Ensemble simulation of the atmospheric general circulation at altitudes up to the lower thermosphere is performed using the 3-D nonlinear mechanistic numerical model MUAM. The residual mean meridional circulation (RMC), which is the superposition of the mean Eulerian and wave-induced eddy components, is calculated for the boreal winter. Changes in the vertical and meridional RMC velocity components are analysed at different stages of a simulated composite sudden stratospheric warming (SSW) event averaged over 19 model runs. The simulation results show a general decrease in RMC velocity components up to 30 % during and after SSW in the mesosphere and lower thermosphere of the Northern Hemisphere. There are also increases in the downward and northward velocities at altitudes of 20–50 km at the northern polar latitudes during SSW. Associated vertical transport and adiabatic heating can contribute to warming the stratosphere and downward shifting of the stratopause during the composite SSW. The residual mean and eddy mass fluxes are calculated for different SSW stages. It is shown that before the SSW, planetary wave activity creates wave-induced eddy circulation cells in the northern upper stratosphere, which are directed upwards at middle latitudes, northward at high latitudes and downwards near the North Pole. These cells increase heat transport and adiabatic heating in the polar region. During SSW, the region of upward eddy vertical velocity is shifted to high latitudes, but the velocity is still downward near the North Pole. After SSW, upward eddy-induced fluxes span the entire polar region, producing upward transport and adiabatic cooling of the stratosphere and providing the return of the stratopause to higher altitudes. The obtained statistically significant results on the evolution of RMC and eddy circulation at different SSW stages at altitudes up to the lower thermosphere can be useful for a better understanding the mechanisms of planetary wave impacts on the mean flow and for the diagnostics of the transport of conservative tracers in the atmosphere.

中文翻译：

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模拟平流层突然变暖事件不同阶段的剩余平均子午环流

使用3-D非线性力学数值模型MUAM，对直到较低热层高度的大气总环流进行了整体模拟。计算了北半球冬季的剩余平均子午环流（RMC），这是平均欧拉和波浪诱发的涡流分量的叠加。在模拟的复合平流层突然变暖（SSW）事件的不同阶段，分析了19个模型运行的平均水平，垂直和子午RMC速度分量的变化。模拟结果表明，在北半球中层和下热层的南南半球期间和之后，RMC速度分量普遍下降达30％。SSW期间，北极纬度在20–50 km处的向下和向北速度也有所增加。在复合SSW期间，相关的垂直输送和绝热加热可有助于平流层变暖和平流层顶向下移动。计算了不同SSW阶段的残留平均和涡流质量通量。结果表明，在南半球前，行星波活动在北平流层上部形成了波浪引起的涡流循环单元，这些单元在中纬度向上指向，在高纬度向北指向北极，而在北极附近向下指向。这些电池增加了极区的热传递和绝热加热。在SSW期间，涡流垂直速度向上的区域移至高纬度，但是在北极附近速度仍然向下。在SSW之后，向上的涡流引起的通量跨越整个极区，产生平流层的向上输送和绝热冷却，并使平流层顶返回高空。在直到低热层高度的不同SSW阶段，RMC和涡旋循环演变的统计意义显着结果，对于更好地了解行星波对平均流影响的机理以及对保守性输运的诊断很有帮助。示踪剂在大气中。