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

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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.