Tropical cyclones and climate of the mid-Piacenzian warm period in a super high resolution atmosphere-ocean coupled simulation

The mid-Piacenzian warm period (3.025 - 3.264 Ma, MPWP) has widely been recognized as an analogue for future climate change. During the MPWP, the global geography and topography were similar to present-day, and the CO2level was between 350 to 450 ppm. Nonetheless, tropical climate structure was different from present-day with enhanced warming in the equatorial and costal upwelling regions of the eastern Pacific, and weaker warming in the western equatorial Pacific and equatorial Indian Ocean. These features are not well simulated in Earth System Models, including the Community Climate System Model version 4 (CCSM4). Here we explore this proxy data-model mismatch using a high-resolution version of Community Earth System Model (CESM, new versions of CCSM) at 0.23×0.31° atmosphere and 1° ocean resolution. This high resolution permits explicit simulations of tropical cyclones, which for the first time, allows physically consistent constraints on responses of atmosphere and ocean energetics to changes in the strength and frequency of tropical cyclones during the MPWP. Specifically, the ongoing experiments will test for two hypotheses regarding the tropical climate structure of the MPWP: 1) Warmer climate and more restricted Indonesian Throughflow relative to present-day have altered the distribution and frequency of tropical cyclones through changing the shape and temperature of the tropical Pacific and Indian Ocean warm pool, and coastal upwelling regions. 2) Changes in cyclone activities feedback to changes in tropical mean climate state through altering the atmosphere and ocean heat budget by dissipating heat away from the warm pool region towards the upwelling regions. Our experiments will bridge the gap between weather and climate in our understandings of MPWP climate, and elucidate the importance of including feedbacks from tropical weather to mean climate state under an enhanced greenhouse warming condition comparable to our near future.