Experimental results on the role of turbulence for the heat budget of the upper atmosphere

A total of 17 profiles of small scale density fluctuations have been measured in the lower thermosphere and upper mesosphere by means of sounding rockets. The fluctuations are used to derive turbulent parameters, such as the turbulent velocity. The accuracy of the absolute numbers is unprecedented thanks to the very high spatial resolution and an 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 in the lower mesosphere (<75 km) and 10-20 mW/kg in the upper mesosphere and lower thermosphere (<100 km). The corresponding heating rates are approximately 0.1 and 1 K/d, respectively. These values are at least one order of magnitude smaller than most of the previous measurements and are also significantly smaller than typical values assumed in models. The observations presented suggest that the heating effect of turbulence is small compared to the most prevailing terms of the heat budget. It can be shown by theoretical considerations that cooling by turbulent heat conduction is also negligible if #epsilon# is small. (orig.) / Available from TIB Hannover: RN 4852(93-51) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / SIGLE / DE / Germany