Mechanisms for El Nino and La Nina Evolution Asymmetry and Formation of Super El Ninos

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项目编号	1565653
	Mechanisms for El Nino and La Nina Evolution Asymmetry and Formation of Super El Ninos
	Tim Li
主持机构	University of Hawaii
项目开始年	2016
	2016-11-01
项目结束日期	2019-10-31
资助机构	US-NSF
项目类别	Continuing grant
项目经费	496497(USD)
国家	美国
语种	英语
英文摘要	ABSTRACT El Nino/Southern Oscillation (ENSO) events, in which the sea surface temperatures (SSTs) warm or cool over a large portion of the central and eastern equatorial Pacific, affect weather and climate worldwide including substantial impacts over the US. The underlying mechanisms of ENSO have been identified and prediction efforts have met with some success, but fundamental questions remain. One such question is why El Nino events (with anomalously warm SSTs in the equatorial Pacific) terminate differently from La Nina events (with cold SSTs), as El Ninos are often followed by La Ninas while La Ninas are more likely to persist or redevelop. Preliminary work by the PI has identified differences in the pattern of surface fluxes and wind stress in the central Pacific during the mature and decaying phases of El Nino and La Nina events. Work performed here uses a combination of ocean mixed layer heat budget analysis and model simulations (primarily with uncoupled ocean and atmosphere models) to determine the origins of these differences and their importance for differences in event termination. A second question is why a few El Ninos, termed "super El Ninos", grow rapidly to substantially larger amplitude (over two standard deviations) than typical events. Preliminary work has identified differences in the onset and development phases of super and ordinary El Ninos including off-equatorial thermocline depth anomalies in the super events, and work here examines these differences through a combination of coupled and uncoupled ocean-atmosphere modeling experiments. A further task of the research is an examination of changes in ENSO amplitude in simulations of greenhouse gas-induced future climate change. A survey of simulations from the Coupled Model Intercomparison Project version 5 (CMIP5) shows substantial disagreement, with roughly equal numbers of models projecting an increase or decrease in the strength of ENSO events. Work here seeks to identify differences in feedback mechanisms (e.g. the Bjerknes feedback) which can account for model to model amplitude differences. Once these are identified they will be related to changes in the model background state through a linear decomposition of the mixed layer heat budget. One hypothesis considered is that amplitude differences are related to changes in the meridional width of the ENSO SST pattern, which is in turn related to the strength of the Pacific Subtropical Cell. The work has societal broader impacts due to the worldwide consequences of ENSO events and the desirability of improved ENSO predictions. Predictions in 2014 of an imminent super El Nino, which did not materialize, suggest a particular need for better understanding of the nature of super events. Work to improve understanding of how climate change affects ENSO events also has societal value, and the PI intends to develop a projection of ENSO amplitude change based on work under this award. In addition, the project provides support and training for a graduate student, thereby promoting workforce development in this research area.
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文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/70581
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Tim Li.Mechanisms for El Nino and La Nina Evolution Asymmetry and Formation of Super El Ninos.2016.