The Momentum Budget in the Stratosphere, Mesosphere, and Lower Thermosphere. Part II: The In Situ Generation of Gravity Waves
The Momentum Budget in the Stratosphere, Mesosphere, and Lower Thermosphere. Part II: The In Situ Generation of Gravity Waves
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DOI：
10.1175/jas-d-17-0337.1
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发表时间：
2018-09
影响因子：
3.1
通讯作者：
Ryosuke Yasui;Kaoru Sato;Y. Miyoshi
中科院分区：
文献类型：
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作者：
Ryosuke Yasui;Kaoru Sato;Y. Miyoshi
利用GAIA（Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy）全大气模式的模拟资料，研究了重力波对中层和低热层动量收支的贡献。无论相对粗糙的模式分辨率，重力波出现在MLT地区。解析重力波对MLT动量收支有很大贡献。在夏季MLT区观测到一对正的和负的解析重力波Eliassen-Palm通量散度，表明解析重力波可能是在MLT区原位产生的。在夏季MLT区域，平均纬向风有很强的垂直切变，这可能是由参数化重力波强迫形成的。在强剪切区，Richardson数有时会小于四分之一，这表明解析重力波是由剪切不稳定性产生的。此外，剪切不稳定性发生在低（中）纬度的夏季（冬季）MLT地区，并与日（半日）迁移潮。解析重力波也从这些区域辐射。本文第一部分指出，MLT区的Rossby波也是由参数化重力波强迫形成的正压和斜压不稳定辐射的。这些结果强烈表明，来自低层大气的重力波的强迫导致的正压/斜压和剪切不稳定性，分别产生Rossby波和重力波，并建议这些波的原位生成和耗散MLT区域的动量收支中发挥重要作用。
The contributions of gravity waves to the momentum budget in the mesosphere and lower thermosphere (MLT) is examined using simulation data from the Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA) whole-atmosphere model. Regardless of the relatively coarse model resolution, gravity waves appear in the MLT region. The resolved gravity waves largely contribute to the MLT momentum budget. A pair of positive and negative Eliassen–Palm flux divergences of the resolved gravity waves are observed in the summer MLT region, suggesting that the resolved gravity waves are likely in situ generated in the MLT region. In the summer MLT region, the mean zonal winds have a strong vertical shear that is likely formed by parameterized gravity wave forcing. The Richardson number sometimes becomes less than a quarter in the strong-shear region, suggesting that the resolved gravity waves are generated by shear instability. In addition, shear instability occurs in the low (middle) latitudes of the summer (winter) MLT region and is associated with diurnal (semidiurnal) migrating tides. Resolved gravity waves are also radiated from these regions. In Part I of this paper, it was shown that Rossby waves in the MLT region are also radiated by the barotropic and/or baroclinic instability formed by parameterized gravity wave forcing. These results strongly suggest that the forcing by gravity waves originating from the lower atmosphere causes the barotropic/baroclinic and shear instabilities in the mesosphere that, respectively, generate Rossby and gravity waves and suggest that the in situ generation and dissipation of these waves play important roles in the momentum budget of the MLT region.