The Easterly Jet Stream in the Tropics

It is shown that in summer an easterly jet stream overlies southern Asia in the high troposphere with core near 15°N. This current is quasi-geostrophic. Below the level of strongest winds temperatures decrease from right to left across the current looking downstream; above the level of strongest wind (150–100 mb) the reverse is true. Distribution of cloudiness and precipitation in the lower monsoon correspond to that noted in association with westerly jet streams in the temperate zone: precipitation downstream from the region with the highest winds to left of the axis, upstream to the right. The foregoing holds on individual days and climatically during the monsoon season as a whole. Since an easterly jet stream is observed only over southern Asia (and Africa), but not over the Pacific and Atlantic oceans, it is suggested that the current originates in connection with the large-scale arrangement of land masses and oceans, and with the elevated heat source of the Tibetan plateau.