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Ocean-atmosphere interactions and multi-scale climate variability in a changing climate
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A simulating and theoretical investigation on the dynamics of the two types of ENSO
Wednesday 9th @ 1430-1450, Concert Hall
Xiang-Hui Fang* , Department of Atmospheric and Oceanic Sciences & Institute of Atmospheric Sciences, Fudan University
Mu Mu, Department of Atmospheric and Oceanic Sciences & Institute of Atmospheric Sciences, Fudan University
Fei Zheng, Institute of Atmospheric Physics, CAS
Presenter Email: fangxh@fudan.edu.cn |
| Severe biases exist in state-of-the-art general circulation models (GCMs) in capturing realistic central-Pacific (CP) El Niño structures. At the same time, many observational analyses have emphasized that thermocline (TH) feedback and zonal advective (ZA) feedback play dominant roles in the development of eastern-Pacific (EP) and CP ENSO (El Niño–Southern Oscillation), respectively. In this work, a simple linear air–sea coupled model, which can accurately depict the strength distribution of the TH and ZA feedbacks in the equatorial Pacific, is first used to investigate these two types of El Niño. The results indicate that the model can reproduce the main characteristics of CP ENSO if the TH feedback is switched off and the ZA feedback is retained as the only positive feedback, confirming the dominant role played by ZA feedback in the development of CP ENSO. Further experiments indicate that, through a simple nonlinear control approach, many ENSO characteristics, including the existence of both CP and EP El Niño and the asymmetries between El Niño and La Niña, can be successfully captured using the simple linear air–sea coupled model. Next, a three-region conceptual model for central Pacific El Niño including zonal advective feedback is constructed. The simple zonal two-region framework of the recharge paradigm can accurately manifest the traditional EP type of ENSO, as its major warming center is located in the EP and the anomalous sea surface temperature (SST) changes monotonically from west to east along the equatorial Pacific. However, it cannot fully depict the variations of the CP type of ENSO, whose major warming center is mainly situated in the CP. Therefore, to better investigate the characteristics of the CP type of ENSO, the recharge paradigm is extended to a three-region conceptual model to describe the entire western, central and eastern equatorial Pacific. The results show that the extended conceptual model can depict the different variations between the CP and EP well. Specifically, with increasing magnitude of the zonal advective feedback over the CP, i.e., imitating the situation for CP ENSO, the period of the system and SST magnitude over the CP and EP both decrease. However, the decreasing amplitude is more intense over the EP, indicating an enlargement of the SST differences between the CP and EP. These results are all consistent with the observational characteristics of CP ENSO. |
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