The role of global circumnavigating mode in the MJO initiation and propagation

A series of convection-permitting regional-model simulations are used to study the influences of intraseasonal forcings from the periphery of the tropical Indian Ocean on the October 2011 Madden-Julian Oscillation (MJO) event well observed during the Dynamics of the Madden-Julian Oscillation field campaign. These sensitivity experiments demonstrate the predominant role of a global circumnavigating mode in the initiation and propagation of this MJO event, although the regional framework would not completely rule out influences from the extratropics through the western boundary of the model domain. It is found that filtering out intraseasonal forcing leads to the absence of Kelvin waves, which may reduce moisture transport and weakened lower level convergence at the leading edge of the westerlies and further leads to diminishing MJO signatures in these sensitivity experiments. Meanwhile, for the same regional domain initiated 2 weeks before the onset of the MJO convection, there is little impact of whether or not the global MJO signals retained in the initial conditions. On the other hand, the removal of the global MJO signals from the lateral boundary conditions will not affect the propagation of the MJO after it has been initiated in the regional model domain.