Research Stay at University of Oklahoma, USA []

Anton Kötsche (University of Leipzig)
Place: University of Oklahoma, USA
Time Period: 24.10.2023 - 08.11.2023
Funded by PROM Network Funds

Work and research were conducted at the National Weather Center in Norman (Oklahoma). The aim of the research trip was the development of a snowfall rate retrieval exploiting the W-Band data collected during the CORSIPP project and to initiate scientific collaboration between the remote sensing group of Heike Kalesse-Los and the group of Alexander Ryzhkov. The scientific presentation by Anton Kötsche in the working group of Alexander Ryzhkov about the CORSIPP campaign and first research results triggered intense discussions about snowfall retrievals exploiting CORSIPP data as well as intriguing KDP signatures anticorrelated with the particle number concentration.

Figure 1: Comparison of the reflectvities from the Uni Leipzig W-Band cloud radar, the ARM Ka-Band and the CSU X-Band radar from a shared measurement volume during the SAIL campaign in December and January 2023. From left to right W vs Ka, W vs X and Ka vs X.

The latter topic especially led to lively ongoing cooperation with Alexander Ryzhkov and Petar Bukovcic. Since Dec 2023, monthly meetings have been organized to discuss and investigate these KDP signatures. During the two weeks, under the guidance of Alexander Ryzhkov and Petar Bukovcic, preparatory research for the snowfall rate retrieval was performed. Data from ARM KAZR Ka-Band radar and the CSU X-Band radar during the SAIL experiment were analyzed. Preliminary triple frequency analysis as well as an investigation of calibration offsets between the radars were performed (see Fig. 1). It was found that the CSU X-Band radarcould have an offset of up to 8 dBz, while the reflectivity of the Uni Leipzig W-Band and ARM Ka-Band radar matched well.

Figure 2: Reflectivity dual wavelength ratio (DWR) of X and W-Band radar in a shared measurement volume vs particle mean mass diameter (Dm) derived from the snowfall camera, both from the CORSIPP campaign between Dec 1 and Dec 15, 2022. Colors refer to the total particle number per cubic meter measured by the snowfall camera. Three fits of the data are plotted, one equation was adapted from Matrosov et al. (2021) and the others were created using the actual data.

Figure 3: KDP of W and X-Band radar (left) along the black lines visible in the right plot. The right plot shows KDP of a X-Band radar RHI scan towards the W-Band radar.

Mean volume diameter measurements (Dm) of the snow particles derived from the Uni Leipzig snowfall camera VISSS (video in-situ snowfall sensor) were related to the reflectivity dual wavelength ratio (DWR) of the X and W-Band radar and compared to similar investigations by Matrosov et al. (2021) (see Fig. 2). It was also found that the dependency of DWR and Dm is weak when rime mass fraction is high and vice versa. Specific differential phase measurements (KDP) profiles of the X-Band and W-Band radar were compared (see Fig. 3). Despite the beams not being aligned, but rather crossing each other, multiplying KDP by wavelength and dividing by cos(elevation) resulted in similar values of KDP. During his research stay in the US, Anton Kötsche also participated in the SAIL workshop in Boulder (Colorado) between 1-3 November 2023 and brought CORSIPP and SPP PROM in general to the attention of the SAIL/SPLASH/SOS communities and new collaborations have been established.