Title: A Framework for Simulating Hurricane Boundary Layers using Large-Eddy Simulation and Its Use in Developing PBL parameterizations
Lecturer: Dr. Xiaomin Chen (University of Alabama in Huntsville)
Inviter: Prof. Kun Zhao
Time: Thursday May 30, 2024 at 2:00 PM
Venue: Lecture Hall D103, School of Atmospheric Sciences
Abstract: Accurately representing planetary boundary layer (PBL) turbulent processes in numerical models is critical for improving hurricane forecasts. However, existing PBL parameterization schemes are mostly designed for low-wind conditions, and assessing their uncertainties in hurricane conditions is challenging, mostly due to very scarce in-situ turbulence measurements. To fill in the gap, this study develops a modeling framework based on a small-domain large-eddy simulation (LES) to evaluate two types of PBL schemes in hurricane conditions. The novelty of this framework includes the usage of a few input parameters to represent the TC vortex and the addition of a simple nudging term for temperature and moisture to account for the complex thermodynamic processes in TCs. This special model setup allows for a fair comparison of PBL schemes under the same controlled thermodynamic conditions against LES. An evaluation reveals the pros and cons of each PBL scheme in hurricane conditions. Using this insight, we recommend suitable PBL schemes for hurricane modeling and propose solutions to improve the high-order PBL scheme used in NOAA’s next-generation hurricane forecast model, Hurricane Analysis and Forecast System (HAFS). HAFS retrospective runs during the 2021 Atlantic hurricane season demonstrate that the improved PBL scheme leads to better structure and intensity forecasts than the original PBL scheme. Importantly, the improved PBL scheme shows promise to improve the forecast skill of rapid intensification events, which are notoriously challenging to predict. Avenues for future development of PBL parameterizations in high-wind conditions will be discussed.
Brief introduction to the speaker: Dr. Xiaomin Chen is an Assistant Professor at the Department of Atmospheric and Earth Science of University of Alabama in Huntsville. His research focuses on different aspects of tropical cyclones, including rapid intensification, boundary layer processes, and numerical modeling and forecasts. His research utilizes a combination of observations and numerical simulations to improve the understanding and modeling of boundary-layer processes in high-wind conditions. He received the Northern Gulf Institute Research Competitive Award and NOAA AOML Outstanding Paper Award. Besides, Dr. Chen serves in the editorial board of several prestigious international journals, including Journal of the Atmospheric Sciences. He also served as a co-rapporteur of the WMO's 10th International Workshop on Tropical Cyclones (IWTC-10) report.