Geography · Ch 16 — Water in the Atmosphere
Types of Rainfall
Types of Rainfall
Rainfall is classified by its origin into three main types: convectional, orographic (or relief), and cyclonic (or frontal). Each arises from a different mechanism that lifts air, cools it, and triggers condensation.
Convectional Rain
When the ground is heated, the air in contact with it becomes warm and light, and rises in convection currents. As this air climbs, it expands because pressure decreases with height, and expansion causes it to lose heat. This cooling leads to condensation, and cumulus clouds form. The result is heavy rainfall accompanied by thunder and lightning, but the downpour does not last long.
This type of rain is typical of summer, or of the hotter part of the day, when surface heating is strongest. It is very common in the equatorial regions and in the interior parts of continents, particularly in the northern hemisphere.
Orographic Rain
When a saturated air mass encounters a mountain, it is forced to ascend. As it rises, it expands, its temperature falls, and its moisture condenses. The chief characteristic of this rain is that the windward slopes — the side facing the wind — receive greater rainfall. …
On the basis of origin, rainfall may be classified into three main types -- the convectional, orographic or relief, and the cyclonic or frontal.
Convectional 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 cumulus 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. …