Gravity Wave Generation around the Polar Vortex in the Stratosphere Revealed by 3-Hourly Radiosonde Observations at Syowa Station
Gravity Wave Generation around the Polar Vortex in the Stratosphere Revealed by 3-Hourly Radiosonde Observations at Syowa Station
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DOI：
10.1175/2008jas2539.1
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发表时间：
2008-12
影响因子：
3.1
通讯作者：
Kaoru Sato;M. Yoshiki
中科院分区：
文献类型：
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作者：
Kaoru Sato;M. Yoshiki
2002 年 3 月、6 月、10 月和 12 月，在昭和站（南纬 69.0°，东经 39.6°）进行了为期约 10 天的密集无线电探空仪观测，以检查南极低平流层的惯性重力波特征。基于每 3 小时的观测数据，利用双傅里叶变换方法检查了风波动的二维（即垂直波数与频率）谱。当极夜急流（PNJ）出现时，在六月和十月检测到重力波的清晰信号，其相位向上传播，表明能量向下传播。另一方面，向下相位传播（即向上能量传播）分量在所有月份中都占主导地位。 12月背景风较弱时，惯性频率附近大范围垂直波数出现谱峰，而6月和10月较低频率区域谱密度较大。这些光谱特征与 Sato 等人使用重力波解析全球环流模型 (GCM) 获得的结果一致。六月，使用测速仪分析方法分别检查了向上和向下传播的重力波的动力特性。结果发现，在同一高度区域同时观测到的向上和向下传播的波包具有相似的水平波长和相速度。这一事实表明这些重力波是由同一来源以相似的机制产生的。观测波包时，在稍微靠近昭和站低纬度的PNJ附近，局部罗斯贝数和利用NCEP-NCAR再分析数据估计的非线性平衡方程中的残差都很大。因此，观测到的惯性重力波很可能是由地转不平衡PNJ周围的自发调整产生的，并向昭和站传播。通过与 Sato 等人的 GCM 模拟的比较，证实了 PNJ 周围自发重力波产生的可能性。
Intensive radiosonde observations were performed at Syowa Station (69.0°S, 39.6°E) over about 10 days in each of March, June, October, and December 2002 to examine inertia–gravity wave characteristics in the Antarctic lower stratosphere. Based on the 3-hourly observation data, two-dimensional (i.e., vertical wavenumber versus frequency) spectra of wind fluctuations were examined, utilizing a double Fourier transform method. Clear signals of gravity waves whose phases propagate upward, suggesting downward energy propagation, are detected in June and October when the polar night jet (PNJ) was present. On the other hand, downward phase propagation (i.e., upward energy propagation) components are dominant in all months. There is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in December when the background wind was weak, whereas large spectral densities are distributed over lower-frequency regions in June and October. These spectral characteristics are consistent with the results obtained using a gravity wave–resolving global circulation model (GCM) by Sato et al. Dynamical characteristics are examined separately for upward- and downward-propagating gravity waves in June, using a hodograph analysis method. As a result, it is found that upward- and downward-propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities. This fact suggests that these gravity waves are generated from the same source with a similar mechanism. When the wave packets were observed, both the local Rossby number and the residual in the nonlinear balance equation estimated using NCEP–NCAR reanalysis data are large around the PNJ situated slightly to the lower latitudes of Syowa Station. Therefore, it is likely that the observed inertia–gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced PNJ and propagate toward Syowa Station. The possibility of spontaneous gravity wave generation around the PNJ is confirmed by comparison with the GCM simulation by Sato et al.