For example, drought or flood rarely extend to multiple years, with rainfall oscillating biennially from slightly above average to slightly below average precipitation. We argue that variability of the monsoon is regulated by negative feedbacks between the ocean and the atmosphere. The annual cycle of the heat balance of the Indian Ocean is such that there is an ocean heat transport from the summer hemisphere from the summer hemisphere resulting principally from wind-driven Ekman transport. Given the configuration of the low-level monsoon winds, the Ekman transport is in the opposite sense to the lower tropospheric divergent wind. Thus, the wind-induced heat transport works to cool the summer hemisphere upper ocean while warming the winter hemisphere.
Similar regulation occurs on interannual time scales.
In this manner, the monsoon regulates itself by reducing summer hemisphere sea-surface temperatures during strong monsoon years and increasing it during weak years. In this manner, the monsoon is self regulating. It is noted, however, that the ocean heat transport theory of monsoon regulation does not necessarily allow heat anomalies to persist from one year to the next. Furthermore, the theory does not include the Indian ocean dipole as a dynamic entity. Finally, we develop a more general theory in which the slow dynamics of the dipole are integral components of a sequence of processes that regulate the monsoon, thus minimizing radical year to year departures of the monsoon from climatology.