Cloud and Precipitation Structure and Processes in Midwest and Northeast North American Snowstorms: Results from IMPACTS

Midlatitude winter snowstorms can have large socio-economic consequences, adversely affecting transportation, safety, and can cause loss of life. Numerical model forecasts of the distribution, intensity and duration of snowfall within these storms are often in error and better understanding of the multi-scale dynamical and microphysical processes in snowstorms is necessary to improve forecasts. In order to address this need, the NASA-led Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign made remote sensing and in situ measurements in a wide variety of East Coast and Midwestern snowstorms during the winters of 2020, 2022 and 2023. The satellite simulating, high altitude ER-2 aircraft was equipped with radars at multiple frequencies, a cloud lidar, microwave radiometers, and a lightning detection system, and the in-situ P-3 aircraft was equipped with microphysical probes, a dropsonde system, and measured environmental conditions along the flight lines. These two aircraft were flown in coordination so that the microphysical measurements made by the P-3 could be directly related to the remote sensing measurements made by the ER-2. Over 35 storms were sampled by IMPACTS aircraft across the three winter seasons, spanning from Alberta Clipper type events to rapidly-deepening nor’easter type storms. Although the analysis of IMPACTS data is ongoing, this presentation will introduce some preliminary results. One such study capitalizes on the use of multi-frequency airborne radars on the ER-2 and relates those data to microphysical properties as sampled by the P-3. The dual-frequency ratio (DFR) derived from the Ku- and Ka-band from the HIWRAP instrument on the ER-2 was analyzed and regions of prominently higher DFR at the in-situ P-3 aircraft location were distinguished using a novel technique for all coordinated flights during IMPACTS. Results across all three deployments indicate that within regions of enhanced DFR, the mass-weighted mean diameter was 63% larger, the effective density was 73% smaller and the normalized intercept parameter was 11% smaller compared to periods outside of regions of enhanced DFR for the particles in the size ranges detectable by the HVPS microphysics probe (0.4–30 mm). These results are consistent with the aggregation process occurring within regions of high DFR, implying this process is potentially detectable in winter storms from satellite-borne remote sensing instruments. Results from observationally-constrained Lagrangian model simulations of stratiform winter storms during IMPACTS that provide insights into the effects of the riming process on reflectivity and Doppler velocity remote sensing measurements will also be presented.