Further Investigation of Severe Weather Events with the Airborne Phased Array Radar (APAR) Observing Simulator

The current landscape of airborne weather radars in the United States consists of the operational Tail Doppler Radars (TDRs) on the NOAA WP-3D hurricane hunter aircraft and various cloud radars within the university community. With the retirement of the NSF ELectra DOppler RAdar (ELDORA) over ten years ago, there has been a gap in our ability to perform innovative research related to high-impact weather events, especially in remote locations. Therefore, NSF and the National Center for Atmospheric Research (NCAR) are in the process of developing a new and transformational airborne radar: the Airborne Phased Array Radar (APAR). This new radar is designed to fly on the NSF/NCAR C-130 aircraft and to provide both dual-Doppler and dual-polarization capabilities using agile scanning methods associated with PAR technology. While APAR is still in development, a tool was created at NCAR that allows scientists to test various uses of APAR in a controlled setting. The APAR Observing Simulator (AOS) uses model output and user-defined radar scan and flight parameters to provide realistic radar output that would be expected with APAR’s given technical specifications.

Airborne radars provide a unique opportunity to understand high-impact weather events, such as hurricanes and mesoscale convective systems, due to their ability to sample large areas of a storm and to follow a storm as it propagates. Previous experiments with the AOS output investigated some of the radar's technical limitations related to flight and scan strategies, expected beam broadening away from the radar boresight, and attenuation comparisons with X-band radars (currently in use on the NOAA WP-3D aircraft). Evaluation of the Doppler winds and their comparison with known storm characteristics confirmed that APAR could provide this information with a high level of accuracy. These experiments show that at a minimum, APAR can support objectives that were designed for mechanically scanning tail Doppler radars. APAR is also equipped with dual-polarimetric capabilities, providing a new opportunity to study the microphysical and precipitation characteristics of these severe storms in new ways.

This presented work discusses the results of several experiments investigating topics related to particle identification (PID) distributions and Quantitative Precipitation Estimates (QPE). The initial PID determination and analysis results suggest that the hydrometeor classifications generally match well between the simulated cases and known distributions. For instance, the rain and snow distributions are well-represented, but there is a noticeable difference in the amount of ice crystals depicted in the simulated storms compared to observations. The information obtained from the PID classifications is used to help determine ice water content (IWC) and ice water path (IWP) in a hurricane case. The results from the QPE analysis indicate that specific methods are preferable for APAR, where “hybrid” rain rate determination schemes tend to provide more accurate results. Additionally, results associated with the hydrometeor classification scheme are discussed for application to APAR and how they can be utilized to provide more specific estimates of particle fall speeds and ultimately generate improved estimates of vertical velocity. More appropriate vertical velocity determination has implications for the trustworthiness of 3-D wind analyses and associated microphysical processes.