Quantifying the Dependence of Cloud Vertical Structure during Cold Air Outbreaks (CAOs) on Environmental Conditions: Preliminary Results from CEASAR
Nick Amundsen is a 2nd year MS student at the University of Oklahoma. Before coming to OU he earned a BS at Florida State University in Meteorology. He is working in the area of Arctic cloud microphysics under Dr. Greg McFarquhar, and is using data from the CAESAR field campaign in his studies.
Abstract
Cold-air outbreaks (CAOs) have an overwhelming influence on global atmospheric and oceanic circulations, yet their cloud regimes remain poorly sampled and are therefore not fully understood nor well-represented in weather models. More data on the vertical variation of cloud microphysical and macrophysical properties, as well as their dependence on environmental conditions, is crucial for enhancing the understanding of processes occurring in clouds and for improving and evaluating the performance of models and remote sensing retrievals over high latitudes. The Cold-Air outbreak Experiment in the Sub-Arctic Region (CEASER) field campaign acquired such in-situ and remote sensing data during eight flights of the National Science Foundation/National Center for Atmospheric Research (NSF/NCAR) C-130 between 22 February and 7 April 2024 over the Norwegian Sea.
In this study, the vertical dependence of microphysical properties of total number concentration, liquid water content, effective diameter, median volume diameters, and particle size distributions using data from the Cloud Droplet Probe (CDP), Two-Dimensional Stereo Probe (2D-S), and High Volume Precipitation Sampler (HVPS) is determined as a function of normalized altitude (zn), where zn = 0 at cloud base and zn =1 at cloud top. According to an applied phase identification algorithm using in-situ cloud probe data, the majority of clouds sampled were either liquid- or mixed-phase, with few entirely ice-phase clouds observed during the campaign, aside from areas of precipitating ice below cloud base. Case studies from 11 March 2024 (RF05) and 12 March 2024 (RF06) are shown to establish a typical structure of clouds sampled during CEASER. In these cases, liquid water content and effective diameter generally increase with zn, while graupel, irregular particles, and rimed snowflakes occur in mid-levels for some vertical profiles. However, when examining data from all 65 vertical profiles, there was a lack of uniformity on how the parameters varied as a function of zn. Therefore, profiles were categorized based on environmental conditions (e.g., cloud base/top temperature, updraft/downdraft characteristics, open vs. closed cells, sea surface temperature, distance from sea ice edge, and aerosol concentration) to better characterize the variability. Implications for the understanding of processes occurring in CAO clouds will be discussed.