Convective scale simulation of the 2006 North American Monsoon season

A fully coupled chemistry-transport model WRF-Chem is used to study the 2006 North American Monsoon season at convective-scale resolution (4 km). The simulation is unprecedented, both in terms of the horizontal resolution, and the spatial (contiguous US and northern Mexico) and temporal (mid July - mid September) domain.

We specifically focus on important dynamical features of the monsoon, such as the southerly low-level jet along the Gulf of California. We first examine how changes in the boundary layer momentum balance lead to the development of the mean southerly jet during the mature stage of the monsoon. We then explore the synoptic-scale forcing of the low-level jet by gulf surge events. These surge periods, which are associated with enhanced southerly flow along the gulf and enhanced convection in the monsoon region, have been linked to tropical cyclone or easterly wave activity to the south of the gulf, but their dynamics remains elusive. The availability of high resolution data in the large model domain will allow us to not only study the synoptic and mesoscale evolution of gulf surges and their underlying dynamical mechanisms, but also to explore their connection with larger-scale tropical disturbances.