- The earth receives almost all of its energy from the sun. The earth in turn radiates back to space the energy received from the sun. As a result, the earth neither warms up nor does it get cooled over a period of time.
- The amount of heat received by different parts of the earth is not the same. This variation causes pressure differences in the atmosphere
- Perihelion and Aphelion determine the insolation. So, The annual insolation received by the earth on 3rd January is slightly more than the amount received on 4th July
Variability of Insolation
The amount and the intensity of insolation vary during a day, in a season and in a year. The factors that cause these variations in insolation are the rotation of earth on its axis
- The angle of inclination of the sun’s rays
- The length of the day
- The transparency of the atmosphere
- The configuration of land in terms of its aspect.
The higher the latitude the less is the angle they make with the surface of the earth resulting in slant sun rays. The area covered by vertical rays is always less than the slant rays. If more area is covered, the energy gets distributed and the net energy received per unit area decreases.
The Passage of Solar Radiation through the Atmosphere
The atmosphere is largely transparent to short wave solar radiation.
Very small-suspended particles in the troposphere scatter visible spectrum both to the space and towards the earth surface. This process adds colour to the sky
The earth after being heated by insolation transmits the heat to the atmospheric layers near to the earth in long wave form. The air in contact with the land gets heated slowly and the upper layers in contact with the lower layers also get heated. This process is called conduction
process of vertical heating of the atmosphere without any contact is known as convection
The transfer of heat through horizontal movement of air is called advection
The earth after being heated itself by short wave radiation, becomes a radiating body and it radiates energy to the atmosphere in long wave form
The atmosphere in turn radiates and transmits heat to the space. Finally the amount of heat received from the sun is returned to space, thereby maintaining constant temperature
Factors Controlling Temperature Distribution
The temperature of air at any place is influenced by
1. The latitude of the place
2. The altitude of the place
3. Distance from the sea
4. The air-mass circulation
5. The presence of warm and cold ocean currents
6. Local aspects
INVERSION OF TEMPERATURE
Normally, temperature decreases with increase in elevation. It is called normal lapse rate. At times, the situations is reversed and the normal lapse rate is inverted. It is called Inversion of temperature
For example, the heat of the day is radiated off during the night, and by early morning hours the earth is cooler than the air above
• Surface inversion promotes stability in the lower layers of the atmosphere. Smoke and dust particles get collected beneath the inversion layer and spread horizontally to fill the lower strata of the atmosphere