Twilight observations from balloon altitude. Part 1: Blue sunlight extinction and scattering by dust in the 60 km altitude atmospheric region

Photographic balloon data obtained in the falls of 1980 and of 1981 and in the spring of 1982 are presented for blue and red light. They indicate the presence of a dust light-absorbing and scattering layer in the mesosphere at altitudes near 60 km with a low scattering albedo (0.1) at 0.44 microns. The optical efficiency of the layer increases more than 10 times when the wavelength of the interacting light changes from 0.65 to 0.44 microns. At the zenith and near sunset, the natural 0.44 micron extinction optical thickness and the sq cm column scattering rate due to this layer are respectively found to be 0.066 and 0.18 mega Rayleigh per A on May 3, 1982 above the southwest of France.