A33J-0303
Central Pacific-like Warming Event Induced by Eastern Pacific Event and Possible Mechanism
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Yang Wang, University of California Los Angeles, Los Angeles, CA, United States; Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China, Yaoming Ma, ITP Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China and Yongkang Xue, University of California Los Angeles, Department of Geography, Los Angeles, CA, United States
Abstract:
In contrast to the canonical eastern Pacific (EP) event, a new type of El Niño, named as central Pacific (CP) event with the warming center locating at the central equatorial Pacific, has been identified in recent years. In this study, we examine the relationship between these two types of ENSOs. Negative correlations between them is found to be up to more than 0.5 with statistical significance at α=0.01 level when the EP index leads the CP one about 20~22 months during the last 35 years, which are also evident in the related atmospheric and oceanic fields. We argue the possible mechanism for the appearance of this relationship lies in the mean climate change in the north extra-tropical Pacific in the last three decades, during which period the mean zonal wind became stronger due to the strengthening of the Subtropical High. Meanwhile, the NPO-like sea level pressure pattern, which forms during the decaying of the cold EP event, induces extratropical SST warm anomalies via surface heat fluxes. Because of the enhancement of the so-called wind-evaporation-SST (WES) feedback associated with the stronger mean zonal wind, these extratropical warming anomalies can be transported to the equatorial band more effectively, which eventually leads to the trigger of a CP-like event. In addition, the eastward expansion of the west Pacific warm pool since 1985 makes the central equatorial Pacific more sensitive to induce deep convection over there, providing a favorable circumstance for the CP regime. Considering the CP and CP-like events only become prevalent in recent decades and its distinct dynamics from the EP events, we speculate that this kind of relationship is a tropical reflection of extratropical climate change under the warming background in the central Pacific. How these kinds of mean state change happened and their relationship with the global climate change and changes in the sea/land thermal gradient in the last three decades need further research.
