What are the climatic implications of the tri-cellular model of global atmospheric circulation?

The tri-cellular model shows how energy is transferred polewards via three cells of air circulation: the Hadley, Ferrel and Polar cells. The Hadley Cell involves the meeting of the trade winds in the Equatorial region, forming the Inter Tropical Convergence Zone (ITCZ). The trade winds are relatively warm and are forced to rise by powerful convection currents. The unstable, warm, moist air is rapidly cooled to produce towering cumulonimbus clouds, frequent late-afternoon thunderstorms and low- pressure, characteristic of the Equatorial climate. At ground level, the ITCZ experiences only very gentle, variable winds known as the doldrums. As rising air cools to the temperature of the surrounding environmental air, uplift ceases and the air begins to move away from the equator. Further cooling causes the air to slow down and subside, forming the descending limb of the Hadley Cell. In the Northern hemisphere, the air subsides at about 30°N of the Equator to create the subtropical high pressure belt with its clear skies and dry, stable conditions. On reaching the Earth’s surface, the cell is completed as some of the air is returned to the Equator as the North East Trade Winds.  The remaining air is diverted polewards in the Ferrel and Polar cells, forming the warm south westerlies, which collect moisture when they cross sea areas. These warm winds meet cold Arctic air at the Polar front (about 60°N) and are uplifted to form an area of low pressure and the rising limb of the Ferrel and Polar cells. The resultant unstable conditions produce the heavy rainfall associated with mid latitude depressions. While some of this rising air eventually returns to the tropics, some travels towards the Poles as part of the Polar Cell, where, having lost its heat, it descends to form another stable area of high pressure. Air returning to the polar front does so as cold polar north easterlies.