Major factors influencing Air Temperature
The sun is the main source of warmth in the Earth’s atmosphere . The Earth’s atmosphere is heated in several periodic ways through the thermal effects of sunlight or insolation. These processes are— (i) radiation process, (ii) transport process, (iii) convection process, (iv) advection and (v) heat absorption.
(i) Radiation method (Radiation)
The method in which heat is transferred from one object to another without any medium or even if there is a medium, is called radiation method. The atmosphere is not directly heated by the sun’s rays. Light waves from the sun penetrate the atmosphere and reach the earth’s surface. Even though the radiant heat coming from the sun reaches the earth’s surface through the atmosphere, it reaches the surface without heating the atmosphere first. The surface absorbs that heat and becomes hot. When the earth’s surface gets heated, the radiation of that heat starts in the form of photomagnetic waves and the air layer adjacent to the earth’s surface gets heated.
A method in which heat is transferred from a hotter part of a substance to a colder part but the molecules of the substance do not change position, is called a conduction method. Radiant heat from the sun passes through the atmosphere but first heats the solid surface without heating the atmosphere. The near-surface air is attached to the surface and the near-surface atmosphere is heated by convection. Gradually, heat is transferred from the warm air layer near the surface to the relatively cooler air layer above. Thus the atmosphere is heated.
As the air layer near the surface becomes more heated, the air expands and becomes lighter and rises. Cooler air then descends to fill the void. Then the air gradually becomes warmer and lighter and rises again. Thus, due to air movement from bottom to top and top to bottom, heat is spread vertically in different layers of the atmosphere and the atmosphere is heated. This process of heating the atmosphere is called conduction process.
When the heat from one place moves horizontally or parallel to the surface through air, it is called advection. In the advection process, cold air flows parallel to the surface of the earth and warms up through heat conduction. E.g. – More warmth from low latitudes is transported to high latitude atmosphere by air currents.
(v) Heat Absorption (Heat Absorption)
When the sunlight comes through the atmosphere, some of its parts like carbon dioxide, other gases, water vapor, dust particles etc. in the atmosphere absorb the heat from the incoming sunlight and make the atmosphere slightly warmer.
Although sunlight is the main source of heating of the earth’s atmosphere, the angle of incidence of sunlight varies according to latitude. Although the sun’s rays fall perpendicularly in the equatorial region, the sun’s rays fall obliquely as one moves from the equatorial region towards the polar regions. Since perpendicularly incident sunlight spreads over a shorter area and penetrates much less air, perpendicular rays are warmer than oblique rays. As you move from the equator to the north or south pole, the sun’s rays fall diagonally on the earth’s surface, so the heat gradually decreases from the equatorial region to both the poles. Generally , warming decreases at a rate of 0.28° C for every 10° difference in latitude north or south of the equator . 23½ 0 on either side of the equatorUp to the latitude of the place belongs to the Tropics or Tropics. This region is warmer than other parts of the world throughout the year. The region extending from 23½ 0 to 66½ 0 latitude north and south of the equator belongs to the temperate zone. This region is neither very hot in summer nor very cold in winter. The area extending from 66½ 0 to 90 0 latitude around the two poles is covered by the ice. Sun rays fall most obliquely in this region. Due to all these these two regions are very cold. Calcutta city is located at 22°30’N latitude and London city is at 51°N latitude, so Kolkata city is relatively near the equator. That is why Calcutta is much hotter than London.
Altitude is a major regulator of atmospheric heat. The lower atmosphere typically warms by 6.4°C per 1 km with increasing height in the troposphere. rate decreases. This is called the normal rate of warming or the normal lapse rate. Therefore, even if it is located at the same latitude, the temperature of the mountainous area is much lower than that of the plain. Siliguri is located at 26°43′ north latitude and Darjeeling at 27°13′ north latitude. Although the two cities are located at almost the same latitude, Darjeeling is about 12°C warmer than Siliguri due to its higher altitude. is less
As the height of the land increases, the temperature of the atmosphere decreases due to:-
(a) As there is less dust in the upper atmosphere, the capacity of that atmosphere to absorb and store heat is less;
(b) As the upper air layer is relatively light, the air in that layer cools easily by radiating heat;
(c) Sun rays come through the atmosphere, but the air has very little ability to directly absorb the heat of the sun rays. The sun’s heat falls on the surface and heats the surface first, then when the heated surface heat is radiated, the lowest layer of the atmosphere receives the most amount of that radiated heat. Because of this, as the air above the air layer near the surface gets progressively less warm, the temperature in the upper air layer decreases;
(d) The warm surface air rises to the surface and cools due to a sudden drop in temperature.
Contrast of warmth[Inversion of Temperature] :- According to the general rule, the temperature of the air decreases with the increase in the height of the surface. During winter nights in calm weather in mountain valleys, the temperature often increases rather than decreases with increasing altitude. This is called contrast heating or heat generation. In the mountain valley region, in the calm weather at night, when the air above the mountain cools rapidly by radiating heat, it descends down the mountain slope under the influence of the earth’s gravity, and the lower part of the mountain becomes colder. It is called katabatic wind. This cold air pushes the warm air from the bottom of the valley up along the slope. This is called anaerobic respiration. Then from the bottom of the valley as high as possible, The temperature is increasing. Agriculture in the valley region is disrupted due to contrasting temperatures. Also, since the surface radiates heat at a faster rate than the atmosphere, the surface and near-surface air also cools more. On the other hand, the air in the upper layer does not cool easily due to the low transport capacity of the air. Due to this contrast heat is created.
Contrast heating is well observed in any rock habitat such as Darjeeling. In the morning, the valleys are covered with clouds due to the contrasting heat here. As the day progresses, the valleys become cloudless as the air heats up.
(Viii) Distance from sea
Air temperature varies with distance from sea.
(a) The farther a part of the earth is from the sea, the more extreme is the temperature, because in summer the land surface of the continents at the same latitude is much hotter than the sea water. As a result, cold air from the ocean flows towards the continents, reducing the warming of the continents.
(b) In winter the land surface of the continents becomes cooler than the sea water and cold air from the continents flows towards the sea. For this reason, the weather in the region near the sea is never extreme, i.e. the temperature is never too high or too low.
(c) Extremes of climate are seen in the interior of the continents which are far from the sea, as the influence of the ocean is not so great, i.e. both cold and hot are very high.
(d) Because of the temperature difference between water and land, during the day relatively cold air from the sea flows towards the land, it is called sea breeze . Again, during the night, cold air flows from land to water, it is called terrestrial air .
(iX) Wind effect
If warm air flows over a region of the earth’s surface, the temperature of the air there is higher and if cold air flows over a region, the temperature of the air in that region is lower. For example, warm ‘lu’ air warms North India in summer, while cold Siberian air cools China in winter.
(X) Ocean currents
Effect of ocean currents on air temperature is observed. Warm currents flowing along the coast increase the temperature of the air and cool currents decrease the temperature of the air. For example, the coast of the British Isles remains ice-free throughout the year due to the influence of the warm Gulf Stream. The British Isles and Western Europe have been warmed by the warm North Atlantic Current and the countries there have been spared from extreme cold in winter. But under the influence of the cold Labrador current, the Labrador coast freezes and under the influence of the cold Bering current, the northern coastal region of Japan becomes colder.
(XI) Slope of the land
Due to the variation in the slope of the land, the temperature of the air varies. Due to the direct sunlight falling on the sunny slope of the land, the warmth is very high. On the opposite slope, the warmth is relatively less in the shade of light. For example, the northern slopes of the Meghalaya plateau are much cooler than the southern sunny slopes. In the Northern Hemisphere, the temperature is high because the mountains like Himalayas, Alps etc. slope towards the equator towards the south, but the temperature is very low because the northern side slopes towards the North Pole.
(XII) Nature of soil
The temperature of the air varies with the type of soil. Due to the higher heat capacity of silty silt soils, the area rich in silt soils is warmer. Again, since the stony laterite soil has a low heat retention capacity, this soil heats up or cools down quickly. Due to this, the temperature of Birbhum district which is rich in laterite soil is extreme compared to silt soil region of Hooghly district of West Bengal. Again, the color of the soil causes the decrease-increase in the temperature of the air. Dark colored soil absorbs more heat and becomes warmer than light colored soil.
(XIII) Location of forest
The temperature of the forest area is generally low as sunlight does not penetrate easily in dense forests of normal vegetation. The sap that the plant absorbs from the soil, releases the sap in the form of vapor through the leaves into the air. As a result, the amount of water vapor in the air increases. Due to this reason, because the forest air is moist, there is no increase or decrease in temperature. Because of this, the temperature of the Selva forest in Brazil is lower than normal. Again water vapor helps to cause precipitation. As a result of precipitation, the air temperature decreases. As a result, the temperature decreases due to more rainfall in forest areas. In this way, the location of natural vegetation directly and indirectly affects the air temperature.
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