Detection of supercooled liquid water containing clouds with ceilometers: development and evaluation of deterministic and data-driven retrievals

[摘要] Cloud and aerosol lidars measuring backscatter anddepolarization ratio are the most suitable lidars to detect cloud phase (liquid, ice, or mixed phase). However, such instruments are not widely deployed as part of operational networks. In this study, we propose a new algorithm to detect supercooled liquid water containing clouds (SLCC) based on ceilometers measuring only co-polarization backscatter. We utilizeobservations collected at Davis, Antarctica, where low-level, mixed-phaseclouds, including supercooled liquid water (SLW) droplets and ice crystals,remain poorly understood due to the paucity of ground-based observations. A 3-month set of observations were collected during the austral summer ofNovember 2018 to February 2019, with a variety of instruments including adepolarization lidar and a W-band cloud radar which were used to build atwo-dimensional cloud phase mask distinguishing SLW and mixed-phase clouds.This cloud phase mask is used as the reference to develop a new algorithmbased on the observations of a single polarization ceilometer operating inthe vicinity for the same period. Deterministic and data-driven retrievalapproaches were evaluated: an extreme gradient boosting (XGBoost) frameworkingesting backscatter average characteristics was the most effective methodat reproducing the classification obtained with the combined radar–lidarapproach with an accuracy as high as 0.91. This study provides a new SLCCretrieval approach based on ceilometer data and highlights the considerablebenefits of these instruments to provide intelligence on cloud phase inpolar regions that usually suffer from a paucity of observations. Finally,the two algorithms were applied to a full year of ceilometer observations to retrieve cloud phase and frequency of occurrences of SLCC: SLCC was present 29  ±  6 % of the time for T19 and 24  ±  5 % of the time for G22-Davis over that annual cycle.

[学科分类] 内科医学