Polytropic Processes in the Lower Thermosphere

The question of the application of Poisson's law PV gamma = const in the analysis of spatiotemporal variations in the parameters of the neutral atmosphere in this region is considered in relation to the existence of heat fluxes in the mesosphere-lower thermosphere (MLT). Poisson's law is valid for adiabatic processes, i.e., in the absence of heat transfer (Delta Q = 0). When internal gravitational waves propagate in this region, which, when dissipated, transfer energy and angular momentum to the medium and can enhance turbulent motions, as well as during the development of the frequently observed dynamic and convective instabilities, the processes in MLT can also be nonadiabatic. In this study, we obtained the values of the n index in the lower thermosphere for polytropic processes PVn = const, when only the heat capacity is constant. To estimate the n index, we use measurements of the temperature and density of the neutral atmosphere by the method of resonant scattering on artificial periodic irregularities of the ionospheric plasma. It is shown that above the turbopause, the polytropic index n lies in the range of 1.8 to 2. The fact that n > gamma indicates the importance of taking the heat transfer in the lower thermosphere into account.