Question

Explain that machism of jet stream

Answer 1

Jet stream, narrow, swift currents or tubes of air found at heights ranging from 7 to 8 mi (11.3–12.9 km) above the surface of the earth.They are caused by great temperature differences between adjacent air masses. There are four major jet streams. Although discontinuous at some points, they circle the globe at middle and polar latitudes, both in each hemisphere.The mean position of the stream in the Northern Hemisphere is between lat. 20 and 50 degrees N; the polar stream is between lat 30 and 70 degrees N.Wind speeds average 35 mi (56.3 km) per hr in summer and 75 mi (120.7 km) per hr in winter, although speeds as high as 200 mi (321.9 km) per hr have been recorded. Instead of moving along a straight line, the jet stream flows in a wavelike fashion.

How do they affect Indian Monsoons ?

The easterly jet stream steers the tropical depressions into India. These depressions play a critical role in distribution of monsoon rainfall over the Indian subcontinent.

During the early summer months, increased solar heating begins to heat the Indian subcontinent, which would tend to set up a monsoon circulation cell between southern Asia and the Indian Ocean.

However, the subtropical jet stream occupies its winter position at about 30 degree N latitude, south of the Himalayan Mountains in 200 hPa.

As summer progress, the subtropical jet slides northward (Fig.9.7). The extremely high Himalayas present an obstacle for the jet; it must "jump over" the mountains and reform over central Asia. When it finally does so, a summer monsoon cell develops, supported by the tropical jet stream overhead.