Solar radiation / Insolation and its impact - Factors which influence them

 Insolation

• The Sun is the primary and the main source of light and heat in solar system. It radiates heat at all times and in all the directions which is called as solar radiation.
• Solar radiation heats both the atmosphere and the Earth. The rays of the Sun pass through the atmosphere but they do not heat the air as much as they heat the Earth's surface.
• The heat received by the Earth from the Sun is called insolation which comes to the Earth in the form of short waves.
• The atmosphere is more heated by insolation than by radiation. The Earth absorbs a lot of Sun's heat and energy but it reflects much of this heat and energy back to the atmosphere in the form of long waves.

Impact of the heated earth:

• The atmosphere is heated more by heated surface of the Earth which radiates back a large portion of that heat into the atmosphere than the incoming solar radiation. 
• Thus the heated surface of the Earth is more responsible for heating the atmosphere than the incoming solar radiation.
• The heated surface of the Earth warms up the atmosphere about two and a half times more than the solar radiation in a ratio of 34 : 14.

The atmosphere gets heated by both these methods, i.e..

• incoming solar radiation and
• insolation on the heat radiated back by the Earth in the atmosphere.

How air circulates in the atmosphere?

• The heating of the atmosphere by radiation and isolation makes it very dynamic. The air near the Earth, when it gets heated expands, becomes lighter and begins to rise.
• The cool air comes down to take its place. All this results in the circulation of air in the atmosphere. This is' called the cyclic circulation of the air

 What are the factors that influence  insolation?

The amount of solar radiation or the variation in temperature depends on two things -

• the angle of the Sun's rays
• Seasons
• the duration of the Sun's light

Angle of the Sun's rays: When the rays of the Sun fall vertically on the Earth, they give more heat because they travel through a small distance and concentrate over a small area. They give less heat when they strike the Earth obliquely because they travel a long distance and cover a larger area. That is why noon is hotter than either the morning or the evening.

Seasons: Summers are hotter than winters because in summer the Sun's rays strike the Earth vertically and the days are longer.

Duration of the daylight. The longer the day the hotter it is and the smaller the day the colder it is. Summers are hot because the days are long. Winters are cold because the days are short. When the days are long more insolation is received and the days become hot. When the days are short less insolation is received and the days become cold.
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