The role of surface heat fluxes in tropical intraseasonal oscillations


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.

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Figure 1: Intraseasonal rainfall variance in the 30–90 day frequency band from the TRMM 3B42 data set (1998–2006).
Figure 2: Climatological mean rainfall from the TRMM 3B42 data set (1998–2006).


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This paper was written while the first author was on sabbatical at the Australian Bureau of Meteorology, and he thanks M. Wheeler, H. Hendon, H. Zhu, S. Cleland and L. Chappell for stimulating discussions on the MJO. This work was supported by the Climate and Large-Scale Dynamics Program of the National Science Foundation under grants ATM-0832868 (E.D.M.) and ATM-054273 (A.H.S.), by the Precipitation Measurement Mission program of the National Aeronautics and Space Administration under grant NNX07AD21G (A.H.S.) and by award NA05OAR4310006 from the National Oceanic and Atmospheric Administration, US Department of Commerce (E.D.M.). The statements, findings, conclusions and recommendations do not necessarily reflect the views of NSF, NASA, NOAA or of the Department of Commerce.

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Correspondence to Adam H. Sobel.

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Sobel, A., Maloney, E., Bellon, G. et al. The role of surface heat fluxes in tropical intraseasonal oscillations. Nature Geosci 1, 653–657 (2008).

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