Urban Influences on Clouds, Precipitation and Lightning

 

Project Summary

This grant is a continuation of modeling research on the urban influence on clouds and precipitation that was supported under NSF Grant #ATM-9900929. In that research we focused on the afternoon urban heat island and its effects on convection (Rozoff, 2002; Rozoff et al., 2003). In that research we employed a storm-resolving version of the RAMS over St. Louis, MO, on 8 June 1999, along with sophisticated surface boundary conditions (Masson 2000; Walko et al., 2000), to simulate the urban atmosphere and its role in deep, moist convection. Results of sensitivity experiments show the urban heat island is dominant in inducing deep, moist convection downwind of the city. Surface convergence driven by the urban heat island (UHI) is enhanced on the leeward side of the city. The nonlinear interaction between urban momentum drag and the urban heat island causes downwind convection to erupt later, and precipitation totals are enhanced downwind of St. Louis. Topography around St. Louis also impacts storm development.

The proposed research focuses on the following topics:

• Modeling the affects of enhanced cloud condensation nuclei and giant cloud condensation nuclei concentrations on
  afternoon Convection over St. Louis, MO

• Case study modeling of urban impacts on organized mesoscale convective systems(MCSs) passing over St. Louis, MO

• Idealized modeling of urban impacts on organized MCSs

• Participation in the HEAT field campaign

• Modeling urban impacts on convection and cloud structures favorable for lightning over Houston, Texas

This research will contribute to fundamental understanding of the influence of major urban centers on convective storms, lightning, and precipitation. The broader impacts of this research will be on urban land-use planning once a full understanding of urban land-use effects on convective storms is obtained. The educational benefit of this research is that results of this work will be immediately incorporated in the course content of first year and advanced courses in cloud physics and cloud dynamics, as well as in the textbook Human Impacts on Weather and Climate by William R. Cotton and Roger A. Pielke, Sr. In addition, the results will be presented in departmental seminars.