Assessing the Great Whirl, despite all the pirates



Each year, the powerful southwest monsoon ramps up in midsummer, bringing life-giving rains to the Indian subcontinent. The monsoon winds also drive dramatic changes in the regional ocean currents, including a reversal in the circulation of the Arabian Sea, an energetic eddy field, and strong coastal upwelling. Off the east coast of Somalia, a large (300- to 550-kilometer wide) anticyclone appears—known since 1876 as the Great Whirl—with surface currents as strong as 2.5 meters per second. The Great Whirl, while associated with the seasonal arrival of the southwest monsoon, is not caused entirely by it; the circulation of the Great Whirl starts a month before and persists for a month after the monsoon.