TEMPERATURE
Introduction
The energy received by the earth from the solar radiation is called Insolation.
Later earth also radiates the energy. It is called terrestrial radiation which is absorbed by the atmosphere.
The amount of heat that atmosphere has absorbed is called Temperature.
The amount of isolation varies from one place to another. It is because of the angle of sun rays, the amount of air the solar rays pass, the duration of day and the distance between the earth and the sun.
Heating and Cooling of Atmosphere
Our Atmosphere do not get its temperature directly by the short waves of the sun but through the long waves of the earth.
The atmosphere is transparent to the solar radiation which is in the form of short waves. It allows them to reach the earth. But it is non-transparent to the radiation of the earth which is in the form of long rays.
The four processes of heating and cooling of the atmosphere are radiation, conduction convection and advection.
I. Radiation
Radiation is the process of heating an object by the transmission of heat waves.
The Earth’s surface gets temperature through solar radiation.
It radiates energy in the form of long waves which are absorbed by the atmosphere.
2. Conduction
It is a process by which heat is transferred directly through matter from point of high temperature.
Heat passes from warmer to colder substances, as long as temperature difference exists.
3. Convection
The transmission of heat from one part of a liquid or gas to another by the movement of particles themselves is called convection.
It is the upward movement of a mobile medium like air or water, which has been heated by contact with the earth’s surface.
Air is therefore, said to rise in a convection current.
4. Advection
The transfer of heat through horizontal movement of air is called advection.
These winds take the characteristics of their source of origin with them.
The temperature of a place will rise if it lies on the path of winds coming from warmer regions.
The temperature will fall if the place lies on the path of the winds blowing from cold regions.
The horizontal movement of the air is relatively more important than the vertical movement.
Factors affecting the distribution of Temperature
Normally the temperature distribution is recorded horizontally and vertically. Horizontal distribution of temperature is determined by latitude.
The general decline in temperature from the equator towards the poles is one of the most fundamental and best-known facts.
The horizontal distribution of temperature is the function of numerous other physical factors.
They are: Latitude, Altitude, Distance from the Sea, Ocean currents, Wind, Clouds & Rainfall, the slope of the land, Vegetation and Nature of the Soil.
STRUCTURE OF ATMOSPHERE:
1. Latitude
Places close to the equator have higher temperature and are warmer than places away from the equator.
This is because the Sun rays reach the Earth after passing through the layers of the atmosphere.
In the low latitudes, the Sun rays are direct and have to travel to a lesser extent through the atmosphere.
Hence, the heat of these rays is more intense. But in high latitudes, the Sun rays are slanting and have to pass through a greater extent of the atmosphere.
These rays lose heat and so the areas in the high latitudes are not very hot as compared to the equatorial regions.
2. Altitude
The height of a place above the mean sea level is the altitude of that place.
The atmosphere is mostly heated by various heat processes.
Air is cooler at higher altitudes than near the Earth’s surface. So the places near the Earth’s surface are warmer than places higher up.
This is because air near the surface is denser and contains gases like carbon dioxide, water vapour and other gases.
So their capacity of heat absorption is more than in the upper layers.
Temperature decreases with an increase in height at an average rate of 1ºC/165 m or 6.4ºC/1000 m.
Sometimes temperature increases with the increase in height known as ‘Inversion of Temperature’.
This feature is common during winter season, less cloudiness, slow movement of winds, clear sky in the mountain valley.
3. Distance from the Sea
This factor also influences on the distribution of temperature and differential heating of land and water.
Land gets heated faster compared to water. Water takes a longer time to get heated and to cool than land.
Hence during the day when the land gets heated quickly, water takes a longer time and remains cool.
Therefore, during the day time land gets more heat than the surrounding water bodies (sea and ocean). The coastal areas are cooler and wetter than the inland areas.
4. Ocean currents
Ocean currents increase or decrease the temperature of the Earth’s surface.
Warm ocean currents along the coast make the coastal areas warmer and cold currents reduce the temperature and cool the coastal areas.
Warm currents can be noticed on the eastern margins of the continents in the middle latitude, while it is cold currents flow at the western margins of the continents.
5. Winds
Winds that blow from the lower latitudes are warm and make the places warmer.
On the other hand, winds that blow from the higher latitudes are cold and make the places cooler.
Winds that blow from the sea bring plenty of rain especially if they are warm winds. While off shore winds hardly bring any rain.
6. Clouds
During the day clouds prevent Insolation from reaching the Earth’s surface.
Clouds also prevent the escape of terrestrial radiation during the night.
Clear sky permits Insolation readily during the day time and allow the rapid escape of terrestrial radiation during the night.
7. Slope, Shelter and aspect
Slopes of a mountain facing the Sun experiences high temperature than the slopes on the leeward side due to more insolation.
A steep slope experiences a more rapid change in temperature than a gentle one.
Mountain ranges that have an east-west alignment like the Alps show a higher temperature on the south-facing ‘sunny slope’ than the north facing ‘sheltered slope’.
Consequently, there are more settlements in southern side and it is better utilized for agricultural and other purposes.
Did You Know?
Isotherms: lines drawn on a map or chart joining points with the same temperature.
Temperature Zones or Heat Zones
The temperature generally decreases as one proceeds from the equator towards the poles. As such, different temperature zones are found on the Earth. They are
- Torrid Zone,
- Temperate Zone
- Frigid Zone.
Torrid Zone
This region receives direct Sun rays throughout the year.
It lies between 0º Equator to 23 ½º N/S latitudes.
The three important latitudes that come under this zone are Equator, Tropic of Cancer and Tropic of Capricorn.
The shape of the Earth, direct sun’s rays make this area always hot with high temperature called ‘Torrid Zone’.
This belt is also known as ‘Tropical Zone’.
Temperate zone
This region lies between 23 ½º N/S to 66 ½º N/S.
It is spread over between Tropic of Cancer to Arctic circle in the Northern Hemisphere and Tropic of Capricorn to Antarctic circle in the Southern Hemisphere.
This zone receives oblique sun rays due to the shape of the Earth, inclination and revolution of the Earth. Therefore, this area neither records high temperature nor low temperature.
The temperature is more or less uniform. Hence this belt is called ‘Temperate Zone’.
Frigid zone
This region receives oblique sun rays for more than 8 to 9 months.
The shape of the Earth and oblique sun rays for a long period form very low temperature with freezing weather conditions in this zone, called ‘Frigid Zone’ or ‘Polar Zone’.
This zone lies between 66 ½º N/S to 90º N/S.
There are two frigid zones
- North frigid zone (66 ½º N to 90º N)
- South frigid zone ( 66 ½º S to 90º S).