| A | B |
|---|
| Air pressure | the force exerted by the weight of a column of air above a particular location. |
| barometer | used to measure air pressure |
| mercury barometer | a tube with a reservoir of mercury at one end. Under average sea level conditions, the atmosphere exerts enough pressure to push a column of mercury up to the height of 29.92 inches. |
| aneroid barometer | uses an aneroid or sylphon cell to measure pressure. |
| aneroid cell | a metal chamber that expands and contracts with changing air pressure. |
| high pressure | defined as values greater than 1013.2 mb |
| low pressure | defined as values below 1013.2 mb. |
| constant height map | shows the distribution of pressure at sea level |
| isobars | lines connecting points of equal air pressure are used to show pressure patterns on constant height maps. |
| constant pressure map | shows the change in elevation of an isobaric surface |
| isobaric surface | which is a surface upon which the pressure is the same at all locations. |
| wind | movement of air molecules from one place to the next. |
| pressure gradient | the spacing of isobars indicates the change in pressure over distance |
| Coriolis force | the effect of earth rotation on the direction of the wind. |
| friction layer | the layer of air that is influenced by friction caused by the surface, generally lies w/in 1 km of the surface |
| anemometer | instrument used to measure wind speed |
| beaufort scale (original) | created in 1805 by Sir Francis Beaufort as a qualitative measure of wind condition effects on the sails of his ship. |
| beaufort scale (new) | In 1906, the descriptions were changed to how seas behaved under different wind conditions. |
| wind vane | an instrument to measure wind direction |
| aerovane | an instrument that can measure both wind direction and speed simultaneously |
| prevailing wind | the direction that the wind comes from the most often |
| high pressure system | air is directed clockwise(N) & outward from the center |
| low pressure system | air is directed counterclockwise(N) & inward toward the center |
| geostrophic winds | Winds that blow roughly parallel to isobars |
| jet stream | a high velocity corridor of air moving through the winds aloft. |
| cyclones | areas of low pressure, usually exhibit nearly circular isobars, ascending air |
| trough | low pressure system, isobars are oblong or elongate with the lowest pressure near the center |
| convergence | at center of low pressure sys, or the upper level of a high pressure system, occurs when air is directed toward a particular location from different directions. |
| divergence | at the center of a high pressure system, or the upper level of a low pressure system, when air is directed away from a particular location in different directions. |
| anticyclone | areas of high pressure that exhibit nearly circular isobars, descending air |
| ridges | isobars are oblong or elongate with the highest pressure near the center |
