Observational and 3D Modeling Studies of the Microphysical, Electrical, and Chemical Nature of Houston Area Thunderstorms (HEAT project)

 

Abstract

As part of the Houston Environmental Aerosol Thunderstorm (HEAT) Project, we propose a program of cooperative field observations and storm numerical model simulations to advance knowledge of thunderstorm processes in three areas. First, we propose to test the hypothesis that urban aerosols, when ingested into thunderstorms, modify precipitation-forming and charge separating processes within the storms to enhance their output of negative cloud-to-ground lightning compared to storms forming in less polluted environments. A second hypothesis to be tested is that this same contrast in aerosol properties leads to a smaller percentage of cloud-to-ground lightning lowering positive charge. In both tests the mechanisms responsible for the contrasting behavior will be elucidated using coordinated observations (including airborne and ground-based aerosol, airborne cloud microphysics, multi-parameter and multiple Doppler radar, lightning mapping array, and cloud-to-ground lightning data) of storms forming in the Houston region, some over the urbanized area, and some over more rural surroundings, along with de-tailed numerical simulations using the SDSMT Storm Electrification Model (SEM). Finally, air-borne and ground-based observations of trace gas chemistry, particularly NOx and O3, around and within HEAT storms will be used, in conjunction with the SEM to better quantify the production of NOx by lightning in thunderstorms. The research includes participation in the HEAT field project in the summer of 2005 followed by data analysis and synthesis, as well as SEM simulations.

Broader Impacts: Results from this research – combined data analysis and model simulations – will advance our knowledge of thunderstorm electrification, in general, and the influence of urban aerosol concentrations on cloud microphysics and storm electrification, in particular. Determination of the effects of urban land-use, especially particulate emissions, on thunderstorm development can have a significant impact on future urban planning. Better understanding of thunderstorm electrification, in general, will contribute to better storm and lightning forecasting. Model simulations will also address the production of NO by lightning in a polluted environment. By helping to improve knowledge of the NO production rate of lightning, uncertainty in the global lightning NOx source term can be refined from its current order-of-magnitude range. This will result in less uncertainty in the role played by lightning-produced NOx in the global modeling of atmospheric chemistry and should impact predictions of the tropospheric/stratospheric ozone burden by reducing a primary source of error. Since ozone is a radiatively active trace gas, this should ultimately improve knowledge about the contribution of tropospheric ozone to global climate predictions. These are very important areas, both to science and society at large. Results obtained from the field project and model simulations will also be incorporated directly into undergraduate and graduate courses taught by the PI and Co-PI.