Streams are the fast blowing winds of a steady velocity moving in a narrow zone of the
upper layer of the atmosphere. Their speed
varies from about 110 km/h in summer to about 184
km/h in winter. Jet streams are located
approximately over 27°-30° north latitude, therefore, they are known as subtropical
westerly jet streams.
A number of separate jet streams have been
identified. The most constant are the mid-latitude and the sub tropical jet
stream. The western cyclonic
disturbances experienced in the north and north-western parts of the country are
brought in by this westerly flow.
The movement of the westerly jet stream to the
north of the Himalayas and the presence of
the tropical easterly jet stream over the Indian
peninsula during summer is an important
facts to keep in mind to also understand the mechanism of Mansoon