Evaluation and Verification of an Experimental Low-Level VAD for Utilization as a High-Resolution Boundary Layer Profiler

Although the Velocity Azimuth Display (VAD) has established itself as a reliable means through which vertical wind profiles can be retrieved from a scanning Doppler radar, there are still uncertainties as to how well it can resolve wind profiles within heterogeneous flow such as that within the planetary boundary layer (PBL). While there is precedence in literature detailing success in depicting complex PBL phenomenon such as the nocturnal low-level jet at high vertical resolution (< 150 m), there is little in the way of analysis detailing the veracity and reproducibility of results such as these. Easily available and operationally relevant VAD results, such as the NEXRAD level 3 VAD product, tend to provide coarse (> 300m) resolution within the PBL leaving only three to five measurements through which various wind-shear parameters can be calculated and thus potentially impacting their accuracy. This is particularly the case in nocturnal severe storm environments, through which strong low-level shear may be misrepresented in the conventional VAD.

In an attempt to evaluate the efficacy of a scanning Doppler radar as a means through which boundary layer wind profiles can be derived, a custom low-level VAD algorithm has been implemented at UAH utilizing the C-band Advanced Radar for Meteorological and Observational Research (ARMOR). This algorithm has been shown to able to retrieve high-temporal (~5 min) and vertical (~100 m) resolution wind profiles with an average first gate of around 50-150 m above radar level (depending on atmospheric conditions), which is nearly 400-1000 m lower than what is typically available from the level 3 NEXRAD product. In this analysis, results from this preliminary Low-Level VAD dataset are compared to wind profiles retrieved from other ground-based remote sensors capable of resolving low-level wind profiles, such as the 915 MHz wind profilers and Doppler Wind Lidars (DWL). Additional results will also be presented from an experimental Mesoscale Perturbation VAD (MP-VAD), a product that combines the low-level VAD retrievals and low-level radial velocity fields, to determine the feasibility of using this methodology to identify regions of boundary layer heterogeneity in real time.