A Parameterization Scheme of Orographic Gravity Wave Drag with Two Different Vertical Partitionings
A Parameterization Scheme of Orographic Gravity Wave Drag with Two Different Vertical Partitionings
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两种不同垂直分区的地形重力波阻力参数化方案
DOI：
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发表时间：
1989
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影响因子：
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通讯作者：
K. Tada
中科院分区：
文献类型：
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作者：
T. Iwasaki;S. Yamada;K. Tada
由于非流体静力学效应，短重力内波（波长<10km）的传播特性与长重力内波（波长100km）的传播特性有很大不同。考虑到这一观察，我们参数化地形重力波阻力（GWD）在两种方式。两种方案的主要区别在于阻力强迫的垂直划分，即，一种主要在平流层（A型），另一种在对流层（B型）。我们将它们应用于全球数值天气预报模式，并研究它们对中期预报的影响。这两种方案分别减小了系统预报误差，而组合方案则达到了最佳预报效果。在对流层，这两种方案的影响，包括时间演变，是非常相似的。因此，对流层被认为是不敏感的垂直分区GWD至少在一个中等范围的时间尺度。在A型方案的情况下，大部分的阻力强迫下平流层平均气流迅速向下转移，并有助于对流层环流的变化。在平流层，A型方案的影响远大于B型方案，特别是在短时间尺度上。B型方案的平流层影响在几天后逐渐增加，可能对应于在对流层低层激发的Rossby波垂直传播所需的时间尺度。在纬向平均场中，预报的改善是明显的。虽然A型方案几乎消除了平流层中的西风误差，但对流层中仍然存在西风误差。类型B方案有效地减少了对流层剩余误差。这可能证明需要对流层阻力强迫，如B型方案。
The wave propagation properties of short internal gravity waves (wave length *<10km) are very different from those of long ones (*100km) owing to nonhydrostatic effects. Considering this observation, we parameterize the orographic gravity wave drag (GWD) in two ways. The major difference between two schemes is in the vertical partitioning of drag forcing, i, e., one weighs mainly in the stratosphere (type A) and the other in the troposphere (type B). We apply them to a global numerical weather prediction model and study their impacts on medium-range forecasts. These two schemes individually reduce systematic forecast errors and their combination achieves the best forecast skill. In the troposphere, the impacts of these two schemes, including time evolutions, are very similar to each other. Hence, the troposphere is considered to be insensitive to the vertical partitioning of GWD at least within a medium-range time scale. In the case of the type A scheme, most of the drag forcing given to the lower-stratospheric mean-flow is rapidly transferred downward and contributes to change in the tropospheric circulations. In the stratosphere, the impacts of the type A scheme is much larger than those of the type B, especially in a short-range time scale. The stratospheric impacts of the type B scheme gradually increase after a few days, possibly corresponding to a time scale required for the vertical propagation of Rossby waves excited in the lower troposphere. The improvement of forecasts is evident in the zonal-mean fields. Although the type A scheme almost eliminates the westerly errors in the stratosphere, there still remain westerly errors in the troposphere. The type B scheme effectively reduces the remaining tropospheric errors. This may justify a need of tropospheric drag forcing, like the type B scheme.