Radiative impact of mineral dust on monsoon precipitation variability over West Africa

Journal Article · Tue Mar 01 04:00:00 EST 2011 · Atmospheric Chemistry and Physics, 11(5):1879-1893

DOI:https://doi.org/10.5194/acp-11-1879-2011· OSTI ID:1008239

Zhao, Chun; Liu, Xiaohong; Leung, Lai-Yung R; Hagos, Samson M

The radiative forcing of dust and its impact on precipitation over the West Africa monsoon (WAM) region is simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem). During the monsoon season, dust is a dominant contributor to AOD over West Africa. In the standard simulation, on 24-hour domain average, dust has a cooling effect (-6.11 W/m2) at the surface, a warming effect (6.94 W/m2) in the atmosphere, and a relatively small TOA forcing (0.83 W/m2). Dust modifies the surface energy budget and atmospheric diabatic heating and hence causes lower atmospheric cooling in the daytime but warming in the nighttime. As a result, atmospheric stability is increased in the daytime and reduced in the nighttime, leading to a reduction of late afternoon precipitation by up to 0.14 mm/hour (30%) and an increase of nocturnal and early morning precipitation by up to 0.04 mm/hour (23%) over the WAM region. Dust-induced reduction of diurnal precipitation variation improves the simulated diurnal cycle of precipitation when compared to measurements. However, daily precipitation is only changed by a relatively small amount (-0.14 mm/day or -4%). On the other hand, sensitivity simulations show that, for weaker-to-stronger absorbing dust, dust longwave warming effect in the nighttime surpasses its shortwave cooling effect in the daytime at the surface, leading to a less stable atmosphere associated with more convective precipitation in the nighttime. As a result, the dust-induced change of daily WAM precipitation varies from a significant reduction of -0.40 mm/day (-12%, weaker absorbing dust) to a small increase of 0.05 mm/day (1%, stronger absorbing dust). This variation originates from the competition between dust impact on daytime and nighttime precipitation, which depends on dust shortwave absorption. Dust reduces the diurnal variation of precipitation regardless of its absorptivity, but more reduction is associated with stronger absorbing dust.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1008239
• Report Number(s): PNNL-SA-76065; KP1703020
• Journal Information: Atmospheric Chemistry and Physics, 11(5):1879-1893, Journal Name: Atmospheric Chemistry and Physics, 11(5):1879-1893 Journal Issue: 5 Vol. 11; ISSN 1680-7316
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ABSORPTION
ABSORPTIVITY
AFRICA
DAILY VARIATIONS
DUSTS
HEATING
METEOROLOGY
MONSOONS
PRECIPITATION
SENSITIVITY
SIMULATION
STABILITY
SURFACE ENERGY