The quasi 2 day wave activities during 2007 austral summer period as revealed by Whole Atmosphere Community Climate Model
The quasi 2 day wave activities during 2007 austral summer period as revealed by Whole Atmosphere Community Climate Model
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DOI：
10.1002/2015ja022225
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发表时间：
2016-03
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影响因子：
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通讯作者：
Sheng‐yang Gu;Han L. Liu;N. Pedatella;X. Dou;Tao Li;Tingdi Chen
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作者：
Sheng‐yang Gu;Han L. Liu;N. Pedatella;X. Dou;Tao Li;Tingdi Chen
利用美国国家大气研究中心（NCAR）开发的全大气社区气候模式（WACCM + Data Assimilation Research Testbed）的资料同化版本，对2007年夏季南半球观测到的准二日波（QTDW）进行了再分析。结果表明，QTDW在1 ~ 2月出现3次峰值，但各峰值的纬向波数不同。诊断分析表明，QTDW的平均流不稳定性、折射率和临界层是其传播和放大的基础，因此，背景风的时间变化是造成不同时刻不同波数结构的原因。当与夏季东风急流有关的平均气流不稳定性被向西传播的波数3（W3）和波数4（W 4）模的临界层所包围时，向西传播的波数2模（W2）在1月上半月增长并达到最大值。这阻止了W3和W 4接近不稳定区域并从不稳定区域提取能量。此后，由于临界层的衰退，W2迅速衰减，因此缺乏平均流不稳定性的额外放大。W3在1月下旬达到峰值，此时不稳定性仍然被W 4的临界层包围。之后W3的衰减也是由于临界层的消失，因此没有过反射。最后，W 4在2月下旬达到峰值，此时不稳定性和临界层都合适。
The quasi 2 day wave (QTDW) observed during 2007 austral summer period is well reproduced in an reanalysis produced by the data assimilation version of the Whole Atmosphere Community Climate Model (WACCM + Data Assimilation Research Testbed) developed at National Center for Atmospheric Research (NCAR). It is found that the QTDW peaked 3 times from January to February but with different zonal wave numbers. Diagnostic analysis shows that the mean flow instabilities, refractive index, and critical layers of QTDWs are fundamental for their propagation and amplification, and thus, the temporal variations of the background wind are responsible for the different wave number structures at different times. The westward propagating wave number 2 mode (W2) grew and maximized in the first half of January, when the mean flow instabilities related to the summer easterly jet were enclosed by the critical layers of the westward propagating wave number 3 (W3) and wave number 4 (W4) modes. This prevented W3 and W4 from approaching and extracting energy from the unstable region. The W2 decayed rapidly thereafter due to the recession of critical layer and thus the lack of additional amplification by the mean flow instability. The W3 peaked in late January, when the instabilities were still encircled by the critical layer of W4. The attenuation of W3 afterward was also due to the disappearance of critical layer and thus the lack of overreflection. Finally, the W4 peaked in late February when both the instability and critical layer were appropriate.