As observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), the migrating diurnal tide (DW1) in the upper mesosphere and lower thermosphere (MLT) region decreased by ∼ 10 % during El Niño in the Northern Hemisphere (NH) winter (December–January–February) from 2002 to 2020. According to the multiple linear regression (MLR) analysis, the linear effects of El Niño on the tropical MLT DW1 are significantly negative in both SABER observations and SD-WACCM (the Specified-Dynamics version of the Whole Atmosphere Community Climate Model) simulations. The DW1 response to El Niño in NH winter is much stronger than its annual mean response. As suggested by SD-WACCM simulation, Hough mode (1, 1) dominates the DW1 tidal variation in the tropical MLT region. The consistency between the (1, 1) mode in the tropopause region and the MLT region and the downward phase progression from 15 to 100 km indicates the direct upward propagation of DW1 from the excitation source in the troposphere. The suppressed DW1 heating rates in the tropical troposphere (averaged over ∼ 0–16 km and 35^∘ S–35^∘ N) during El Niño winter contribute to the decreased DW1 tide. To evaluate the effect of the gravity waves (GWs) on the tide, the GW forcing is calculated as the GW drag weighted by the phase relation between DW1 GW drag and DW1 wind. The negative GW forcing in the tropical upper mesosphere would significantly suppress the MLT DW1 tide during El Niño winter. This tide–GW interaction could be a dominant mechanism for DW1 response in the MLT to El Niño. During El Niño winter, the increased ratio of the absolute and planetary vorticity (R) suppresses the waveguide and thus the DW1 amplitude in the subtropical mesosphere. However, the effect of the waveguide might play a secondary role due to its relatively weak response.

中文翻译：

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北方冬季厄尔尼诺期间中层和低热层区的日潮迁移抑制及其可能机制

正如使用宽带发射辐射测量法 (SABER) 的大气探测所观察到的那样，中层上层和热层下层 (MLT) 区域的迁移日潮 (DW1) 减少了~ 2002年至2020年北半球（NH）冬季（12月-1月-2月）厄尔尼诺期间10%。根据多元线性回归（MLR）分析，厄尔尼诺对热带MLT DW1的线性影响显着负在 SABRE 观测和 SD-WACCM（整个大气社区气候模型的指定动力学版本）模拟中。北半球冬季对厄尔尼诺的 DW1 响应比其年平均响应强得多。正如 SD-WACCM 模拟所表明的那样，霍夫模式 (1, 1) 主导了热带 MLT 地区的 DW1 潮汐变化。对流层顶区和 MLT 区 (1, 1) 模式的一致性以及从 15 到 100 km 的向下相位进展表明 DW1 从对流层中的激发源直接向上传播。 厄尔尼诺冬季~  0–16 km 和 35 ^∘  S–35 ^{∘ N) 导致 DW1 潮汐减少。}为了评估重力波 (GWs) 对潮汐的影响，GW 强迫计算为 GW 阻力，由 DW1 GW 阻力和 DW1 风之间的相位关系加权。在厄尔尼诺冬季，热带上层中层的负重力引力将显着抑制 MLT DW1 潮。这种潮汐-GW 相互作用可能是 MLT 中 DW1 响应厄尔尼诺现象的主要机制。在厄尔尼诺冬季，增加的绝对涡度和行星涡度比（R）抑制了波导，从而抑制了副热带中间层的 DW1 幅度。然而，波导的影响可能由于其相对较弱的响应而起次要作用。