Abstract
Abstract. The impact of a typical pre-monsoon season (April–June) dust storm event on the regional aerosol optical properties and radiation budget in northern India is analyzed. The dust storm event lasted from 17 to 22 April 2010 and the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) estimated total dust emissions of 7.5 Tg over the model domain. Both in situ (AERONET – Aerosol Robotic Network) and satellite observations show significant increase (> 50%) in local to regional scale aerosol optical depth (AOD) and decrease (> 70%) in the Ångström exponent (α) during this period. Amongst the AERONET sites in this region, Kanpur was influenced the most, where the AOD reached up to 2.1 and the α decreased to −0.09 during the dust storm period. The WRF-Chem model reproduced the spatial and temporal distributions of dust plumes and aerosol optical properties but generally underestimated the AOD. The average MODIS and WRF-Chem AOD (550 nm) values in a subregion (70–80° E, 25–30° N) affected the most by the dust storm are estimated as 0.80 ± 0.30 and 0.68 ± 0.28, respectively. Model results show that dust particles cool the surface and the top of the atmosphere, but warm the atmosphere itself. The radiative perturbation due to dust aerosols averaged over the subregion is estimated as −2.9 ± 3.1 W m−2 at the top of the atmosphere, 5.1 ± 3.3 W m−2 in the atmosphere and −8.0 ± 3.3 W m−2 at the surface. The simulated instantaneous cooling under the dust plume was much higher and reached −227 and −70 W m−2 at the surface and the top of the atmosphere, respectively. The impact of these radiative perturbations on the surface energy budget is estimated to be small on a regional scale but significant locally.
Highlights
Dust storms frequently occur throughout the desert regions of the world, especially during springtime, injecting large amounts of mineral dust aerosols into the atmosphere
In light of the above conditions, the main objective of this study is to understand the regional distribution of dust aerosols and their impact on the regional-scale aerosol optical properties and radiation budget during a typical premonsoon dust storm, applying the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) to a dust storm event that occurred in northern India during 17– 22 April 2010
aerosol optical depth (AOD) levels at some Aerosol Robotic Network (AERONET) sites were still high on 22 April (Sect. 4.3) despite the decreased dust emission, and further analysis in this study is restricted to the period of 17–22 April 2010, unless stated otherwise
Summary
Dust storms frequently occur throughout the desert regions of the world, especially during springtime, injecting large amounts of mineral dust aerosols into the atmosphere. Dust aerosols perturb the Earth’s radiation budget directly by interacting with both short- and long-wave radiation (e.g., Seinfeld et al, 2004; Ge et al, 2010; Zhao et al, 2011) and indirectly by modifying cloud microphysics and cloud optical properties (Haywood and Boucher, 2000; Satheesh and Moorthy, 2005) They provide large surfaces for heterogeneous chemistry and deposition of different trace gases (e.g., Dentener et al, 1996; Wang et al, 2012), and influence oceanic and terrestrial biogeochemistry by transporting nutrients like iron (Jickells et al, 2005; Kalenderski et al, 2013).
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