Environmental Systems Science Centre, University of Reading, 3 Earley Gate, Reading, Berkshire RG6 6AL, UK.
Nature. 2010 Sep 16;467(7313):309-12. doi: 10.1038/nature09388.
Every winter, the high-latitude oceans are struck by severe storms that are considerably smaller than the weather-dominating synoptic depressions. Accompanied by strong winds and heavy precipitation, these often explosively developing mesoscale cyclones-termed polar lows-constitute a threat to offshore activities such as shipping or oil and gas exploitation. Yet owing to their small scale, polar lows are poorly represented in the observational and global reanalysis data often used for climatological investigations of atmospheric features and cannot be assessed in coarse-resolution global simulations of possible future climates. Here we show that in a future anthropogenically warmed climate, the frequency of polar lows is projected to decline. We used a series of regional climate model simulations to downscale a set of global climate change scenarios from the Intergovernmental Panel of Climate Change. In this process, we first simulated the formation of polar low systems in the North Atlantic and then counted the individual cases. A previous study using NCEP/NCAR re-analysis data revealed that polar low frequency from 1948 to 2005 did not systematically change. Now, in projections for the end of the twenty-first century, we found a significantly lower number of polar lows and a northward shift of their mean genesis region in response to elevated atmospheric greenhouse gas concentration. This change can be related to changes in the North Atlantic sea surface temperature and mid-troposphere temperature; the latter is found to rise faster than the former so that the resulting stability is increased, hindering the formation or intensification of polar lows. Our results provide a rare example of a climate change effect in which a type of extreme weather is likely to decrease, rather than increase.
每年冬季，高纬度海洋都会遭受规模远小于天气主导性天气系统的剧烈风暴袭击。这些风暴伴随着强风和强降水，通常会迅速发展成中尺度气旋，即极地低气压。极地低气压对海上活动（如航运或石油和天然气开采）构成威胁。然而，由于规模较小，极地低气压在观测和全球再分析数据中代表性较差，而这些数据通常用于大气特征的气候学研究，且无法在可能未来气候的粗分辨率全球模拟中进行评估。本文表明，在人为变暖的未来气候中，极地低气压的频率预计将会下降。我们使用一系列区域气候模型模拟，对政府间气候变化专门委员会（IPCC）提供的一组全球气候变化情景进行降尺度处理。在此过程中，我们首先模拟了北大西洋极地低气压系统的形成，然后对各个案例进行计数。先前使用 NCEP/NCAR 再分析数据的研究表明，1948 年至 2005 年期间极地低气压的频率并没有系统地变化。现在，在二十一世纪末的预测中，我们发现极地低气压的数量明显减少，其平均生成区域向北移动，这是对大气温室气体浓度升高的响应。这种变化与北大西洋海表温度和中层大气温度的变化有关；后者的上升速度快于前者，导致稳定性增加，从而阻碍了极地低气压的形成或加强。我们的研究结果提供了一个罕见的气候变化效应的例子，即一种极端天气类型可能会减少，而不是增加。
