Investigation of Microphysical Properties within Regions of Enhanced Dual-Frequency Ratio During the IMPACTS Field Campaign

Abstract:

Measurements from multi-frequency airborne radars have emerged in recent years as a means to evaluate the performance of satellite retrievals and improve our understanding of microphysical properties from a remote sensing perspective. The dual-frequency ratio (DFR), defined as the reflectivity difference between two radar frequencies, is typically influenced by the size, density, and shape of particles. Furthermore, regions of enhanced DFR may be associated with the presence of larger or more heavily rimed particles, and have implications regarding snowfall at the surface. The inclusion of coincident airborne in situ microphysical observations allows for these DFR measurements to be evaluated at multiple frequencies, and provides additional insight into the concentrations, shapes, sizes, and habits of the hydrometeors observed within these enhanced DFR regions.

The Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) is a three-year NASA-funded field campaign aimed at understanding the mechanisms associated with snowband formation, organization, and evolution. The NASA ER-2 housed a suite of radar instruments as it flew above winter mid-latitude cyclones and measured the finescale structure while the P-3 flew in cloud to collect microphysical measurements. Five coordinated flights were conducted during the 2020 deployment, providing coincident radar and microphysical measurements. In this study, we take advantage of these colocated observations to explore DFR characteristics and their relationships to microphysical parameters in snow-producing storms.

An algorithm was developed to directly relate DFR measurements to microphysical properties collected by the P-3. Of the 5800 5-second periods where coincident data were available, approximately 11% of the observations had DFR Ku-Ka > 5 dB. Bulk microphysical quantities such as characteristic size and effective density in relation to these enhanced DFR signatures, and possible mechanisms for the enhancement of DFR, such as stronger vertical motions due to elevated instability or shear-induced turbulence, are explored.