From Glossary of Meteorology
(Also spelled Krakatau; formerly called overtrades.) A layer of easterly winds over the Tropics at an altitude of about 18–24 km.
This layer tops the midtropospheric westerlies (the antitrades), is at least 6 km deep, and is based at about 2 km above the tropopause. This easterly current is more prominent and better defined in the summer hemisphere. It derives its name from the observed behavior of the volcanic dust carried around the world after the great eruption of Krakatoa (6°S, 105°E) in 1883.