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研究认为夏季变暖是冷冬形成的原因  

2012-02-26 11:10:15|  分类: 天气学与气候背景 |  标签: |举报 |字号 订阅

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研究认为夏季变暖是冷冬形成的原因
发布时间:2012-02-14
文章出自:译言
原文链接:点击查看

1月13日《环境研究快报》上发表文章,认为夏季北极洋冰融化,极地空气中水蒸汽含量增加,在冬季带来了更多的降雪,最终导致北半球中低纬度地区的冬天变得更冷。这项研究为现有的气候变化模型提供了一个新的参考因素。

科学日报(2012年1月12日)——科学家们为北半球近来经历的严冬提供了一个有说服力的解释:北极地区不断升高的温度和融化的极冰在较低纬度的秋季制造了更多的降雪。

他们的发现可能能解释一些特殊的天气事件,比如弗罗里达2010年导致大量热带生物冻死的极其寒冷的冬天,以及英国2010年12月造成混乱的大雪。

1月13日在IOP出版社旗下的杂志《环境研究快报》(IOP Publishing's journal Environmental Research Letters)上发表的新研究成果表明,过去二十年来不断变冷的冬季可以用秋季的温度上升来解释。秋季升温对正常天气模式的显著影响导致了接下来冬季温度的骤然下降。

冬季变冷的趋势在美国东部,加拿大南部和北欧亚大陆的大部分地区表现得最明显,马萨诸塞大学和阿拉斯加费尔班克大学的大气和环境研究组(AER)的研究者们认为这个趋势不能完全用气候系统的自然变化来解释。

他们的研究结果显示,整个7月、8月和9月北极的剧烈升温,在秋天会继续延续,而且,根据他们观察到的数据,这似乎加剧了洋冰的融化。

变暖的大气和融化的洋冰一起,使得北冰洋大气层水蒸汽的含量,引起较南地区例如欧亚大陆降水的可能性变大,而当温度低于零度时,就会形成降雪。研究者们的观察显示,过去二十年欧亚大陆的平均降雪覆盖率的确增加了。

他们认为,降雪的增加对“北极涛动”——中高纬度的一种大气压力形式——有着复杂的影响,以致其一直处于“负相”。

在“负相”,北极地区被高压覆盖,将冷空气推向中纬度地区,比如美国和加拿大北部,造成了被观察到的冷冬。

研究的主要作者,贾达·科恩(Judah Cohen)说:“我以为,毫无疑问全球都在变暖,而且这会使所有地区在所有季节都会更热;尽管如此,我还是认为积雪增加的趋势导致了局部地区变冷,像这篇文章中讨论的那样,而且我找不到在短期内这个现象不会持续的任何理由。此外,如果秋天继续变暖,现在的降雪会变成降雨,减少冬天变冷的情况。”

研究者们还推断,传统气候模型不能解释冷冬现象的主要原因之一,是它们都没有考虑到积雪的变化,而正如这项研究所证明的,这能大大提高季节和长期天气预测的准确度。

“我们在文章中展示了如何在季节预测中利用降雪,来提供更熟练或者说精确的预报。少了冬季气候变化模式和降雪变化之间的耦合,现在政府中心使用的模型就缺少了冬季的一个重要影响因素,导致对冬季天气的预测在季节尺度甚至更长时间的十年际尺度上存在的不足延续下去。”科恩继续说。

 

Cold Winters Caused by Warmer Summers, Research Suggests

ScienceDaily (Jan. 12, 2012) — Scientists have offered up a convincing explanation for the harsh winters recently experienced in the Northern Hemisphere; increasing temperatures and melting ice in the Arctic regions creating more snowfall in the autumn months at lower latitudes.

Their findings may throw light on specific weather incidents such as the extremely harsh Florida winter of 2010 which ended up killing a host of tropical creatures, as well as the chaos-causing snow that fell on the UK in December 2010.

Published January 13, in IOP Publishing's journal Environmental Research Letters, this new research suggests that the trend of increasingly cold winters over the past two decades could be explained by warmer temperatures in the autumn having a marked effect on normal weather patterns, causing temperatures to plummet in the following winter.

The strongest winter cooling trends were observed in the eastern United States, southern Canada and much of northern Eurasia, which the researchers, based at Atmospheric and Environmental Research (AER), the University of Massachusetts and the University of Alaska Fairbanks, believe cannot be entirely explained by the natural variability of the climate system.

Their results showed strong warming throughout July, August and September in the Arctic, which continued through the autumn and, according to their observational data, appeared to enhance the melting of sea ice.

This warmer atmosphere, combined with melting sea ice, allows the Arctic atmosphere to hold more moisture and increases the likelihood of precipitation over more southern areas such as Eurasia, which, in the freezing temperatures, would fall as snow. Indeed, the researchers' observations showed that the average snow coverage in Eurasia has increased over the past two decades.

They believe the increased snow cover has an intricate effect on the Arctic Oscillation -- an atmospheric pressure pattern in the mid- to high-latitudes -- causing it to remain in the "negative phase."

In the "negative phase, " high pressure resides over the Arctic region, pushing colder air into mid-latitude regions, such as the United States and northern Canada, and giving the observed colder winters.

The lead author of the study, Judah Cohen, said: "In my mind there is no doubt that the globe is getting warmer and this will favour warmer temperatures in all seasons and in all locations; however, I do think that the increasing trend in snow cover has led to regional cooling as discussed in the paper and I see no reason why this won't continue into the near future. Also if it continues to get much warmer in the fall, precipitation that currently falls as snow will fall as rain instead, eliminating the winter cooling."

It is also deduced that one of the main reasons conventional climate models fail to pick up on this observed winter cooling is their failure to account for the variability of snow cover, which, as demonstrated in this study, can greatly improve the accuracy of seasonal, and lengthier, forecasts.

"We show in the paper how using the snow cover in a seasonal forecast can provide a more skilful or accurate forecast. Without correctly simulating the coupling of winter climate patterns and the variability of snow fall, the models currently used by Government centres miss an important influence on winter and will therefore continue to be deficient in predicting winter weather on seasonal time scales, and even longer decadal time scales, " continued Cohen.

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