Useful notes on Latitudinal Heat Balance

While discussing the terrestrial heat budget it was made clear that the amount of incoming solar radiation is almost equal to the amount of outgoing earth radiation for the earth as a whole. But when we consider the heat budget of different latitudes, it is found that the terrestrial heat balance does not hold good for each attitude.

In fact, there is a great imbalance between different parts of the earth and the atmosphere as can be seen in Table 22.6. There is a pronounced excess of incoming over outgoing radiation in low- latitudes and a marked deficit in high latitudes.

In other words, at latitudes below 40° the total amount of solar radiation received at the surface far exceeds the total amount of radiation lost to space by the earth. In case of higher latitudes, the situation is reversed, for in these latitudes more heat is lost through radiation than is received.

But despite this fact, neither the tropics are getting progressively warmer, nor are Polar Regions getting progressively colder. In view of the imbalance at high and low latitudes, it may look strange.

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But one must not lose sight of a continuous large-scale transfer of heat from the tropics to high latitudes. This is achieved mostly by atmospheric and oceanic circulations.

Amount of heat that must be transferred pole-ward to preserve the latitudinal heat balance

°Lat. North		10¹⁹ cal per day	“Lat. North	10¹⁹ cal per day
0	0	50	9.61
10	4.05	60	6.68
20	7.68	70	3.41
30	10.46	80	0.94
40	11.42	90	0.00

It may be noted that most of the heat transfer takes place across the middle latitude region lying between latitudes 30° and 50°. Nature has provided a mechanism of heat transfer from the tropics towards the poles in the form of middle-latitude storms.

According to one estimate, about 75 per cent of heat transfer is carried out by atmospheric circulation and the remaining 25 per cent by the ocean currents.

In fact, it is the latitudinal imbalance of heat that drives the wind and the ocean currents. It is only trough the transfer of heat by winds and oceanic circulations that the latitudinal imbalances of energy are equalized and the heat balance in the various latitudes of the earth is preserved.