CHAPTER-8 Process of precipitation, Types of precipitation- rain, snow, sleet, and hail, Cloud formation, Classification of cloud, Artificial rain making, Monsoon mechanism, Monsoon importance in Indian agriculture PRECIPITATION Precipitation is any form of liquid or solid water particles that fall from the atmosphere and reach the surface of the Earth. PROCESS OF PRECIPITATION Precipitation only comes down to the ground after it condenses in the atmosphere. Condensation is when water vapor turns to liquid water. We are surrounded by water vapor - it's an important component of the atmosphere. But if it changes back into liquid water and builds up around dust particles in the air, we get clouds. If the cloud droplets get heavy enough, they fall back to the ground for the very same reason you would – gravity. TYPES OF PRECIPITATION 1. RAIN It’s a type of liquid precipitation and seen as drops of liquid water falling from the sky. 2.SNOW Snow forms when tiny ice crystals in clouds stick together to become snowflakes. If enough crystals stick together, they'll become heavy enough to fall to the ground. 3. SLEET Simultaneous precipitation of the mixture of rain and snow is called as sleet. It is known as true frozen rain. 4. HAIL Hail is a precipitation of solid ice on a warm sunny day .A strong convective current may cause the formation of hails .Hails fall from cumulo-nimbus clouds and are often associated with thunderstorm and heavy rains. Rainfall associated with the hailstones is called as hailstorm. CLOUD FORMATION Clouds form when the invisible water vapour in the air condenses into visible water droplets or ice crystals. There is water around us all the time in the form of tiny gas particles, also known as water vapour. There are also tiny particles floating around in the air - such as salt and dust - these are called aerosols. The water vapour and the aerosols are constantly bumping into each other. When the air is cooled, some of the water vapour sticks to the aerosols when they collide - this is condensation. Eventually, bigger water droplets form around the aerosol particles, and these water droplets start sticking together with other droplets, forming clouds. CLASSIFICATION TYPE NAME HEIGHT High Clouds Cirrus,Cirrostratus,Cirrocumulus 5-13 Km Middle clouds Altostratus, Altocumulus, Nimostratus 2-7 Km Low clouds Stratus, stratocumulus 0-2 Km Vertical cloud Cumulus, cumulonimbus 0-5 km Cirrus It is the highest of all clouds .It has a typical fibrous structure and a delicate silky appeareance. Cirro-stratus It is thin, whitish sheet of cloud ,covering the whole sky and giving it milky or web like fibre appearance. Cirro-cumulus It develops from cirro stratus and consists of small white flakes of clouds in the form of globules. Alto-stratus It is a dense sheet of gray-coloured cloud, often showing a fibrous structure. These are generally, rain clouds and produce steady and continuous rain. Alto-cumulus It differs from cirro-cumulus only in the fact that it contains larger globules than the taller cloud. This develops from dissolving alto-stratus. Strato-cumulus It is a cold layer with large lumpy masses or dull grey colour with bright intensities. It occurs during rainy weather in monsoon. Nimbo-stratus It is dense, shapeless and ragged layer which causes steady and continuous rain during monsoon. Cumulus It is a very thick cloud having dome-shaped upper surface that resembles a cauliflower, its base is horizontal. Flat and towering cumulus with instability and turbulence developing into cumulo nimbus are also present. Cumulo-nimbus It is also known as thunder clouds rise like mountain towers. Their base is like a ragged mass of nimbo-stratus while their tops are, generally, surrounded by false cirrus. Stratus It is a uniform layer of cloud like fog nearest to the surface of earth. This usually occurs in the vicinity of monsoon depressions. ARTIFICIAL RAINMAKING Rainmaking, also known as artificial precipitation, artificial rainfall and pluviculture, is the act of attempting to artificially induce or increase precipitation, usually to stave off drought. According to the clouds' different physical properties, this can be done using airplanes or rockets to sow to the clouds with catalysts such as dry ice, silver iodide and salt powder, to make clouds rain or increase precipitation, to remove or mitigate farmland drought, to increase reservoir irrigation water or water supply capacity, or to increase water levels for power generation. MECHANISM OF MONSOON As a consequence of high temperature over the Tropic of cancer, the region develops low pressure. The winds from high pressure water-belts such as Bay of Bengal, Arabian sea and Indian ocean, starts moving towards the low-pressure belts. They shift their direction while crossing the equator and start blowing from the south-west direction. The wind gets moistened while passing along these seas. This moisture-laden wind causes heavy rainfall across the various places in India. South West Monsoon wind direction: During South West Monsoon period of June to September, the westerly winds prevail on the west of Kerala and south winds on the west of northern Circars, Orissa and Bengal. During April and May the region of high temperature is shifted to north viz., upper Sind, lower Punjab and Western Rajasthan. This area becomes the minimum barometric pressure area to which monsoon winds are directed. North East Monsoon wind direction: During North East Monsoon period of October to December, on account of the increase in barometric pressure in Northern India, there is a shift in the barometric pressure to the South East and North Easterly winds begin to flow on the eastern coast, by the end of September. These changes bring on heavy and continue rainfall to the Southern and South Eastern India. IMPORTANCE OF MONSOON IN INDIAN AGRICULTURE In India, Monsoon refers to the rainy season. The humid south-west monsoon winds cause plenty of rainfall during the period between early June and October. A large portion of Indian farmers still depends upon rain-fall to carry out the agricultural activities. Since, agriculture is one of the most important constituent on Indian economy (contributing around 16 percent of its total GDP), monsoon season has an indirect impact on its economy as well. India has a tropical monsoon type of climate. So here the temperature in the summer months is high and the rainfall is heavy. High temperature and heavy rainfall in the summer months are important for the growth of different types of kharif crops in different parts of India. Unlike other countries in high latitudes, India enjoys long hours of sunshine even during the winter months. So with winter precipitation (supplemented by irrigation) a second rabi crop is easily grown. The amount of rainfall is the most important determinant of the type of crop raised. Wet crops are raised in wet zone and dry crops in the dry zone. Crops like rice, jute, sugarcane, etc. require high temperature and heavy rainfall for their cultivation. So these crops are cultivated in summer. Crops like wheat, barley etc. require moderate temperature and rainfall. So these are cultivated in winter. Rubber trees require uniformly high temperature and regular rainfall all the year round. In the southern parts of the Deccan, the temperature is fairly high all the year round and the rainfall is well-distributed over 6 to 8 months. So rubber is grown in the southern parts of the Deccan. A large number of farmers depend upon monsoon-rains to meet the food requirement of their family. They engage in agricultural activities not to sell the crops, but for their own needs. Normal rainfall is essential for adequate agricultural output. In a large country like India, it is essential to maintain the food prices. Food inflation may destabilize the entire nation. The food prices depend upon the agricultural output. .