CBSE Class 9 Answered

Jet streams are a narrow belt of high altitude (above 12,000 m) westerly winds in the troposphere.  The jet streams are high altitude (9000-12000 m) westerly winds between middle latitudes (summer 35°N-45°N; winter 20°N-35°N) in the Northern Hemisphere.

Western Jet Streams: The upper air westerly jet streams are extended up to 20°N-35°N (Nagpur, Raipur latitudes) due to equator-ward shift of upper air north polar whirl during northern winter (October to February). In the winter season, the upper air westerly jet streams are bifurcated into two branches due to physical obstruction of the Himalayas and Tibetan Plateau. The western cyclonic disturbances are weather phenomena of the winter months brought in by the westerly flow from the Mediterranean region. They usually influence the weather of the north and north-western regions of India.

Eastern Jet Stream: The tropical easterly jet stream extends far to the north of Tibet. An easterly jet stream, called the sub-tropical easterly jet stream blows over peninsular India, approximately over 14°N during the summer months. It is the main causative factor for determining the vigour of the summer monsoon in India. In Ealry June, the North eastern Indian states receive rainfall due to the effects of the easterly jet streams.