HOPKINS GLOSSARY OF WEATHER TERMS A
air pressure (or barometric pressure
- A measure of the weight of an entire air column of unit area
cross section above the barometer, as a consequence of
gravitational attraction, or equivalently, the force exerted by
molecules of air acting on a unit area of any surface. See also
station pressure and sea level corrected pressure.
The units of pressure are the millibar, Pascal or
centimeters of mercury in a mercury barometer.
- A liquid-in-glass thermometer containing an alcohol
liquid, such as ethanol. Because alcohol has a low freezing point,
alcohol thermometers are as minimum thermometers
at stations where temperatures routinely reach -40 degrees C (-40
- An instrument that indicates the altitude (1)
of an object with respect to a reference level such as sea level;
examples include pressure altimeters and radio altimeters
- Any instrument that measures wind speed. Several types
of anemometers include the hot wire, rotation and
pressure-type anemometers .
- An instrument that measures the atmospheric (barometric)
pressure. and operates on the principle of having changing
air pressure bend a flexible metallic canister, which is partially
evacuated. An external or internal spring prevents the capsule
from collapsing. Changes in the size of this aneroid capsule are
proportional to the difference between external and internal pressures,
which in turn, move a pointer across an indicator scale or a pen
on a recorder chart.
- Maximum altitude of a rocket above a reference plane, typically
mean sea level.
azimuth or azimuth angle
- An angular direction described as the length of arc (in degrees)
measured clockwise along the local horizon, from a reference point
(usually true north), to that point on the horizon where the particular
object or its projection is located; north is defined as having
an azimuth of 0 degrees (or 360degrees), east is 90 degrees, and
Last update 6 June 1996
Edward J. Hopkins, Ph.D.
Department of Atmospheric and Oceanic Sciences
University of Wisconsin-Madison