Brandon Cohen - April 15

Convective Meteorology (Mesoscale Dynamics)

Examining Meteorological Benefits of Rapid-Scan, Dual-Polarization, All-Digital PAR Observations for Detecting Tornado Formation and Intensification

Brandon Cohen

Friday, April 15

03:00 PM

Phased array radar (PAR) is widely considered the future for a replacement to the current operational radar network, NEXRAD. In particular, an all-digital operational PAR network offers a range of benefits, including adaptive scanning techniques, higher temporal resolution especially via radar imaging modes, and vertically continuous data to allow for more complete observations of severe hazard structure and evolution. This study focuses on the application of future operational radar systems to observe tornadoes and their formation. To best understand the benefits of a future all-digital operational PAR, we generate synthetic PAR observations from archived mobile rapid-scan observations collected by the Rapid X-band Polarimetric radar (RaXPol). Data from mobile radars like RaXPol constitute a good basis for synthetic PAR data given their higher temporal resolution as well as their low-level and spatial sampling capabilities. The synthetic PAR observations are generated by spatially averaging data in both range and azimuth to emulate typical operational radar ranges, with additional factors such as reflectivity weighting of Doppler velocities accounted for during this process. PAR scanning strategies for both focusing and imaging have also been implemented.

For this study, the synthetic PAR tool is applied to two datasets from RaXPol: the 24 May 2011 El Reno, Oklahoma tornado and the 24 May 2016 Dodge City, Kansas tornadoes. Range and azimuth averaging is applied over different windows to emulate different standoff ranges more comparable to operational, fixed-site radars. Using dealiased velocity data, we analyze the intensity of synthetic PAR tornado vortex signatures (TVS) through Delta-V plotted as a function of time and height for each different standoff range. Despite increasingly coarse resolution, we find similar qualitative trends in the vertical evolution of TVS intensity even though the magnitude of Delta-V decreases. TVS intensification is found to occur in an ascending or simultaneous manner, even for data that has undergone spatial resampling to much longer standoff ranges (e.g., 80 km). Thus, it appears that detection of rapid TVS intensification occurring in an upward or simultaneous manner, as seen previously with mobile radars, can be used to detect tornadogenesis with future operational PARs. Additional work has focused on comparison of expected PAR revisit times in comparison to NEXRAD volume scan times. Update times of 60 seconds or faster are found enhance the data available to forecasters by better capturing critical evolution steps currently missed at NEXRAD update times. Finally, work and analysis has been done on the implementation of focusing and imaging scanning strategies. Ultimately, through understanding the meteorological benefits from the synthetic PAR data we should be able to contribute to improved planning for future all-digital operational PARs and warning decisions for tornadic storms.