Precipitation- Types of Rainfall

Precipitation- Types of Rainfall


Precipitations any form of solid or liquid water that falls from the atmosphere to the earth's surface. Rain, drizzle, hail, and snow are examples of precipitation. In the India, rain is the most common form of precipitation, and then others most common.

Precipitation is formed from water vapor in the atmosphere. As the air in the atmosphere cools, its capacity to hold water decreases. When air's capacity to hold water is reached, it is said to be saturated. For example, at 70°F, given volume of saturated air contains nearly four times the water vapor that it contains at 32 of. The figure shows the relationship between air temperature and the amount of water contain ed at saturation. Moist, unsaturated air can become saturated a sit cools. Continued cooling beyond saturation will cause the transition or condensation of some water vapor in the air into a liquid or solid water. The condensation process can be seen when droplets of water form on the outside of a glass of a cold beverage because the moist air next to the glass has cooled below the temperature of saturation or dew point.

If all the atmospheric water were precipitated at one time, it would result in an average depth of the only 1inch of water on the earth's surface. However, a one-hour storm has resulted in water depths in excess of 4inches overland areas of a few square miles. Such local storms result from the lateral flow of moist air from surrounding areas to the storm center.

A meteorologist generally concerned with the flow of moist air masses from their sources (lakes, oceans, and transpiration from land areas) and their associated effects on precipitation and temperature. A hydrologist considers such phenomena in relation to water supplies and movement to, on, and beneath the earth's surface. Hydrologists usually become involved in meteorology in the planning, study, and evaluation of the interaction between the climate, surface water, and subsurface water.

The atmosphere around the earth is a dynamic system of air masses in constant motion and collision. The weather system is driven by solar energy from the sun.

Generally, daytime radiation is absorbed nearer the earth's tropics, and radiant energy losses occur mainly during nighttime hours and from the earth's Polar Regions. These energy gain sand losses result in keeping dynamic air masses in constant motion, continually exchanging water vapor with the land, vegetation, and water on the earth's surface. The movement and collision of air masses lead to atmospheric instability, often resulting in precipitation.

There is always some water vapor in the air, and there is always some condensation occurring in the atmosphere, even on the fairest of days. Clouds may become posted of water vapor, water droplets and/or ice crystals. The precipitation process begins by the condensation of water molecules on precipitation nuclei such as smoke, dust, or sea salt particles. As clouds cool, a number of condensed water increases. Precipitation begins when the air is cooled, increasing cloud formation, and the condensed water droplets or ice crystals reach a size that causes them to fall toward the earth's surface. Some of these droplets will collect additional condensed water vapor as they fall. Others may evaporate and return to the atmosphere.

In the atmosphere, the cooling of the air is mainly caused by lifting the air mass. At higher elevations, atmospheric pressure and temperature are lower. Both the reduced pressure and lower temperature reduce the temperature of the rising air mass. Air may be lifted by three processes. There are mainly three types of rainfall-

1. Frontal
Precipitation occurs when a warm or light air mass meets a cold or heavy air mass, and the lighter air rides up over the heavier air. The zone where the two air masses meet is commonly called a front, and the resulting precipitation is frontal. Frontal precipitation is the dominant type of precipitation in the north east India or Gangetic plain regions. And other continental areas.

2. Convective
Air expands when heated by solar energy and becomes lighter than the air around it. The lighter air rises by convection, causing convective precipitation. In humid climates, convective precipitation frequently occurs on hot mid-summer days in the form of late afternoon thunderstorms. Convective precipitation also results from the movement of air into a low-pressure atmospheric system. Air at the center of the low-pressure region rises, causing surface air to flow to the center. As the air rises, it can cool until it reaches saturation. Severe storms of rain and hail may follow.

3. Orographic
Air currents force air masses to rise over hills or mountains. Precipitation that results from this process is called orographic precipitation. This is the dominant source of precipitation in the mountains in the western India and contributes to precipitation in most mountainous areas.

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