Mechanism for northward propagation of boreal summer intraseasonal oscillation: Convective momentum transport

Abstract

This study demonstrates that the momentum transport by cumulus convection plays a significant role in the organization and northward propagation of intraseasonal (ISO) convection anomalies over the Indian and western Pacific regions during boreal summer. A version of Seoul National University's atmosphere-ocean coupled general circulation model simulates northward propagation when convective momentum transport (CMT) is implemented; the northward propagation disappears when CMT is disabled. An axially symmetric shallow water model with a parameterized CMT is used to understand the role of CMT in the northward propagation of ISO. The basic mechanism of northward propagation is the lower-level convergence to the north of convection, which is induced by the secondary meridional circulation associated with large momentum mixing by convection in the region of large mean vertical shear. A large mean vertical shear exists in South Asian region during boreal summer. Citation: Kang, I.-S., D. Kim, and J.-S. Kug (2010), Mechanism for northward propagation of boreal summer intraseasonal oscillation: Convective momentum transport, Geophys. Res. Lett., 37, L24804, doi:10.1029/2010GL045072.