ENSO connections and processes

厄尔Niño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，但它们的影响是通过连接遥远地区的所谓遥相关在全球传播的。远程连接通过大气环流的变化起作用，它们造成区域气候干扰，可能具有非常大的破坏性，如洪水和干旱。尽管欧洲远离太平洋的行动中心，ENSO也是英国/欧洲气候变化的一个因素。ENSO循环具有温暖阶段（El Niño）和寒冷阶段（La Niña），它们的物理影响基本相反。最近的研究表明，根据赤道太平洋区域内的位置不同，ENSO的类型也不止一种，而且远相关效应因类型而异。需要进一步了解这些不同的影响和潜在的过程，以改进对ENSO事件发生时后果的预测。本建议的工作目的是通过(a)分析观测数据和现实气候模式，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)使用简化的大气环流模式进行数值实验，研究系统中类似ENSO强迫引起的动力相互作用，来研究ENSO和远相关。虽然简化模式不太现实，但通过减少这种模式中所代表的物理机制，可以将注意力集中在与实际气候变率有关的特定动力过程和因果上。简化模型实验也为测试(a)中使用的分析方法的优缺点提供了机会。这些结果将帮助我们理解为什么远相关效应可能因ENSO事件而异，以及热带和温带过程是如何相互关联的。一个重要的潜在好处是，长期预报的生产者将能够检查用于预测ENSO及其影响的系统中是否正确地代表了相关的路径：因此，英国气象局通过每月到十年的预测小组参与了这个项目。

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.