Formation of a Mesospheric Inversion Layer and the Subsequent Elevated Stratopause Associated With the Major Stratospheric Sudden Warming in 2018/19
Formation of a Mesospheric Inversion Layer and the Subsequent Elevated Stratopause Associated With the Major Stratospheric Sudden Warming in 2018/19
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DOI：
10.1029/2021jd034681
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发表时间：
2021-08
期刊：
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
自2004年以来，在平流层持续的突然变暖（SSW）事件之后，观测到平流层顶消失并在更高的高度重新形成，形成了一个升高的平流层顶（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。我们使用重力波（GW）允许的大气环流模型对2018/19年SSW事件进行了后报，该模型解决了中间层和低热层（MLT），并分析了整个中层大气的动力学现象。ES在2019年1月1日的主要变暖之后形成。2018年12月28日左右，在与SSW相关的下降平流层顶消失之前，极地上层中层有一个明显的温度最高值。这种温度结构被称为中层逆温层（MIL）。我们发现，绝热加热的残余环流驱动的GW强迫（GWF）造成正压和/或斜压不稳定的MIL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（向西）强迫，这有助于MIL的形成。恢复的东向急流上方的GWF和PW强迫（PWF）在ES的形成中起着至关重要的作用。调节GWF和PWF高度的恢复的东向急流的高度可能受到MIL结构的影响。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。
Since 2004, following prolonged stratospheric sudden warming (SSW) events, it has been observed that 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 that resolves the mesosphere and lower thermosphere (MLT) and analyzed dynamical phenomena throughout the entire middle atmosphere. An ES formed after the major warming on January 1, 2019. There was a marked temperature maximum in the polar upper mesosphere around December 28, 2018 prior to the disappearance of the descending stratopause associated with the SSW. This temperature structure is referred to as a mesospheric inversion layer (MIL). We show that adiabatic heating from the residual circulation driven by GW forcing (GWF) causes barotropic and/or baroclinic instability before the MIL formation, causing in situ generation of planetary waves (PWs). These PWs propagate into the MLT and exert negative (westward) forcing, which contributes to the MIL formation. Both GWF and PW forcing (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 MIL structure. Simple vertical propagation from the lower atmosphere is insufficient to explain the presence of the GWs observed in this event.