Tropical widening: From global variations to regional impacts
Tropical widening: From global variations to regional impacts
复制标题
热带扩张：从全球变化到区域影响
DOI：
10.1175/bams-d-19-0047.1
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发表时间：
2020
影响因子：
8
通讯作者：
Simpson, Isla R.
中科院分区：
文献类型：
--
作者：
Staten, Paul W.;Grise, Kevin M.;Davis, Sean M.;Karnauskas, Kristopher B.;Waugh, Darryn W.;Maycock, Amanda;Fu, Qiang;Cook, Kerry;Adam, Ori;Simpson, Isla R.
过去 15 年里，大量研究表明，地球哈德利环流的下沉分支和相关的亚热带干旱区在 20 世纪末和 21 世纪初已向极地方向移动。根据卫星观测和重新分析，对这种热带范围扩大的早期估计在每十年纬度 0.25° 到 3° 之间变化，而全球气候模型的估计显示，这种热带范围扩大在观测范围的下端。 2016 年，成立了两个工作组，即美国气候变率和可预测性 (CLIVAR) 热带带宽度变化工作组和国际空间科学研究所 (ISSI) 热带宽度诊断比对项目，以综合目前对观测中明显热带扩张的幅度、原因和影响的理解。这些工作组得出的结论是，早期研究指出的观测到的热带扩张率很高，是由于他们使用的指标未能很好地捕捉哈德利环流的变化，或者是由于使用了包含虚假趋势的重新分析。考虑到这些问题，观测到的膨胀率范围缩小到了 0.25°–0.5° 纬度十年一 1——在模型模拟的范围内。模型表明，最近的北半球热带扩张大部分与自然变率一致，而温室气体的增加和平流层臭氧的减少可能在南半球的扩张中发挥了重要作用。无论扩张的原因或速度如何，了解热带扩张的区域影响都需要额外的工作，因为不同的强迫会产生不同的区域扩张模式。
Over the past 15 years, numerous studies have suggested that the sinking branches of Earth’s Hadley circulation and the associated subtropical dry zones have shifted poleward over the late twentieth century and early twenty-first century. Early estimates of this tropical widening from satellite observations and reanalyses varied from 0.25° to 3° latitude per decade, while estimates from global climate models show widening at the lower end of the observed range. In 2016, two working groups, the U.S. Climate Variability and Predictability (CLIVAR) working group on the Changing Width of the Tropical Belt and the International Space Science Institute (ISSI) Tropical Width Diagnostics Intercomparison Project, were formed to synthesize current understanding of the magnitude, causes, and impacts of the recent tropical widening evident in observations. These working groups concluded that the large rates of observed tropical widening noted by earlier studies resulted from their use of metrics that poorly capture changes in the Hadley circulation, or from the use of reanalyses that contained spurious trends. Accounting for these issues reduces the range of observed expansion rates to 0.25°–0.5° latitude decade‒1—within the range from model simulations. Models indicate that most of the recent Northern Hemisphere tropical widening is consistent with natural variability, whereas increasing greenhouse gases and decreasing stratospheric ozone likely played an important role in Southern Hemisphere widening. Whatever the cause or rate of expansion, understanding the regional impacts of tropical widening requires additional work, as different forcings can produce different regional patterns of widening.