Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events
Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events
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DOI：
10.1002/2015ja020998
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发表时间：
2015-04
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影响因子：
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通讯作者：
Jorge L. Chau;Peter Hoffmann;N. Pedatella;V. Matthias;G. Stober
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作者：
Jorge L. Chau;Peter Hoffmann;N. Pedatella;V. Matthias;G. Stober
近年来，出现了一系列关于平流层突然变暖（SSW）事件周围赤道和低纬度电离层/热层的月球潮汐特征的地面和卫星观测报告。这种低层大气/电离层耦合被认为是通过 E 区发电机实现的。在这项工作中，我们介绍了中纬度 (54°N) 站和高纬度 (69°N) 站上空镜面流星雷达 6 年每小时的中层上层风的分析结果。我们没有将我们的结果与 SSW 的典型定义相关联，而是使用了张和福布斯使用的极涡弱化 (PVW) 的定义 ( )。该定义更好地表示了中层大气动力学的强度，该强度应负责传播到 E 区域的波。我们对 21 天段内的每小时风数据进行了波浪分解，偏移 1 天。除了雷达风数据外，该分析还应用于整个大气群落气候模型扩展版和热层-电离层-中间层电动力学大气环流模型的模拟。我们的结果表明，北半球冬季的半日月潮（M2）在中纬度和高纬度地区均增强。 M2的时间和强度与PVW的时间和相关纬向风高度相关。在中高纬度地区，上层中间层的M2发生在PVW之后/之前。在两个纬度上，M2的最大幅值与PVW西风的强度成正比。我们发现 M2 振幅可以与半日太阳潮汐振幅相媲美，特别是在 PVW 和春分点附近。除了这些一般结果之外，我们还发现了一些事件的特殊性，特别是在高纬度地区。这些特性表明需要考虑极地平流层以及中层上部和热层下部区域的纵向特征。例如，在 SSW 2009 期间，我们发现 M2 在 PVW 之前增强许多天，这与我们的大多数结果不一致。
In recent years there have been a series of reported ground‐ and satellite‐based observations of lunar tide signatures in the equatorial and low latitude ionosphere/thermosphere around sudden stratospheric warming (SSW) events. This lower atmosphere/ionosphere coupling has been suggested to be via the E region dynamo. In this work we present the results of analyzing 6 years of hourly upper mesospheric winds from specular meteor radars over a midlatitude (54°N) station and a high latitude (69°N) station. Instead of correlating our results with typical definitions of SSWs, we use the definition of polar vortex weaking (PVW) used by Zhang and Forbes ( ). This definition provides a better representation of the strength in middle atmospheric dynamics that should be responsible for the waves propagating to the E region. We have performed a wave decomposition on hourly wind data in 21 day segments, shifted by 1 day. In addition to the radar wind data, the analysis has been applied to simulations from Whole Atmosphere Community Climate Model Extended version and the thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model. Our results indicate that the semidiurnal lunar tide (M2) enhances in northern hemispheric winter months, over both middle and high latitudes. The time and magnitude of M2 are highly correlated with the time and associated zonal wind of PVW. At middle/high latitudes, M2 in the upper mesosphere occurs after/before the PVW. At both latitudes, the maximum amplitude of M2 is directly proportional to the strength of PVW westward wind. We have found that M2 amplitudes could be comparable to semidiurnal solar tide amplitudes, particularly around PVW and equinoxes. Besides these general results, we have also found peculiarities in some events, particularly at high latitudes. These peculiarities point to the need of considering the longitudinal features of the polar stratosphere and the upper mesosphere and lower thermosphere regions. For example, during SSW 2009, we found that M2 enhances many days before PVW which is not in agreement with most of our results.