African Easterly Wave

A tropical easterly wave that is generated due to a combined baroclinic and barotropic instability of the African jet. African easterly waves have a period of three to four days, a horizontal wavelength of 2000-2500 km, and maximum amplitude in the lower troposphere. An average of 60 African easterly waves form between May and October while large-scale environmental conditions favor the existence of the African jet. African easterly waves may propagate westward across the tropical and subtropical North Atlantic and may reach the Caribbean Sea and western North Atlantic. Some African easterly waves become hurricanes.

(term added 9/24/2013)

Any function of time f(t) is periodic with period t if f(t) = f(t + τ) for all times t, where τ is the smallest number for which this equality holds.

1. Regular markings on an instrument used to allow the reading of the measured quantity or setting.

A low-level easterly jet in the summer months over the Sahara Desert of North Africa.