Detection of supercooled liquid in mixed‐phase clouds using radar Doppler spectra

Abstract

Cloud phase identification from active remote sensors in the temperature range from 0 to −40°C, where both liquid and ice hydrometeor phases are sustainable, is challenging. Millimeter wavelength cloud radars (MMCR) are able to penetrate and detect multiple cloud layers. However, in mixed‐phase conditions, ice crystals dominate the radar signal, rendering the detection of liquid droplets from radar observables more difficult. The technique proposed here overcomes this fundamental limitation by using morphological features in MMCR Doppler spectra to detect supercooled liquid droplets in the radar sampling volume in the presence of ice particles. High lidar backscatter and near‐zero lidar depolarization measurements (good indicators of the presence of liquid droplets) from the Mixed‐Phase Arctic Clouds Experiment (MPACE) conducted in Barrow, Alaska, are used to train the technique and evaluate its potential for detecting mixed‐phase conditions. Ceilometer, microwave radiometer, and radiosonde measurements provide additional independent validation. Because of the ability of MMCRs to penetrate multiple liquid layers, this radar‐based technique does not suffer from the extinction limitations of lidars and is thus able to expand cloud phase identification methods to cloud regions beyond where lidars can penetrate, providing output at the native radar resolution. The technique is applicable to all profiling radars that have sufficient sensitivity to observe the small amount of liquid in mixed‐phase clouds.