Mise au point d'une méthode de détermination de la température moyenne de la mésosphère à partir de la mesure de la vitesse de phase des ondes longues sur un trajet grande distance

Abstract

The.mechanism of the Lyman α ionization of nitric oxide, which is mainly responsible for the formation of the D region, the lowest part of the ionosphere, is first briefly reviewed. From equations of the photochemical equilibrium, a model of the height distribution of the electron density is proposed as a function of the solar angle Θ and the scale height H, which is a function of the mesospheric temperature T. A method named Geoscanner based upon a set of curves that illustrate the theoretical relations between the phase of a continuous VLF radio wave for a long-distance transmission and the different parameters of the daytime atmosphere is described. This method is applied to analyse experimental data obtained by phase measurements for the 10.2 kHz transmission Trelew (Argentina) – Caen (France), nearly 12 000 km distant. It provides a mean value of the mesospheric temperature that is a characteristic of the studied path and day. The significance of such an integrated temperature, ranging between 190 and 200 K, is discussed.