiment to study the radiation budget and atmospheric aerosols and gases.   ERBS Web page The ERBS Spacecraft
Image courtesy NASA
E
evaporation:
the process where liquid water is converted to water vapor (gaseous state). The air above the evaporating surface must be unsaturated for evaporation to occur (relative humidity less than 100 percent).  
E
exosphere:
The outermost layer of the Earth's atmosphere.   The Layers of the Earth's Atmosphere
F
Fahrenheit:
A scale for the measurement of temperature named after Gabriel Daniel Fahrenheit, a German physicist who invented the mercury thermometer and this scale. Water freezes at 32 degrees F and boils at 212 degrees F.   Temperature conversion tool Fahrenheit, Celsius and Kelvin temperature scales
Image courtesy NASAexplores
F
feedback cycle:
a process that has interconnected links and passages which influence its components. A positive feedback increases or enhances the process or activity. A negative feedback reduces or reverses the process.   Image of feedback cycle where one variable affects another.
Image courtesy NASA Goddard
F
Ferrel Cell:
a major Earth atmospheric circulation pattern that consists of sinking air near 30 degrees N or S and rising air near 60 degrees N or S. This circulation pattern is directly connected to the Hadley cell.   More information about atmospheric circulation The major atmospheric circulation patterns
Image courtesy Wikipedia
F
flux:
the rate of transfer of a fluid, particles or energy across a unit area. In the atmosphere, this can be air, a particular pollutant or aerosol, or light or heat energy (which has units of Watts per square meter).   Illustration of flux
F
force:
The perceived push or pull experienced by a mass being accelerated. Newton's Second Law of Motion defined as F=ma.   Newton's Laws of Motion
F
fossil fuel:
any fuel that is created from decomposed carbon-based plant and animal organisms. Examples of fossil fuels: oil, coal, natural gas.  
F
frequency:
the number of occurrences of a particular event over a specified time.   Images of varying frequency waves from low to high.
Image courtesy NASA
F
front:
the boundary between two distinct air masses which differ in temperature and humidity. There are different types of fronts such as cold front, warm front, stationary front and occluded front.   UIUC tutorial on fronts A diagram of cold and warm fronts
Image courtesy University of Illinois WW2010 Project
G
GIS:
Geographical Information Systems; merges computerized data with its spatial location on a digital map.  
G
glacier:
a body of moving ice on the land, formed by accumulation of snow.   View of the Malaspina glacier in Alaska from space.
Image courtesy MY NASA DATA
G
global warming:
an increase of Earth's average temperature which could lead to climate change. Scientists are concerned that human activities are altering the concentration of greenhouse gases and might cause such global warming. See definition of greenhouse effect.  
G
GPS:
Global Positioning System; a satellite-receiver system used to determine a precise location on or above Earth's surface.  
G
GRACE:
the Gravity Recovery and Climate Experiment. GRACE maps variations in the Earth's gravity field by making accurate measurements of the distance between two specially-designed satellites using an ultra-precise microwave ranging system. The gravity variations that GRACE is observing include changes due to surface and deep currents in the ocean, runoff and ground water storage on land masses, exchanges between ice sheets or glaciers and the oceans, and variations of mass within the Earth.   More Information GRACE satellite
Image courtesy JPL
G
gravity:
A physical force that is responsible for the attraction between any two bodies that have mass. The Earth's gravity is what keeps us from floating into space.  
G
greenhouse effect:
The greenhouse effect is a naturally occurring process that aids in heating the Earth's surface and atmosphere. It results from the fact that certain atmospheric gases absorb longwave radiation from the Earth's surface. Without the greenhouse effect, life on this planet would probably not exist as we know it since the average temperature of the Earth would be a chilly -18 degrees Celsius, rather than the present 15 degrees Celsius. However, it is theorized that manmade perturbations to the greenhouse gases such as carbon dioxide may be causing global warming.   EPA Global Warming Kids Site
G
grid box:
a four-sided geographical area defined by given latitude and longitude boundaries, used for the representation of data for an area of Earth's surface or atmosphere.   example of grid box
G
Gulf Stream:
a warm ocean current that flows from the Gulf of Mexico northeastward along the coast of North America and across the North Atlantic Ocean to the British Isles.  
G
gyre:
a large-scale circular current of water driven by winds at the ocean surface. Several gyres drive the ocean surface circulation patterns of Earth.   ocean gyres
Image courtesy UWGB
H
Hadley Cell:
a major Earth atmospheric circulation pattern that consists of rising air at or near the Equator and sinking air at or near 30 degress north or south of the Equator.   More information on atmospheric circulation Diagram of Hadley Cell
Image courtesy NASA
H
heat:
The energy transferred from one body or system to another as a result of a difference in temperature.  
H
high clouds:
We define clouds using three broad altitude ranges, and the various cloud types are assigned to one of these ranges. For satellite observations, some measure of the cloud's altitude (often cloud top or effective cloud height) is used to place the cloud into an altitude range. The satellite does not have the qualitative information to pick a cloud type.   Information on cloud types and levels from the S'COOL Project. The 4 high cloud types
Image courtesy The S'COOL Project
H
horizontal resolution:
indicates the horizontal distance between data point measurements or increments with respect to the Earth's surface (said to be coarse resolution if data points are farther apart or grid boxes are larger, said to be fine if data points are closer together or grid boxes are smaller).  
H
human-made aerosols:
Human activities, such as the burning of fossil fuels and vegetation and the alteration of natural surface cover, generate aerosols. Averaged over the globe, aerosols made by human activities are currently estimated to account for about 10 percent of the total amount of aerosols in our atmosphere. The concentration of aerosols is highest in the northern hemisphere where industrial activity is centered.   NASA Aerosols Fact Sheet
H
humidity:
a measure of moisture (water vapor) in the atmosphere.  
H
hurricane:
a giant swirling storm characterized by a low pressure center and numerous thunderstorms that produce strong winds and flooding rain. A hurricane has wind speeds of 74 mph or greater.   Large hurricane with a well defined eye at the center.
Image courtesy NOAA
H
hydrocarbon:
An organic compound made of the elements hydrogen and carbon. Examples are methane (CH4), propane (C3H8).   The Molecularium Project
I
image resolution:
for pictures or imager data, indicates the number of pixels per unit of length, often measured in dpi (dots per inch). Said to be higher resolution as dpi increases, showing more image detail.  
I
independent variable:
a variable that can be manipulated or changed, e.g. time scale divisions: hours, days, weeks, etc. On a simple X-Y coordinate graph the independent variable is always on the X-axis.   example of independent variable
I
infrared:
Of or relating to invisible (to the human eye) radiation with wavelengths in the range from about 750 nanometers, just longer than red in the visible spectrum, to 1 millimeter, on the border of the microwave region.   The Electromagnetic Spectrum
I
in situ:
a measurement taken at a location of interest, usually in the troposphere by ground or airborne instruments, as opposed to a measurement made routinely by satellite.  
I
insolation:
an abbreviated term for incoming solar radiation.  
I
ionosphere:
The part of the atmosphere between the mesosphere and exosphere. Sufficient quantities of ions and free electrons exist to reflect or refract electromagnetic (especially radio) waves. This layer is what makes long-distance radio communication on Earth possible.   The Earth's Atmosphere
I
irradiance:
the rate of energy transfer onto a unit surface area from a hemisphere of directions. Usually measured as watts (energy) per square meter (area).   Illustration of irradiance
Image courtesy MIT
I
ISCCP:
The International Satellite Cloud Climatology Project was established in 1982 as part of the World Climate Research Programme (WCRP) to collect and analyze the global distribution of clouds, their properties, and their diurnal, seasonal, and interannual variations.   The ISCCP Web Site
I
ITCZ:
The Intertropical Convergence Zone; a zonal band of low atmospheric pressure and thunderstorms caused by converging Trade Winds, rising air and intense thermal heating at or near the Equator; the location of the ITCZ shifts throughout the year resulting in wet and dry seasons in countries located in the tropics.   Satellite image of the ITCZ
Image courtesy NASA's Visible Earth
J
jet stream:
a current of fast moving air in the upper levels of the troposphere. Its position and strength relate to the surface temperature contrast between warm and cold areas on Earth.   UIUC tutorial on the jet stream Illustration of the jet stream
Image courtesy University of Illinois WW2010 Project
J
joule:
a standard unit of energy (radiation) or work (mechanics). For energy, one joule is equal to one watt second.   unit relationships
Image courtesy NASA
K
Kelvin:
An absolute temperature scale invented in the 1800's by William Thompson, Lord Kelvin. It places the zero point of the scale at absolute zero, the temperature which scientists believe is the lowest possible. All molecular motion would stop there. A Kelvin degree is the same size as a Celsius degree, so the two scales simply have a constant offset.   Fahrenheit, Celsius and Kelvin temperature scales
Image courtesy NASAexplores
K
kilometer:
A metric unit of distance equivalent to 1,000 meters. One kilometer is a little more than one half of a mile.   The Metric System
L
LAI:
Leaf Area Index is a satellite measurement of vegetation density and greenness. It is generally aimed to analyze forested areas where trees create a canopy over the ground (agricultural areas can also be detected during the growing season). LAI is the ratio of the one-sided green broadleaf area (or needleleaf area) per unit ground area. LAI significantly varies seasonally for deciduous trees, but varies little for coniferous forests as expected. Values typically range from zero (no vegetation) to 5-7 (very dense forest).  
Image courtesy MISR Science Team
L
land mask:
identifies the parts of Earth's surface that are land-covered for data analysis purposes. This allows other Earth science parameters, such as snow and cloud cover, to be averaged separately for land vs water areas. Typically, a resolution and land percentage are chosen based on the intended data use. For example, a 1 degree resolution gridbox area that contains greater than 90 percent land may be considered as land and analyzed as land even though water may be present in the form of rivers and lakes. Often, the number 1 is used for a land gridbox (white in the figure) and the number 0 is used for a water gridbox (blue in the figure). Coastal areas may be noted using the number 2 (black in the figure). These identify gridbox areas that are partially land, for example between 10 and 90 percent land. Note the areas of permanent sea ice around Antarctica that are denoted as land.     Related MY NASA DATA Activity:  Land Mask Detailed Explanation image of land mask data
Image courtesy CERES Science Team
L
La Nina:
the term used to identify opposite conditions from an El Nino when the Trade Winds strengthen and colder ocean surface water extends off the coast of Equador and Peru into the central Pacific Ocean.   NOAA El Nino Education Page La Nina SST example
L
latent heat:
the energy required to change a substance to a higher state of matter (solid to liquid to gas). This same energy is released from the substance when the change of state is reversed (gas to liquid to solid).  
L
latitude:
a measure which identifies the north - south location of a point on the Earth. It is the angle between the line connecting a point on the Earth and the Earth's center, and the equatorial plane of the Earth. There are three ways to express latitude. You may be most familiar with 0-90 North and 0-90 South. In the computer era this became -90 to +90, where -45 equivalent to 45 South. The third method is less familiar and is called the colatitude. Colatitude is 0 at the north pole, 90 at the equator, and 180 at the south pole. So, 45 South is equivalent to a colatitude of 135.     Related MY NASA DATA Activity:  Latitude and longitude tool. diagram showing latitude
L
limb scanning:
A technique used by some instruments in space which looks sideways through the atmosphere rather than down at the Earth. It can provide information about how certain components of the atmosphere change with altitude above the Earth's surface.   Orbit Visualization simulator tool Solar occultation is one example of a limb scan
Image courtesy The SOLAR project
L
longitude:
a measure which identifies the east - west location of a point on the Earth. It is the angular distance along a line of latitude from the Greenwich Meridian - a reference longitude set to be zero degrees. There are three equivalent ways to express longitude, and scientists tend to use them interchangeably. You may be most familiar with longitude as 0-180 East, and 0-180 West. It can also be expressed as 0-360 East, or just 0-360. In that case, 270 East is equivalent to 90 West. The third system arose in the computer era, when carrying both a number (0-180) and a character (East or West) was inconvenient. The new convention of -180 to +180 was then developed. In this case,-90 is equivalent to 90 West.     Related MY NASA DATA Activity:  Latitude and longitude tool. diagram showing longitude
L
longwave radiation:
Electromagnetic radiation with a wavelength longer than about 5 microns. Bodies with temperatures in the range of the Earth System have a peak energy emission in this wavelength range.   Radiation Explanation
L
low cloud:
We define clouds using three broad altitude ranges, and the various cloud types are assigned to one of these ranges. For satellite observations, some measure of the cloud's altitude (often cloud top or effective cloud height) is used to place the cloud into an altitude range. The satellite does not have the qualitative information to pick a cloud type.   Information on cloud types and levels from the S'COOL Project. The 6 low cloud types
Image courtesy The S'COOL Project
M
MCSST:
acronym for the Multi-Channel Sea Surface Temperature, a product derived from NOAA's AVHRR instrument. The data provide vital water surface temperature information in near real-time for a variety of applications such as offshore fishing operations, hurricane monitoring, El Nino and other climate studies.   Oceans and Climate Gulf Stream SST
M
mesosphere:
The layer of the Earth's atmosphere between the stratosphere and the ionosphere.   The Earth's Atmosphere
M
methane:
An odorless, colorless, flammable gas, the major constituent of natural gas. It is a major greenhouse gas that occurs naturally. It consists of one carbon atom and four hydrogen atoms.  
M
micrometer or micron:
one-millionth of a meter (10.e-6 or 0.000001 m). Human hair is approximately 100 microns in diameter.   The Metric System
M
microset:
a small part of a larger data set, usually a subset of certain parameters for a given time or a distinct geographical area of interest.  
M
mid clouds:
We define clouds using three broad altitude ranges, and the various cloud types are assigned to one of these ranges. For satellite observations, some measure of the cloud's altitude (often cloud top or effective cloud height) is used to place the cloud into an altitude range. The satellite does not have the qualitative information to pick a cloud type.   Information on cloud types and levels from the S'COOL Project. The 2 mid-level cloud types
Image courtesy The S'COOL Project
M
millibar:
a unit of measure used for atmospheric pressure. Standard atmospheric pressure is 1013.25 millibars, or mb, so this offers a very sensitive scale: 1 millibar represents a one tenth of one percent change in atmospheric pressure.   More about surface pressure units
M
MISR:
The Multi-angle Imaging SpectroRadiometer. MISR views Earth with cameras pointed in 9 different directions such that it can distinguish different types of clouds, particles and surfaces.   The MISR Web Site MISR observing concept
Image courtesy MISR Science Team
M
mm per day:
this unit provides a measure of the amount of precipitation in one day. Precipitation is measured in units of height as if a layer of water or condensed snow exists at the surface. It is NOT measured in units of volume. Within the LAS, Monthly Precipitation is the average amount of rain or snowfall per day that fell over one month's time. To obtain the total monthly precipitation estimate, multiply this measurement by the number of days in that month.     Related MY NASA DATA Activity:  Science Project: Measuring Local Precipitation
M
mole:
a standard unit of measure for the amount of a substance. One mole (mol) of a substance is numerically equal to the molecular weight of that substance. For gases, one mole is equal to Avogadro's number of molecules (6.022e23). In atmospheric chemistry, moles are sometimes used to quantify atmospheric constituents or pollutants.  
M
MOPITT:
MOPITT, which stands for Measurements Of Pollution In The Troposphere, is an instrument flying on NASA's EOS Terra spacecraft, measuring the global distributions of carbon monoxide (CO) and methane (CH4) in the troposphere. MOPITT is a joint effort between the US and Canada..   Terra's MOPITT website, which points to several other sites
N
nadir:
the point on Earth directly below a satellite orbiting the Earth, that is, the down direction. Opposite of zenith.  
N
nanometer:
One billionth of a meter (10.e-9 or 0.000000001 m). There are a billion (1,000,000,000) nanometers in one meter.   The Metric System
N
NASA:
acronym for National Aeronautics and Space Administration.   The NASA Web site
N
NCDC:
acronym for the National Climatic Data Center.   The NCDC Web site
N
NDVI:
Normalized Difference Vegetation Index is a measurement of vegetation from satellite. NDVI is calculated by using the amount of visible light and near-infrared light reflected from Earth's surface. Healthy and dense vegetation will absorb most visible light and reflect near-infrared light, whereas unhealthy or sparse vegetation will reflect more visible light and less near-infrared. Low values of NDVI (0 - 0.1) indicate barren or snow-covered land. Middle values (0.2 - 0.5) indicate shrubs and grasslands, and high values (0.6 - 0.9) indicate temperate and dense tropical forests.   Measuring Vegetation Health
Image courtesy MISR Science Team
N
net radiation:
the amount of radiation that actually is added to a surface, taking into account all wavelengths and incoming as well as outgoing radiation.   Visualization of net radiation from the Earth Observatory Image of net radiation for March 2000
Image courtesy CERES Science Team
N
nitrogen oxide:
refers to a family of oxygen compounds of nitrogen (NOx) that are produced by combustion and result in harmful chemical reactions that produce smog, tropospheric ozone and acid rain.   More about NOx
N
NOAA:
acronym for National Oceanic and Atmospheric Administration. Two NOAA satellites (in addition to the ERBS satellite) that carried ERBE instruments were NOAA-9 and NOAA-10. NOAA satellites also provide the satellite imagery for weather forecasting.   The NOAA Web site
N
non-scanning instrument:
An instrument that is fixed with respect to the spacecraft on which it flies. This gives a broad field of view fixed around a point directly below the satellite. ERBE's non-scanning instruments contained 5 detectors which measured radiation reflected and emitted by the Earth-atmosphere system.   The ERBE non-scanning instrument The ERBE Non-Scanner
Image courtesy NASA
N
number density:
A unit often used in chemistry and physics. The number of something (particles, atoms, molecules, ...) in a given volume. The volume could be a cubic centimeter, cubic meter, or some other volume. This can be used in atmospheric science to describe the concentration of aerosols or trace gases. Because the number of atoms or molecules is usually large, scientific notation is used. For example: 3.e12 ozone molecules in a cubic centimeter inside the ozone layer (3,000,000,000,000 ozone molecules in a cubic centimeter).     Related MY NASA DATA Activity:  Parts Per Billion Activity (PowerPoint)
O
OMI:
acronym for the Ozone Monitoring Instrument that is flying aboard NASA's Aura satellite. OMI will continue the data record for total ozone and other atmospheric parameters related to ozone chemistry and climate.   NASA's OMI Web page
O
open source:
an online interface that allows Web site users to submit relevant material to the Web site authors for sharing with other users. For MY NASA DATA, lesson plans, computer tools and other suggestions corresponding to the MY NASA DATA microsets are welcome.  
O
optical depth:
a measure of the reduction of light or energy transmitted through the atmosphere due to interactions with air, cloud or aerosol particles. Optical depth is much more significant to Earth's energy budget than the physical thickness of cloud or aerosol layers.   How energy transmission varies with optical depth
O
overlay plot:
a plot of two or more sets of data on the same graph. The data values may be distinguished by using different colors or contours. Data values for different variables do not have to use the same units of measurement.  
O
ozone:
a molecule consisting of 3 oxygen atoms found primarily in the stratosphere. When ozone is created in the troposphere, it can be a harmful pollutant.   More information on ozone The formation of ozone from regular diatomic oxygen
Image courtesy NASA's Earth Observatory
O
ozone layer:
a region within the stratosphere that contains a high amount of ozone. This layer provides a protective shield againist harmful UV radiation from the Sun.   How the ozone layer protects the Earth Image showing the ozone layer
Image courtesy NASA's Earth Observatory
O
ozonesonde:
an instrument carried on board a weather ballon. It contains an ozone sensor that measures ozone in the vertical air column.   Stratospheric Ozone Monitoring and Research
P
PAR:
acronym for Photosynthetically Active Radiation, energy in the visible light region of the electromagnetic spectrum (400 - 700 nanometer wavelength) that plants use for photosynthesis, measured in watts per meter squared. PAR is an important parameter of interest for ecological and hydrological climate studies (carbon, oxygen and water cycles).   More Information about Photosynthesis tree canopy
Image courtesy MY NASA DATA
P
parameter:
a measureable or derived earth science quantity within a data set, such as temperature, that usually varies by location and in time.  
P
parts per billion volume:
one method of expressing chemical concentration, usually of a gas. For example, 20 ppbv of ozone means that, if a sample of gas contained one billion units, then 20 of the units would be ozone.     Related MY NASA DATA Activity:  Parts Per Billion Activity (PowerPoint)
P
Pascal:
The SI unit for pressure measurement, named after Blaise Pascal, a French mathematician and physicist. 1 Pa = 1000 millibars (mb). Atmospheric pressure at Earth's surface averages 101325 Pa.  
P
percentage:
proportion in regard to the whole, or a fraction or ratio measured as part of 100.  
P
phase:
the physical state of matter of a substance: gas, liquid or solid; for water, phases include water vapor, liquid water or ice.  
P
photometer:
An instrument for measuring the amount of light. Depending on the purpose, a variety of filters can be used to measure light of specific wavelengths. A photometer can also be used to measure ambient light, or only a narrow beam that comes directly from a source like the Sun.   An AERONET sun photometer installed on an ocean platform
Image courtesy The NASA Langley COVE Surface Validation Group
P
photosynthesis:
the chemical process by which plants and some bacteria capture the energy of the Sun, and convert it to food. This chemical reaction combining carbon dioxide and water is catalyzed by chlorophyll, a green pigment in plant cells. The main product of photosynthesis is a carbohydrate, such as the sugar glucose, and oxygen which is released to the atmosphere.  
P
phytoplankton:
small plant-like organisms, such as the algae and bacteria found in marine ecosystems, that perform photosynthesis.   More information about phytoplankton   Related MY NASA DATA Activity:  Lesson: Phytoplankton in the Gulf of Maine
P
pixel:
a picture element, the smallest element that can be displayed on an image or computer monitor, often used as a unit of measurement for image size and resolution.   More information about pixels
P
pollution:
a general term refering to increased concentrations of undesired matter (solids, liquids or gases) in Earth's water, atmosphere or land that is manmade.  
P
population density:
number of people per unit area.  
P
precipitable water:
the amount of water in the form of vapor (gas) that is in a column of atmosphere. Under the right conditions, this water vapor can condense into liquid water and turn into clouds or precipitation. Precipitable water has units of centimeters, so one must imagine condensing all the moisture in the column of air into a small layer of water and then measuring its height.  
P
precipitation:
Water that falls from clouds to the ground. This can be in the form of rain, snow, sleet, hail, etc.   More info from the Global Precipitation Measurement mission   Related MY NASA DATA Activity:  Science Project: Measuring Local Precipitation
P
pressure:
see definition for atmospheric pressure.  
Q
quality:
a general standard or grade; for air quality, a measure of pollution at a given time and place; for data quality, the scientific value, accuracy or correctness of measurement.  
R
radiation:
energy that is emitted from a source in the form of rays or waves. Solar and terrestrial radiation are said to be electromagnetic, made up of oscillating electric and magnetic fields which propogate at the speed of light. Solar radiation is shortwave and terrestrial radiation is longwave.   More about electromagnetic waves
R
radiation budget or balance:
The difference between absorbed and emitted radiation. See shortwave and longwave radiation.   The Balance of Power in the Earth-Sun System Fact Sheet The Earth's Radiation budget
Image courtesy Kiehl and Trenberth, 1997
R
radiosonde:
a weather balloon and receiver system used to collect a vertical profile of data, usually temperature, dew point temperature and atmospheric pressure at a particular time and location. The data is often used as input for numerical forecast models and local severe weather forecasting. Some radiosondes are also equipped to measure the speed and direction of winds (rawinsondes) or ozone (ozonesondes).   image of a radiosonde
R
rainshadow effect:
the reduction of precipitation commonly found on the leeward side of a mountain range. The reduction in precipitation is the result of descending air that warms and reduces convection and condensation.  
R
Rayleigh scattering:
In the 19th century, Lord Rayleigh theorized that the sky is blue because our atmosphere causes the sun's light to bend or scatter into the colors of the visible light spectrum, thus we see blue because blue light scatters more than do other colors of light.  
R
reflection:
the return of sound or light back to its source. In the atmosphere, the process where incoming solar rays are redirected back upwardly after striking particles. Cloud water and ice account for most reflection of solar radiation.   Diagram of reflection and refraction
Image courtesy University of Virginia
R
reflectivity:
The fraction of radiation (for example, light) reaching a surface that is reflected by that surface. A mirror has a very high reflectivity, near 1. In contrast, black objects generally have a very low reflectivity. A perfect blackbody (see definition) would have a reflectivity of 0..   Surface Reflectivity
R
refraction:
the redirection of light after entering a medium; in the atmosphere, solar rays are redirected by interactions with air, cloud and aerosol particles.  
R
relative humidity:
the ratio between the amount of water vapor in the air and the amount required for saturation; depends on atmospheric temperature and pressure.  
R
renewable energy:
energy that can be replenished in a short period of time such as energy from solar, wind, water or geothermal sources. Typically, there is little concern that these sources of energy will become scarce or used up, unlike fossil fuels.  
R
resolution:
refers to the separation of data points, whether in space or in time. See also pixel.  
S
SAGE III:
Stratospheric Aerosol and Gas Experiment is one of the scientifc satellite instruments developed for NASA's Earth Observing System (EOS). SAGE III's role is to provide global, long-term measurements of key components (aerosols and ozone) of the Earth's atmosphere. Measurements are taken from the uppper troposphere through the stratosphere.   SAGE III Science Team Website Picture of SAGE III Instrument
Image courtesy The SAGE III Science Team
S
satellite:
Something that is in orbit around something else. For example, the Moon is a natural satellite in orbit around the Earth. Terra and Aqua are artificial satellites put into Earth orbit. The Mars Reconnaissance Orbiter is an artificial satellite put into orbit around Mars.   Satellite Tracking site Diagram of TRMM satellite in Earth orbit
Image courtesy NASA
S
saturation:
the atmospheric condition when water will begin to change phase from vapor to liquid or solid; occurs when relative humidity reaches 100 percent, usually by cooling.  
S
scanning instrument:
An instrument which is attached to a spacecraft on an assembly that is designed to move. The field of view of a scanning instrument sweeps back and forth across the Earth under the satellite's path, or using some other pre-determined pattern.   The ERBE scanning instrument The three telescopes at the bottom are mounted on a rotating device
Image courtesy NASA
S
scatter plot:
a plot used to compare pairs of values where one variable (x) is graphed versus another variable (y), usually to determine any correlation.   More about scatter plots Correlated parameters graphed by scatter plot
S
sea breeze:
Wind that occurs in a coastal area and blows from ocean to land, usually during the day, due to differences in the heating of the land and sea surface. At night the process reverses and a land breeze blows from land to ocean.   Diagrams illustrating sea and land breezes
S
sea level:
the average height or elevation of Earth's ocean surface. This height or level defines the zero value of elevation for land masses and ocean depths.  
S
sea surface temperature:
the temperature of the very top layer of water (or the effective temperature of a thicker layer that includes the top) of Earth's oceans and other large bodies of water. The satellite remote sensing method used determines which sea surface temperature (SST) can be measured. See also the definition for surface temperature.  
S
SeaWiFS:
the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project. SeaWiFS provides quantitative data on global ocean bio-optical properties. Subtle changes in ocean color represent various types and quantities of marine phytoplankton. The ocean color in the visible light region (wavelengths of 400-700 nm) varies with the concentration of chlorophyll and other plant pigments present in the water. The more phytoplankton present, the greater the concentration of plant pigments and the greener the water. These microscopic marine plants, such as algae and some bacteria, exist at the lowest levels of the food chain and use sunlight or chemical energy, rather than organic material, as sources of energy. It is thought that marine plants remove carbon from the atmosphere at a rate equivalent to terrestrial plants, but knowledge of interannual variability is needed.   The SeaWiFS Project the SeaWiFS instrument
S
shortwave radiation:
Electromagnetic radiation with a wavelength shorter than about 5 microns. Bodies with temperatures in the range of our Sun have a peak energy emission in this wavelength range.   Radiation Explanation
S
slope:
the steepness of a line on a coordinate plane, usually defined as the vertical change (rise) over the horizontal change (run) traveling along the line. The slope of a line may be positive or negative, zero or undefined. The image to the right illustrates a positive slope.   graphical definition of slope
S
snow and ice:
The amount of snow and ice cover detected on the surface of the Earth from satellite observations. A key challenge to this observation is the detection of clouds, which can look confusingly like snow or ice when viewed from space.   The Cryosphere - Where the World is Frozen
S
snow cover:
See snow and ice.  
S
snow pit:
A hole that is dug into the snow to be able to see all the layers from the ground to the top of the snowpack. This is used to study layers in the snow from different snowfall events, and changes in the snow from any warming (melting) events or other weather conditions that can affect snow cover.  
Image courtesy NASA GSFC
S
solar collector:
a device that captures the Sun's energy and focuses it in a small area as a more usable or storable form. These devices can be simple, such as a greenhouse, or complex like solar panels or solar concentrators.  
S
Solar constant:
the amount of solar radiation received at the top of the atmosphere on a normal plane at the mean Earth-sun distance; the value is generally accepted to be 1365 Watts per square meter (although this value is still subject to debate).  
S
solar declination:
the latitude on Earth where the sun is directly overhead at solar noon.  
S
solar occultation:
A technique of measuring vertical profiles of atmospheric optical depth form Earth orbit using the Sun as a light source..   SAGE III SOLAR
S
solar radiation:
the electromagnetic radiation or energy emitted by the Sun. The energy coming from the Sun peaks in visible wavelengths, but also includes ultraviolet and infrared wavelengths.   the solar energy spectrum
S
solar zenith angle:
the angle between the local zenith (up) and the line of sight to the sun.   Illustration of the solar zenith angle
S
solstice:
the date when solar declination - the latitude on the Earth where the Sun is directly overhead at noon - is +/-23.5 degrees. This occurs twice yearly on June 21 (summer solstice, +23.5 degrees, over Northern Hemisphere) and December 21 (winter solstice, -23.5 degrees, over Southern Hemisphere).   Diagram of the seasons and solstice
Image courtesy NOAA
S
spatial resolution:
refers to the horizontal and/or vertical resolution of a data set.  
S
SRB:
The Surface Radiation Budget Project. SRB data sets contain global averages of surface longwave and shortwave radiative properties, cloud amount, and meteorology using computer models.   The SRB Web Site
S
steradian:
a standard unit of solid angle. One steradian is the solid angle made at the center of a sphere by an area on the surface of the sphere equal to the square of the sphere's radius.   Illustration of a steradian
S
stratosphere:
the region of the atmosphere located about 10-50km above the surface of the Earth. It contains the benefical ozone layer.   Layers of the atmosphere animation Graphic shows the different layers of Earth's atmosphere
Image courtesy NASA
S
sublimation:
the change from solid phase directly to gas phase without passing through a liquid phase. For example, an ice crystal may sublime to water vapor where humidity is low and temperature is below freezing, such as when ice falls from cirrus clouds.  
S
sulfur dioxide:
A heavy toxic gas that is easily condensed to a colorless liquid and is a major air pollutant. Certain large volcanic eruptions release enough aerosols in the form of sulfur dioxide to noticeably cool the Earth System for several years. Composed of a sulfur atom and two oxygen atoms.  
S
surface ozone:
a trace gas consisting of three oxygen atoms that is measured at the ground to monitor pollution. Although it is the same ozone as found in the stratospheric ozone layer that beneficially blocks ultraviolet radiation, ozone at the surface is very harmful to humans and plants when its concentration exceeds natural levels. Increases often occur in urban and industrial areas during summer.   Monitoring surface ozone
S
surface temperature:
The temperature (may be in degrees F or C, or Kelvin) that is characteristic of the Earth's surface. While we understand this concept since we live on the surface, a little care is needed for remote sensing data. This may refer to the temperature of the air above the surface (what we typically mean by surface temperature and what is in the weather forecast). It can also mean the actual temperature of the surface (think of a black top road on a summer day). For the ocean, it can mean the temperature of the very top layer of water, or the effective temperature of a thicker layer that includes the top. The remote sensing method used determines which temperature can be measured.  
S
swath:
the portion of Earth's surface or atmosphere measured by an instrument during a single satellite overpass.   India Cyclone from October 2002
Image courtesy TRMM Science Team
T
temperature:
a relative degree of heat, usually measured on a scale such as the Fahrenheit or Celsius scale.   Temperature Conversion Tool
T
temperature inversion:
an instance when a warm air layer overlays a cooler air layer in the atmosphere, often suppressing vertical mixing of air.   Illustration of a temperature inversion
T
temporal resolution:
indicates the time increment of a data set, or the frequency at which data was measured.  
T
Terra:
The flagship of NASA's Earth Observing System (EOS), Terra is collecting a global data set to enable research into the ways that Earth's land, oceans, atmosphere, ice, radiant energy, and life function as a whole system.   The Terra website Terra spacecraft
Image courtesy NASA
T
thermal expansion:
the relative increase in the volume of a substance such as water or air with increasing temperature (assumes pressure stays the same).  
T
thermochron:
Small, long-lasting device used to monitor changes in diurnal temperature in snow formations.   Thermochron lodged in snow pit
Image courtesy NASA GSFC
T
thermocline:
the boundary in a body of water between the top layer of warm water near the surface that is mixed and the cold deep water layer. This boundary is usually the transition zone where the greatest vertical change in temperature occurs.  
T
time plot:
also called a time series, a graph of one or more variables over time, usually resulting in a line or lines showing trends, patterns or correlations.   example of a time plot
T
TOA:
top of atmosphere. See definition.  
T
TOA All-sky Albedo:
This parameter tells how much sunlight is reflected from the Earth system at the top of the atmosphere (see definition for TOA) under All-sky conditions (meaning the combination of clear and cloudy situations as they happen to occur). This parameter is available on a monthly timescale and a 72-day average from the older ERBE measurements..   Topical Explanation of Radiation parameters TOA All-sky Albedo for May 1999
Image courtesy MY NASA DATA
T
TOA All-sky LW Upward Flux:
The amount of longwave energy (infrared or heat) leaving the top of the atmosphere (see TOA definition) under All-sky conditions (meaning the combination of clear and cloudy situations as they happen to occur). This parameter is available for daily, monthly, and 72-day averages, the latter from the older ERBE measurements..   Topical Explanation of Radiation parameters TOA All-sky LW Upward Flux for October 2004
Image courtesy MY NASA DATA
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TOA All-sky Net Flux:
The net amount of energy (in minus out) measured at the top of the atmosphere (see TOA definition) under All-sky conditions (meaning the combination of clear and cloudy situations as they happen to occur). This parameter is available for monthly averages and as a 72-day average from the older ERBE measurements. This parameter combines both shortwave (visible or light) and longwave (heat or infrared) energy..   Topical Explanation of Radiation parameters TOA All-sky Net Flux for October 2004
Image courtesy MY NASA DATA
T
TOA All-sky SW Downward Flux:
The amount of shortwave (visible or light) energy entering the Earth system at the top of the atmosphere (see TOA definition) under All-sky conditions (meaning the combination of clear and cloudy situations as they happen to occur). This parameter is available in daily, monthly and 72-day averages, the latter from the older ERBE measurements..   Topical Explanation of Radiation parameters TOA All-sky SW Downward Flux for October 2004
Image courtesy MY NASA DATA
T
TOA All-sky SW Upward Flux:
The amount of shortwave (visible or light) energy leaving the Earth system at the top of the atmosphere (see TOA definition) under All-sky conditions. This parameter is available for daily, monthly and 72-day averages, the latter from the older ERBE measurements..   Topical Explanation of Radiation parameters TOA All-sky SW Upward Flux for October 2004
Image courtesy MY NASA DATA
T
top of atmosphere:
a given altitude where air becomes so thin that atmospheric pressure or mass becomes negligible. TOA is mainly used to help mathematically quantify Earth science parameters because it serves as an upper limit on where physical and chemical interactions may occur with molecules in the atmosphere. The actual altitude used for calculations varies depending on what parameter or specification is being analyzed. For example, in radiation budget, TOA is considered 20 km because above that altitude the optical mass of the atmosphere is negligible. For spacecraft re-entry, TOA is rather arbitrarily defined as 400,000 ft (about 120 km). This is where the drag of the atmosphere starts to become really noticeable. In meteorology, a pressure of 0.1 mb is used to define this location. The actual altitude where this pressure occurs varies depending on solar activity and other factors.   Layers of the Earth's Atmosphere
T
topographic map:
a map that shows the elevation or relief of Earth's surface using contour lines. The zero contour line is typically set to mean sea level.  
T
TOR:
Tropospheric Ozone Residual. The measure of ozone in the troposphere derived from satellite observations. It is called a residual because it is obtained by subtracting an estimate of stratospheric ozone from a total column measurement.   The TOR Web site Tropospheric Ozone Residual for September 1998
Image courtesy the MY NASA DATA Live Access Server
T
trace gas:
a gas found in very small amount in the atmosphere, such as water vapor, carbon dioxide, methane, and ozone. These gases while small in volume have major impacts on Earth's weather and climate.   Trace Gases Are Key To Halting Global Warming
T
Trade Winds:
the surface winds that predominate in the tropics, blowing from 30 degrees north and south towards and westwardly along the Equator.  
T
trend:
a general tendency over time as seen in data graphs or plots. A data trend could be toward higher, lower or steady values (no change). Trends are often used to predict future values when other factors or influences are held constant.  
T
TRMM:
Tropical Rainfall Measuring Mission. Satellite launched by Japan and the United States to study rainfall and its relationship to the release of energy, especially in the Tropical regions of the Earth.   The TRMM website The TRMM Spacecraft
Image courtesy NASA
T
tropical storm:
swirling storm characterized by a low-pressure center and numerous thunderstorms that produce strong winds and flooding rain. A tropical storm is characterized by having wind speeds ranging from 39-73 mph.   Counter clockwise moving mass of clouds over South Florida
Image courtesy NOAA
T
tropics:
The part of the Earth bounded to the north by the Tropic of Cancer, at 23.5 degrees north latitude, and to the south by the Tropic of Capricorn, at 23.5 degrees south latitude, is known as the tropics.  
T
tropopause:
the top of the troposphere. A thin transition layer of air between the troposphere and stratosphere characterized by a sharp temperature inversion which suppresses vertical mixing between the two layers.  
T
troposphere:
the bottom layer of the atmosphere extending from the surface to an altitude between 8 kilometers (at poles) and 14 kilometers (in tropics); most weather occurs in this layer.   Graphic shows the different layers of Earth's atmosphere
Image courtesy NASA
T
tropospheric ozone:
a trace gas consisting of three oxygen atoms that exists in the troposphere, the lowest layer of the atmosphere. Although it is the same gas found in the ozone layer of the stratosphere that beneficially blocks ultraviolet radiation, ozone in the troposphere is harmful to humans and plants when it exceeds natural concentrations. Increases often occur seasonally and regionally due to biomass burning and industrial pollution.  
T
Tropospheric Ozone Residual Monthly Averages:
This derived parameter comes from subtracting stratospheric column ozone from the total amount of ozone in the atmospheric column. The amount left over - the residual - is the amount of ozone in the troposphere. The LAS contains monthly average values for this parameter.   Diagram showing the process of identifying residuals
U
ultraviolet radiation:
shortwave electromagnetic waves having wavelengths between 0.1 and 0.4 micrometers; ultraviolet (UV) radiation from the sun is significantly absorbed by the ozone layer in the stratosphere. It is harmful to plants and animals, including humans.   The ultraviolet region of the spectrum
Image courtesy NASA Mission to Planet Earth
U
upwelling:
ocean circulation which brings cold, nutrient-rich deep water to the surface, usually occurring along western coasts of continents.   Illustration of ocean upwelling
Image courtesy NASA Mission to Planet Earth
V
validation:
the act of verifying the value of data, usually by comparing the data with other data sources. For satellite data, often ground or aircraft based measurements at a particular time and location will be compared to determine how well the data correlates.  
V
vapor pressure:
Pressure exerted by a vapor in equilibrium with its solid or liquid phase.   More information on vapor pressure
V
variable:
A quantity that changes over time; or, a quantity which can be assigned different values.  
V
variance:
The difference between what is expected and what actually occurs. In statistics, the variance is defined as the square of the standard deviation.  
V
velocity:
Speed of an object in a certain direction.  
V
vertical resolution:
for three-dimensional data, that is, a data set with an element of height such as atmospheric data, indicates the vertical distance between data point measurements or increments.  
V
volatile organic compounds:
Chemical compounds that contain hydrogen (H), and carbon (C), and evaporate easily. Commonly called VOC.  
V
volcanic aerosols:
Aerosols released during volcanic eruptions, notably ash, soot, and sulfur dioxide. These aerosols reflect sunlight, reducing the amount of energy reaching the lower atmosphere and the Earth's surface, and thus have a cooling effect.   Introduction to Volcanic Aerosols
V
volcano:
A vent in the Earth's crust through which molten lava and gases are released.   Volcano World Aerial view of Mount St. Helens crater rim and recent plume, from the south.
Image courtesy USGS Cascades Volcano Observatory
W
water vapor:
water in its gaseous state, and one of the most important constituents of the atmosphere. Not only does water vapor contribute to cloud formation and precipitation, but it also regulates the atmospheric temperature by being a vital greenhouse gas and transporter of energy (latent heat). The amount of water vapor in the atmosphere varies by location and time due to processes of evaporation and condensation, but over half of its amount can be found close to the surface, below two kilometers.  
W
watt:
a standard unit of power. In radiation studies, watts are used to quantify the flux of shortwave or longwave energy across a unit area such as Earth's surface (watts per meter squared).   unit relationships
Image courtesy NASA
W
wavelength:
The distance between two adjacent wave crests.   Electromagnetic Waves Illustration of a wave
Image courtesy NASA
W
weather:
The state of the atmosphere at a particular place and time. Weather includes variables such as temperature, atmospheric pressure, wind, cloudiness, precipitation, and relative humidity.  
W
weather balloon:
see definition for radiosonde.   weather balloon
Image courtesy MY NASA DATA
W
wet bulb temperature:
The temperature taken on a sling psychrometer from the thermometer with its bulb covered in a wet wick (piece of fabric), after slinging or whirling the psychrometer for the prescribed amount of time.   Picture of a sling psychrometer
Image courtesy NOAA Photo Library
W
wind:
movement of air from one place to another.  
W
wind vector:
an arrow on a map that represents both the direction and magnitude (speed) of the wind at a particular location for a particular time. The direction that the arrow points illustrates the direction of wind flow, and the length of the arrow tail indicates the wind speed proportional to a unit scale such as knots, meters per second or miles per hour.  
X
x-axis:
The horizontal axis of a Cartesian (coordinate) plane.   Cartesian plane axis
Y
y-axis:
The vertical axis of a Cartesian (coordinate) plane.   Cartesian plane axis
Z
zenith:
the point directly above a location on Earth's surface, that is, the up direction.  
Z
zonal band:
a latitudinal circle (east-west direction) having any width in degrees latitude, used for the representation of data for an area of Earth's surface or atmosphere.   example of a zonal band

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