Effects of aerosols on precipitation in north-eastern North America

Authors:
  • RMR. Mashayekhi
    R. Mashayekhi
  • JSJ. J. Sloan
    J. J. Sloan
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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.
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