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This study presents a large-eddy simulation (LES) study of the convective boundary layer on August 1, 1999 over Philadelphia, PA during a summer ozone episode. The study is an evaluation of the Colorado State University's Regional Atmospheric Modeling System Version 4.3 (RAMS4.3) with the LES option using Northeast Oxidant and Particulate Study (NE-OPS) data. Simulations were performed with different imposed sensible heat fluxes at the ground surface. The model was initialized with the atmospheric sounding data collected at Philadelphia at 1230 UTC and model integrations continued till 2130 UTC. The resulting mean profiles of temperature and humidity obtained from the LES model were compared with atmospheric soundings, tethered balloon and aircraft data collected during the NE-OPS 1999 field campaign. Also the model-derived vertical profiles of virtual temperature were compared with NE-OPS Radio Acoustic Sounder System (RASS) data while the humidity profiles were compared with NE-OPS lidar data. The comparison of the radiosonde data with the LES model predictions suggests that the growth of the mixing layer is reasonably well simulated by the model. Overall, the agreement of temperature predictions of the LES model with the radiosonde observations is good. The model appears to underestimate humidity values for the case of higher imposed sensible heat flux. However, the humidity values in the mixing layer agree quite well with radiosonde observations for the case of lower imposed sensible heat flux. The model-predicted temperature and humidity profiles are in reasonable agreement with the tethered balloon data except for some small overestimation of temperature at lower layers and some underestimation of humidity values. However, the humidity profiles as simulated by the model agree quite well with the tethered balloon data for the case of lower imposed sensible heat flux. The model-predicted virtual temperature profile is also in better agreement with RASS data for the case of lower imposed sensible heat flux. The model-predicted temperature profile further agrees quite well with aircraft data for the case of lower imposed heat flux. However, the relative humidity values predicted by the model are lower compared with the aircraft data. The model-predicted humidity profiles are only in partial agreement with the lidar data. The results of this study suggest that the explicitly resolved energetic eddies seem to provide the correct forcing necessary to produce good agreement with observations for the case of an imposed sensible heat flux of 0.1 K m s-1 at the surface. [ABSTRACT FROM AUTHOR]

The present study investigates the usefulness of coupling the prognostic MM5 mesoscale model with the CALMET diagnostic model for producing high resolution wind fields in a computationally efficient manner. Wind fields derived from this system are compared with the wind profiler observations from the Northeast-Oxidant and Particle Study (NE-OPS) field campaign over Philadelphia, PA undertaken during one of the summer ozone episodes in 1999 (23–24 July 1999). The MM5 simulations were performed on a nested grid (36, 12 and 4 km horizontal resolution) with 14 layers in the vertical direction for the period 21 July 1999; 00 UTC to 25 July 1999; 05 UTC. The CALMET meteorological model was applied with 14 layers in the vertical direction, a horizontal resolution of 4 km and a domain which includes New Jersey and the Philadelphia region and was employed in two modes. In the first mode, the MM5 model wind and mixing ratio output results (for 36, 12 and 4 km horizontal resolution) are ingested every hour into the CALMET diagnostic meteorological model along with an objective analysis procedure using all available observations. In the second mode, no MM5 results were utilized and CALMET employed the objective analysis procedure. All the above simulations are compared with the wind profiler data collected during the NE-OPS program. The results of this study indicate that utilizing the coarsest prognostic meteorological model output in a diagnostic model provides an attractive option for generating accurate meteorological inputs for air quality modeling studies, especially for long-term simulations of periods lasting from several weeks to a year. While the mean relative errors for the meridional component of velocity decreased significantly when the CALMET model was operated in the first mode, there was no corresponding significant decrease in the relative errors for the zonal component of velocity in the above mode. [Copyright &y& Elsevier]