Séminaire
South Asian monsoon low pressure systems, referred to as synoptic-scale monsoonal disturbances (SMDs), are convectively-coupled cyclonic disturbances that are responsible for up to half of the total monsoon rainfall. In spite of their importance, the mechanisms that lead to the growth of these systems have remained elusive.
Here we present a framework that may explain the growth of SMDs and may also be applicable to other modes of tropical variability. Moisture is prognostic and is coupled to precipitation through a simplified Betts-Miller scheme. Interactions between moisture and potential vorticity (PV ) in the presence of a moist static energy gradient can be understood in terms of a “gross” PV (qG) equation. qG summarizes the dynamics of SMDs and reveals the relative role that moist and dry dynamics play in these disturbances, which is largely determined by the gross moist stability.
Linear solutions to the coupled PV and moisture equations reveal Rossby-like modes that grow due to a moisture-vortex instability. Meridional temperature and moisture advection to the west of the PV maximum moisten and destabilize the column, which results in enhanced convection and SMD intensification through vortex stretching. This instability occurs only if the moistening is in the direction of propagation of the SMD and is strongest at the synoptic scale.
Si vous souhaitez assister à ce séminaire en visioconférence, merci de contacter marie-pierre.lefebvre@lmd.jussieu.fr