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(1) Conventional rainfall
Convectional rainfall
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PTR SCIENCE
★ Moisture
Moisture refers to the water vapour in air. water evaporates from the ocean surface and other water bodies, and forms water vapour. Moisture in the air is known as humidity.
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| Moisture |
Humidity refers to the amount of water vapour present in air at a given temperature. It is related to temperature. If temperature increases, the capacity of air to hold moisture increases the vice-versa. Air is more dance at sea level than in cooler mountains areas.
when the capacity of air to hold moisture is curtailed, the water vapour condenses into minute water droplets. Water droplets join together to form clouds. When this droplets become too heavy to float in the air then they fall on the ground as precipitation. Rainfall is the feeling of water droplets on the ground.
★Types of Rainfall
Rainfall can be categorised into three types of the basis of mechanism.
(i) Conventional rainfall
(ii) Oragraphic rainfall
(iii) Cyclonic rainfall
(1) Conventional rainfall
: Vertical transfer of heat is not as convection process. Hence, when the air above the surface get heated, it rises up and after reaching sufficient height, cools down. Condensation take place and in this way, convectional rainfall occurs.
(2) Orographic rainfall : This is also known as relief rainfall because the rainfall takes place along the mountain slopes. When most wind rises along the slope, due to the vertical ascent the cooling starts and clouds are formed and rainfall take place. The side which faces the wind experiences maximum rainfall and is known as windward side. The side away from the wind is known as leeward side.
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| Orographic or relief rainfall |
Italy mance aur receives very little Moisture.
(3) Cyclonic rainfall : Cyclone is closed circulation of winds with a low pressure centre. As the worm tropical air mass moves towards poles the cold polar air mass moves toward the tropics to take its place. On the way they close with each other. The warm air being lighter overrides the colder and heavier air mass. Due to rise of most air, condensation takes place. The rainfall that takes place is named cyclonic rainfall. It is often accompanied by tunder and lighting.
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| Cyclonic rainfall |
★ Importance of Moisture and Rainfall
• Most of the groundwater comes from rainfall. Plants help preserve water.
• It is important for the survival of plants and animals.
• It is a source of fresh water on the Earth's surface.
• If rainfall is scarce, water scarcity and drought occur.
• it is important for cultivation of crops. Even today, India's cropping pattern is largely dictated by the monsoon (rains).
• While rainfall has many benefits, we need to remember that excess rainfall is a cause of concern as it can cause much destruction through floods, erosion of fertile soil, landsides, and loss of lives and livelihood.
• Rainfall is measured in millimetres and the instrument used to to measure rain in Rain Gauge.
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ATMOSPHERE