Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension simulations are used to investigate the solar migrating semidiurnal tide (SW2) around September equinox at middle to high latitudes in the Northern Hemisphere. A pronounced minimum in SW2 occurs around September equinox, and is characterized by a ∼50% reduction in tidal amplitudes for 20–30 days. Analysis of the simulation results indicates that the SW2 minimum occurs due to the seasonal transition of the zonal mean zonal winds, which alter the generation and propagation of different symmetric and antisymmetric modes of SW2. In particular, the antisymmetric modes notably decrease due to the more hemispherically symmetric zonal winds around equinox. It is further demonstrated that interannual variability in the timing of the SW2 minimum is related to the timing of the seasonal transition of the zonal mean zonal winds in the middle atmosphere. This leads to an earlier occurrence of the SW2 minimum during years when the seasonal transition occurs earlier, such as the recent 2019 September equinox which saw an earlier transition of the Southern Hemisphere zonal mean zonal winds following the occurrence of a sudden stratosphere warming. The connection between the timing of the SW2 minimum in the Northern Hemisphere and the timing of the seasonal transition in the middle atmosphere winds is confirmed by seasonal variability of 12‐h tides deduced from specular meteor radar observations at middle to high latitudes in the Northern Hemisphere.

中文翻译：

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北半球9月春分过渡期间的半日潮迁移

使用指定热力学-电离层扩展模拟的整个大气共同体气候模型来研究北半球中高纬度地区在9月春分前后的太阳迁移半日潮（SW2）。SW2的最小最小值出现在9月的春分左右，其特征是20-30天的潮汐振幅降低了约50％。对模拟结果的分析表明，SW2最小值出现的原因是纬向平均纬向风的季节转换，从而改变了SW2不同对称和反对称模式的产生和传播。特别地，由于围绕春分点的半球对称的纬向风，反对称模式显着降低。进一步证明，SW2最小值时间的年际变化与中间大气中纬向平均纬向风的季节转换时间有关。这导致SW2最小值在较早发生季节过渡的年份中更早出现，例如最近的2019年9月春分，平流层突然变暖之后，南半球纬向平均纬向风的过渡更早。北半球的SW2最小值时间与中层大气风的季节转变时间之间的联系由北半球中高纬度的镜面流星雷达观测得出的12 h潮的季节变化确定。 。