Atmos. Chem. Phys. Discuss., 13, 27937-27969, 2013
www.atmos-chem-phys-discuss.net/13/27937/2013/
doi:10.5194/acpd-13-27937-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Effects of aerosols on precipitation in north-eastern North America
R. Mashayekhi and J. J. Sloan
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo ON N2L 3G1, Canada

Abstract. The changes in precipitation over north-eastern North America caused by chemistry – and particularly anthropogenic aerosols – are investigated using the Chemistry version of the Weather Research and Forecasting (WRF/Chem v3.4) model. The simulations were carried out for a five-month period from April to August 2009. The model results show that non-negligible changes in both convective and cloud-resolved (non-convective) precipitation are caused by chemistry and/or aerosols over most parts of the domain. The changes can be attributed to both radiative and microphysical interactions with the meteorology. A chemistry-induced change of approximately −15% is found in the five-month mean daily convective precipitation over areas with high convective rain; most of this can be traced to radiative effects. Although, total non-convective rain is less than total convective rain in the domain, chemistry-induced effects on the former are more pronounced than those on the latter. A chemistry-induced increase of about +30% is evident in the five-month mean daily non-convective precipitation over the heavily urbanized parts of the Atlantic coast. The effects of aerosols on cloud microphysics and precipitation were examined for two particle size ranges: 0.039–0.1 μm and 1–2.5 μm. Strongly positive spatial correlation between cloud droplet number and non-convective rain are found for activated (cloud-borne) aerosols in both size ranges. Non-activated (interstitial) aerosols have a positive correlation with cloud droplet number and non-convective rain when they are small and an inverse correlation for larger particles.

Citation: Mashayekhi, R. and Sloan, J. J.: Effects of aerosols on precipitation in north-eastern North America, Atmos. Chem. Phys. Discuss., 13, 27937-27969, doi:10.5194/acpd-13-27937-2013, 2013.
 
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