Exploring Convective Boundary Layer Depth and Entrainment Zone Properties with Dual-Polarization Radar Observations

Convective boundary layer (CBL) characteristics, especially depth, play an important role in many atmospheric processes. However, frequent observations of CBL depth and other CBL characteristics are not routinely available from current operational observation systems. Recent work has taken advantage of the existing network of dual-polarization WSR-88D radars to investigate CBL depth estimates that can be produced for every radar volume scan (roughly every 10 minutes or less) at every WSR-88D site. This study further examines signals from dual-polarization radar observations to retrieve more information on the structure of CBLs observed with the WSR-88D radars.

Utilizing differential reflectivity (ZDR) data from the WSR-88D radar in State College, Pennsylvania (KCCX), CBL depth and entrainment zone (EZ) properties are investigated across 30 days starting in summer 2022. These signals are compared to atmospheric observations collected by Windsond weather balloons launched from The Pennsylvania State University, University Park campus. Preliminary results confirm that the minima in quasi-vertical profiles (QVPs) of ZDR values during the daytime correlate well with Windsond-observed CBL depths. It is also found that QVPs of azimuthal variance of ZDR can provide further information on CBL and EZ characteristics, especially when the ZDR signal alone is unclear. Exploration of a large number of QVPs identifies several characteristic structures for the minimum ZDR channel that tracks the diurnal evolution of CBL top: narrow channels, wide channels, and uncapped channels. These ZDR and ZDR variance channel structures are investigated using both surface and Windsond observations, as well as simple CBL parameterizations to investigate the physical processes that lead to their formation.