Abstract
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.
Highlights
Mixed-phase clouds are ubiquitous, long-lived, and cover extended areas (e.g., Shupe et al, 2008; Zhang et al, 2010; Kanitz et al, 2011)
An intensive observation period focusing on winter precipitation (BAECC-Snowfall Experiment (SNEX)) organized in collaboration with the National Aeronautics and Space Administration (NASA) Global Precipitation Measurement (GPM) ground validation program and Colorado State University was conducted from 1 February to 30 April 2014
For a frontal winter snowfall event observed at the SMEAR II site in Hyytiälä in Finland during the BAECC-SNEX field experiment in 2014, we show that by disentangling the contributions of the different hydrometeor populations to total vertically pointing cloud radar returns, it is possible to follow www.atmos-chem-phys.net/16/2997/2016/
Summary
Mixed-phase clouds are ubiquitous, long-lived, and cover extended areas (e.g., Shupe et al, 2008; Zhang et al, 2010; Kanitz et al, 2011). The complex interaction between atmospheric vertical motions, aerosol particles, water vapor, liquid water, and ice determine the radiative and microphysical properties of mixed-phase clouds to a large extent (Gregory and Morris, 1996). The temporal (height) evolution of the radar Doppler spectrum is analyzed along slanted fall streaks from cloud top to cloud base to optimally follow the particles’ history in order to gain insight into microphysical processes occurring in different layers of the mixed-phase cloud (Marshall, 1953; Hogan and Kew, 2005). This study illustrates the objective steps in identifying the impact of a microphysical process (riming) on radar observations (fingerprints) and the steps required to analyze a multisensor data set containing radar Doppler spectra.
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