Impact of the Desert dust on the summer monsoon system over Southwestern North America

摘要

The radiative forcing of dust emitted from theSouthwest United States (US) deserts and its impact on monsoon circulationand precipitation over the North America monsoon (NAM) region are simulatedusing a coupled meteorology and aerosol/chemistry model (WRF-Chem) for 15years (1995–2009). During the monsoon season, dust has a cooling effect(?0.90 W m?2) at the surface, a warming effect (0.40 W m?2) in theatmosphere, and a negative top-of-the-atmosphere (TOA) forcing (?0.50 W m?2)over the deserts on 24-h average. Most of the dust emitted fromthe deserts concentrates below 800 hPa and accumulates over the westernslope of the Rocky Mountains and Mexican Plateau. The absorption ofshortwave radiation by dust heats the lower atmosphere by up to 0.5 K day?1over the western slope of the Mountains. Model sensitivity simulations withand without dust for 15 summers (June-July-August) show that dust heating ofthe lower atmosphere over the deserts strengthens the low-level southerlymoisture fluxes on both sides of the Sierra Madre Occidental. It alsoresults in an eastward migration of NAM-driven moisture convergence over thewestern slope of the Mountains. These monsoonal circulation changes lead toa statistically significant increase of precipitation by up to ~40 %over the eastern slope of the Mountains (Arizona-New~Mexico-Texas regions).This study highlights the interaction between dust and the NAM system andmotivates further investigation of possible dust feedback on monsoonprecipitation under climate change and the mega-drought conditions projectedfor the future.