The Easterly Jet Stream in the Tropics

Abstract

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.

A sensitivity study on the role of the swamps of southern Sudan in the summer climate of North Africa using a regional climate model

“…The TEJ develops between 200 and 150 mb in the upper troposphere over India in response to a large meridional thermal gradient and settles during the northern summer Asian monsoon season between the Tibetan Highlands and the Indian Ocean (Fontaine and Janicot 1992;Koteswaram 1958;Chen and van Loon 1987). It stretches from the Indochina peninsula, across the African continent, to the tropical Atlantic (Wu et al 2009), and it is linked to anomalous SSTs on a planetary scale (Chen and van Loon 1987).…”

The Inter-Relations of Monsoon Rainfall in Different Sub-Divisions of India

“…The subtropical westerlies over North India weaken (Yin 1949, Koteswaram 1958, Flohn 1958) . The westerly jet stream and the subtropical ridge shift to northern latitudes across peninsular India.…”

Onset characteristics of the southwest monsoon over India

“…These include the northward displacement of upper tropospheric westerly flow to the north of the Himalayas, establishment of the upper tropical easterly jet (TEJ) stream (Koteswaram, 1958) and lower tropospheric westerly jet (Somali jet) over the Arabian Sea (Findlater, 1969). The intensification of the monsoon flow is mainly dictated by the release of convective instability and tropospheric diabatic heating (Krishnamurti and Ramanathan, 1982;Mohanty et al, 1983;Pearce and Mohanty, 1984;Rao and Aksakal, 1994).…”