Articles | Volume 16, issue 5
Atmos. Chem. Phys., 16, 2997–3012, 2016
https://doi.org/10.5194/acp-16-2997-2016
Atmos. Chem. Phys., 16, 2997–3012, 2016
https://doi.org/10.5194/acp-16-2997-2016

Research article 09 Mar 2016

Research article | 09 Mar 2016

Fingerprints of a riming event on cloud radar Doppler spectra: observations and modeling

Heike Kalesse1,a, Wanda Szyrmer1, Stefan Kneifel1,b, Pavlos Kollias1,c, and Edward Luke2 Heike Kalesse et al.
  • 1McGill University Montreal, Montréal, QC, Canada
  • 2Brookhaven National Laboratory, Upton, NY, USA
  • anow at: Leibniz-Institute for Tropospheric Research, Leipzig, Germany
  • bnow at: University of Cologne, Cologne, Germany
  • cnow at: Stony Brook University, Stony Brook, NY, USA

Abstract. Radar Doppler spectra measurements are exploited to study a riming event when precipitating ice from a seeder cloud sediment through a supercooled liquid water (SLW) layer. The focus is on the "golden sample" case study for this type of analysis based on observations collected during the deployment of the Atmospheric Radiation Measurement Program's (ARM) mobile facility AMF2 at Hyytiälä, Finland, during the Biogenic Aerosols – Effects on Clouds and Climate (BAECC) field campaign. The presented analysis of the height evolution of the radar Doppler spectra is a state-of-the-art retrieval with profiling cloud radars in SLW layers beyond the traditional use of spectral moments. Dynamical effects are considered by following the particle population evolution along slanted tracks that are caused by horizontal advection of the cloud under wind shear conditions. In the SLW layer, the identified liquid peak is used as an air motion tracer to correct the Doppler spectra for vertical air motion and the ice peak is used to study the radar profiles of rimed particles. A 1-D steady-state bin microphysical model is constrained using the SLW and air motion profiles and cloud top radar observations. The observed radar moment profiles of the rimed snow can be simulated reasonably well by the model, but not without making several assumptions about the ice particle concentration and the relative role of deposition and aggregation. This suggests that in situ observations of key ice properties are needed to complement the profiling radar observations before process-oriented studies can effectively evaluate ice microphysical parameterizations.

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Short summary
Mixed-phase clouds are ubiquitous. Process-level understanding is needed to address the complexity of mixed-phase clouds and to improve their representation in models. This study illustrates steps to identify the impact of a microphysical process (riming) on cloud Doppler radar observations. It suggests that in situ observations of key ice properties are needed to complement radar observations before process-oriented studies can effectively evaluate ice microphysical parameterizations in models.
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