Investigations of Microphysical Processes in US Northeast Coast Winter Storms Using Millimeter-Wavelength Cloud Radar Measurements

Aggregation and riming are important microphysical processes influencing the density and size of snow particles in US Northeast winter storms. Understanding the intricate processes of aggregation and riming in stratiform snow events is a complex task, largely due to their simultaneous occurrence and intertwined influence. Detecting and distinguishing riming as well as quantifying its degree — factors that strongly affect snowfall quantities — present significant challenges.

Multi-frequency radar observations from the Stony Brook University – Brookhaven National Laboratory Radar Observatory (SBRO) are used here to enhance our understanding of snowfall processes and to achieve quantitative and qualitative analysis of the riming process. These observations were carried out using a W-band profiling radar (94 GHz), a next-generation K-band (24 GHz) micro rain radar (MRRPro), and a Ka-band (35 GHz) scanning polarimetric radar (KASPR).

Utilizing the radar dual-wavelength ratio (DWR) from K- and W-bands and Doppler velocity (V), we quantify the degree of riming represented by effective liquid water path and the water-equivalent mean diameter of snow particles. In our observation, a high degree of riming is consistently aligned with supercooled liquid cloud droplet layers. We explore the W-band reflectivity (Z) and fall speed (V) in an exponential relation form (V=aZ^b). From the data collected during a winter snow event, the coefficient 'a' showed a positive correlation with particle fall speed. The coefficient 'b' negatively correlates with riming degree derived from DWR-V relation, suggesting rapid growth by riming in its early stages. Moving forward, we intend to leverage the V-Z relation of the W-band radar for riming degree quantification and further exploration of the microphysical processes using multi-sensor observations, encompassing polarimetric variables and Doppler spectra.