The millennium water vapour drop in chemistry–climate model simulations
The millennium water vapour drop in chemistry–climate model simulations
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DOI：
10.5194/acp-16-8125-2016
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发表时间：
2015-09
影响因子：
6.3
通讯作者：
S. Brinkop;M. Dameris;P. Jöckel;H. Garny;S. Lossow;G. Stiller
中科院分区：
文献类型：
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作者：
S. Brinkop;M. Dameris;P. Jöckel;H. Garny;S. Lossow;G. Stiller
抽象的。这项研究调查了从2000年开始平流层中突然和严重的水蒸气减少（“千年水蒸气下降”）和其他类似的平流层水蒸气强烈减少，方法是利用最先进的化学-气候模式（CCM）EMAC（ECHAM/MESSy大气化学模式）进行各种模拟。模型模拟不同的规定的海面温度（SST）和是否轻推应用或不。CCM EMAC能够最接近地再现水汽下降的特征和模式，与卫星观测结果一致，如果模型被推动的话。模式结果证实，这种异常的水汽减少在热带平流层低层特别明显，与冷点温度的大幅下降有关。下降信号在稀释下传播到较高的平流层，并通过布鲁尔-多布森环流（BDC）传播到两极。我们发现，这种水汽混合比显著下降的驱动力是热带海表温度（SST）的变化，这是由于与前一次强厄尔尼诺-南方涛动事件相吻合（1997/1998）之后发生了一次强烈的拉尼娜事件（1999/2000），并得到2000年赤道平流层准两年振荡（QBO）西风向东风位相变化的支持。正确的（观测到的）SST对于触发水蒸气的强烈下降很重要。有迹象表明，至少部分地，SST有助于2001年至2006年的长期低水汽值。在此期间，大气的特定动力状态（整个大气大尺度风和温度分布）也很重要，因为它导致观测到的持续低温点温度。这些都是由一段时间的上升流增加，然而，没有相应的显着签名在热带SST异常。我们的自由运行模拟没有捕捉到所观察到的下降，因为a）冷点温度具有低偏差，因此水蒸气可变性降低，以及B）因为它们没有模拟适当的动态状态。大的负水汽下降也发现在其他年份，似乎是一个功能，可以发现在强组合的厄尔尼诺/拉尼娜事件后，如果QBO在拉尼娜的西相变化到东相。
Abstract. This study investigates the abrupt and severe water vapour decline in the stratosphere beginning in the year 2000 (the "millennium water vapour drop") and other similarly strong stratospheric water vapour reductions by means of various simulations with the state-of-the-art Chemistry-Climate Model (CCM) EMAC (ECHAM/MESSy Atmospheric Chemistry Model). The model simulations differ with respect to the prescribed sea surface temperatures (SSTs) and whether nudging is applied or not. The CCM EMAC is able to most closely reproduce the signature and pattern of the water vapour drop in agreement with those derived from satellite observations if the model is nudged. Model results confirm that this extraordinary water vapour decline is particularly obvious in the tropical lower stratosphere and is related to a large decrease in cold point temperature. The drop signal propagates under dilution to the higher stratosphere and to the poles via the Brewer–Dobson circulation (BDC). We found that the driving forces for this significant decline in water vapour mixing ratios are tropical sea surface temperature (SST) changes due to a coincidence with a preceding strong El Nino–Southern Oscillation event (1997/1998) followed by a strong La Nina event (1999/2000) and supported by the change of the westerly to the easterly phase of the equatorial stratospheric quasi-biennial oscillation (QBO) in 2000. Correct (observed) SSTs are important for triggering the strong decline in water vapour. There are indications that, at least partly, SSTs contribute to the long period of low water vapour values from 2001 to 2006. For this period, the specific dynamical state of the atmosphere (overall atmospheric large-scale wind and temperature distribution) is important as well, as it causes the observed persistent low cold point temperatures. These are induced by a period of increased upwelling, which, however, has no corresponding pronounced signature in SSTs anomalies in the tropics. Our free-running simulations do not capture the drop as observed, because a) the cold point temperature has a low bias and thus the water vapour variability is reduced and b) because they do not simulate the appropriate dynamical state. Large negative water vapour declines are also found in other years and seem to be a feature which can be found after strong combined El Nino/La Nina events if the QBO west phase during La Nina changes to the east phase.