Dependence of Marine Boundary Layer Cloud Properties on Environmental Conditions during Cold Air Outbreaks over the North Atlantic: Results from CAESAR
Zeqian is a PhD student working with Dr. Greg McFarquhar. Her research generally is examining how cold air outbreaks will influence the boundary layer clouds using the measurements from COMBLE (Cold-air Outbreaks in the Marine Boundary Layer Experiment) project. This seminar is an annual PhD update.
Abstract
The accurate representation of mixed-phase marine boundary layer clouds (MBCs) in models is challenging. There is a compelling need to determine how MBC properties and formation mechanisms vary with surface, environmental and aerosol conditions in high-latitudes during cold air outbreaks (CAOs). During the CAO Experiment in the Sub-Arctic Region (CAESAR) field campaign, the National Science Foundation (NSF)/National Center for Atmospheric Research (NCAR) C-130 aircraft was deployed to Kiruna, Sweden with a variety of in situ and remote sensors to sample Arctic air masses as they transformed downstream from the CAO origin at the ice edge. This study uses CAESAR measurements to examine the vertical structure of MBCs and their evolution downstream during CAOs, with a focus on the dependence of thermodynamic and cloud microphysical properties in the marine boundary layer (BL) on environmental conditions. The 16 March 2024 flight (RF07) is chosen as a case study because this was a full-fetch flight aligned well with cloud streets, where a very cold CAO was sampled by the release of 36 dropsondes allowing for a fine-scale characterization of how cloud properties depend on the varying structure of the BL as it transformed in a north-south direction. Wyoming W-band radar (WCR) measurements are utilized for detecting the vertical structure of MBCs. Depolarization and the ratio of total backscattering to molecular return (LSR) from the Multi-function Airborne Raman Lidar (MARLi) are used for cloud phase identification. The G-band vapor radiometer (GVR) provides measurements of liquid water path (LWP) within the MBCs. The upward- and downward-looking visible and infrared radiometers provide irradiance measurements near cloud top. The MBCs observed from RF07 exhibit differences in cloud top/base heights, moisture within the BL, wind shear, and atmosphere stability as the distance from the ice edge increased. It is uncertain whether these variations are due to environmental factors, such as thermodynamic changes in the BL, or microphysical processes occurring within these clouds, such as precipitation. Further studies are required to investigate these questions.