IN-SITU MEASUREMENTS OF THE VERTICAL STRUCTURE OF A NOCTILUCENT CLOUD

During the NLC-93 rocket campaign at Esrange, Sweden, the vertical str ucture of a noctilucent cloud layer has been investigated in situ. As in earlier rocket flights, combinations of scattered light detectors a nd electrostatic impact probes have been applied. While the photometri c measurement provides the total downward radiance scattered from the cloud particles, the impact probe yields local information about the p article properties. The responses of both techniques scale differently with the particle size. This feature is utilized to derive informatio n about the height dependence of the particle population. The analysis of three NLC passages indicates little vertical variation of the popu lation throughout most of the layer. The lower part of the cloud is ch aracterized by an increase in particle size and a decrease in particle density towards the cloud base. This is to be expected for an NLC bri ghtness peak caused by large particles sedimenting out of the cloud. I mplications for the dynamical structure of the cloud are discussed.