Quantifying Ice and Snow Particle Terminal Velocities, Backscatter Cross-Sections and Snowfall Rates Using Aircraft and Ground-Based Doppler Radar and In-Situ Aircraft Measurements from IMPACTS

Multi-Wavelength Aircraft and Ground-Based Doppler radar measurements are used in conjunction with in-situ aircraft measurements to better quantify the scattering and microphysical properties of snow particle populations and the development of snow in snowbands. The data were obtained during the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) in 2022

In our study, we compare calculated to measured reflectivity at X, Ku, Ka and W bands several backscattering methods. We use direct measurements of the ice water content to constrain the mass of the ice particles. This allows us the unprecedented ability to evaluate our recent terminal velocity parameterizations, by comparing calculated to measured Doppler velocities.

This investigation has led to the finding that it may not be the terminal velocity parameterization that is inaccurate, but it is the mass estimated from a reliable mass dimensional relationship that is in error. Using the particle size distributions together with the in-situ measured ice water content and collocated X band radar data from the overflying ER-2 aircraft, we could derive the best estimates of the mass dimensional relationship that would fit the observations.

With the improvement of the Doppler fallspeeds for snow from IMPACTS, we are now able develop Doppler terminal velocities as a function of the radar reflectivity that will provide reliable estimates of the air vertical motions from the ground-based radars. We can also develop reliable, multi-wavelength relationships between radar reflectivity and snowfall rate. Applying this analysis and the in-situ observations, we investigate the vertical changes in the snowfall rate in snowbands sampled during the IMPACTS field programs.