Types of Rainfall – Geography
Convectional rainfall or vapor-induced rainfall is caused by the rising of air caused due to its expansion from adiabatic cooling, resulting in the expulsion of moisture from the rising air.
It is more commonly known as Steam-induced rain, especially if it is associated with a surface steam explosion. Such thunderstorms usually develop during short-lived temperature inversions between a low and a ridge or a high and a warm front.
If the atmosphere overlying a warm sea is sufficiently moist, vigorous convection can take place when there is an area of light winds on the sea surface.
Convectional Rainfall
Convectional rainfall is a type of rainfall caused by the ascending air currents, which makes the air to rise and form clouds. These types of clouds are cumulus clouds.
This type of atmospheric circulation happens as soon as the temperature gets high and the air starts to rise as a result.
As this hot air rises, it expands and cools down as well. When it cools down, it forms cloud droplets and finally, we get the form of rain.
The, air on being heated, becomes light and rises up in convection currents. As it rises, it expands and loses heat and consequently, condensation takes place and cumulous clouds are formed.
With thunder and lightning, heavy rainfall takes place but this does not last long.
Such rain is common in the summer or in the hotter part of the day. It is very common in the equatorial regions and interior parts of the continents, particularly in the northern hemisphere.
Orographic Rain
The Orographic theory states that clouds are formed as a result of the obstruction to the horizontal movement of the air, such as mountains or high ridges.
The moist winds coming from oceans and sea breeze which contains little amount of atmospheric moisture rise over the ridge and form clouds.
When wind blows over high mountains, it is forced upward due to pressure difference, and the cooler air above the mountain condenses and forms clouds that produce rainfall if it is saturated.
The chief characteristic of this sort of rain is that the windward slopes receive greater rainfall.
After giving rain on the windward side, when these winds reach the other slope, they descend, and their temperature rises. Then their capacity to take in moisture increases and hence, these leeward slopes remain rainless and dry.
The area situated on the leeward side, which gets less rainfall is known as the rain- shadow area. It is also known as the relief rain.