Exploiting cloud radar Doppler spectra of mixed-phase clouds during ACCEPT field experiment to identify microphysical processes

Cloud radar Doppler spectra offer a wealth of information about cloud processes. By looking at the evolution of millimeter radar Doppler spectra from cloud-top to cloud-base in mixed-phase clouds in which one or multiple super-cooled liquid-layers are present we try to tell the microphysical evolution story of the hydrometeor populations that are present by disentangling the contributions of the solid and liquid particles to the total radar returns. Instead of considering vertical profiles, dynamical effects are taken into account by following the particle population evolution along slanted paths which are caused by horizontal advection of the cloud.

The synergy of lidar-radar-microwave radiometer (MWR) observations is used in several ways: The presence of super-cooled liquid layers is identified by positive liquid water paths in MWR measurements, the vertical location of liquid layers (in non-raining systems and below lidar extinction) is derived from regions of high-backscatter and low depolarization in Raman lidar observations. In collocated cloud radar measurements, we try to identify cloud phase in the cloud radar Doppler spectrum via location of the Doppler peak(s), the existence of multi-modalities or the skewness of the spectrum as previously done in e.g., Shupe et al., 2004 and Luke et al., 2010.

Additionally, within the super-cooled liquid layers, the radar-identified liquid droplets are used as air motion tracer to correct the radar Doppler spectrum for vertical air motion w. These radar-derived estimates of w are validated by independent estimates of w from collocated Doppler lidar measurements.

The methodology is demonstrated using 35GHz vertically pointing cloud Doppler radar measurements with a METEK MIRA-35 (Görsdorf et al., 2015) in linear depolarization (LDR) mode from the deployment of the Leipzig Aerosol and Cloud Remote Observations System (LACROS) during the Analysis of the Composition of Clouds with Extended Polarization Techniques (ACCEPT) field experiment in Cabauw, Netherlands in Fall 2014. There, a second MIRA-35 was operated in simultaneous transmission and simultaneous reception (STSR) mode for obtaining for obtaining measurements of differential reflectivity (ZDR) and correlation coefficient &rhohv. From these observations, an algorithm to derive the shape of pristine ice crystals from the polarimetric measurements was developed (Myagkov et al., 2015, in preparation; presented here at conference).

For several case studies, we analyze the presence and microphysical development of different hydrometeor populations by tracking the evolution of the cloud Radar Doppler spectra. The goal is to identify regions in which different microphysical processes such as new particle formation (nucleation), water vapor deposition, aggregation, riming, or sublimation occur. Cloud radar measurements are supplemented by Doppler lidar and Raman lidar observations as well as observations with MWR, wind profiler, and radio sondes.

References:

Luke, E., et al., 2010: Detection of supercooled liquid in mixed-phase clouds using radar Doppler spectra, J. Geophys. Res., 115, D19201. Shupe, M., et al., 2004: Deriving mixed-phase cloud properties from Doppler radar spectra, J. Atmos. Ocean. Tech., 21, 660-670.

Görsdorf, U., V. Lehmann, M. Bauer-Pfundstein, G. Peters, D. Vavriv, V. Vinogradov, and V. Volkov, 2015: A 35 GHz polarimetric Doppler radar for long term observations of cloud parameters - Description of system and data processing. J. Atmos. Oceanic Technol., in press, doi:10.1175/JTECH-D-14-00066.1.

Shupe, M., et al., 2004: Deriving mixed-phase cloud properties from Doppler radar spectra, J. Atmos. Ocean. Tech., 21, 660-670.