Tuesday, 8 January 2013
Sea breeze is a prevailing wind near the coastal areas induced by the increasing temperature differences between the land and the sea. When the cold moist air from the sea meets the warmer air from the land, a shallow cold front boundary is created and cumulonimbus clouds are triggered. A two-moment bulk microphysical scheme has been implemented into the Weather Research and Forecasting (WRF) model to investigate the effects of aerosols on cloud and precipitation processes associated with the sea breeze frontal event occurring on 24 August 2000 in Houston, Texas. The anthropogenic sulfate aerosols from the Houston urban area are simulated using a constant local emission source, and the production of sea salt particles is simulated using an empirical parameterized scheme over the ocean surface in the model. In comparison of the National Mosaic Reflectivity Images, the modeled evolutions of column-maximal radar reflectivity exhibit a qualitatively good agreement with the measurements. Sensitivity simulations are initialized using a set of aerosol profiles. The results show that aerosols, serving as cloud condensation nuclei, can significantly alter the cloud number concentration, liquid and ice water content, cloud optical thickness and cloud coverage associated with the sea breeze front. In the downwind of the urban area, the precipitation has been redistributed due to the modified convection core affected by the aerosols. The response of precipitation amount to the elevation of aerosol concentrations is non-monotonic because of the complicated interaction between cloud microphysics and dynamics. The aerosol radiative effects on the atmospheric stability and the sea breeze formation will be examined in the next step through incorporating the aerosol optical properties in the radiative scheme of the model.
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