Aerosol Impacts on Warm Season Precipitation over New York City

The research presented herein is directed towards determining aerosol particle size-distribution (PSD) and urban effects on precipitation for the coastal urban environment of New York City (NYC). It is known that urban environments influence precipitation formation via response to dynamic effects, while aerosols are intrinsically necessary for rainfall formation; however, the partial contributions of each on urban precipitation are not yet well known. This research aims to investigate this with the higher goal of improving precipitation forecasts in complex urban environments. The Regional Atmospheric Modeling System (RAMS) was used to simulate July 2007 summer precipitation scenarios for NYC. Aerosol PSDs from the NASA Aerosol Robotic Network (AERONET) were processed and ingested directly into RAMS to represent cloud condensation nuclei (CCN) and giant CCN (GCCN) PSDs for selected events. High resolution land data acquired from the National Land Cover Database (NLCD) was assimilated to provide land cover land use (LCLU) of the city. An ensemble of simulations that varied PSD and LCLU were configured. Results for two one-day events, 11 and 18 July 2007, which were localized and regional, respectively, showed that sea-breezes fueled precipitation formation. Topography also played a strong role in initiating precipitation for the localized event, but had a lesser effect on the regional event. Results also suggest that LCLU provides the dominant forcing for urban precipitation, affecting precipitation rates, rainfall amounts, and spatial precipitation patterns. PSD then acts to modify cloud physics. These results are then the first demonstration of the interactions of the urban-dynamics and urban-aerosol impact-theories of R. Bornstein and D. Rosenfeld, respectively.