Role of gravity waves in the forcing of quasi two-day waves in the mesosphere: An observational study
Role of gravity waves in the forcing of quasi two-day waves in the mesosphere: An observational study
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DOI：
10.1029/2012jd018208
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发表时间：
2013-05-16
影响因子：
4.4
通讯作者：
Riese, M.
中科院分区：
文献类型：
--
作者：
Ern, M.;Preusse, P.;Riese, M.
准二日波振幅是由高分辨率动力学临边探测仪的温度观测和宽带发射辐射测量（SABER）卫星大气探测得到的。特别是，QTDW振幅的全球气候来自10年的SABER数据，覆盖中层和低热层。这种气候学与地转风和气候学的重力波（GW）动量通量和GW阻力绝对值来自同一个数据集。我们发现，QTDWS被迫不久后的最大值的中层夏季纬向风急流在准地转纬向平均位涡的纬向梯度的射流不稳定的区域是强烈的负。射流不稳定区域与增强的GW阻力密切相关，GW阻力可能通过使射流减速并导致负位涡梯度的射流曲率来播种这些不稳定性。利用SABER数据计算了QTDW的垂直相结构和Eliassen-Palm通量，并进行了研究。结果表明，QTDWs从射流不稳定区开始向上传播。它们在喷流核心产生向东的阻力，在较高高度产生强烈的向西的阻力。引人注目的是，QTDW被迫在全球GW分布的地区表现出特征的纵向结构所造成的GW源模式在夏季半球。这种纵向结构可能发挥了重要作用，强迫QTDW，但是，没有明确的联系已被发现所观察到的QTDW纬向波数。
Amplitudes of quasi two-day waves (QTDWs) are derived from temperature observations of the High Resolution Dynamics Limb Sounder and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instruments. In particular, a global climatology of QTDW amplitudes is derived from 10 years of SABER data, covering the mesosphere and lower thermosphere. This climatology is compared with geostrophic winds and climatologies of gravity wave (GW) momentum flux and GW drag absolute values derived from the same data set. We find that QTDWs are forced shortly after the maximum of the mesospheric summertime zonal wind jet in regions of jet instability where the meridional gradient of quasi-geostrophic zonal mean potential vorticity is strongly negative. The jet instability regions are closely linked to enhanced GW drag that likely seeds those instabilities by decelerating the jet and causing the jet curvature responsible for the negative potential vorticity gradient. The vertical phase structure and the Eliassen-Palm flux of the QTDWs are derived from SABER data and investigated. It is shown that QTDWs propagate upward starting from the jet instability regions. They exert eastward drag in the jet core, and strong westward drag at higher altitudes. Strikingly, the QTDWs are forced in regions where the global distribution of GWs exhibits a characteristic longitudinal structure caused by the GW source patterns in the summer hemisphere. This longitudinal structure might play an important role in the forcing of QTDWs; however, no clear link has been found to the observed QTDW zonal wavenumbers.