Sensitivity of ENSO Variability to Pacific Freshwater Flux Adjustment in the Community Earth System Model

• Published in: Advances in atmospheric sciences Vol. 31; no. 5; pp. 1009 - 1021
• Main Authors: Kang, Xianbiao, Huang, Ronghui, Wang, Zhanggui, Zhang, Rong-Hua
• Format: Journal Article
• Language: English
• Published: Heidelberg Science Press 01.09.2014; Springer Nature B.V; Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100190; University of the Chinese Academy of Sciences, Beijing 100029; University of the Chinese Academy of Sciences, Beijing 100029%Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071; National Marine Environmental Forecasting Center, State Oceanic Administration, Beijing 100081%Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100190
• Subjects: Atmospheric models; Atmospheric Sciences; Earth and Environmental Science; Earth Sciences; El Nino; ENSO事件; Freshwater resources; General circulation models; Geophysics/Geodesy; Meteorology; Ocean circulation; Thermocline; Variability; 地球系统; 敏感性; 模型; 水通量; 热带太平洋地区; 社区; 调整; IS, Tropical Pacific; ENSO; freshwater flux; CESM
• ISSN: 0256-1530; 1861-9533
• DOI: 10.1007/s00376-014-3232-2

The effects of freshwater flux （FWF） on modulating ENSO have been of great interest in recent years. Large FWF bias is evident in Coupled General Circulation Models （CGCMs）, especially over the tropical Pacific where large precipitation bias exists due to the so-called ＂double ITCZ＂ problem. By applying an empirical correction to FWF over the tropical Pacific, the sensitivity of ENSO variability is investigated using the new version （version 1.0） of the NCAR＇s Community Earth System Model （CESM1.0）, which tends to overestimate the interannual variability of ENSO accompanied by large FWF into the ocean. In response to a small adjustment of FWF, interannual variability in CESM1.0 is reduced significantly, with the amplitude of FWF being reduced due to the applied adjustment part whose sign is always opposite to that of the original FWF field. Furthermore, it is illustrated that the interannual variability of precipitation weakens as a response to the reduced interannual variability of SST. Process analysis indicates that the interannual variability of SST is damped through a reduced FWF-salt-density-mixing-SST feedback, and also through a reduced SST-wind-thermocline feedback. These results highlight the importance of FWF in modulating ENSO, and thus should be adequately taken into account to improve the simulation of FWF in order to reduce the bias of ENSO simulations by CESM.