The Role of Aerosols on Precipitation for the New York Metro Region

Several studies have found evidence of warm-season rainfall increases over and downwind of major cities such as Atlanta, Phoenix, Mexico City, St. Louis, and Chicago. This precipitation has been predominately attributed to the induced updraft of warm air masses. Aerosols are abundant in urban environments, and it has been hypothesized that they may play a key role in the water balance of urban humid regions. High concentrations of cloud condensation nuclei (CCN) may induce precipitation in humid urban environments. However, it is also noted that precipitation may also be reduced due to excess CCNs or by the presence of large aerosols, which are also known as giant cloud condensation nuclei (GCCN). The present research is directed towards improving our understanding of the role of aerosols in cloud processes in complex coastal urban environments through ground observations obtained from remote sensors (AERONET, local lidar) and a very dense network of ground stations (NOAA Cooperative, Weatherflow) and high resolution numerical analysis across the New York-New Jersey Metro Region (NY-NJ). Growth of particles from CCN to rain droplet sizes is explored for characteristic aerosol distributions obtained from these observations for summer time conditions. The role of aerosols in precipitation is investigated through numerical analysis of cloud microphysics by implementing population growth by condensation, collision, and coalescence within the computational model. A Lagrangian modeling approach is used to describe these three processes that also allows for in-situ data assimilation from observations. Particle size distributions are assimilated into the Regional Atmospheric Model System (RAMS) in order to explore the fundamental questions associated to the effects of aerosols on cloud microphysics and precipitation, and to discern between local precipitation attributed solely to the presence of atmospheric aerosols, and precipitation caused by convection. The cases are investigated for summer 2007 for the NJ-NY where local and synoptic precipitation observations where indentified. Comparisons of the predicted precipitation with ground stations and radar observations help to validate the hypotheses.