Abstract

The tropics sustain strong, coherent variations in wind and precipitation on the intraseasonal (30–60 day) timescale. In their active phases, these intraseasonal oscillations are characterized by the slow eastward movement of stronger-than-average precipitation and westerly winds. In northern summer, rainfall and wind anomalies also propagate northward on the intraseasonal timescale over India, southeast and east Asia and the adjacent oceans, pacing the active and break cycles of the monsoons and thus exerting a direct control on the livelihoods of large populations dependent on rain-fed agriculture. We argue that heat fluxes from ocean to atmosphere play a fundamental role in driving the intraseasonal oscillations. We also propose that the current generation of numerical models may enable us to test this and other hypotheses about the dynamics of intraseasonal oscillations more convincingly than has been done in the past.