how does the surplus heat at the tropics drive GAC

• • The unequal distribution of heat across the Earth’s surface means there is a need for vertical and horizontal transfers of heat to re-distribute the heat across the globe 
  • Along the equator, strong solar heating causes air to expand upwards and diverge towards the poles. This creates a zone of low pressure at the equator called the ITCZ. Air in the upper troposphere moves polewards towards the subtropics, to about 20 to 30 N & S.
• • Upon reaching 20 to 30 latitude, air sinks towards the surface to form the subtropical highs, which are large bands of high surface pressure. The air from the subtropical highs is directed towards the ITCZ as trade winds due to the pressure gradient force. 
• • In the northern hemisphere, the Coriolis force deflects the air slightly to the right to form the northeast trade winds. 
  • In the southern hemisphere, the north-ward moving air from the subtropical high is deflected to the left to create the southeast trade winds. This complete the hadley cells circulation operating in each of the hemispheres