The horizontal distribution of temperature means the distribution according to the latitude of temperature. Often the temperature decreases as the latitude increases. The temperature distribution on the map is always represented by isotherms . The Isothermal line is the hypothetical line that joins places with similar temperatures. In order to keep the temperature of a place free from the influence of height, the temperature there is adjusted according to the sea level.(Isotherms are imaginary lines drawn on a map joining places having the same temperature reduced to sea level.)
Salient Features of Isothermal Maps
(1) Most of the Isothermal maps are drawn for the months of January and July as the northern and southern spheres of these months have minimum and maximum temperatures respectively.
(2) The Isothermal line generally extend in an east-west direction parallel to the equator, indicating that all places at the same latitude receive the same amount of sunset and that the temperature is almost the same.
(3) The Isothermal line show that the amount of heat decreases as the latitude increases from the equator to the poles.
(4) Both maximum and minimum temperatures are found on continents only because the terrestrial parts are warmer and cooler than the aquatic parts.
(5) All the Isothermal line turn north between January and July and turn south between July and January. This phenomenon is caused by seasonal movement of the Sun.
(6) The north-south shift of the Isothermal line is greater on the continents than on the seas. The reason that land has to be warmer and colder than water bodies.
(7) In the Southern Hemisphere, due to the greater expansion of the water bodies, the Isothermal line is more regular and far-flung while in the Northern Hemisphere the stratosphere is irregular and near.
(8) Due to differing water and land temperature, the Isothermal line on the coasts suddenly turn.
(9) Closer Isothermal line shows the excess of heat gradient.
(10) The presence of Isothermal line show sea currents also. The warm current bends the Isothermal line towards the poles and the cold current bends them towards the equator.
Horizontal distribution of January and July temperature
January. Sun shines almost vertically over Tropic of Capricorn in the month of January. It iswinter in the Northern Hemisphere and summer in the Southern Hemisphere.
Temperature is, therefore, high over the land mass in the Southern Hemisphere rising over 30°C in North-west Argentina, East-central four areas - Africa, Borneo and Central Australia. In the Northern Hemisphere, land mass is cooler than the oceans. As a result, lowest temperature occurs in North-east Asia and Greenland. Verkhoyansk (Siberia) experiences mean January temperature of -50°C.
As the air over the ocean is warmer than that over the landmasses in the Northern Hemisphere, the isotherms bend equatorward while crossing the land masses and poleward while crossing the oceans. In the Southern Hemisphere, the conditions during this season are just the reverse. Therefore, the isotherms bend equatorward while crossing the oceans and poleward while crossing the land masses. Due to the presence of vast expanse of land masses, isotherms are irregular and closely spaced in the Northern Hemisphere. They are more regular and widely spaced in the Southern Hemisphere .
Temperature is, therefore, high over the land mass in the Southern Hemisphere rising over 30°C in North-west Argentina, East-central four areas - Africa, Borneo and Central Australia. In the Northern Hemisphere, land mass is cooler than the oceans. As a result, lowest temperature occurs in North-east Asia and Greenland. Verkhoyansk (Siberia) experiences mean January temperature of -50°C.
As the air over the ocean is warmer than that over the landmasses in the Northern Hemisphere, the isotherms bend equatorward while crossing the land masses and poleward while crossing the oceans. In the Southern Hemisphere, the conditions during this season are just the reverse. Therefore, the isotherms bend equatorward while crossing the oceans and poleward while crossing the land masses. Due to the presence of vast expanse of land masses, isotherms are irregular and closely spaced in the Northern Hemisphere. They are more regular and widely spaced in the Southern Hemisphere .
July. At this time of the year, the sun shines almost vertically above the Tropic of Cancer in the Northern Hemisphere. It is summer for the Northern Hemisphere and winter for the Southern Hemisphere. Maximum temperature of over 30°C occurs in most parts of the Northern Hemisphere between 10° and 40° N latitudes. The areas of high temperature include the South-eastern USA, the Sahara, Arabia, Iraq, Iran, Afghanistan, large part of China and a small part of South India. However, the temperature remains below freezing point in Greenland and the mountain highlands. In the Northern Hemisphere, the isotherms bend equatorward while crossing the oceans and poleward while crossing the land masses. In the Southern Hemisphere, it is vice versa. Isotherms reveal wider spacing on the ocean than on the continents
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