Understanding Climate Change in the North Atlantic Region

了解北大西洋地区的气候变化

• 批准号: NE/E012744/1
• 负责人: Tim Woollings
• 金额: $ 28.76万
• 依托单位: University of Reading
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE012744%2F1
• 关键词: Understanding; Climate; Change; North; Atlantic

Many of the impacts of anthropogenic greenhouse gas emissions on the global average climate are now well-known. However much uncertainty remains over aspects of the regional impact, especially in a region as complex as the North Atlantic. The western edge of the Atlantic is one of the world's premier growth regions for mid-latitude storms. These are then steered along the jet stream, forming the North Atlantic storm track and bringing precipitation and milder temperatures to Europe. Variability associated with the strength and location of the Atlantic jet has caused dramatic variations in European winter climate over recent decades, from the bitterly cold winters of the 1960s to much milder and wetter conditions in the 1990s. This variability is described by the North Atlantic Oscillation, or NAO, which is essentially a measure of the average strength of the westerly winds across the North Atlantic. If the westerly winds are stronger than usual, Europe is affected more by the mild maritime influence of the Atlantic, and the NAO is said to be in a positive phase, whereas if they are weaker than normal the influence is more from the colder Eurasian continent (the negative phase). The NAO is widely recognised as the dominant pattern of natural climate variability affecting Europe. Much remains to be understood of the mechanisms behind changes in the NAO. There is no consensus on whether the changes over the last few decades are a result of anthropogenic climate change or simply due to natural variability. Modern climate models also disagree over the response of the NAO to climate change. Several models predict more positive conditions in the future, but other models do not. Climate models are only just beginning to converge on the response of the storm tracks to climate change. In the Pacific most current models now predict that the storm track will move polewards, but in the Atlantic there is less agreement. Here the situation is more complicated because different models predict different changes in the NAO, and also in the Atlantic Meridional Overturning Circulation in the ocean, which transports heat towards the far north. These disagreements between models are a key source of uncertainty in the regional effects of climate change over Europe. This work aims to improve our understanding of the reasons behind the disagreements, so that this uncertainty can be reduced. Recent work at the University of Reading has suggested that the long-term variations in the NAO are largely due to variations in the occurrence of a particular kind of weather system in the Atlantic. These systems result from the breaking of large scale waves in the upper atmosphere, and are very similar to the blocking high pressure systems often seen over Europe. Periods during which these events occur frequently will exhibit weak westerly winds on average, and so will be classed as negative NAO periods. In this project, data from state of the art climate models contributing to the latest IPCC report will be studied, using this new perspective in an attempt to understand the reasons behind the NAO responses they predict. If we can understand how changes in the mean climate of a model will affect the likelihood, or preferred location, of wave-breaking, we can then understand its NAO response. It is likely that the disagreement over North Atlantic storm track changes in climate models arises at least partly because there are several competing mechanisms at work. For example, the pattern of atmospheric warming would act to push the storm track polewards, as seen in other ocean basins, but sea surface temperature changes associated with a weakening of the Meridional Overturning Circulation are likely to lead to an equatorwards shift. Here we plan to use a new technique recently developed at the Met Office to separate out these different effects, and quantify the relative importance of each one.

人为温室气体排放对全球平均气候的许多影响现已众所周知。然而，区域影响的各个方面仍然存在很大的不确定性，特别是在北大西洋这样一个复杂的区域。大西洋西部边缘是世界上中纬度风暴的主要增长区域之一。然后，这些气流被沿着急流引导，形成北大西洋风暴路径，给欧洲带来降水和温和的气温。近几十年来，与大西洋急流的强度和位置相关的变化导致欧洲冬季气候发生了巨大变化，从20世纪60年代的严寒冬季到20世纪90年代的温和多雨。这种变化被北大西洋涛动（NAO）所描述，它基本上是对北大西洋西风平均强度的测量。如果西风比平时强，欧洲受大西洋温和的海洋影响更大，NAO被认为处于正相位，而如果西风比平时弱，则影响更多来自较冷的欧亚大陆（负相位）。NAO被广泛认为是影响欧洲的自然气候变率的主要模式。NAO变化背后的机制仍有待了解。对于过去几十年的变化是人为气候变化的结果还是仅仅由于自然变异，没有达成共识。现代气候模式也不同意NAO对气候变化的反应。有几个模型预测未来会出现更积极的情况，但其他模型则不然。气候模型才刚刚开始在风暴路径对气候变化的反应上趋于一致。在太平洋，目前大多数模型都预测风暴路径将向极地移动，但在大西洋，这一点就不那么一致了。这里的情况更加复杂，因为不同的模型预测了NAO的不同变化，也预测了海洋中的大西洋经向翻转环流的不同变化，该环流将热量输送到遥远的北方。模型之间的这些分歧是欧洲气候变化区域影响不确定性的主要来源。这项工作旨在提高我们对分歧背后原因的理解，从而减少这种不确定性。阅读大学最近的研究表明，北大西洋涛动的长期变化主要是由于大西洋某种特定天气系统的变化。这些系统是由高层大气中大尺度波浪的破裂造成的，与欧洲上空经常看到的阻塞高压系统非常相似。这些事件频繁发生的时期平均会出现弱西风，因此被归类为负NAO时期。在这个项目中，将研究来自最新IPCC报告的最先进气候模型的数据，使用这种新的视角试图了解他们预测的NAO响应背后的原因。如果我们能理解一个模式的平均气候变化将如何影响波浪破碎的可能性或首选位置，那么我们就可以理解它的NAO响应。气候模式中对北大西洋风暴路径变化的分歧至少部分是因为有几种相互竞争的机制在起作用。例如，大气变暖的模式会将风暴轨迹推向极地，就像在其他海洋盆地看到的那样，但与经向翻转环流减弱相关的海面温度变化可能会导致向赤道移动。在这里，我们计划使用英国气象局最近开发的一种新技术来区分这些不同的影响，并量化每一种影响的相对重要性。

项目成果

Atmospheric Blocking and Mean Biases in Climate Models

• DOI: 10.1175/2010jcli3728.1
• 发表时间: 2010-12
• 期刊: Journal of Climate
• 影响因子: 4.9
• 作者: Adam A. Scaife;T. Woollings;J. Knight;G. Martin;T. Hinton

Can the Frequency of Blocking Be Described by a Red Noise Process?

阻塞频率可以用红噪声过程来描述吗？

• DOI: 10.1175/2008jas2907.1
• 发表时间: 2009
• 期刊: Journal of the Atmospheric Sciences
• 影响因子: 3.1
• 作者: Woollings T

On the persistence and predictability properties of North Atlantic climate variability

• DOI: 10.1175/2010jcli3739.1
• 发表时间: 2011-01
• 期刊: Journal of Climate
• 影响因子: 4.9
• 作者: C. Franzke;T. Woollings

Persistent Circulation Regimes and Preferred Regime Transitions in the North Atlantic

• DOI: 10.1175/jas-d-11-046.1
• 发表时间: 2011-12-01
• 期刊: JOURNAL OF THE ATMOSPHERIC SCIENCES
• 影响因子: 3.1
• 作者: Franzke, Christian;Woollings, Tim;Martius, Olivia
• 通讯作者: Martius, Olivia