Evidence for a 2200 km extended wave system at the mesopause level Original Research Article

A panoramic view of the nightglow atmospheric emission in the 780–1000 nm spectral range is constructed using CCD images taken at the Pic de Châteaurenard (Altitude 2989 m, Hautes-Alpes) on July 14–15, 1999. A set of 28 images each having a 36° × 36° field of view is assembled to form a panorama covering 360° in azimuth and extending from the horizon to the zenith. Each photograph is processed in order to invert the perpective effect assuming that the emission comes from a thin layer located at the altitude of 85 km. The effect of refraction is calculated and taken into account. The stars are removed using a numerical filter. The inverted panorama appears as a disk having a radius equal to 1100 km. It is comparable to a satellite view of the emissive layer. A wave system extends in the W-NW to E-SE direction over more than 2200 km. A second set of 30 successive images of the same field of view taken on May 18–19, 1998 is used to determine the wave parameters. The main horizontal wavelength is equal to 42 km and the horizontal phase velocity has a value of 40 ± 2 m.s−1. The images show that the atmospheric OH emission is a tracer of the dynamics of the atmosphere at the level where the excited OH radicals are produced. The OH* radical population depends upon its quenching by O, O2 and N2. As a result, the emission intensity is a function of the air temperature and density which are subject to variations due to gravity and windshear waves and other dynamic processes such as tides and turbulence.