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，特别是在像北大西洋这样复杂的地区。大西洋西缘是世界上中纬度风暴的主要增长区之一。然后它们沿着急流引导，形成北大西洋风暴路径，为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了欧洲冬季气候的巨大变化，从 20 世纪 60 年代的严寒冬季到 1990 年代的更加温和和湿润的气候。这种变化通过北大西洋涛动（NAO）来描述，它本质上是衡量跨北大西洋西风平均强度的指标。如果西风比平时更强，则欧洲更多地受到大西洋温和海洋影响，据说NAO处于积极阶段，而如果西风比平时弱，则更多来自较冷的欧亚大陆的影响（负相）。 NAO 被广泛认为是影响欧洲的自然气候变率的主导模式。 NAO 变革背后的机制仍有许多待了解。对于过去几十年的变化是人为气候变化的结果还是仅仅是自然变化造成的，目前尚未达成共识。现代气候模型对于 NAO 对气候变化的反应也存在分歧。一些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集中于风暴路径对气候变化的响应。在太平洋，目前大多数模型预测风暴路径将向极地移动，但在大西洋，共识较少。这里的情况更加复杂，因为不同的模型预测了 NAO 以及海洋中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气候变化对欧洲区域影响的不确定性的一个关键来源。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。雷丁大学最近的研究表明，NAO 的长期变化很大程度上是由于大西洋特定天气系统发生的变化造成的。这些系统是高层大气中大规模波浪破裂的结果，与欧洲上空常见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微弱的西风，因此将被归类为负 NAO 时期。在该项目中，将利用这一新视角来研究为最新 IPCC 报告提供的最先进气候模型的数据，试图了解他们预测的 NAO 反应背后的原因。如果我们能够了解模型平均气候的变化将如何影响破浪的可能性或首选位置，那么我们就可以了解其 NAO 响应。气候模型中关于北大西洋风暴路径变化的分歧可能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路径推向极地，就像在其他海洋盆地中看到的那样，但与经向翻转环流减弱相关的海面温度变化可能会导致赤道移动。在这里，我们计划使用英国气象局最近开发的一项新技术来区分这些不同的影响，并量化每种影响的相对重要性。

项目成果

Vertical structure of anthropogenic zonal-mean atmospheric circulation change

人为纬向平均大气环流变化的垂直结构

• DOI: http://dx.10.1029/2008gl034883
• 发表时间: 2008
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Woollings T

Enhanced signature of solar variability in Eurasian winter climate

欧亚冬季气候中太阳变率的增强特征

• DOI: 10.1029/2010gl044601
• 发表时间: 2010-10-01
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: T. Woollings;M. Lockwood;G. Masato;C. Bell;L. Gray
• 通讯作者: L. Gray

The solar influence on the probability of relatively cold UK winters in the future

太阳对未来英国冬季相对寒冷的可能性的影响

• DOI: http://dx.10.1088/1748-9326/6/3/034004
• 发表时间: 2011
• 期刊: Environmental Research Letters
• 影响因子: 6.7
• 作者: Lockwood M

Atmospheric Blocking and Mean Biases in Climate Models

气候模型中的大气阻塞和平均偏差

• DOI: 10.1175/2010jcli3728.1
• 发表时间: 2010-12-01
• 期刊: Journal of Climate
• 影响因子: 4.9
• 作者: Adam A. Scaife;T. Woollings;J. Knight;G. Martin;T. Hinton
• 通讯作者: T. Hinton

Response of the North Atlantic storm track to climate change shaped by ocean-atmosphere coupling

北大西洋风暴路径对海洋-大气耦合影响的气候变化的响应

• DOI: http://dx.10.1038/ngeo1438
• 发表时间: 2012
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: Woollings T