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Special Session 5: Ocean-atmosphere interaction, multi-scale climate variability and their implication for biogeochemical processes |
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The increased influence of Atlantic Ocean on Pacific climate after early-1990s
Tuesday 10th @ 1445-1505
Room 1
Jin-Yi Yu* , University o California, Irvine
Houk Paek, University o California, Irvine
Kewei Lyu, University o California, Irvine
Lei Wang, University o California, Irvine and Guangdong Ocean University
Presenter Email: jyyu@uci.edu
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| The El Niño-Southern Oscillation (ENSO) is the most powerful interannual variability in Earth’s climate system, affecting the livelihoods of people worldwide. Most previous studies have emphasized processes within the tropical Pacific or Indian Oceans for the generation of ENSO. However, recent studies have increasingly suggested that the Atlantic Ocean may play an active role in forcing ENSO variability. In this talk, I will present evidence from observational analyses and modeling experiments to show that the Atlantic Ocean became more capable of influencing ENSO properties after the Atlantic Multidecadal Oscillation (AMO) changed to its positive phase in the early-1990s. A wave source mechanism is proposed to explain how the positive phase of the AMO can intensify the North Pacific Subtropical High (NPSH) to change the ENSO from the Eastern Pacific (EP) type to the Central Pacific (CP) type. A sequence of processes are identified to suggest that the AMO can displace the Pacific Walker circulation, induce a wave source in the tropical central Pacific, and excite a barotropic wave train toward higher-latitudes to enhance the NPSH, which then triggers subtropical Pacific atmospheric forcing and atmosphere-ocean coupling to increase the occurrence of the CP ENSO. An Atlantic capacitor mechanism is also proposed to explain how the positive phase of the AMO can intensify the quasi-biennial (QB) component of ENSO resulting in a more frequent occurrence of ENSO events. I will show that the capacitor mechanism works only after the AMO warmed up the Atlantic sea surface temperatures after the early-1990s. The increased feedback from the Atlantic to the Pacific has enabled the Atlantic capacitor mechanism to intensify the biennial variability in the Pacific during the past two decades. My suggestion is very different from the previous prevailing views that have emphasized the Indo-Pacific Oceans as the pacemaker for the biennial variability in ENSO. The increasing control of the Atlantic has enabled the CP ENSO dynamics to influence most of the ENSO events during the past two decades, including the most recent 2015-16 El Niño. I explained how the CP ENSO dynamics made the 2015-16 “Godzilla” El Niño different from the 1997-98 “Godzilla” El Niño and why these two extreme El Niño events produced different impacts on the US climate (e.g., California rainfall and temperatures). I will show that the 1997/98 event is characterized by the conventional EP ENSO dynamics, whereas the 2015/16 event is characterized by a mixture of the EP El Niño dynamics and the CP El Niño dynamics that involves subtropical atmospheric forcing. |
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