Atmospheric Mixed Layer Convergence from Observed Madden-Julian oscillation Sea Surface Temperature Anomalies Journal of Climate

The Madden–Julian oscillation (Madden-Julian oscillation) dominates tropical weather on intraseasonal 30–90-day time scales, yet mechanisms for its generation, maintenance, and propagation remain unclear. Although surface moist static energy (MSE) flux is greatest under strong winds in the convective phase, sea surface temperature (SST) warms by ~0.3°C in the clear nonconvective phase of the Madden-Julian oscillation. Winds converging into the hydrostatic low pressure under warm air over the warm SST increase the vertically integrated MSE. We estimate column-integrated MSE convergence using a model of mixed layer (ML) winds balancing friction, planetary rotation, and hydrostatic pressure gradients. Small (0.3 K) SST anomalies associated with the Madden-Julian oscillation drive 7 W m−2 net column MSE convergence averaged over the equatorial Indian Ocean ahead of Madden-Julian oscillation deep convection. The MSE convergence is in the right phase to contribute to Madden-Julian oscillation generation and propagation. It is on the order of the total MSE tendency previously assessed from reanalysis, and greater than surface heat flux anomalies driven by intraseasonal SST fluctuations. Grant no. NA18OAR4310299 Grant no. NA15OAR4310240