Upscale effects of deep convection during the North American monsoon

The North American monsoon is a regional-scale convective weather phenomenon that influences both Mexico and the southwestern United States. The monsoon typically begins in May along the southern coast of Mexico and expands northward reaching northwestern Mexico and the southwestern United States during July. Higgins et al. (2004) show that the location of the upper-level anticyclone over the United States influences monsoon precipitation. However, a related question is how the monsoon convection influences the upper-level anticyclone. Attempting to answer this question is the goal of this study.

Two six-day simulations using the Advanced Research Weather Research and Forecasting (WRF) model are made. The simulations use two domains: a coarse domain covering most of North America at 30 km and a nested domain centered over the monsoon region at 10 km. The control simulation uses a complete set of parameterization schemes on both domains. The no-latent heating simulation turns off all latent heating effects due to convection on the nested domain, but keeps the full set of parameterization schemes on the coarse domain. By using two-way nesting, the effects of turning off latent heating on the nested domain affect the coarse domain. Results indicate that deep convection does play a role in the strength and location of the upper-level anticyclone during the monsoon. The anticyclone is stronger and farther west in the control run compared to the no latent heating run. In addition, the structure of a tropical easterly wave that passes across Mexico during the simulation is altered when latent heating effects are neglected. These results and others will be discussed at the conference.