Mapping gravity waves and turbulence in the stratosphere using satellite measurements of stellar scintillation
Résumé
If stellar light passed through the atmosphere is measured on board a satellite with a high-frequency device, the stellar flux exhibits fluctuations that may exceed the mean value by several hundred per cent. This effect is called scintillation. Stellar scintillations are caused by air density irregularities generated mainly by internal gravity waves (GWs) and turbulence. Exploitation of stellar scintillation is a new approach in studying small-scale air density irregularities in the stratosphere. In this paper, we explain the methodology for reconstructing GW and turbulence spectra parameters from scintillation measurements. The analysis is based on fitting the modeled scintillation spectra to the measured ones. We use a two-component spectral model of air density irregularities: the first anisotropic component corresponds to the GW spectrum, while the second one describes locally isotropic turbulence resulting from GW breaking and other instabilities. The retrieval of GW and turbulence spectra parameters--structure characteristics, inner and outer scales of the GW component--is based on the maximum-likelihood method. We review the main results of analyses of the scintillation measurements by GOMOS fast photometers on board the Envisat satellite and discuss the global distributions of turbulence structure characteristic CT2 in the stratosphere, at altitudes of 30-50 km.