ENSO connections and processes

厄尔尼诺南方涛动(ENSO)现象是气候系统年际变化的最大来源。ENSO事件是由热带太平洋的自然海洋-大气相互作用引起的，但它们的影响通过连接遥远地区的所谓遥相关传播到全球。遥相关通过大气环流的变化发挥作用，它们会造成区域气候扰动，造成非常严重的破坏，如洪水和干旱。尽管欧洲远离太平洋活动中心，但ENSO也是英国/欧洲气候变化的一个因素。ENSO循环有暖(厄尔尼诺)和冷(拉尼娜)两个阶段，在很大程度上有相反的物理影响。最近的研究表明，根据赤道太平洋区域的位置不同，ENSO的类型也不止一种，而且遥相关效应因类型而异。需要更多关于这些不同影响和潜在过程的信息，以改进对ENSO事件发生时后果的预测。这项工作的目的是研究ENSO和遥相关，方法是：(A)分析来自观测和实际气候模式的数据，利用数学方法确定ENSO演变和相关大气变化的各种‘模式’，以及(B)利用简化的大气环流模式进行数值试验，以研究系统中类似ENSO的强迫所引起的动力相互作用。虽然简化模型不太现实，但通过减少这种模型中所代表的物理机制，可以将注意力集中在特定的动力过程和因果关系上，这些过程和因果关系仍然与实际的气候可变性有关。简化模式实验亦让我们有机会测试(A)项所用分析方法的长处和短处，结果将有助我们了解为何不同的ENSO事件会有不同的遥相关效应，以及热带和温带的过程是如何相互关联的。一个重要的潜在好处是，长期预报制作者将能够检查用于预测ENSO及其影响的系统中是否适当地表示了相关路径：因此，气象局通过每月至十年的预报小组成为该项目的合作伙伴。

The El Niño Southern Oscillation (ENSO) phenomenon is the largest source of year-to-year variability in the climate system. ENSO events are caused by natural ocean-atmosphere interactions in the tropical Pacific, but their impacts are transmitted globally through so-called teleconnections linking distant areas. Teleconnections act through changes in the atmospheric circulation, and they cause regional climate disturbances that can be very damaging, such as floods and droughts. Although Europe is far from the Pacific centre of action, ENSO is also a factor in UK/Europe climate variability. The ENSO cycle has warm (El Niño) and cold (La Niña) phases with largely opposite physical impacts. Recent studies have demonstrated that there is also more than one type of ENSO, depending on location within the equatorial Pacific region, and that teleconnection effects differ from one type to another. Further information about these differing effects, and the underlying processes, is required to improve the prediction of the consequences when an ENSO event arises. The aim of the work in this proposal is to investigate ENSO and teleconnections by (a) analysing data from observations and realistic climate models, with the use of mathematical methods to determine various 'modes' for ENSO evolution and associated atmospheric changes, and by (b) carrying out numerical experiments with simplified atmospheric circulation models to study the dynamical interactions induced by ENSO-like forcing of the system. Although simplified models are less realistic, by reducing the physical mechanisms represented in such models attention can be focussed on particular dynamical processes and causes and effects which are nevertheless relevant to actual climate variability. The simplified model experiments also provide an opportunity to test the strengths and weaknesses of the analysis methods used in (a).The results will help us to understand why teleconnection effects may differ from one ENSO event to another, and how processes in the tropics and extratropics are inter-related. An important potential benefit is that long-range forecast producers will be able to check whether the relevant pathways are properly represented in the systems used to predict ENSO and its impacts: accordingly the Met Office is a partner in this project through the monthly-to-decadal forecast group.