Chapter - 9
Solar radiation, heat balance and temperature
️ Solar radiation :-
The main source of energy on the Earth's surface is the Sun. The Sun is a very hot, gaseous mass . Its surface temperature is 6000 ° C. This gaseous body constantly radiates heat around the space, which is called solar radiation .
️ Albedo Albedo :-
27 units of solar radiation coming from the Sun is reflected from the upper ends of the clouds and 2 units are reflected back by the snow - covered regions of the Earth . This reflected amount of solar radiation is called the Earth's albedo . This reflected quantity is in the form of 49 units .
️ Solar constant :-
Earth receives an average of 1.94 calories / per square centimeter of energy per minute on the upper surface of the atmosphere. This is called the solar constant.
️ Calories :-
The heat used to raise the temperature of one gram of water by one degree Celsius is called a calorie .
️ Planck's law :-
Planck's law states that the hotter an object is, the more energy it radiates and the shorter its wavelength.
️ Specific heat :-
The amount of heat required to raise the temperature of one gram of a substance by one degree is called specific heat.
️ Isotherms :-
Imaginary lines drawn on a weather map that join places of equal temperature. They are called isotherms.
️ Apsour Aphelion :-
During the revolution around the Sun, the Earth is farthest from the Sun on 4th July i.e. 15 crore 20 lakh kilometers. This position of the earth is called Perihelion.
( Perihelion ) :-
On January 3, the Earth is closest to the Sun, that is, 140 million 70 lakh kilometers away. This condition is called subsolar.
️ Insolation :-
The energy received by the Earth from the Sun is called insolation or incoming solar radiation. It comes to Earth in the form of short wavelengths.
️ Clear insolation and temperature difference :-
Generally, insolation and temperature are considered as synonyms, but these two words have different meanings:
Insolation :-
- Insolation is heat that produces heat.
- This is the energy the earth receives from the sun. Insolation is measured in calories.
- This is 1.94 calories/sq.cm. per minute. Heat is the only reason.
- When a substance is given heat, its temperature increases.
Temperature :-
- Temperature is the measure of heat produced by heat.
- Temperature is measured by thermometer in degrees Celsius, Kelvin, Fahrenheit.
- Temperature is the effect of heat.
- The temperature increases with the heat.
️ Factors affecting insolation :-
The inclination of the Sun's rays: - Due to the shape of the Earth being spherical, their inclination is different when the Sun's rays fall on the surface of the Earth. Vertical rays fall on a small area. That's why she heats this region more. As the angle of inclination of the rays decreases. By the way, the area increases and that part gets less hot.
Effect of Atmosphere on Insolation:- The changing conditions like clouds, humidity and dust particles in the atmosphere absorb, reflect and scatter the insolation coming from the Sun. Due to which there is a change in the insolation reaching the earth.
Effect of land and water: - Due to the effect of the sun's rays, the terrestrial surface heats up more quickly while the water surface heats up slowly and less.
Length of day or duration of sunshine :- The amount of insolation received at a place depends on the length of day or duration of sunshine. In summer the days are longer and the insolation is more. In contrast, in winter the days are shorter and insolation is less.
Slope of the land: - If there is a slope facing the sun, more insolation is received. Whereas when the slope is opposite, less insolation is received.
Earth 's distance from the Sun: - On January 3, the Earth is closest to the Sun, while on July 4 it is farthest. Therefore, the insolation is also less and more in the same way.
️ Ways of heating and cooling of the earth :-
Conduction :- When two bodies of unequal temperature come in contact with each other. Energy flows from the hot body to the cold body until the temperature of both the bodies becomes equal.
Convection :- By the process of convection, there is a gradual transfer of heat vertically in the atmosphere. This process takes place in gaseous and liquid substances. This process does not happen in solids. The transfer of heat from one part of a gaseous or liquid substance to another by its molecules is called convection.
Convection :- In this process heat is transferred in horizontal direction. The variations in weather in mid-latitudes are due to convection. Ocean currents driven by wind also transmit heat from the tropics to the polar regions. This process occurs in solid, gaseous and liquid substances.
️ Terrestrial Radiation :-
Solar radiation heats the earth's surface in the form of short waves. After heating the earth itself, it starts radiating energy in the form of long waves in the atmosphere. Which is called terrestrial radiation.
How is terrestrial radiation beneficial?
This process heats the atmosphere. Atmospheric gases (green house gases) absorb long waves and indirectly heat the atmosphere. After that gradually this heat is transmitted into space. The earth cools down during the night if the sky is clear.
️ Factors affecting the distribution of temperature on the surface of the earth :-
Heat refers to the movement of molecules in the particles of a substance, the same temperature refers to the heating or cooling of a substance or place, which is measured in degrees. The air temperature at any place is affected by the following factors:
Latitude :- The temperature of any place depends on the insolation received by that place. The amount of insolation varies according to latitude.
Altitude : - The atmosphere is heated from bottom to top by terrestrial radiation. This is the reason that the temperature is higher at the places near the sea level and the temperature is lower at the places located in the higher part.
Distance from sea :- Another important factor affecting the temperature of any place is the distance of that place from the sea. The sea gradually warms and cools slowly as compared to the land. There is a general effect of sea and land breeze on the areas located near the sea.
Air Masses and Oceanic Currents :- Air zodiac also affects the temperature. The temperature of places affected by warm air masses is high and the temperature of places affected by cold air masses is low. Similarly, ocean currents also have an effect on temperature.
️ Temperature Inversion :-
The lowest layer of the atmosphere, the troposphere, which is adjacent to the Earth's surface, decreases with altitude under normal conditions. But in some special circumstances the temperature increases with altitude instead of decreasing. The increase in temperature with altitude is called inversion. It is clear that in the inversion of temperature there is cold air near the surface and warm air above.
️ Geographical conditions required for reversal :-
The following geographical conditions are helpful for the inversion of temperature:-
Long nights:- The earth acquires heat during the day and gives off heat during the night. The earth cools down due to the release of heat during the night. And the air around the earth also becomes cold and the air above it is relatively warm.
Clear sky:- It is very necessary to have a clean or cloudless sky for the cooling of the earth by terrestrial radiation, clouds obstruct the radiation and prevent the earth and its surrounding air from cooling down.
Calm air: - Due to the movement of air, there is an exchange of heat between adjacent areas. Due to which the air below does not cool down and the reversal of temperature does not happen.
Dry air:- Dry air has more capacity to absorb heat. Due to which there is no change in the rate of decline of temperature. But dry air cannot absorb ground radiation. Therefore, cooling creates a situation of inversion of temperature.
Snow cover: Snow reflects most of the solar radiation. Due to which the lower layer of air remains cool and inversion of temperature occurs. Inversions occur throughout the year in regions.
️ Normal Decreasing Rate of Temperature :-
With increasing altitude, the temperature goes down. 1000 m. There is a decrease in temperature by 6.5 ° C at altitude. This is called the normal rate of decline of temperature.
The description of the Earth's heat budget in detail :-
The upper surface of the atmosphere receives 100 units of insolation. Its details are as follows:-
Radiation of insolation :-
The reflected amount of solar radiation is called albedo.
- 1. 16% is absorbed by dust particles and vapor particles.
- 2. 3% is absorbed by clouds.
- 3. 6% gets reflected by air.
- 4. 20% gets reflected by clouds.
- 5. 4% gets reflected by water and land.
- 6. 51% of the insolation is absorbed by water and land on Earth.
33 + 16 = 49 units
Terrestrial radiation :- out of 51% units
- 1. 17% of the units go straight into space.
- 2. 6% is absorbed by the atmosphere.
- 3.9% is absorbed through convection.
- 4. 19% as latent heat of condensation.
17 + 6 + 9 + 19 =51 units
Features of isotherms of July and January :-
January :-
In January, the isotherms bend north in the oceans and south on the continents. The mean monthly temperature in January is over 27 °C over the equatorial oceans, over 24 °C in the tropics, 20 °C to 0 °C at mid-latitudes, and -18 °C to -48 in the interior of Eurasia. °C is denoted.
The temperature variation is less in the Southern Hemisphere because there is more water, so the isotherms run almost parallel to the latitudes.
July :-
In this season, the isotherms form a cell of more than 30 ° C in the tropics within the continents. Here isotherms of 10 ° C are observed at 40 ° North and South latitudes. The isotherms of the southern hemisphere are seen to be more straight and straight than those of the north.
In July, the isotherms turn north while entering the continents and turn south while entering the oceans.
The annual temperature difference is highest in the plain of Siberia. Why ?
The warm ocean current, the Gulf Stream, turns north and raises the temperature of those areas. And due to the presence of the North Atlantic Drift, the North Atlantic Sea is warmer and the temperature above the surface decreases rapidly.
️ Oceans on temperature in the Southern Hemisphere :-
Here the isotherms run almost parallel to the latitudes.
The variation in these lines is less intense than in the Northern Hemisphere.
20 ° C. , 10 ° C. and from 0. The isotherms of 35°N respectively. , 45 ° D. And is found parallel to 60 ° South.
