92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012: 4:30 PM
How Aerosols Impact Convection and Large-Scale Circulation Through Deep Convection? (invited)
Room 244 (New Orleans Convention Center )
Jiwen Fan, PNNL, Richland, WA; and D. Rosenfeld, L. R. Leung, Y. Ding, and Z. Li

Aerosol-cloud interaction is recognized as one of the key factors influencing cloud properties and precipitation regimes. For deep convection clouds (DCCs), the vertical distribution of latent heating could be significantly changed through aerosol microphysical effects, which could impact large-scale circulation. This study explores the potential influence on large-scale circulation through aerosol microphysical effect by examining how aerosols change horizontal and vertical mass fluxes, latent heat and radiation fluxes under different wind shear conditions for typical convective clouds (i.e., warm- and cold-based) from the AMF-China field campaign and the SGP IOP 2006. Using model simulations from the Weather Research and Forecasting (WRF) model coupled with a spectral-bin microphysics (SBM) and observational analysis from long-term data at the SGP site, we demonstrate that large-scale circulation can be dramatically changed by aerosols through changes in latent heat and updraft and downdraft mass fluxes. Under weak wind shear conditions, aerosol microphysical effects invigorate DCC, enhance latent heat release, and increase vertical velocity and subsidence. The effects are particularly significant for warm-based DCC. However, when wind shear becomes stronger, the changes in latent heat, vertical velocity and vertical mass fluxes are becoming much smaller for both warm- and cold-based DCC. We note that increasing wind shears could change the sign of aerosol impact on convective strength: from invigoration under weak wind shear to suppression when wind shear gets stronger, consistent with our previous finding for isolated DCC case. This finding enhances our understanding of aerosol-deep convection interactions and provides the scientific basis to better parameterize aerosol effects on convection and large-scale circulation.

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