Wednesday, 12 February 2003: 4:30 PM
Characterization of Nocturnal Jets Over Philadelphia During Air-Pollution Episodes
Raman lidar employed simultaneously with wind measurements of a Radar/RASS profiler can be used to characterize features of nocturnal boundary layer jets (LLJs). While the profiler/RASS measurements document the kinematic and thermodynamic structure by identifying the velocity and virtual temperature distributions, the lidar observations provide high temporal and spatial resolution of the water vapor mixing ratio, temperature, ozone concentration, and optical extinction. Case studies are presented which describe the use of the Penn State University (PSU) Raman lidar and Radar/RASS profiler near Philadelphia during NE-OPS to delineate the physical characteristics of the LLJ, its development and evolution, relationship to the nocturnal inversion and residual boundary layer, and the variations in observed parameters associated with LLJ phenomena. An important finding is the intrusion of drier air, often with elevated ozone concentrations as the LLJ oscillates to become a westerly conveyor of air from the western boundary region in the early morning hours. The periods of well-developed nocturnal jet are highly correlated with the major air-pollution episodes observed during the summer.