LAUSR

AbstractA theory for intraseasonal atmosphere–ocean–atmosphere feedback is supported whereby oceanic equatorial Rossby waves are partly forced in the eastern Indian Ocean by the Madden–Julian oscillation (MJO), reemerge in the western Indian Ocean ~70 days later, and force large-scale convergence in the atmospheric boundary layer that precedes MJO deep convection. Downwelling equatorial Rossby waves permit high sea surface temperature (SST) and enhance meridional and zonal SST gradients that generate convergent circulations in the atmospheric boundary layer. The magnitude of the SST and SST gradient increases are 0.25°C and 1.5°C Mm−1 (1 megameter is equal to 1000 km), respectively. The atmospheric circulations driven by the SST gradient are estimated to be responsible for up to 45% of the intraseasonal boundary layer convergence observed in the western Indian Ocean. The SST-induced boundary layer convergence maximizes 3–4 days prior to the convective maximum and is hypothesized to serve as a trigger for ...