Formation of the double stratopause and elevated stratopause associated with the major stratospheric sudden warming in 2018/19
Formation of the double stratopause and elevated stratopause associated with the major stratospheric sudden warming in 2018/19
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DOI：
10.5194/egusphere-egu21-9322
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发表时间：
2021-02
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影响因子：
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通讯作者：
H. Okui;Kaoru Sato;D. Koshin;S. Watanabe
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作者：
H. Okui;Kaoru Sato;D. Koshin;S. Watanabe
在最近的几次平流层突然变暖（SSW）事件之后，平流层顶消失并在更高的高度重新形成，形成了升高的平流层顶（ES）。大气波动在ES形成机制中的相对作用仍然没有完全了解。我们使用包含中间层和低热层（MLT）的重力波（GW）允许大气环流模型对2018/19 SSW事件进行了后报，并分析了整个中层大气的动力学现象。在2019年1月1日的主要变暖之后形成了ES。2018年12月28日左右，在与SSW相关的下降平流层顶消失之前，极地上层中间层有一个明显的温度最高值。这种在垂直方向上具有两个最大值的温度结构被称为双平流层顶（DS）。我们发现，绝热加热的残余环流驱动的GW强迫（GWF）导致正压和/或斜压不稳定DS形成之前，导致在原地产生的行星波（PWs）。这些PW传播到MLT并施加负强迫，这有助于DS的形成。恢复的东向急流上方的负GWF和PWF对ES的形成起着决定性的作用。恢复的东向急流的高度，调节GWF和PWF的高度，可能是受DS结构。来自低层大气的简单垂直传播不足以解释在这次事件中观察到的GW的存在。
After several recent stratospheric sudden warming (SSW) events, the stratopause disappeared and reformed at a higher altitude, forming an elevated stratopause (ES). The relative roles of atmospheric waves in the mechanism of ES formation are still not fully understood. We performed a hindcast of the 2018/19 SSW event using a gravity-wave (GW) permitting general circulation model containing the mesosphere and lower thermosphere (MLT), and analyzed dynamical phenomena throughout the entire middle atmosphere. An ES formed after the major warming on 1 January 2019. There was a marked temperature maximum in the polar upper mesosphere around 28 December 2018 prior to the disappearance of the descending stratopause associated with the SSW. This temperature structure with two maxima in the vertical is referred to as a double stratopause (DS). We showed that adiabatic heating from the residual circulation driven by GW forcing (GWF) causes barotropic and/or baroclinic instability before DS formation, causing in situ generation of planetary waves (PWs). These PWs propagate into the MLT and exert negative forcing, which contributes to DS formation. Both negative GWF and PWF above the recovered eastward jet play crucial roles in ES formation. The altitude of the recovered eastward jet, which regulates GWF and PWF height, is likely affected by the DS structure. Simple vertical propagation from the lower atmosphere is insufficient to explain the presence of the GWs observed in this event.