Environmental Engineering Reference
In-Depth Information
Figure 7.2
The effect of surface warming and cooling on
lapse rates.
WEATHER
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FORMING SYSTEMS OF TEMPERATE LATITUDES
ANTICYCLONES
An anticyclone is a mass of relatively high pressure within which the air is subsiding. The
major anticyclonic belts are in the subtropics, centred about 30° from the equator. They
are located under the descending arm of the Hadley cell circulation of the tropics, and
hence act to link the upper and lower atmosphere. As air descends it gets warmer and
drier (Figure 7.3), but in these regions its descent is restricted by the layer of cool oceanic
air below. The result is a semi-permanent inversion. This combination of circumstances
gives rise to very stable atmospheric conditions, reducing the possibility of precipitation.
Even over heated desert surfaces the effects of subsidence dominate, so these
anticyclonic belts are associated with the main dry zones of the world.
In the middle latitudes, anticyclones often develop as a result of convergence in the
upper westerlies, particularly where the waves in those westerlies have a large
Figure 7.3
The effect of large-scale subsidence on lapse
rates. DALR, dry adiabatic lapse rate.
AIR STREAMS
concepts
There are other ways of classifying air than by its source regions as is done in air mass
