Investigating KDP signatures inside and below the dendritic growth layer with W-band Doppler radar and in situ snowfall camera

Abstract. Polarimetric radars provide variables like the specific differential phase (KDP) to detect fingerprints of dendritic growth in the dendritic growth layer (DGL) and secondary ice production, both critical for precipitation formation. A key challenge in interpreting radar observations is the lack of in situ validation of particle properties within the radar measurement volume. While high KDP in snow is usually associated with high particle number concentrations, only few studies attributed KDP to certain hydrometeor types and sizes. To address this, we combined surface in situ observations from the Video In Situ Snowfall Sensor (VISSS) with remote sensing data from a polarimetric W-band radar and an X-band radar, along with modeling approaches. Data were collected during the CORSIPP project, part of the ARM SAIL campaign (winter 2022/2023, Colorado Rocky Mountains). We found that at W-band, KDP > 2 ° km−1 can result from a broad range of particle number concentrations, between 1 and 100 L−1. Blowing snow and increased ice collisional fragmentation in a turbulent layer enhanced observed KDP values. T-matrix simulations indicated that high KDP values were primarily produced by particles smaller than 0.8 mm in the DGL and 1.5 mm near the surface. Discrete dipole approximation simulations based on VISSS data suggested that dendritic aggregates larger than 2.5 mm contributed 10 %–20 % to the measured W-band KDP near the surface. These findings highlight the complexity of interpreting W-band KDP in snowfall and emphasize the need for combined in situ observations and radar forward simulations to better understand snowfall microphysical processes.