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- Created 2012-03-12
, is a region where the
is lower than that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the
. The formation process of a low-pressure area is known as
. Within the field of meteorology, atmospheric divergence aloft occur in two areas. The first area is on the east side of upper troughs which form half of a
(a trough with large
which extends through the troposphere). A second area of wind divergence aloft occurs ahead of
embedded shortwave troughs
which are of smaller wavelength. Diverging winds aloft ahead of these troughs cause
lift within the troposphere below, which lowers surface pressures as upward motion partially counteracts the force of gravity.
s form due to localized heating caused by greater sunshine over deserts and other land masses. Since localized areas of warm air are less dense than their surroundings, this warmer air rises which lowers atmospheric pressure near that portion of the
's surface. Large-scale thermal lows over
s help drive
circulations. Low-pressure areas can also form due to organized thunderstorm activity over warm water. When this occurs over the tropics in concert with the
Intertropical Convergence Zone
, it is known as a
. Monsoon troughs reach their northerly extent in August and their southerly extent in February. When a convective low acquires a well-hot circulation in the tropics it is termed a
. Tropical cyclones can form during any month of the year globally, but can occur in either the northern and southern hemisphere during November.
Atmospheric lift will also generally produce
cooling once the air becomes saturated as it rises, although the low-pressure area typically bring cloudy skies, which act to minimize
diurnal temperature extremes
. Since clouds reflect
is less which causes lower
s during the day. At night, the absorptive effect of clouds on outgoing
, such as heat energy from the surface, allows for warmer diurnal low temperatures in all seasons. The stronger the area of low pressure, the stronger the
s which are experienced in its vicinity. Globally, low-pressure systems are most frequently located over the
and in the lee of the
. In Europe (particularly in the
), recurring low-pressure weather systems are typically known as depressions.
from Wikipedia (last updated: 25 May), licensed under
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Intertropical Convergence Zone
Surface weather analysis
East Asian Monsoon
North American Monsoon
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