The latitudinal heat zones of Earth are majorly governed by variability of the insolation at Earth's surface and geoidal shape of the Earth. However, the boundaries of the zones are finally delineated by taking into account the role of planetary winds and ocean currents which maintain heat balance on earth. This gives rise to the three heat zones on the earth surface:

• Torrid or tropical zone: This zone lies between the Tropic of Cancer and the Tropic of Capricorn. The apparent movement of the sun
during a year is between these two latitudes. The sun's rays here are almost vertical and it receives maximum insolation.
• Temperate zones: This zone lies between the torrid zone and the Frigid zone. It shares features of both the surrounding zones. Sun is never directly overhead, thus it possess moderate temperature.
• Frigid zones: Here the sun rays fall at low angles because the sun does not rise much above the horizon. Thus, these zones are the
coldest regions of Earth.

The temperature distribution on Earth is represented with the help of isotherms, which are the lines joining places having equal temperatures. They generally lie parallel to the latitude due to the pronounced effect of the latitude on temperature of an area. However, they take sudden bends where land-water contrasts are maximum. Thus, there are deviations in the isotherms in northern and southern hemispheres.

Pattern of isotherm in Northern hemisphere

• In the northern hemisphere the land surface area is much larger than in the southern hemisphere. Hence, the effects of land mass and the ocean currents are well pronounced.
• In January the isotherms deviate to the north over the ocean and to the south over the continent. This can be seen on the North Atlantic Ocean.
• The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north. Over the land the temperature decreases sharply and the isotherms bend towards south in Europe.

These deviations are more pronounced in January than in July. In July, the isothermal behavior is opposite of what it is in January. Isotherms bend poleward over the landmass as they are overheated.

Pattern of isotherm in Southern hemisphere

• In the southern hemisphere, the effect of the ocean is well pronounced. Thermal equator lies to the south of Geographical equator.
• Here the isotherms are more or less parallel to the latitudes and the variation in temperature is more gradual.
• However, the gradient shows slight bend towards the equator at the edges of the continent as shown in the figure.