Summer current, winter current

Image of the Month - October 2002

Mean over several years of sea level anomalies (cm) and geostrophic currents (cm/s) from Topex/Poseidon in January (winter monsoon) and July (summer monsoon). (Credits National Institute of Oceanography, Goa, Inde).

Monsoon is one of the major climatic features on Earth, vital for people living around the Indian Ocean. It involves both ocean and atmophere, with a seasonal shift : the Summer monsoon (May-September) is wet whereas the Winter monsoon (November- February) is dry. In winter, ocean is hotter than land, and winds blow from the NorthEast, from land to sea. In summer the reverse occurs, blowing wet air over land from the SouthWest with much more force, and carrying welcome, if heavy, rains. Variations in this cycle - too much or too little rain -, can have a catastrophic impact on the countries neighbouring the Indian Ocean. Studying this cycle and predicting its shifts is thus of foremost importance for the South Asian people.

Like the winds and rain, ocean currents also change with season, flowing eastward in summer from the western Arabian Sea to the Bay of Bengal, and westward in winter. Topex/Poseidon and now Jason-1 able us to study these currents and their variations; used in coupled ocean-atmosphere forecasting models, their data could help estimate the next monsoon.

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