Internal Gravity Waves as the Background Disturbance in the Earth's Atmosphere

京都大学MU雷达自1982- 1985年中期大气计划（MAP）以来对大气动力学的连续观测，提出了地球大气是由内部重力波重新分配动量来实现的假设。本研究旨在定量地验证这一假设。第一财政年度（1988年），我们开展了(1)基于MU雷达观测的大气中层风扰动垂直波数和频谱分析；(2) MU雷达观测证实了内部重力波的饱和和破碎；(3)探空仪对温度波动的观测与分析。这些研究为引力波的饱和和破裂提供了一些明确的证据，如振幅变化和选择性传输。在最后一个财政年度（1989年），我们进行了(4)垂直波数谱、动量通量、垂直群速度和湍流强度的气候学分析；(5)内部重力波活动和破碎湍流的初步模拟。现在我们可以得出结论：(1)日本附近的内部重力波的垂直波长比平流层/中间层的密度尺度高度短/长；（ii）它们似乎在冬季/夏季最活跃于平流层/中间层；(3)内重力波的全球分布具有显著的垂直相关性和弱的经向和时间相关性；（iv）这些波浪的产生不能用一个独特的来源来解释，例如地表地形和对流层气旋。需要更多的观测，特别是对热层和赤道区域的观测，以便扩展本研究的结果。

Continuous observations on the middle-atmosphere dynamics by the MU radar of Kyoto University since the MAP (Middle Atmosphere Program; 1982-85) period lead to a hypothesis that the earth's atmosphere is fulfilled by the internal gravity waves re-distributing momentum. This study is to verify this hypothesis quantitatively.In the first fiscal year (1988), we carried out (1) vertical-wavenumber and frequency spectral analyses of the middle-atmospheric wind disturbances based on the MU radar observations; (2) confirmation of the saturation and breaking of the internal gravity waves by the MU radar observations; and (3) observations and analyses of temperature fluctuations by radiosondes. These studies have provided us some clear evidences of gravity-wave saturation and breaking such as an amplitude modification and a selective transmission. In the final fiscal year (1989), we made (4) climatological analyses of vertical-wavenumber spectrum, momentum flux, vertical group velocity and turbulence intensity; and (5) a preliminary modeling of activities of internal gravity wave and breaking turbulence.Now we can conclude that(i) the internal gravity waves near Japan have vertical wavelengths shorter/longer than the deilsity scale height in the stratosphere/mesosphere;(ii) they seem most active in winter/summer in the stratosphere/mesosphere;(iii) the global distribution of the internal gravity waves has a striking vertical dependence and weak meridional and time dependences; and(iv) the generation of those waves cannot be explained by a unique source such as surface orography and tropospheric cyclones.Much more observations are necessary in particular for thermospheric and equatorial regions in order to extend the results of this study.