Comment on acp-2021-1072

Abstract

The role of clouds for the surface radiation budget is particularly complex in the rapidly changing Arctic. However, despite their importance, long-term observations of Arctic clouds are relatively sparse. Here we present observations of cold clouds based on 7 years (2011–2017) of ground-based lidar observations at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in Andenes in the Norwegian Arctic. In two case studies, we assess (1) the agreement between a collocated cirrus cloud observation from the ground-based lidar and the spaceborne lidar onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, and (2) the ground-based lidar’s capability of determining cloud phase in mixed-phase clouds from depolarization measurements. We then compute multi-year statistics of cold clouds from both platforms with respect to their occurence, cloud top and base height, cloud top temperature and thermodynamic phase for the period 2011–2017. We find that satellite and ground-based observations agree well for the coincident cirrus measurement, and that the vertical phase distribution within a liquid-topped mixed-phase cloud could be identified from depolarization measurements. On average, 8 % of all satellite profiles were identified as single-layer cold clouds with no apparent seasonal differences. The average cloud top and base heights combining the ground-based and satellite instrument are 9.1 km and 6.9 km, respectively, resulting in an average thickness of 2.2 km. Seasonal differences between the average top and base heights are on the order of 1–2 km and are largest when comparing autumn (highest) and spring (lowest). However, seasonal variations are small compared to the observed day-to-day variability. Cloud top temperatures agree well between both platforms with warmer cloud top temperatures in summer. The presented study demonstrates the capabilities of long-term cloud observations in the Norwegian Arctic from the ground-based lidar at Andenes.