The earth receives energy in the form of solar radiation. The incoming solar energy passes through the atmosphere, enters the surface (land or ocean), and eventually appears as land or ocean heating.
At the same time, the earth emits longwave (infrared) radiation to space, mainly due to thermal properties of the atmosphere. This process is termed radiate emission.
The net exchange between the earth and space is the difference between these two fluxes (terrestrial radiation and radiate emission).
The climate’s heat engine must not only redistribute solar heat from the equator toward the poles but also from the Earth’s surface and lower atmosphere back to space.
When the flow of incoming solar energy is balanced by an equal flow of heat to space, Earth is in radiative equilibrium, and global temperature is relatively stable.
Regions within the equator and 40° N and S latitudes receive abundant sunlight and hence they are energy surplus regions. Regions beyond 40° N and S latitudes lose more heat than that gained from sunlight and hence they are energy deficit regions.
Most of the heat transfer takes place across the mid-latitudes (30° to 50°)[more while studying jet streams and cyclones], and hence much of the stormy weather is associated with this region.
Thus, the transfer of surplus energy from the lower latitudes to the deficit energy zone of the higher latitudes maintains an overall balance over the earth’s surface.
