Synoptic scale(6)

Used to classify large-scale weather systems more than 200 miles across.


The northern coniferous forest. also a name applied to the subarctic climate.


A strong statistical relationship between weather in different parts of the globe. For example. there appears to be a teleconnection between the tropics and North America during El Ni�o.

Temperature (TEMP)(6)

A measure of the energy in a substance. The more heat energy in the substance. the higher the temperature. The Earth receives only one two-billionth of the energy the sun produces. Much of the energy that hits the Earth is reflected back into space. Most of the energy that isn't reflected is absorbed by the Earth's surface. As the surface warms. it also warms the air above it.

Temperature inversion(6)

An extremely stable air layer in which temperature increases with altitude. the inverse of the usual temperature profile in the troposphere.

Terminal velocity(6)

The constant speed obtained by a falling object when the upward drag on the object balances the downward force of gravity.

Terrestrial radiation(1)

The total infrared radiation emitted by the Earth and its atmosphere in the temperature range of approximately 200 to 300 Kelvin. Terrestrial radiation provides a major part of the potential energy changes necessary to drive the atmospheric wind system and is responsible for maintaining the surface air temperature within limits of livability.


An explanation for some phenomenon that is based on observation. experimentation. and reasoning.

Thermal expansion(5)

Expansion of a substance as a result of the addition of heat. In the context of climate change. thermal expansion of the world's oceans in response to global warming is considered the predominant driver of current and future sea-level rise.


Of. making use of. producing. or caused by heat.


As one descends from the surface of the ocean. the temperature remains nearly the same as it was at the surface. but at a certain depth temperature starts decreasing rapidly with depth. This boundary is called the thermocline. In studying the tropical Pacific Ocean. the depth of 20�C water ('the 20�C isotherm') is often used as a proxy for the depth of the thermocline. Along the equator. the 20�C isotherm is typically located at about 50m depth in the eastern Pacific. sloping downwards to about 150m in the western Pacific.


A recording instrument that gives a continuous trace of temperature with time.

Thermohaline Circulation ((THC))(2)

Density-driven circulation system for the world's oceans. Warm Atlantic water moves northward along the axis of the Gulf Stream. evaporation makes the water more and more dense while releasing heat to the colder atmosphere in the North Atlantic. Once dense enough. the water sinks into the deep ocean. forming a downward limb of a giant conveyor-like circulation that extends around the world's oceans.


An instrument used to measure temperature.


The atmospheric layer above the mesosphere. It extends from 90 km to outer space.


The sound due to rapidly expanding gases along the channel of a lightning discharge.

Tipping bucket rain gage(6)

A device that accumulates rainfall in increments of 0.01 in. by containers that alternately fill and empty (tip).


An intense. rotating column of air that protrudes from a cumulonimbus cloud in the shape of a funnel or a rope and touches the ground. (See Funnel cloud.)


A system of low-level winds occurring in the tropics. the tradewinds blow from the northeast to the equator in the Northern Hemisphere and from the southeast to the equator in the Southern Hemisphere.


The release of water vapor to the atmosphere by plants.

Tropical air mass(6)

A warm-to-hot air mass that forms in the subtropics.

Tropical depression(6)

A mass of thunderstorms and clouds generally with a cyclonic wind circulation of between 20 and 34 knots

Tropical disturbance(6)

An organized mass of thunderstorms with a slight cyclonic wind circulation of less than 20 knots.

Tropical storm(6)

Organized thunderstorms with a cyclonic wind circulation between 35 and 64 knots.


The boundary between the troposphere and the stratosphere.


The lowest portion of the atmosphere which lies next to the earth's surface where most weather occurs. The absorption of UV by stratospheric ozone and atmospheric oxygen prevents very little ultraviolet radiation to reach earth's surfaces where it cans detrimental effects on human health and property

Tundra Climate(6)

Found almost exclusively in the northern hemisphere or at high altitudes in many mountainous regions. A treeless climatic realm of sedges. grasses. mosses. and lichens that is dominated by a lng. bitterly cold winter.


Any irregular or disturbed flow in the atmosphere that produces gusts and eddies.


The time immediately before sunrise and after sunset when the sky remain illuminated.


A hurricane that forms in the western Pacific Ocean.

Ultraviolet (UV)(3)

Ultraviolet radiation from the sun plays a role in the formation of the ozone layer by acting as a catalyst for a chemical reaction that breaks apart oxygen molecules which then recombine to form ozone. The absorption of UV by stratospheric ozone and atmospheric oxygen prevents very little ultraviolet radiation to reach earth's surfaces where it cans detrimental effects on human health and property.


Uncertainty is a prominent feature of the benefits and costs of climate change. Decision makers need to compare risk of premature or unnecessary actions with risk of failing to take actions that subsequently prove to be warranted. This is complicated by potential irreversibilities in climate impacts and long term investments.


In weather observing. the term applies to the portion of the atmosphere that is above the lower troposphere. generally 850 hPa and above.

Upslope fog(6)

Fog formed as moist. stable air flows upward over a topographic barrier.

Upslope precipitation(6)

Precipitation that forms due to moist. stable air gradually rising along an elevated plain. Upslope precipitation is common over the western Great Plains. especially east of the Rock Mountains.


In ocean dynamics. the upward motion of sub-surface water toward the surface of the ocean. This is often a source of cold. nutrient-rich water. Strong upwelling occurs along the equator where easterly winds are present. Upwelling also can occur along coastlines. and is important to fisheries and birds in California and Peru.

Urban heat island(6)

The increased air temperatures in urban areas as contrasted to the cooler surrounding rural areas.


Universal Time Coordinated is the same as Greenwich Mean Time.


Comparing a climate model's predictions with observations of the real climate. in order to test the reliability and accuracy of the model. The most obvious way to test a climate model is to use it to analyze past events. and then see whether its simulated prediction 'came true.' or how close it was to being correct.

Vapor pressure(6)

The pressure exerted by the water vapor molecules in a given volume of air.

Vernal equinox(6)

The equinox at which the sun approaches the Northern Hemisphere and passes directly over the equator. Occurs around March 20.


Precipitation that falls from a cloud but evaporates before reaching the ground. (See Fall streaks.)

Virtual temperature(6)

An adjustment applied to the real air temperature to account for a reduction in air density due to the presence of water vapor.


The resistance of fluid flow.


The greatest distance an observer can see and identify prominent objects.

Visible light(6)

That portion of the electromagnetic spectrum from 0.4 to 0.7 m wavelengths that is visible.


A measure of the spin of a fluid. usually small air parcels. Absolute vorticity is the combined vorticity due to the earth's rotation and the vorticity due to the air's circulation relative to the earth. Relative vorticity is due to the curving of the air flow and wind shear.

Warm front(6)

The leading edge of a warm air mass.

Water balance(6)

The comparison of actual and potential evapotranspiration with the amount of precipitation. usually on a monthly basis.

Water budget(6)

Balance sheet for the inputs and outputs of water to and from the various global water reservoirs.
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Americans’ health, security and economic wellbeing are tied to climate and weather. Every day, we see communities grappling with environmental challenges due to unusual or extreme events related to climate and weather. In 2011, the United States experienced a record high number (14) of climate- and weather-related disasters where overall costs reached or exceeded $1 billion. Combined, these events claimed 670 lives, caused more than 6,000 injuries, and cost $55 billion in damages. Businesses, policy leaders, resource managers and citizens are increasingly asking for information to help them address such challenges.