Observing Ice Processes Using Fully Polarimetric Radar Signals and IMPACTS Aircraft Data

Understanding ice processes is critical to understanding the broader picture of winter weather. The Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign provides a unique opportunity to combine research-grade radar and in-situ observations. From this campaign, we have a wealth of information to contribute to our understanding of the processes leading to, and detailed microphysical properties of, winter precipitation events.

Ice multiplication is a significant, and yet poorly understood process. Ice multiplication leads to particle number concentrations orders of magnitude greater than the available ice nuclei concentrations. Ice multiplication processes fundamentally change the sizes, distributions, and shapes of ice crystals in clouds. In principle, such hydrometeor changes are observable by polarimetric radar. Indeed, signals observed in several radar variables, including differential reflectivity (Z_DR), and specific differential phase (K_DP), often are associated with ice multiplication. Cross-polar signals such as the linear depolarization ratio (LDR), cross-polar correlation coefficient (𝜌_XH) and cross-polar phase shift (φ_XH) relate to the depolarization of the radar signal and are connected to ice particle properties.

During IMPACTS, the Ka-band Scanning Polarimetric Radar (KASPR) located at Stony Brook University collected data. KASPR is a great asset for observing winter precipitation, given its fine spatial resolution and fully polarimetric capabilities, allowing for observations of variables including LDR, 𝜌_XH, and φ_XH. From KASPR, we can also use spectrograms to identify multi-modal layers, which contain two or more types of particles with different vertical speeds. Secondary modes may be composed of liquid or ice modes, which can be distinguishable through polarimetric signals or particle imagery. During IMPACTS, probes aboard the P-3 such as the 2D Stereo Probe (2DS) and Hawkeye Cloud Particle Imager (CPI) measured and imaged ice crystals, providing ice and liquid water content and habit information. These in situ measurements help to explain what particles are responsible for observed radar signals.

This study seeks to improve our understanding of the radar signals associated with ice processes and ice multiplication events. This project will examine the fully polarimetric radar signals from KASPR in harmony with in situ measurements from the IMPACTS P-3 aircraft probes to determine the processes associated with those radar signals in multiple IMPACTS cases. Dual-wavelength ratio analysis using Ka- and W-band radars can further elucidate whether riming was occurring and help to determine potential processes. Because we are focusing on lesser-studied fully polarimetric variables including the cross-polar correlation coefficients and phases, this work will be supplemented by scattering calculations for ice particles. Ultimately this will help improve future remote sensing and radar studies of ice multiplication.