工厂排放的烟雾让空气变得更差
龙卷风破坏力增强
近几年，中东和东南亚地区曾遭受几次具有破坏性的龙卷风袭击。一项新研究发现，中东和东南亚发展中国家因煤烟和浮质造成的空气污染提高了龙卷风的破坏性。刊登在《自然》杂志上的研究论文指出，燃烧化石燃料产生的排放与风模式之间的相互作用减弱了风切变作用，进而导致龙卷风规模增大，更具有破坏性。通常情况下，风切变会在龙卷风达到确定规模时将其“撕裂”。
研究过程中，科学家将1979年至1996年出现的龙卷风与1997年至2010年出现的龙卷风进行比较，结果发现最近出现的龙卷风强度是此前的3倍，不仅风速更快，风切变层也更低。此外，他们还发现这两个地区的浮质数量自上世纪30年代以来增加了5倍，在印度洋上空形成3公里厚的污染层，被称之为“东南亚大气褐云”。大气褐云吸收阳光，导致海洋温度降低，进而影响风循环。
科学家长久以来就认为空气污染能够影响季风，但证明空气污染与破坏性更强的风暴有关还是第一次。研究论文主执笔人阿马托·埃文在接受SciDev.Net网站采访时表示：“我认为浮质对龙卷风的影响与对季风环流和降雨的影响存在密切联系，它们往往减弱季风环流和减少降雨。”
埃文说：“我们的研究显示人类活动造成的空气污染——例如烧木头或者驾驶柴油机汽车——能够以一种非常显著的方式改变这些大规模大气现象。这一研究发现再一次强调了减少当地污染物排放的重要性。如果生活在一个强龙卷风登陆的地区，遏制空气污染就显得尤为重要。阿拉伯海历史上曾多次出现强热带气旋登陆印度、巴基斯坦、阿曼和伊朗等地区，每一次都造成巨大的人员财产损失。”这项研究有助于提高公众对空气污染的关注，空气污染不仅会导致呼吸系统疾病，同时也会提高龙卷风的破坏性，必须采取措施加以遏制。(生物谷 Bioon.com)
doi:10.1038/nature10552
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Arabian Sea tropical cyclones intensified by emissions of black carbon and other aerosols
Amato T. Evan,1 James P. Kossin,2, 3 Chul ‘Eddy’ Chung4 & V. Ramanathan5
Throughout the year, average sea surface temperatures in the Arabian Sea are warm enough to support the development of tropical cyclones1, but the atmospheric monsoon circulation and associated strong vertical wind shear limits cyclone development and intensification, only permitting a pre-monsoon and post-monsoon period for cyclogenesis1, 2, 3, 4. Thus a recent increase in the intensity of tropical cyclones over the northern Indian Ocean5 is thought to be related to the weakening of the climatological vertical wind shear3, 4. At the same time, anthropogenic emissions of aerosols have increased sixfold since the 1930s, leading to a weakening of the southwesterly lower-level and easterly upper-level winds that define the monsoonal circulation over the Arabian Sea6, 7, 8, 9. In principle, this aerosol-driven circulation modification could affect tropical cyclone intensity over the Arabian Sea, but so far no such linkage has been shown. Here we report an increase in the intensity of pre-monsoon Arabian Sea tropical cyclones during the period 1979–2010, and show that this change in storm strength is a consequence of a simultaneous upward trend in anthropogenic black carbon and sulphate emissions. We use a combination of observational, reanalysis and model data to demonstrate that the anomalous circulation, which is radiatively forced by these anthropogenic aerosols, reduces the basin-wide vertical wind shear, creating an environment more favourable for tropical cyclone intensification. Because most Arabian Sea tropical cyclones make landfall1, our results suggest an additional impact on human health from regional air pollution.
