How do jet streams affect the Indian climate?

Jetstreams are a narrow belt of high altitude (above 12,000 m) westerly winds in the troposphere. They affect the Indian climate in the following ways.

• Westerly Jetstream brings the western cyclonic disturbances(originate over the Mediterranean Sea) that enter the Indian subcontinent from the west and the northwest during the winter months. An increase in the prevailing night temperature generally indicates an advance in the arrival of these cyclones disturbances. 
• An easterly jet stream, called the sub-tropical easterly jet stream blows over peninsular India, approximately over 14°N during the summer months. Tropical cyclones occur during the monsoon as well as in October – November and are part of the easterly flow. These disturbances affect the coastal regions of the country. 

Further Reading:

• Jet Stream
• Geography Notes