Investigating tropical cyclone-climate interactions using the high-resolution Community Earth System Model (CESM)

Tropical cyclones, climate

Li, Hui

关键词: Tropical cyclones, climate;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/101347/LI-DISSERTATION-2018.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Tropical cyclone (TC) - induced ocean vertical mixing can alter the upper ocean temperature structure, influencing ocean heat content variability and meridional ocean heat transport. This TC-ocean interaction process has important implications for the Earth’s climate system on seasonal to interannual timescales. The new generation of high-resolution Atmosphere General Circulation Models (AGCMs) are capable of directly simulating realistic TC wind structure and TC statistics within the modeled large-scale environment, providing an innovative and promising approach for TC-climate studies. The goal of the research described herein is to advance understanding about TCs’ role within the Earth’s climate system utilizing various configurations of the high-resolution “TC-resolving” state-of-the-art Community Earth System Model (CESM). The key scientific questions addressed here are: 1) What is the contribution of TCs to the annual average ocean heat uptake, and what is the sensitivity of simulation results to ocean model resolution (“eddy-permitting” vs. “eddy-resolving”)?2) How does the choice of ocean coupling affect the model-simulated TC activity?3) What is the impact of the model’s self-generated TCs on the modeled global ocean from seasonal to interannual time-scales?We first investigate TCs’ contribution to annual upper ocean heat content and examine the sensitivity of the result to ocean model grid resolution.We analyze the upper ocean’s responses to TC wind forcing using a suite of ocean-only simulations featuring three different horizontal ocean grid resolutions (3˚, 1˚, and 0.1˚). The ocean simulations are forced with identical atmospheric inputs from the Coordinated Ocean-Ice Reference Experiments version 2 (COREv2) normal year forcing conditions, featuring 18 months of global blended TC winds from a fully coupled CESM simulation with a 25 km atmosphere. We find that ocean horizontal and vertical grid resolutions affect TC-induced heat and momentum fluxes, post-storm cold wake features, ocean subsurface temperature profiles, and the annually accumulated TC-induced ocean heat uptake, which have important implications for modeled ocean heat budgets and variability. To understand the impact of ocean coupling on the model-simulated TC activity, we performed a suite of high-resolution, multi-decadal CESM simulations in which the 25 km atmosphere is configured with three different levels of ocean coupling: prescribed climatological sea surface temperature SST, mixed layer ocean, and dynamic ocean. We find that different levels of ocean coupling can influence simulated TC frequency, geographic distributions, and storm intensity. Key differences in storm number and geographic distribution can be attributed to variations in the modeled large-scale climate mean state and variability that arise from the combined effect of intrinsic model biases and air-sea interactions. Results help to improve our understanding about the representation of TCs in high-resolution coupled Earth system models.We investigate the impact of TCs on the global ocean and the associated feedbacks on seasonal to interannual time-scales by performing two multi-decadal ocean-only simulations with the identical atmosphere boundary forcing from a 30-year fully-coupled simulation configured with 0.25˚ atmosphere and 1˚ ocean. TC features are filtered out in one of the simulations (OCN_FILT) while fully retained in the other (OCN_TC). The effect of TCs on the global ocean can then be isolated by comparing between the two simulations. We find that the model-simulated TCs can alter ocean temperature patterns and variability, affect ocean energetics, and influence ocean heat content and meridional heat transport.Results help reveal the impact of the high-resolution model’s self-generated TCs on the simulated global climate, and provide insights into the long-term effect of TC-ocean interactions within the Earth system.