The impact of Great Basin Desert on summer monsoon precipitation over Southwest North America: the role of mineral dust

The radiative forcing of dust emitted from the Great Basin Desert and its impact on monsoon circulation and precipitation over the North America monsoon (NAM) region are simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem) for multiple years. During the monsoon season, dust has a cooling effect (-0.90 W m-2) at the surface, a warming effect (0.35 W m-2) in the atmosphere, and a top-of-the-atmosphere (TOA) forcing (-0.50 W m-2) over the Great Basin Desert region on 24-hour average. Most of dust emitted from the desert concentrates below 800 hPa and stacks over the western slope of the Rocky Mountains and the Sierra Madre Occidental. The absorption of shortwave radiation by dust heats the lower atmosphere by up to 0.3 K/day over the western slope of the Mountains. The model sensitivity simulations show that the dust heating of lower atmosphere strengthens the low level southerly moisture fluxes on both sides of the Sierra Madre Occidental. It also results in the eastward migration of NAM-driven moisture convergence over the western slope of the Mountains. This migration leads to a statistically significant increase of precipitation by up to ~40% over the eastern slope of the Mountains. This study highlights the interaction between dust and NAM system, which deserves further investigation under future climate conditions to include the climate change feedbacks.