Fig.1 Winter and summer monsoon

( Source: Lutgens and Tarbuck, 2001.)

• Monsoon is the greatest seasonal change in Earth‘s global circulation. Monsoon refers to a wind system that exhibits a pronounced seasonal reversal in direction.
  
• It is driven by the seasonal reversal of the temperature differences between land to ocean.
  
• In the summer: land surface is warmer than the ocean and the wind blows towards the land (low-pressure area).
  
• In the summer:
  
  • high temperatures generate a low-pressure area over S-Asia. This encourages inward-flow of moisture-laden air from the ocean to the continent and results in heavy rainfalls (see 1b, Fig.1)
    
• In the winter:
  
  • The Siberian high over North-Russia dominates the winter-circulation over Asia. It generates off-shore winds and by the time this flow reaches India: is warm and dry (1a, Fig.1).
    
• Note: the Asian monsoon is associated with a larger than average seasonal migration of the Innertropical Convergence Zone ( ITCZ).
  
• Monsoon and its relevance for agricultural production: half of the world population lives in regions that are influenced by the monsoon. Often, farmers are strongly dependent upon the beginning of the monsoon on time.