Air

Atmosphere is the thick blanket of air that surrounds the surface of the earth. It is divided into different layers.

(a) Troposphere: It is the first layer of the atmosphere that is just above the surface of the earth. The air that we breathe is present in this layer. This supports life on the earth.

(b) Stratosphere: Above the troposphere lies the stratosphere. It extends up to a height of 50 km. The ozone layer is present in this layer. Airplanes fly in this layer.

(c) Mesosphere: This is the third layer of the atmosphere. It lies above the stratosphere. It extends up to the height of 80 km. Meteorites burn up in this layer on entering from the space.

(d) Thermosphere: In thermosphere temperature rises very rapidly with increasing height. Ionosphere is a part of this. This layer helps in radio transmission.

(e) Exosphere: The upper most layer of the atmosphere is known as exosphere. This layer has very thin air.

(a) Nitrogen. It occupies about 78% of the air around us.

(b) Oxygen. It occupies about 21% of the air around us.

Carbon dioxide. Carbon dioxide, along with other gases such as methane and carbon monoxide, is one of the major contributor in causing the greenhouse effect.

Weather includes the atmospheric conditions that change hour-to-hour. Weather of a place keep changing day-to-day and even hour-to-hour. A record of these atmospheric conditions over a long period of time determines the climate of that place.

(i) The convectional rainfall: when water vapors rise up, they reach high above the surface of the earth and cool down to form clouds. When clouds cannot hold any more water, they fall down as rainfall.

(ii) The Orographic rainfall: It occurs when the moist air rises up the mountain, forms the orographic clouds and falls as rainfall.

(iii) The Cyclonic rainfall: It occurs when the cyclonic winds of different temperature, humidity densities meet.

The air that is present around us exerts pressure on almost everything. This is called air pressure or atmospheric pressure. The air pressure decreases as we go up in the air. This is why mountaineers face difficulty in breathing and sometimes their nose bleeds because pressure of blood inside the veins becomes more than the air pressure.

It is the layer that prevent harmful ultraviolet rays from reaching the surface of the earth.

It is the most important layer of the atmosphere because it is the only layers that supports life.

This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes.

As we go up the atmosphere the air pressure decreases. The air pressure is highest at sea level and decreases with height.

The water vapor condenses when they reach high up in the air and forms cloud. The clouds are just masses of such water droplets. When these droplets of water become too heavy to float in air, then they come down as precipitation or rain.

(i)Trade winds (c) Permanent wind

These winds blow constantly throughout the year in a particular direction.

(ii) Loo (d) Local wind

These blow only during a particular period of the day or year in a small area.

(iii) Monsoon (a) Seasonal

The monsoon winds carry clouds that cause rains in the monsoon season. This is why monsoon winds are seasonal winds.

(iv) Wind (b) Horizontal movement of air

When the air moves horizontally from high pressure to low pressure, winds blow.

On a humid day, the air already contains a lot of moisture or water vapours in it. This is why wet clothes take longer time to dry as very less water evaporates from them.

Insolation is the incoming solar energy intercepted by the earth. The amount of insolation decreases from the equator towards the poles. It happens as the sunrays fall slanting on the poles while they fall straight at the equator.

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