The term monsoon is derived from an Arabic word meaning 'season', and was originally used to describe the winds of the Arabian Sea which blow for about 6 months from the northeast and 6 months from the southwest. It is now used to describe other markedly seasonal winds. The principal driving mechanism of a monsoon is the differential heating of large land and sea areas which varies seasonally.
The rainy season in India and other parts of Southeast Asia is the outstanding feature of the climate of these regions, and the term 'monsoon' is popularly used there to denote the rains.
The animation on this page has been produced using the NCEP/NCAR Reanalysis dataset.