Circulation Patterns of the Atmosphere
Glossary

Azonal flow

The meridional (north-south) flow of upper atmospheric winds (poleward of 15 degrees of latitude), particularly the subtropical and Polar Front jet streams; periodic departures from the zonal (west-to-east) flow of these air currents are important because they help to correct the heat imbalance between the polar and equatorial regions.

Equatorial low

The Inter-Tropical Convergence Zone (ITCZ) or thermal low-pressure belt of rising air that straddles the equatorial latitudinal zone; fed by the windflows of the converging Northeast and Southeast Trades.

General circulation

The global atmospheric circulation system of windbelts and semipermanent pressure cells. In each hemisphere, the windbelts include the Trades, Westerlies, and Polar Easterlies. The pressure cells include the Equatorial Low (ITCZ), and, in each hemisphere, the Subtropical High, Upper-Midlatitude Low, and Polar High.

Inter-Tropical Convergence Zone (ITCZ)

The thermal low-pressure belt of rising air that straddles the equatorial latitudinal zone, which is fed by the windflows of the converging Northeast and Southeast Trades.

Jet stream

The two concentrated, high-altitude, west-to-east flowing “rivers” of air that are major features of the upper atmospheric circulation system poleward of latitude 15 degrees in both the Northern and Southern Hemispheres; because of their general occurrence above the subtropical and subpolar latitudes, they are respectively known as the subtropical jet stream and the Polar Front jet stream. A third such corridor of high-altitude, concentrated windflow is the tropical easterly jet stream, a major feature of the upper-air circulation equatorward of 15 degrees North. This third jet stream, however, flows in the opposite, east-to-west direction and occurs only above the tropics of the Northern Hemisphere.

Monsoon

Derived from the Arabic word for “season,” a regional windflow that streams onto and off certain landmasses on a seasonal basis; the moist onshore winds of summer bring the wet monsoon, whereas the offshore winds of winter are associated with the dry monsoon.

Northeast Trades

The surface wind belt that generally lies between the Equator and 30 degrees North; the Coriolis force deflects equatorward-flowing winds to the right, thus recurving north winds into northeast winds.

Polar Easterlies

The high-latitude wind belt in each hemisphere, lying between 60 and 90 degrees of latitude; the Coriolis force is strongest in these polar latitudes, and the equatorward-moving air that emanates from the Polar High is sharply deflected in each hemisphere to form the Polar Easterlies.

Polar Front

The latitudinal zone, lying at approximately 60 degrees north and south, where the equatorward-flowing Polar Easterlies meet the poleward-flowing Westerlies; the warmer Westerlies are forced to rise above the colder Easterlies, producing a semipermanent surface low-pressure belt known as the Upper-Midlatitude Low.

Polar High

Large semipermanent high-pressure cell centered approximately over the pole in the uppermost latitudes of each hemisphere.

Southeast Trades

The surface wind belt that generally lies between the Equator and 30 degrees South; the Coriolis force deflects equatorward-flowing winds to the left, thus recurving south winds into southeast winds.

Subtropical High

The semipermanent belt of high pressure that is found at approximately 30 degrees of latitude in both the Northern and Southern Hemispheres; the subsiding air at its center flows outward toward both the lower and higher latitudes.

Upper-Midlatitude Low

The semipermanent surface low-pressure belt, lying at approximately 60 degrees north and south, where the equatorward-flowing Polar Easterlies meet the poleward-flowing Westerlies; at this sharp atmospheric boundary, known as the Polar Front, the warmer Westerlies are forced to rise above the colder Easterlies.

Westerlies

The two broad midlatitude belts of prevailing westerly winds, lying between approximately 30 and 60 degrees in both hemispheres; fed by the Coriolis-force-deflected, poleward windflow emanating from the Subtropical High on the equatorward margin of the Westerlies wind belt.

Zonal flow

The westerly flow of winds that dominates the upper atmospheric circulation system poleward of 15 degrees latitude in each hemisphere.

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Links

It's About Time: A New Upper-Atmosphere Model
A discussion of the general model of upper air circulation, and of new models being developed by researchers.

How the Atmosphere Influences Aridity (USGS)
Article relating the effects of the atmosphere on aridity, including a discussion of the major global wind belts.

Animated Asian Monsoons
Description of Asian monsoon with 2D and 3D animations.