Having completed the last session about weather and climate, today’s 5th geography session started by briefing the class on the topic “INSOLATION”
- The Earth’s surface receives most of its energy from
the sun, in short wavelengths(E=1/λ) and this energy is
termed as INSOLATION-Incoming Solar Radiation.
- The Earth receives a certain amount of Insolation (short waves) and gives back heat into space by terrestrial radiation (longwave terrestrial radiation).
- During the Earth’s revolution around the sun, the Earth is farthest from the sun on 4th July- aphelion. The Earth is nearest to the sun on 3rd January-perihelion.
MAJOR FACTORS AFFECTING VARIABILITY OF INSOLATION AT EARTH’S SURFACE:
- Rotation of the Earth
- The Earth’s axis makes an angle of 66° with the plane of its orbit round the sun.
- The rotation of the Earth on this inclined axis has a greater influence on the amount of insolation at different latitudes.
- Angle of Inclination
- Depends on the latitude of the place.
- The area covered by the vertical rays is always less than the slant rays
- Nature of slope
- Slopes more exposed to the sun receive more solar radiation.
- Slopes that are devoid of direct sunlight are usually well forested.
- Transparency of the atmosphere
- Depends upon the cloud cover and its thickness.
- Thick cloud hinders the solar radiation to reach the Earth’s surface.
- Sun spots
- In a fluctuating 11-year solar cycle, sunspots diminish the amount of insolation reaching the Earth’s surface.
HEATING AND COOLING OF
ATMOSPHERE:
The incoming solar radiation gets distributed throughout the Earth’s surface by different processes of heating and cooling of the atmosphere:
- Radiation
- The Earth after being insolated transmits heat to the atmospheric layers in the form of longwave terrestrial radiation.
- It heats up from bottom of the Earth’s surface towards the upper atmosphere.
- Conduction
- Heat transfer from a warmer body to a cooler body.
- The air in contact with the land gets heated slowly, becomes less dense and moves to troposphere.
- Convection
- Process of vertical heating.
- The air which is in contact with the Earth’s surface raises vertically on heating.
- Advection
- Transfer of heat through horizontal movement of air(wind).
- Temperature of a place will rise if it lies in the path of winds coming from warmer regions
When Earth keeps receiving the insolation, it cannot accumulate or lose heat as a whole. This will harm the survival of living beings. Hence, a conducive temperature is maintained.
- Amount of heat received in form of insolation = Amount of
heat lost by Earth through terrestrial radiation.
- This balance between the insolation and outgoing terrestrial radiation- heat budget or heat balance of the Earth.
- If this heat budget is not balanced, Earth’s temperature will increase it’ll cause ice caps and glaciers to melt.
- As a result, sea level will rise and coastal countries will submerge.
VERTICAL HEAT BUDGET:
- Isolation received at the top of the atmosphere – 100%
- 35 units - return
back to space before reaching Earth’s surface.
27 units - reflected
back from the top of the clouds
2 units -
reflected from the snow and ice-covered areas of the earth. The reflected
amount of radiation is called the “Albedo of the Earth”.
6 units - scattered back to space.
- 65 units - are absorbed.
14 units - absorbed within atmosphere.
51 units - in the form of terrestrial radiation
(17 units
radiated to space)
- Thus, the total radiation returning from the Earth and the atmosphere balance the total of 65 units received from the sun.
HORIZONTAL HEAT BUDGET (Latitudinal variation):
- Tropical regions, amount of insolation is higher than the amount of terrestrial radiation-region of surplus heat.
- Polar Regions have a deficit heat.
- Thus, the insolation creates an imbalance of heat at different latitudes.
- Surplus heat energy from tropics – redistributed pole wards to nullify this imbalance (by winds and ocean currents).
We saw a glimpse of the topic – Temperature.
The temperature is the measurement in degrees of how hot (or cold) a thing (or a place) is.
FACTORS CONTROLLING TEMPERATURE DISTRIBUTION:
- LATITUDE
- Insolation differs according to the latitude. Therefore, the temperature also differs consequently.
- Angle of incidence of sun’s rays decreases from the equator towards the poles.
- Hence, temperature is higher near the tropical regions and decreases towards the polar regions.
- ALTITUDE
- Temperature decreases with increasing height- Normal Lapse Rate 6.5 °C per kilometre
- Example – weather of Bangalore (Karnataka plateau) is cooler than Chennai as its altitude is 1km above the sea level.
- DISTANCE FROM THE SEA
- Compared to land, sea heats up and loses heat slowly.
- The places situated near the sea come under the moderating influence of the sea
- Example- Since Delhi is away from the sea, it has heat waves during the summer and stubble burning during winter (extreme climate).
- Whereas Chennai is near the sea coast, so it’s moderate and humid.
- OCEAN CURRENTS AND AIR MASSES
- Places under the effect of warm air masses have higher temperature.
- Places located on the coast where the warm ocean currents flow record higher temperature
- LOCAL ASPECTS
- Temperature variations in densely forested areas are lower than those in desert areas.
- A steep slope experiences a more rapid change in temperature.
- Natural vegetation and soil affect temperature.
Credits: Leo Praneetha
