An easterly jet stream that develops in the eastern hemisphere, at approximately 10° N, during the northern summer (particularly in the months of July and August). It lies at altitudes of 15–20 km, and extends from Asia to Africa, but is not observed over the western hemisphere. It arises because of the steep temperature gradient from north to south in the upper troposphere—the coldest air lying over the Equator. A weaker, broad, low-level easterly jet, at 4–5 km altitude, may form over Africa during the same period and at approximately the same latitude. Oscillations beneath this jet create westward-moving tropical waves, disturbance lines, and thunderstorms.
Subjects: Meteorology and Climatology.