How do monsoon winds affect Indian Ocean surface currents?

In the northern Indian Ocean, surface currents are uniquely defined by the seasonal reversal of monsoon winds, which causes circulation to shift every half year.12

• Northeast Monsoon (November–March): The North Equatorial Current flows westward. During this period, a weak counterclockwise gyre forms in the Arabian Sea, while a strong clockwise gyre develops in the Bay of Bengal. An Equatorial Countercurrent also flows eastward between 2° and 10° S.12
• Southwest Monsoon (April–October): The wind direction reverses, pushing the Monsoon Current eastward. This flow sends branches into the Arabian Sea and Bay of Bengal and reverses the circulation in both seas. Notably, the Somali Current strengthens and flows northeastward along the coast of East Africa, reaching high velocities.123

This seasonal variability distinguishes the Indian Ocean from the Atlantic and Pacific, where currents remain more consistent.1