Ice sheet (continental glacier)(1)

A glacier of considerable thickness and more than 50.000 sq km in area. It forms a continuous cover of ice and snow over a land surface. An ice sheet is not confined by the underlying topography but spreads outward in all directions. During the Pleistocene Epoch. ice sheets covered large parts of North America and northern Europe but they are now confined to polar regions (e.g.. Greenland and Antarctica).

Ice shelf(1)

A thick mass of ice extending from a polar shore. The seaward edge is afloat and sometimes extends hundreds of miles into the sea.

In situ(1)

Latin for 'in original place.' Refers to measurements made at the actual location of the object or material measured. Compare remote sensing.

Indian summer(6)

An unseasonably warm spell with clear skies near the middle of autumn. Usually follows a substantial period of cool weather.

Infrared radiation(4)

The heat energy that is emitted from all solids. liquids. and gases. In the context of the greenhouse issue. the term refers to the heat energy emitted by the Earth's surface and its atmosphere. Greenhouse gases strongly absorb this radiation in the Earth's atmosphere. and radiate some back towards the surface. creating the greenhouse effect. See radiation. greenhouse effect. enhanced greenhouse effect. global warming.


The incoming solar radiation that reaches the earth and the atmosphere.


Solar radiation incident upon a unit horizontal surface on or above the Earth's surface. Kelvin Waves cause variations in the depth of the oceanic thermocline. the boundary between warm waters in the upper ocean and cold waters in the deep ocean.

Intergovernmental Panel on Climate Change (IPCC)(5)

The IPCC was established in 1988 by the World Meteorological Organization and the UN Environment Programme. The IPCC is responsible for providing the scientific and technical foundation for the United Nations Framwork Convention on Climate Change (UNFCCC). primarily through the publication of periodic assessment reports (see 'Second Assessment Report' and 'Third Assessment Report').

International System of Units (SI)(1)

The International System of Units prescribes the symbols and prefixes shown in the table to form decimal multiples and submultiples of SI units. The following examples illustrate the use of these prefixes- 0.000.001 meters = 1 micrometer = 1�m. 1000 meters = 1 kilometer = 1 km. 1.000.000 cycles per second = 1.000.000 hertz = 1 megahertz =1 MHz..

Intertropical convergence zone ((ITCZ))(6)

The boundary zone separating the northeast trade winds of the Northern Hemisphere from the southeast trade winds of the Southern Hemisphere.

Intraseasonal Oscillations(3)

Variability on a timescale less than a season. One example is the Madden-Julian Oscillation.


An increase in air temperature with height.


An electrically charged atom. molecule. or particle.


An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist.


A line connecting points of equal pressure.


A line connecting points of equal wind speed.


A line connecting points of equal wind temperature.

January thaw(6)

A period of relatively mild weather around January 20 to 23 that occurs primarily in New England. an example of a singularity in the climatic record.

Jet Stream(3)

Strong winds concentrated within a narrow zone in the atmosphere in the upper troposphere. about 30.000 feet aloft that generally move in an easterly direction that drive weather systems around the globe. In North America jet streams are more pronounced in winter.

Katabatic wind(6)

Any wind blowing downslope. Usually cold.

Kelling Curve(6)

The name given to a graph that measured the rise of carbon dioxide gas in our atmosphere. Carbon Dioxide has been measured continuously since 1958 and follows an oscillating line. The line was named after Dr. Charles David Keeling. professor at Scripps Institution of Oceanography.

Kelvin Waves(3)

Fluctuations in wind speed at the ocean surface at the Equator result in eastward propagating waves. known as Kelvin Waves. Kelvin Waves cause variations in the depth of the oceanic thermocline. the boundary between warm waters in the upper ocean and cold waters in the deep ocean. They play an important role in monitoring and predicting El Ni�o episodes.

Kyoto Protocol(5)

An international agreement adopted in December 1997 in Kyoto. Japan. The Protocol sets binding emission targets for developed countries that would reduce their emissions on average 5.2% below 1990 levels.

La Ni�a(3)

La Ni�a. a phase of ENSO. is a periodic cooling of surface ocean waters in the eastern tropical Pacific along with a shift in convection in the western Pacific further west than the climatological average. These conditions affect weather patterns around the world. The preliminary CPC definition of La Ni�a is a phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface temperature departure from normal (for the 1971-2000 base period). averaged over three months. greater than or equal in magnitude to 0.5�C in a region defined by 150�W-160�E and 5�N-5�S (commonly referred to as Ni�o 4).

Lake breeze(6)

A wind blowing onshore from the surface of a lake.

Lake-effect snows(6)

Localized snowstorms that form on the downwind side of a lake. Such storms are common in late fall and early winter near the Great Lakes as cold. dry air picks up moisture and warmth from the unfrozen bodies of water.

Land breeze(6)

A coastal breeze that blows from land to sea. usually at night.

Lapse rate(6)

The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.)

Latent heat(1)

The heat that is either released or absorbed by a unit mass of a substance when it undergoes a change of state. such as during evaporation. condensation. or sublimation.


The angle between a perpendicular at a location. and the equatorial plane of the Earth.

Lenticular cloud(6)

A cloud in the shape of a lens.


A visible electrical discharge produced by thunderstorms.

Little Ice Age(1)

A cold period that lasted from about A.D. 1550 to about A.D. 1850 in Europe. North America. and Asia. This period was marked by rapid expansion of mountain glaciers. especially in the Alps. Norway. Ireland. and Alaska. There were three maxima. beginning about 1650. about 1770. and 1850. each separated by slight warming intervals.

Long Wave(4)

In meteorology. a long wave in atmospheric circulation in the major belt of westerlies has different characteristics than rapidly moving storms nearer the Earth�s surface. (or Planetary Wave)


The angular distance from the Greenwich meridian (0�). along the equator. This can be measured either east or west to the 180th meridian (180�) or 0� to 360�W.

Longwave radiation(1)

The radiation emitted in the spectral wavelength greater than 4 micrometers corresponding to the radiation emitted from the Earth and atmosphere. It is sometimes referred to as terrestrial radiation or infrared radiation. although somewhat imprecisely. See infrared radiation.


The region around the earth in which the earth's magnetic field plays a dominant part in controlling the physical processes that take place.

Mammatus clouds(6)

Clouds that look like pouches hanging from the underside of a cloud.

Marine climate(6)

A climate dominated by the ocean. because of the moderating effect of water. sites having this climate are considered relatively mild.

Maritime air mass(6)

An air mass that originates over the ocean. These air masses are relatively humid.

Maritime polar air(6)

Cool. humid air mass that forms over the cold ocean waters of the North Pacific and North Atlantic.

Maritime tropical air(6)

Warm. humid air mass that forms over tropical and subtropical oceans.

Mauna Loa Record(5)

The record of measurement of atmospheric CO2 concentrations taken at Mauna Loa Observatory. Mauna Loa. Hawaii. since March 1958. This record shows the continuing increase in average annual atmospheric CO2 concentrations.

Mean annual temperature(6

The average temperature at any given location for the entire year.

Mean sea level(1)

The average height of the sea surface. based upon hourly observation of the tide height on the open coast or in adjacent waters that have free access to the sea. In the United States. it is defined as the average height of the sea surface for all stages of the tide over a nineteen-year period. Mean sea level. commonly abbreviated as MSL and referred to simply as 'sea level.' serves as the reference surface for all altitudes in upper atmospheric studies.


he arithmetic average. or the middle point between two extremes.


The scale of meteorological phenomena that ranges in size from a few km to about 100 km. It includes local winds. thunderstorms. and tornadoes.


The atmospheric layer between the stratosphere and the thermosphere. Located at an average elevation between 50 and 80 km above the earth's surface.


The scientific study of the physics. chemistry. and dynamics of the Earth�s atmosphere. especially weather and climate.

Methane (CH4(5)

CH4 is among the six greenhouse gases to be curbed under the Kyoto Protocol. Natural processes produce atmospheric CH4. but there are also substantial emissions from human activities such as landfills. livestock and livestock wastes. natural gas and petroleum systems. coalmines. rice fields. and wastewater treatment. CH4 has a relatively short atmospheric lifetime of approximately 10 years. but its 100-year GWP is currently estimated to be approximately 23 times that of CO2.
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