Leveraging Emerging Centimeter-Wavelength Rapid-Scan Radar Technologies to Improve Sampling of Microphysical and Dynamic Processes in Deep Convection

Understanding precipitation processes requires fine spatiotemporal sampling to capture the characteristic scales of underlying microphysical and dynamic processes. In deep convection, convective updrafts and downdrafts are unsteady and have relatively short lifecycles. For example, convective initiation and precipitation formation can occur within 15 – 20 min, and unsteady updraft characteristics (e.g., depth, width, 3D velocity) in turn affect precipitation formation and the development of hazards (flooding, hail). Rapid-scan radars have the potential to capture this unsteady evolution of updraft dynamics while simultaneously collecting polarimetric measurements to extract information about hydrometeor types, sizes, concentrations necessary to characterize microphysical processes.

Most existing dish-based centimeter(cm)-wavelength radars scan too slowly to capture the evolution of deep convection and to provide sufficient vertical sampling to enable holistic studies of convective processes. In contrast, phased array radars employ adaptive sampling techniques to acquire volume scans in 1 min or less and obtain bottom-to-top coverage of deep convection without vertical gaps. Adaptive sampling with phased arrays can also prioritize measurements of the boundary layer to characterize subcloud and mesoscale processes preceding convective initiation while concurrently tracking deep convection initiation.

This study will examine how rapid-scan radars can improve observations of vertical motions and microphysical characteristics of deep convection. Vertical velocity estimates are improved through rapid-scan radar observations that minimize non-linear advection and evolution of deep convection during volume scan times. Continuous vertical profiles of polarimetric observations above regions with different precipitation rates or hail sizes can enable important information about microphysical processes. These applications will be demonstrated using data collected from rapid-scan weather radars, including the Rapid-scan X-band Polarimetric radar (RaXPol) and Atmospheric Imaging Radar (AIR). The benefits of imaging, enabled by phased array radars, will be demonstrated for examining the fine-scale (sub-km) structure of convective updrafts and downdrafts will be shown. In addition, a descending hail core example will be shown to illustrate rapid changes in polarimetric signatures associated with melting, size sorting, and drop shedding.