Session: Warm Climates (Mid-Holocene, Last interglacial, Deep-time, Pliocene)
Author: Zheng Weipeng / email@example.com / LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, 100029, Beijing
Co-author: CHEN Lin, IPRC and Department of Atmospheric Sciences, SOEST, University of Hawaii at Manoa, Honolulu, USA;
Pascale Braconnot, LSCE/IPSL, unite mixte CEA-CNRS-UVSQ, Université Paris Saclay, orme des merisers, bât. 712, 91191 Gif sur Yvette Cedex;
The mechanism of El Niño-Southern Oscillation (ENSO) amplitude change during the mid-Holocene (MH) is investigated by the Bjerknes stability (BJ) index through the model simulations from the Paleoclimate Modelling Intercomparison Project Phases (PMIP) 2 and 3. Results show that the weakening of thermocline (TH), zonal-advection (ZA) and Ekman (EK) feedback terms are the major drivers for the weakened ENSO amplitude in MH. And then we go one step further to discuss the key factors in regulating the above drivers and reveal that the weakening of TH, ZA, and EK terms are attributed to the weakened thermocline response to zonal wind stress anomaly in MH compared to PI. Such changes are due to the flattened meridional structure of ENSO-related interannual anomaly field (e.g, zonal wind stress anomaly field) in MH. The meridional structure change of ENSO-related anomaly field results from the strengthening of mean surface poleward meridional current (or mean subtropical cell). Quantitative diagnosis of PMIP simulations shows that the mean STC change might be a key factor, which plays an essential role in determining the changes of TH, ZA, and EK feedback terms, and thus the change of ENSO amplitude in MH.