Beneath the overhead midday sun, heating is at a maximum within the tropics. Hot air rises rapidly within this zone, leading to deep tropical rainclouds. At the same time, the resultant vacuum of low pressure at the surface causes air from either side to converge and then, in turn, rise. This is termed the Inter-Tropical Convergence Zone (ITCZ) and is one of the wettest climate zones on Earth. The focus for this ‘engine’ of intense downpours progresses north and then south again through the year between the Tropics of Capricorn and Cancer, either side of its average position near the Equator.