They are imaginary lines connecting the places on the surface of the earth with the same temperature.
Distribution of isotherms during the month of January:
1) The isotherms on the northern hemisphere deviate northwards along the ocean and southwards along the land. As the Sun shines above the tropic of Capricorn during the month of January, its winter season in the northern hemisphere, the land cools faster than the water due to its low specific heat. This is the reason for the above mentioned pattern of isotherms.
2) In the Southern hemisphere, due to the large expanse of water , the isotherms lie widely spaced and parallel to the latitude.
3) Due to the position of Sun, the Thermal equator( 30°C) lies below the geographical Equator.
Distribution of isotherms during the month of July:
1) Here the Thermal equator ( 30°C) lies above the the
Equator, as the Sun shines right above the Tropic of Cancer.
2) Due to the presence of Oceans , the isotherms in the southern hemisphere are widely spaced and parallel to the latitude.
Temperature Inversion:
It is the increase in temperature as the altitude from the surface of the earth increases within the troposphere region of the atmosphere. This is an irregular phenomenon as the temperature usually decreases with height in this troposphere region( ie. For every 1 km increase in height , there is 6.5°C decrease in temperature).
Temperature inversion is a region specific phenomenon.
Reasons for temperature inversion:
1) Long Winter Night:
During long winter nights, the earth's surface gets cooled and the moisture is precipitated for 2km in that specific region and we can notice an increase in temperature from cooler to hotter, as we move above the earth's surface . This occurs till a certain distance and again the usual temperature phenomenon is experience.
2)Cloudless sky:
Due to the absence of clouds , no reflection of earth's heat waves by the clouds take place , making the heat radiation escape into the space. This allows cold moisture to precipitate on the surface allowing the temperature inversion phenomenon to take place till a certain distance from the surface.
3)Snow Clouded Ground:
Here temperature inversion takes place due to the high precipitation of snow on the surface of the earth.
4) Formation of Fronts:
When cold and hot air masses converge and hot air mass rises up, this temperature inversion phenomenon can be noticed.
5) Calm and Stable air:
Due to a stable air and absence of winds, a cool precipitation is formed on the earth's surface . This leads to temperature inversion till a certain distance from the earth's surface.
6) Mountain and valley winds:
During night time, the temperature of the Mountain valley is higher than that of the mountain slopes. So the wind breeze blow from slopes ( high pressure region) to valleys( low pressure region). Here the valley gets cooler and temperature inversion can be felt.
Content credits: Leo.A.Vishnu Varthan
