The Atmosphere: Basics of Weather

THE ATMOSPHERE: BASICS AND EVERYDAY WEATHER

Atmosphere

The air surrounding and bound to earth's surface.

Troposphere

The layer of the atmosphere from earth's surface up to the tropopause. Most of earth's weather occurs and is influenced by what happens in the troposphere.

Typical Heights of Various Pressure Levels

Jet Stream

Relatively strong winds concentrated in a narrow stream in the atmosphere, normally referred to high altitude winds. The upper level jet stream is a driving force in day to day weather patterns.

Upper Level System

A general term for any large-scale or mesoscale disturbance capable of producing upward motion (lift) in the middle/upper parts. Can also be referred to as an upper level impulse or shortwave.

Lift

Rising motion of air in the atmosphere over a rather large area.

Subsidence

Descending motion of air in the atmosphere over a rather large area.

Moisture

Refers to the water vapor content in the atmosphere, or total water, liquid, solid or vapor, in a given volume of air.

Warm Advection

Transport of warm air into an area by horizontal winds.

Cold Advection

Transport of cold air into the region by horizontal winds.

Adiabatic

Changes in temperature caused by the expansion or compression of a body of air as it rises or descends in the atmosphere with no exchange of heat with the surrounding air.

Diurnal Temperature Range

The temperature range between the minimum at night and the maximum during the day.

Diabatic

A process which occurs with the addition or loss of heat. The opposite of adiabatic. Meteorological examples include air parcels warming due to the absorption of infrared radiation or release of latent heat.

An elongated area of relatively high atmospheric pressure; the opposite of trough. A bump or crest in a wave pattern associated with higher heights at a certain pressure level.

Ridge

Trough

An elongated area of relatively low atmospheric pressure, usually not associated with a closed circulation, and thus used to distinguish from a closed low. The opposite of ridge. In a wave pattern, typically associated with lower heights at a certain pressure level.

Shortwave Trough (aka Shortwave)

A disturbance in the mid or upper part of the atmosphere which induces upward motion ahead of it. If other conditions are favorable, the upward motion can contribute to thunderstorm development ahead of a shortwave trough.

Dewpoint

A measure of atmospheric moisture. It is the temperature to which air must be cooled in order to reach saturation (assuming air pressure and moisture content are constant).

Temperature

A measure of the internal energy that a substance contains. This is the most measured quantity in the atmosphere.

Relative Humidity

A measure of how much or how close an air mass is to being saturated. Highly dependent upon temperature.

Wind

The horizontal motion of the air past a given point. Winds begin with differences in air pressures. Pressure that's higher at one place than another sets up a force pushing from the high toward the low pressure.

Pressure

The weight of the column of air above a unit area.

Wind Chill

Heat Index

The Heat Index (HI) or the "Apparent Temperature" is an accurate measure of how hot it really feels when the Relative Humidity (RH) is added to the actual air temperature.