Assessment of scanning strategies on the characterization and detection of downburst and its precursors with all-digital polarimetric phased array weather radar

Strong winds produced by downbursts can be hazardous to aviation and public safety. However, the update time and vertical sampling from a conventional weather radar are often limited and thus prevent timely detection and characterization of downburst precursors. The recently proposed all-digital architecture for polarimetric phased array radar offers maximum flexibility in scanning patterns and can significantly improve update time, which can lead to the improvement of the warning lead time for downburst. In this presentation, we will introduce a simulation framework that was developed to assess the impact of different scanning strategies on weather observations including microburst. This framework takes the output from Cloud Model 1 (CM1) to simulate polarimetric weather observations based on the user-defined radar specification and scanning pattern. Additionally, artifacts such as measurement errors, clutter contamination, range-velocity ambiguity can also be included in the simulation. One of the candidate technologies for a future operational PAR network, a rotating S-band all-digital radar, is simulated, and the imaging technique is used as the main scanning pattern to provide fast update time for downburst observations. Specifically, a spoiled transmitted beam is produced in the elevation direction and multiple narrow received beams are formed simultaneously, which provides continuous vertical sampling within the spoiled beam and faster update times. The tradeoffs of spoiled beam with 2.5, 5.0, and 10 degrees for characterizing the evolution of downburst and its precursors are assessed both qualitatively and quantitively. Imaging results are then compared with range height indication (RHI) scans and pseudo-RHI derived from a volume coverage pattern (VCP) of 212. Our preliminary results have shown that even though the update time can be improved by using a larger spoiled beam, the associated sidelobe contamination can hinder detection and characterization of downburst precursor signatures. The spoiled beams of 2.5 and 5.0 degree can provide reliable signatures with improved update time compared to RHI and pseudo-RHI. One of the quantitative results is shown in the table below, where the root mean square error (RMSE) is used as a performance metric. The downburst signatures are characterized by the surface divergence and the area of surface divergence, while the precursor signatures are characterized by the midlevel convergence, the volume of descending reflectivity core (DRC), the volume of specific differential phase, the rate of 95 percentile change in time for reflectivity and specific differential phase.