Evidence of preferential directions for gravity wave propagation due to wind filtering in the middle atmosphere
Evidence of preferential directions for gravity wave propagation due to wind filtering in the middle atmosphere
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DOI：
10.1029/92ja02604
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发表时间：
1993-04
影响因子：
--
通讯作者：
M. Taylor;E. Ryan;T. Tuan;R. edwards
中科院分区：
文献类型：
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作者：
M. Taylor;E. Ryan;T. Tuan;R. edwards
1988年5月、6月和7月，在科罗拉多州尼德兰附近的山地研究站(40°N，105.6°W，3050m)的一个高海拔站点，记录了3个月的近红外氢氧化物(OH)夜辉发射的全天空电视图像。与短周期(<；1小时)重力波的传播相关的明确的相干波型总共观察到22次。各月的波动具有相似的时空特征，但在整个过程中有明显的北传趋势(68%的波方位角在±40.0°N范围内)，5、6月份有一些东移。虽然理论上众所周知，向上传播的重力波可以在波与水平背景风相互作用产生的临界层被阻挡，但这种现象的观测证据很少。为了探讨波传播方向的不对称性是由临界层引起的可能性，建立了一个基于平均气候背景风和潮波数值模式的模式，该模式适用于任何中纬度站点和一年中的任何时间，以显示临界层理论禁止重力波向上传播的区域。这些随高度和时间变化的“方块图”是为本文所用的OH高度(∼87公里)绘制的。将预测的(即最小限制的)波动方向与观测到的方向进行比较，显示出几乎完全一致。这表明，中层大气风可以在决定到达高层大气的短周期波的通量和方位分布方面发挥重要作用。
All-sky TV images of wave structure in the near-infrared hydroxyl (OH) nightglow emission were recorded over a 3-month period during May, June, and July 1988 from a high-altitude site at the Mountain Research Station (40.0° N, 105.6° W, 3050 m), near Nederland, Colorado. Well-defined, coherent wave patterns associated with the passage of short period (<1 hour) gravity waves were observed on a total of 22 occasions. The wave motions exhibited similar spatial and temporal properties during each month but a distinct tendency for northward propagation (68% of the wave azimuths within ± 40.0° N), with some eastward motion in May and June, was observed throughout the campaign. Although it is theoretically well known that upward propagating gravity waves can be blocked at a critical layer produced by the interaction of the waves with the horizontal background wind, observational evidence of this phenomenon is rare. To investigate the possibility that the asymmetry in the wave propagation directions was caused by the critical layer, a model based on mean climatological background winds and numerical tidal wave modes valid for any mid-latitude site and time of the year was constructed to show the regions forbidden to upward gravity wave propagation from critical layer theory. These “blocking diagrams” which vary with height and time were constructed for the OH altitude (∼87 km) for the present paper. Comparison of the predicted (i.e., least restricted) and the observed directions of the wave motion show almost complete agreement. This suggests that middle atmospheric winds can play an important role in determining the flux and the azimuthal distribution of short-period waves reaching the upper atmosphere.