On the hiatus in the acceleration of tropical upwelling since the beginning of the 21st century
On the hiatus in the acceleration of tropical upwelling since the beginning of the 21st century
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DOI：
10.5194/acp-14-12803-2014
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发表时间：
2014-01-01
影响因子：
6.3
通讯作者：
Thompson, A. M.
中科院分区：
文献类型：
--
作者：
Aschmann, J.;Burrows, J. P.;Thompson, A. M.
化学气候模型预测，由于大气温室气体水平升高，全球地表温度上升，布鲁尔多布森环流的上升流分支将加速。在20世纪的最后几十年里，观测到的热带平流层下部臭氧的减少与预期的上升流加速是一致的。然而，最近对臭氧的卫星观测表明，这种减少在世纪的第一个十年中出人意料地停止了，这对热带上升流持续加速的隐含假设提出了挑战。在这项研究中，我们使用了三十年的化学传输模型模拟（1980-2013）来研究这一现象并解决这一明显的矛盾。除了1985-1990年之间的高偏差，我们的模式是能够重现观测到的热带平流层臭氧记录。回归分析表明，在早期出现了显著下降，2002年之后出现了统计上的强劲趋势变化，与观察结果在质量上一致。我们表明，这种趋势变化与垂直运输的结构变化，代表在模型中的非绝热加热率从再分析产品年代中期。这些变化导致在过去十年中，70-30百帕热带上升流加速中断，30和100百帕热带管道南移，这似乎是所观察到的臭氧趋势变化的主要原因。
Chemistry climate models predict an acceleration of the upwelling branch of the Brewer Dobson circulation as a consequence of increasing global surface temperatures, resulting from elevated levels of atmospheric greenhouse gases. The observed decrease of ozone in the tropical lower stratosphere during the last decades of the 20th century is consistent with the anticipated acceleration of upwelling. However, more recent satellite observations of ozone reveal that this decrease has unexpectedly stopped in the first decade of the 21st century, challenging the implicit assumption of a continuous acceleration of tropical upwelling. In this study we use three decades of chemistry-transport-model simulations (1980-2013) to investigate this phenomenon and resolve this apparent contradiction. Aside from a high-bias between 1985-1990, our model is able to reproduce the observed tropical lower stratosphere ozone record. A regression analysis identifies a significant decrease in the early period followed by a statistically robust trend-change after 2002, in qualitative agreement with the observations. We demonstrate that this trend-change is correlated with structural changes in the vertical transport, represented in the model by diabatic heating rates taken from the reanalysis product Era-Interim. These changes lead to a hiatus in the acceleration of tropical upwelling between 70-30 hPa and a southward shift of the tropical pipe at 30 and 100 hPa during the past decade, which appear to be the primary causes for the observed trend-change in ozone.