The MJO and Air–Sea Interaction in TOGA COARE and DYNAMO

Abstract

Abstract Dynamics of the Madden–Julian Oscillation (DYNAMO) and Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) observations and reanalysis-based surface flux products are used to test theories of atmosphere–ocean interaction that explain the Madden–Julian oscillation (MJO). Negative intraseasonal outgoing longwave radiation, indicating deep convective clouds, is in phase with increased surface wind stress, decreased solar heating, and increased surface turbulent heat flux—mostly evaporation—from the ocean to the atmosphere. Net heat flux cools the upper ocean in the convective phase. Sea surface temperature (SST) warms during the suppressed phase, reaching a maximum before the onset of MJO convection. The timing of convection, surface flux, and SST is consistent from the central Indian Ocean (70°E) to the western Pacific Ocean (160°E). Mean surface evaporation observed in TOGA COARE and DYNAMO (110 W m−2) accounts for about half of the moisture supply for the mean precipitation (210 W m−2 for DYNAMO). Precipitation maxima are an order of magnitude larger than evaporation anomalies, requiring moisture convergence in the mean, and on intraseasonal and daily time scales. Column-integrated moisture increases 2 cm before the convectively active phase over the Research Vessel (R/V) Roger Revelle in DYNAMO, in accordance with MJO moisture recharge theory. Local surface evaporation does not significantly recharge the column water budget before convection. As suggested in moisture mode theories, evaporation increases the moist static energy of the column during convection. Rather than simply discharging moisture from the column, the strongest daily precipitation anomalies in the convectively active phase accompany the increasing column moisture.