Quantifying the Dependence of Cloud Vertical Structure during Cold Air Outbreaks on Environmental Conditions: Preliminary Findings from CAESAR

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 dependence of the microphysical and macrophysical properties of clouds in CAOs and its variability and 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 (CAESAR) field campaign acquired such in-situ and remote sensing data during 8 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, ice crystal concentration, ice mass content, liquid and ice effective radius, and median volume diameters 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. The majority of clouds sampled were either liquid- or mixed-phase, with few entirely ice-phase clouds sampled during the campaign. Case studies from 2 April 2024 (RF09) and 3 April 2024 (RF10) are shown to establish a typical structure of clouds sampled during CAESAR with liquid water content and effective diameter increasing with zn, with graupel, irregular particles and rimed snowflakes occurring in mid-levels for some vertical profiles. However, when examining data from all 70 vertical profiles there was a lack of uniformity on how the parameters varied as a function of zn. Therefore profiles were cataloged according to environmental conditions (e.g., cloud base temperature, updraft/downdraft characteristics, open vs. closed cells, presence of cloud streets, distance from sea ice edge, aerosol concentration) in an attempt to better characterize the variability. Implications for the understanding of processes occurring in CAO clouds will be discussed.