The Easterly Jetstream MET

The Equatorial Easterly jetstream occurs in northern hemisphere summer only. At that time, because of the very large amount of land in the northern hemisphere, the ITCZITCZ —Inter Tropical Convergence Zone moves so far north than the boundary between equatorial and tropical air (the Hadley-Ferrell boundary, which follows the ITCZITCZ —Inter Tropical Convergence Zone north and south) crosses from the south to the northern hemisphere. Because of the change in the way Coriolis acts, this now turns "the other way" and flows from the east, rather than the west.

This easterly jetstream creates "waves" between the ITCZITCZ —Inter Tropical Convergence Zone and the subtropical highs. In the low pressure behind each "wave" (so to the east, as it is flowing from east to west) there are often heavy thunderstorms and rain, caused by the conditions being hot, moist and the trigger action of the low pressure.