This paper characterizes the impacts of sudden stratospheric warmings (SSWs) and mesospheric coolings (MCs) on the light species distribution (i.e., helium [He], and atomic hydrogen [H]) of the thermosphere using a combined data‐modeling approach. Performing a set of numerical experiments with a general circulation model whose middle atmospheric dynamical and thermodynamical fields were constrained using a numerical weather prediction system, we simulate the effects of SSWs and MCs on light chemical species, and via comparisons with two data sets taken from the mesosphere and thermosphere, we quantify the associated variability in light species abundances and mass density. Large depletions in the observed and modeled polar H abundance in the mesosphere and lower thermosphere (MLT) occur with MC onset, as opposed to SSW onset. Depletions in all light thermospheric species at high northern latitudes extend up to the exobase in our model simulations during the January 2013 SSW/MC period, with the largest depletions simulated for the lightest species. Further, our modeling work substantiates the paradigm of increased mixing in the MLT driven by a meridional residual circulation during SSWs resulting from enhanced small‐scale gravity wave and migrating semidiurnal tidal forcing; the former being the primary driver and the latter of secondary but notable importance in our model simulations. SSW/MC induced light species variability then gets projected upward into the thermosphere through molecular diffusion. Modeled light species variability during the January 2013 SSW/MC event suggests SSW/MC signatures could be present in the topside ionosphere and plasmasphere.

中文翻译：

---

从中层大气到外基的耦合：对轻化学物质的动态扰动效应

本文采用组​​合数据建模方法，描述了平流层突然变暖（SSWs）和中层冷却（MCs）对热层轻物质分布（即氦[He]和原子氢[H]）的影响。使用通用天气预报模型执行一组数值实验，该通用模型使用数值天气预报系统限制了中间大气动力和热力学场，我们模拟了SSW和MC对轻化学物质的影响，并通过与两个数据集的比较进行了比较中层和热层，我们量化了轻物质的丰度和质量密度的相关变异性。在中层和下热层（MLT）中观测到的和模型化的极性氢丰度大幅度减少，发生于MC爆发，而不是SSW爆发。在我们于2013年1月SSW / MC期间进行的模型模拟中，北部高纬度地区所有轻热层物种的消耗一直扩展到系外基底，而最轻物种的消耗最大。此外，我们的建模工作证实了SSW期间子午残留循环驱动的MLT中混合增加的范式，这是由于小尺度重力波增强和半日潮汐力的迁移引起的。前者是主要驱动力，后者是次要驱动力，但在我们的模型仿真中非常重要。然后，SSW / MC引起的光物种变异性通过分子扩散向上投射到热层中。在2013年1月的SSW / MC事件中模拟的轻物种变异性表明，SSW / MC特征可能存在于顶面电离层和等离子层中。