Speaker: Prof. Hui Su, The Hong Kong University of Science and Technology

Host: Prof. Yan Yu, Peking University (yuyan@pku.edu.cn)

Time: 13:30-15:00 pm, March 3, 2023, GMT+8

Venue: Tecent Meeting ID: 499-968-818

Abstract:

Both tropical and extratropical marine low cloud feedbacks contribute significantly to the uncertainty in equilibriu climate sensitivity(ECS). In the models that participated in the Coupled Model Intercomparison Project Phase 6 (CMIP6), we found that the model spread in the tropical low cloud fraction change is correlated with the magnitude of large-scale subsidenee rate change per unit warming,which can be traced to how models parameterize tropical deep convection and high cloud amount change, suggesting a strong coupling between deep convection in the ascent regime and the low cloud response in the descent regime. Moreover,we found that the inter-model spread in the extratropical marine low cloud fraction (LCFe) feedback under long-term warming is highly correlated with the seasonal variation of LCFe per degree of sea surface temperature change.The models with ECS greater than 4.5 K (termed high ECS models)tend to have stronger seasonal cycle in LCFe than the models with ECS lower than 3.3 K(termed low ECS models). Further analysis of cloud vertical structures reveal that the strong seasonal cycle of LCFe in the high ECS models is primarily driven by the variability of low-to-middle clouds associated with midlatitude storm tracks, while the seasonal variability of LCFe in the low ECS models is decoupled from the storm track activity. The new emergent constraints on ECS based on these studies indicate that the high ECS models tend to be more consistent with the satellite observations than the low ECS models.

Biography:

Hui Su is a Global STEM Professor in the Department of Civil and Environmental Engineering,the Hong Kong University of Science and Technology (HKUST).She received a B.S.in Atmospheric Dynamics from Peking University and a Ph.D. in Atmospheric Sciences from the University of Washington. She conducted postdoctoral research in UCLA. She was a principal scientist and weather discipline program manager at NASA's Jet Propulsion Laboratory (JPL), California Institute of Technology before joining the HKUST in September 2022.Dr.Su received the JPL Lew Allen Award in 2008, the Edward Stone Award in 2021, the NASA Exceptional Scientific Aehievement Medal in 2010 and again in 2022. She is an Editor of the Geophysical Research Letter and a fellow of American Meteorological Society. She has published over 120 peer-reviewed articles.Her research interests are primarily in tropical convection and climate change.

Source: School of Physics