5
Causes of Precipitation
The science of Meterology deals with the causes of precipitation, its prediction
etc. We shall discuss briefly the causes of precipitation, weather conditions
which is again influenced by atmospheric vapour pressure (presence of
moisture), temperature etc.
The upward movement of evaporated air mass causes cooling which ultimately
condenses and forms clouds or fog. Clouds or fog consists of small ice
particles and droplets of water. As has been discussed when the available space
is saturated with such ice particles and water droplets, precipitation
occurs. Formation of clouds is, thus, a pre requisite for precipitation. There are
different types of clouds formation of which depends upon the upward motion of
the air mass.
(1)
Stratiform clouds :
Prolonged wide spread slow ascent of air in the low
pressure area gives rises to stratified layers of cloud and is known as
stratiform clouds and is responsible for cyclonic precipitation.
(2)
When the air mass consisting of large bubbles starts upward motion
abruptly and violently and meets warmer air mass, heap type of clouds
are formed, commonly known as cumuliform clouds. Such clouds cause
corrective precipitation.
(3)
When air is forced to ascend hill or a mountain barrier, typical orographic
clouds are formed and lead to orographic precipitation.
Forms of cloud are mainly classified into (a) Stratiform (b) Cumuliform and
(c) Fibrous.
Formation of clouds and its heights are dependent at different geographical
regions : (1) Tropical or equatorial region, (ii) temperate latitude regions,
(iii) polar regions. Clouds can also be classified depending upon its altitude as
shown in the Table :
