Interannual teleconnections in the Sahara temperatures associated with the North Atlantic Oscillation (NAO) during boreal winter
Interannual teleconnections in the Sahara temperatures associated with the North Atlantic Oscillation (NAO) during boreal winter
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DOI：
10.1007/s00382-023-06962-w
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发表时间：
2023-09
期刊：
影响因子：
4.6
通讯作者：
Liming Zhou;W. Hua;S. Nicholson;J. P. Clark
中科院分区：
文献类型：
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作者：
Liming Zhou;W. Hua;S. Nicholson;J. P. Clark
北大西洋涛动（NAO）是在北方大西洋地区观测到的最重要的大气变率模态，其通过大尺度遥相关对北大西洋和欧亚大陆天气气候的影响已被广泛研究。在这里，我们使用多数据合成方法来分析来自多个长期观测和再分析数据集的地表和对流层变量，以确定NAO在卫星时代（1979-2022）和长达一个世纪的12月-1月-2月-3月期间对撒哈拉沙漠年际温度变化的影响。我们的研究结果提出了一个坚实的遥相关模式的证据与NAO在撒哈拉沙漠的表面和对流层温度和文件的一些主要的时空和垂直特性，这种模式。研究发现，撒哈拉地区的温度异常与NAO指数呈负相关，这种相关性在不同时期和不同数据集之间非常强，一致，并且具有统计学意义。遥相关是密切相关的大规模的环流异常，在整个对流层的北南极-撒哈拉部门，异常的水平风分量和位势高度表现出相反的变化与高度从低到高对流层。在负NAO期间-（正NAO+）期，高于正常撒哈拉沙漠地区的气温异常主要由三个过程来解释：（1）气候暖湿气流的平流输送北大西洋上空的（寒冷干燥的）空气（北方高纬度地区）由异常的西南风（2）对流层中上层气候性强西风带对北大西洋异常暖（冷）空气的平流输送;（3）加强（减弱）大气边界层的垂直混合。这些结果表明，NAO起着重要的作用，在调制的年际温度变率在撒哈拉沙漠，这NAO足迹主要是通过水平温度平流和湍流混合的垂直传热实现的。
The North Atlantic Oscillation (NAO) is the most recognized and leading mode of atmospheric variability observed over the Atlantic sector of the Northern Hemisphere, and its impacts on weather and climate over the North Atlantic and Eurasia via large-scale teleconnections have been extensively studied. Here we use a multidata synthesis approach to analyze surface and tropospheric variables from multiple long-term observational and reanalysis datasets to identify the NAO’s footprint on interannual temperature variability over the vast but least-studied Sahara Desert during December–January–February–March for the satellite era (1979–2022) and century-long periods. Our results present evidence for a solid teleconnection pattern in surface and tropospheric temperatures associated with the NAO over the Sahara and document some major spatial–temporal and vertical characteristics of this pattern. It is found that the Saharan temperature anomalies are negatively correlated with the NAO index and this correlation is very strong, consistent, and statistically significant between different periods and across different datasets. The teleconnection is closely linked to large-scale circulation anomalies throughout the troposphere over the North Atlantic–Sahara sector, where the anomalous horizontal wind components and geopotential height exhibit opposite changes in sign with altitude from the lower to upper troposphere. During the negative NAO− (positive NAO+) phase, above-normal (below-normal) temperatures over the Sahara could be mainly explained by three major processes: (1) advection of climatological warm and moist (cold and dry) air over the North Atlantic (northern higher latitudes) by the anomalous southwesterly (northeasterly) flow in the lower troposphere; (2) advection of anomalous North Atlantic warm (cold) air by the climatological strong westerlies in the middle and upper troposphere; and (3) strengthened (weakened) vertical mixing in the atmospheric boundary layer. These results suggest that the NAO plays an important role in modulating the interannual temperature variability over the Sahara, and that this NAO footprint is mostly realized through horizontal temperature advection and vertical heat transfer by turbulent mixing.