TYPE OF PRECIPITATION 

Precipitation occurs when the moist air mass undergoes condensation. This process happens when the air is cooled and saturated with the same amount of moisture. This process of cooling air mass is performed only when the air mass moves up to higher altitudes. The air mass can be lifted to higher altitudes mainly by three methods based on which there are three types of precipitation namely:. Convective precipitation is generally more intense, and of shorter duration, than stratiform precipitation. Orographic precipitation occurs when moist air is forced upwards over rising terrain and condenses on the slope, such as a mountain.

Convective Precipitation

The air above the land area gets heated up by some cause. The most warmer air rises up and cools and precipitates. Convective precipitation is showery in nature. This type of precipitation happens in varying intensities. The areal extent of convective precipitation is small in the range of less than 10km in diameter.

Convection is air that has been warmed from below, rising upwards. The “rising” bit is important: air can also be warmed by touching warm land or sea, but if that transfer of heat just makes the air warmer - without lifting it - that's called conduction, not convection.

The heat comes from the surface, so as the warm air rises (“convects”), it becomes cooler. If it cools enough, the water vapour in the air becomes liquid water - drizzle or rain drops. Now a different type of heat called “latent heat” kicks in and drives the cloud upwards into towers. Hence, convective clouds are generally much taller than they are broader. “The towers provide the showers”!

Convective precipitation is always showers, but sometimes convective clouds merge to give longer spells of precipitation. So if someone mentions a “shower” they usually mean precipitation lasting less than an hour. “prolonged showers” can mean the precipitation will last more than an hour.

“Rain” or “prolonged rain” falls from flat-looking “layer” cloud. Because these clouds are flat, they can cover a very wide area, so “Rain” can last all day/several days sometimes.

There are 2 types of convective cloud: the most common type is called Cumulus, but the tallest and most dangerous type are called Cumulonimbus and these bring the thunderstorms and showers of hailstones.

Orographic Precipitation

Moving air masses have chances to strike barriers like mountains. Once they strike, they rise up which causes condensation and precipitation. The precipitation is greater in the windward side of the barrier compared to the leeward side of the barrier.

Orographic rainfall occurs in the mountainous regions near the coastal lines in general. Conditions favoring orographic rainfall in India is seen only over the Western ghats during monsoon period. Monsoon winds from Arabian sea gets blocked by Western ghats and gets lifted over the ranges and precipitates leaving dry winds to blow over Peninsular India.

Orographic rainfall results in heavier rainfall along the western side of Western ghats leading to more than 250cm rainfall per year..

Similarly Himalayas blocks the monsoon winds and precipitates rain over the ranges of Himalayas. Cherrapunji and Mawsynram are the wettest place in the world due to its location in the windward side of Himalayas and Tibet remains dry being in the leeward side.

During winter, Western Himalayas block the warm moist air from Mediterranean sea and results in orographic precipitation. This results in snow over the higher reaches of Himalayas in Himachal and Jammu and Kashmir.

Cyclonic Precipitation

A cyclone is a region in the atmosphere with large low pressure having circular wind motion. The cyclonic precipitation is caused by the movement of moist air mass to this region due to the difference in pressure. Cyclones can be of two types frontal and non-frontal precipitation.

a. Frontal

It is the hot moist air mass boundary that occurs due to the expansion of air near the frontal surface.

b. Non-Frontal

It is a cold air mass boundary that occurs due to the movement of the cold mass of moist air that results in precipitation.