Optical and microphysical properties of ice crystals in Arctic clouds from lidar observations

• Main Authors: Chazette, Patrick, Raut, Jean-Christophe
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; Norway; Hammerfest
• Online Access: https://doi.org/10.5194/amt-2023-122; https://amt.copernicus.org/preprints/amt-2023-122/

The vertical profiles of the optical properties, effective radius of ice crystals and ice water content (IWC) in Arctic semi-transparent stratiform clouds were assessed using quantitative ground-based lidar measurements performed from 13 to 26 May 2016 in Hammerfest (north of Norway, 70° 39′ 48″ North, 23° 41′ 00″ East). The field campaign was part of the Pollution in the ARCtic System (PARCS) project of the French Arctic Initiative. The presence of low-level semi-transparent stratus clouds was noted on 16 and 17 May, and they were sampled continuously by a ground-based Raman-N 2 lidar emitting at the wavelength of 355 nm. These clouds were located just above the atmospheric boundary layer where the 0 °C isotherm reached around 800 m above the mean sea level (a.m.s.l.). To ensure the best penetration of the laser beam into the cloud, we selected case studies with cloud optical thickness (COT). Lidar-derived multiple scattering coefficients were found to be close to 1 and ice crystal depolarization around 10 %, suggesting that ice crystals were small and had a rather spherical shape. This agrees with our Mie computations determining effective radii between ~5 and 20 µm in the clouds for ice water contents between 1 and 8 mg m -3 , respectively. Direct estimate of the microphysical parameters of ice clouds via lidar measurements is a significant asset for the study of their large-scale radiative impact, while reducing the need for experimental resources.