The boreal summer intraseasonal variability (BSISV) has a space-time coherent variability, characterized by eastward propagation near the equator and northward propagation in the Indian Ocean and western Pacific region. The northward propagation is closely related to the “active” and “break” period of the summer monsoon. Therefore, it is important to understand the initiation and propagation mechanisms of BSISO for practical reasons (e.g. water resource management).

In previous mechanisms suggested to explain this phenomenon, the role of convection is only to heat the atmosphere, responding to the large-scale forcing. As well as heating, however, the convection plays a role in altering atmospheric circulation throughout vertical momentum transport. Recently, climate modeling society has paid attention to the role of the convective momentum transport (CMT) in climate simulation such as seasonal cycle and ENSO. In this study, we emphasize the role of CMT in northward propagation of monsoon convection.

The roles of internal dynamics of the atmosphere – interactions between climatological wind shear and vertical momentum mixing induced by cumulus convection - and air-sea coupled processes on the northward propagation of monsoon convection are investigated using Seoul National University general circulation model (SNUGCM). We compared two versions of GCM in which the momentum transport by convection is turned on/off. Further, such comparison was done in coupled and uncoupled frameworks to examine the role of air-sea interactions on the BSISV northward propagation.

We suggest that CMT has significant role on the northward propagation of monsoon convection. When the CMT is turned on, SNUGCM simulated more coherent eastward propagation in monsoon region in coupled model simulations. The characteristics (e.g. period) and the spatial structures of simulated northward propagating waves are presented. This study has implication to climate modeling group because many climate models still do not include CMT and many of them are suffering from simulating northward propagation of monsoon convection correctly in boreal summer season.