On the Meteorological Conditions during Postprecipitation Periods: Implications to Pollutant Dispersion

Abstract

The various processes within the atmospheric boundary layer (ABL) during precipitation events tend to thermally stabilize the ABL. Selected observations are presented in order to illustrate this thermal stabilization for convective and stratified cloud systems. A tendency towards the onset of moist-adiabatic temperature profiles is suggested during stratified precipitation events. Conceptual, analytical, and numerical model evaluations were performed, suggesting that pollutant dispersion characteristics during the postprecipitation periods are likely to be modified considerably compared to these in the preprecipitation periods. When a moist-adiabatic temperature profile is generated as a result of a precipitation event, the significance of the impact on pollutant dispersion under light wind conditions is dependent on the environmental background temperature, where in a warm environment the reduction in pollutant dispersion is most pronounced. Thermal circulations related to cool air pools typical of postprecipitation events and their implications to pollutant dispersion were evaluated by illustrative numerical model simulations. The simulation results imply that the reduction of postprecipitation turbulence effect, due to thermal stabilization of the ABL, may be offset in many situations by the thermal circulations mostly when convective precipitation is involved. Differences between the daytime and nocturnal development of these circulations were found to be significant.