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Journal article

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

Zhao C, Liu X, Leung L ...see all

Atmospheric Chemistry and Physics, vol. 12, issue 8 (2012) pp. 3717-3731

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Abstract

The radiative forcing of dust emitted from the Southwest United States
(US) deserts 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 15 years
(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 the
atmosphere, 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 from
the deserts concentrates below 800 hPa and accumulates over the western
slope of the Rocky Mountains and Mexican Plateau. The absorption of
shortwave radiation by dust heats the lower atmosphere by up to 0.5 K
day(-1) over the western slope of the Mountains. Model sensitivity
simulations with and without dust for 15 summers (June-July-August) show
that dust heating of the lower atmosphere over the deserts strengthens
the low-level southerly moisture fluxes on both sides of the Sierra
Madre Occidental. It also results in an eastward migration of NAM-driven
moisture convergence over the western slope of the Mountains. These
monsoonal circulation changes lead to a statistically significant
increase of precipitation by up to similar 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 and motivates
further investigation of possible dust feedback on monsoon precipitation
under climate change and the mega-drought conditions projected for the
future.

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