Experiments revealing small impact of turbulence on the energy budget of the mesosphere and lower thermosphere

We have measured a total of 17 in situ profiles of small‐scale density fluctuations (typical resolution: meters) in the lower thermosphere and upper mesosphere, which are used to derive turbulent parameters, such as the turbulent energy dissipation rate ε, the turbulent diffusion coefficient K , and the mean turbulent velocity w turb . The accuracy of the absolute numbers is unprecedented thanks to the very high spatial resolution and a recently improved data analysis procedure. Concentrating on the 12 flights which were performed during winter conditions at high latitudes (69°N), we find mean energy dissipation rates of 1–2 mW kg −1 in the lower mesosphere (<75 km) and 10–20 mW kg −1 in the upper mesosphere and lower thermosphere (<100 km). The corresponding heating rates are approximately 0.1 and 1 K d −l , respectively. These values are at least 1 order of magnitude smaller than most of the previous measurements and are also significantly smaller than typical values assumed in models. Our observations suggest that the heating effect of turbulence is negligible compared to the most prevailing terms of the heat budget. It can be shown by theoretical considerations involving the turbulent energy budget equation that cooling by turbulent heat conduction is also negligible if ε is small.