The Southern Westerlies during the last glacial maximum in PMIP2 simulations
The Southern Westerlies during the last glacial maximum in PMIP2 simulations
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DOI：
10.1007/s00382-008-0421-7
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发表时间：
2009-03-01
期刊：
影响因子：
4.6
通讯作者：
Hope, Pandora
中科院分区：
文献类型：
--
作者：
Rojas, Maisa;Moreno, Patricio I.;Hope, Pandora
南半球西风是半球和全球气候系统的重要组成部分。由于其对深海环流和大气二氧化碳变化的影响，冰河时代循环期间其强度和纬度位置的变化被认为是全球气候变化的重要驱动因素。然而，从经验和模型的角度来看，末次盛冰期（LGM）期间南西风带的位置、强度和相关气候仍然知之甚少。在这里，我们使用古气候模拟比对项目第二阶段（PMIP2）进行的四次海洋-大气耦合模拟来分析末次盛冰期期间南西风的行为。我们通过直接检查风并使用气旋跟踪软件来指示风暴路径来分析大气环流。模型表明，变化在冬季和太平洋上空最为显着。对于这个季节和地区，四分之三的模型表明近地表和对流层上层的风强度减弱。尽管末次盛宴的大气层较冷，赤道到极地表面的温度梯度通常会增加，但对流层温度梯度实际上会减小，这解释了环流较弱的原因。我们通过研究风应力对埃克曼抽水的影响来评估大气对南大洋的影响。同样，三个模型表明南大洋纬度带的上升流减少。所有模型都表明末次盛冰期比目前更加干燥，南纬 40 度以南海洋上空的降水量明显减少。我们发现了区域尺度上陆地降水异常的重要差异，包括新西兰气候干燥，巴塔哥尼亚西北部气候湿润。
The Southern Hemisphere westerly winds are an important component of the climate system at hemispheric and global scales. Variations in their intensity and latitudinal position through an ice-age cycle have been proposed as important drivers of global climate change due to their influence on deep-ocean circulation and changes in atmospheric CO2. The position, intensity, and associated climatology of the southern westerlies during the last glacial maximum (LGM), however, is still poorly understood from empirical and modelling standpoints. Here we analyse the behaviour of the southern westerlies during the LGM using four coupled ocean-atmosphere simulations carried out by the Palaeoclimate Modelling Intercomparison Project Phase 2 (PMIP2). We analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone tracking software to indicate storm tracks. The models suggest that changes were most significant during winter and over the Pacific ocean. For this season and region, three out four models indicate decreased wind intensities at the near surface as well as in the upper troposphere. Although the LGM atmosphere is colder and the equator to pole surface temperature gradient generally increases, the tropospheric temperature gradients actually decrease, explaining the weaker circulation. We evaluated the atmospheric influence on the Southern Ocean by examining the effect of wind stress on the Ekman pumping. Again, three of the models indicate decreased upwelling in a latitudinal band over the Southern Ocean. All models indicate a drier LGM than at present with a clear decrease in precipitation south of 40A degrees S over the oceans. We identify important differences in precipitation anomalies over the land masses at regional scale, including a drier climate over New Zealand and wetter over NW Patagonia.