Evaluating The Relationship Between Low Cloud Fraction And Atmospheric Stability Indices Over The Western North Atlantic
Presenter: Lauren Cutler1
Co-Author(s): Michael Brunke, Annalisa Minke, Yike Xu, Xubin Zeng
Advisor(s): Xubin Zeng
1Department of Hydrology and Atmospheric Sciences, University of Arizona
Marine low clouds and cloud-aerosol interactions are large sources of uncertainty in global climate models. Well known atmospheric stability parameters (i.e. lower tropospheric stability (LTS), and estimated inversion strength (EIS)) are used to predict seasonal low cloud amount. Recently, we found that the traditional atmospheric stability relationships between monthly-mean low cloud fraction and LTS and EIS are not as robust as originally established. This study seeks to understand how these relations perform on shorter time scales using dropsonde and HSRL-2 lidar data from the ACTIVATE field campaign. This campaign sampled cloud and aerosol properties over the Western North Atlantic Ocean across six campaigns from 2020-2022. Besides LTS and EIS, this study evaluated the performance of other stability parameters, like the cold-air outbreak index (CAO) and estimated cloud-top entrainment index (ECTEI) and evaluate how low cloud fraction relates to other cloud and aerosol variables from HSRL-2. The stability indices were calculated using dropsonde data while low cloud fraction was calculated from HSRL-2. A seasonal linear regression for December-February, March-May, and June-August was calculated for all four indices. Preliminary results show that LTS, EIS, and ECTEI do not have a significant relationship with low cloud fraction over the Western North Atlantic for two out of the three seasons. CAO has a significant relationship for all three seasons. We also compare these observational results with model output from E3SMv2 to evaluate if the model relationship between low cloud fraction and stability indices is similar to what we find in the observations.