[1] Spatial spectra and characteristic scales of stratospheric density fluctuations obtained from the space station Mir observations of stellar scintillations are analyzed in this paper. The remote sensing method described is based on a well-known stellar scintillation phenomenon that arises when observing the stars through the Earth's atmosphere. To interpret scintillation spectra, a model of the three-dimensional (3-D) spectrum of atmospheric density fluctuations consisting of both turbulent and internal wave-associated spectral components is presented here. With the model chosen, we explain scintillation spectra at low frequencies by suggesting the atmospheric density fluctuations to be caused by a random ensemble of internal waves with the À5 power law decay for their 3-D energy spectrum. For the wave-associated anisotropic part of the spectrum, so-called outer and internal vertical scales are introduced to explain behavior of the observed scintillation spectra in their low-frequency range. These scales being earlier proposed only theoretically have been simultaneously revealed in the scintillation spectra presented here. The estimates of the outer scale for the different orbits of the space station are obtained and compared with those found from lidar and rocket soundings of the stratosphere. A possible cause of the observed variation in the wave number bandwidth of the waveassociated part of the spectrum of air density fluctuations is discussed.Citation: Gurvich, A., and I. Chunchuzov (2005), Estimates of characteristic scales in the spectrum of internal waves in the stratosphere obtained from space observations of stellar scintillations,
The wind velocity structure in the upper stratosphere, mesosphere, and lower thermosphere (MLT) is studied with the recently developed method of infrasound probing of the atmosphere. The method is based on the effect of infrasound scattering from highly anisotropic wind velocity and temperature inhomogeneities in the middle and upper atmosphere. The scattered infrasound field propagates in the acoustic shadow zones, where it is detected by microbarometers. The vertical profiles of the wind velocity fluctuations in the upper stratosphere (30–52 km) and MLT (90–140 km) are retrieved from the waveforms and travel times of the infrasound signals generated by explosive sources such as volcanoes and surface explosions. The fine‐scale wind‐layered structure in these layers was poorly observed until present time by other remote sensing methods, including radars and satellites. It is found that the MLT atmospheric layer (90–102 km) can contain extremely high vertical gradients of the wind velocity, up to 10 m/s per 100 m. The effect of a fine‐scale wind velocity structure on the waveforms of infrasound signals is studied. The vertical wave number spectra of the retrieved wind velocity fluctuations are obtained for the upper stratosphere. Despite the difference in the locations of the explosive sources all the obtained spectra show the existence of high vertical wave number spectral tail with a −3 power law decay. The obtained spectral characteristics of the wind fluctuations are necessary for improvement of gravity wave drag parameterizations for numerical weather forecast.
[1] Measurements of stellar scintillations caused by the atmosphere, conducted on board the space station Mir, are analyzed here. From scintillation spectra we obtained the parameters of spatial spectra of atmospheric density fluctuations (the altitudes 20-70 km) with vertical scales from hundreds of meters to tens of centimeters. The observed characteristic scales of atmospheric inhomogeneities are interpreted with a nonlinear model of internal wave spectrum and a theory of locally homogeneous and isotropic turbulence.
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