Cloud and Precipitation

Cloud and Precipitation

Cloud is formed when the rising air (convecting air) which contains moisture condenses to form tiny water droplets around a condensation nuclei like dust particles.

For this to happen, the parcel of air must be saturated and the temperature must fall below the dew point.

Various terminology related to types of cloud 

• Cirrus - It means high altitude with feathery appearance
• Alto - It means mid latitude
• Cumulo - It means cotton wool like appearance
• Stratus/Strato - It means different stratified layers
• Nimbus - It means rain bearing

Types of Clouds 

1.   Cirrus Clouds 

• These are thin feather like clouds.
• They are fibrous in appearance with white colour.
• They are found at very high altitude (above 18000 ft).
• They indicate fair weather.

2.   Cirrocumulus clouds 

• They are found in patches of globular masses.
• They have cotton wool like appearance.
• They are found at very high altitude (above 18000 ft)
• They are also known as Mackerel sky.

3.   Cirrostratus clouds 

• These are the layered clouds found at very high altitude with milky appearance.

4.   Altocumulus clouds 

• These are globular masses of cloud (cotton wool like appearance) found at mid altitude (6000-20000 ft).

5.   Altostratus clouds 

• These are layered clouds found in different sheets along the mid altitude.

6.   Stratocumulus clouds 

• These are globular masses of clouds with cotton wool like appearance regularly arranged at low altitude (below 6000 ft).

7.   Stratus clouds 

• These are the low uniform layer of clouds found near to the ground level (below 6000 ft) and produces light drizzle.

8.   Cumulus clouds 

• These are thick cloud with cotton wool like appearance with dome shaped cauliflower top and horizontal base.
• They are formed near to the ground (below 6000 ft).

9.   Cumulonimbus clouds 

• These are over grown cumulus clouds.
• These are dark, heavy and denser with an anvil top.
• They cause heavy showers with thunderstorm and lightning.
• They extends from near to the ground to 50000 ft.

Rainfall

Conditions necessary for precipitation/Rainfall 

1. Evaporation (to add more moisture content to the atmosphere)
2. Mechanism to uplift the moist air (convecting air)
3. Saturation and cooling of air below the dew point.
4. Presence of condensation nuclei like dust particles around which the water droplets can accumulate.

Note - In Artificial cloud formation, scientists spread condensation nuclei artificially which promotes formation of cloud. Most commonly used artificial nuclei is Silver Iodide. This method is also known as Cloud Seeding.

Types of Rainfall 

1.   Convectional Rainfall 

• It occurs in the region of intense heating near to the ground surface causing the air to expand and rise.
• Often it is accompanied by thunderstorm and lightning.
• It is experienced throughout the year in Equatorial region and in summer in other regions.

2.   Orographic Rainfall 

• When warm and moist air is forced to rise across the mountain slope, it cools down the air causing precipitation along the windward side of the mountain.
• However, the leeward side which experiences the descending air, lacks precipitation leading to the formation of rain shadow region.
• Example - Eastern side of Western Ghats experience rain shadow region.

3.   Cyclonic/Frontal Rainfall 

• It occurs along the frontal zone due to the convergence of different types of air masses.
• It is best developed along the polar fronts where the warm air rises above the cold air causing precipitation.

Distribution of Rainfall/Precipitation 

1.   At different latitudes 

• Along the Equatorial zone, highest rainfall above 200 cm per annum is received due to convectional rainfall because of high temperature and high humidity level all throughout the year.
• At Sub-tropical region, minimum rainfall of 25 cm per annum is received due to the development of high pressure belts, subsiding air and offshore winds.
• At Mid-latitude region/Temperate regions, average to above average rainfall between 100-125 cm per annum is received. Rainfall is due to onshore westerlies, interaction of different air masses along the fronts and convection in the summer. Rainfall increases from interior towards the coastal regions.
• At polar regions, low rainfall is received due to very low temperature.

2.   At different locations 

• Oceans receive more rainfall due to moist maritime air mass.
• Coastal regions receive higher rainfall than the interior due to moisture laden onshore winds.

Thunderstorm

• Due to intense heating and strong vertical convection cumulonimbus clouds are formed.
• The rain drops in these clouds move up and down creating electric charges due to friction.
• Gradually, the positive and negative charges accumulates on opposite side of the cloud.
• When both the types of charges are attracted, a flash of light is produced due to exchange of charges which is known as lightning.
• Lightning causes rapid heating of air and the expansion which results in the creation of vacuum. It is filled by the surrounding cold air producing a clap of thunder.

Cloud Burst - Indian Meteorological Department (IMD) defines cloud burst as the rainfall over 10 cm in 1 hour concentrated over a small area of few kilometer.

Process involved in the formation of cloud burst 

1. Rapid convection of highly humid warm air.
2. funneling effect experienced along the steep topography results in the growth of huge cloud without precipitation.
3. After a point raindrops become too heavy for the cloud to hold on and drops together in a quick flash.

Example - Mumbai cloud burst of 2005, Leh cloud burst of 2010 and Kedarnath cloud burst of 2013.

Mountain valley, coastal areas and deserts are more prone to cloud burst.

• Mountain valley - due to funneling effect
• Coastal areas - due to huge moisture content from oceans
• Hot desert - due to very high temperature
• Cold desert - due to low temperature

Tornados - 

• It is a  violently rotating column of air that extends from a thunderstorm to the ground.
• It appears like a funnel descending from a cloud. 
• The wind speed goes upto 400 KM/Hr.
• It is formed when there is a change in windspeed and direction which creates a horizontal spinning effect within a storm cell.
• This effect is tipped vertical by rising air moving up through the thunder clouds.
• It is more prevalent in USA.

Water Spouts - It is the whirling column of air and water and mist. It is similar to the tornadoes but on water surface. They are associated with severe thunderstorm and winds along the water surface.

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Note - This is my Vision IAS Notes (Vision IAS Class Notes) and Ashutosh Pandey Sir's Public Administration Class notes. I've also added some of the information on my own. 

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