First Na lidar measurements of turbulence heat flux, thermal diffusivity, and energy dissipation rate in the mesopause region

Turbulence is ubiquitous in the mesopause region, where the atmospheric stability is low and wave breaking is frequent. Measuring turbulence is challenging in this region and is traditionally done by rocket soundings and radars. In this work, we show for the first time that the modern Na wind/temperature lidar located at Andes Lidar Observatory in Cerro Pachón, Chile, is able to directly measure the turbulence perturbations in temperature and vertical wind between 85 and 100 km. Using 150 h of lidar observations, we derived the frequency (ω) and vertical wave number (m) spectra for both gravity wave and turbulence, which follow the power law with slopes consistent with theoretical models. The eddy heat flux generally decreases with altitude from about −0.5 Km s⁻¹ at 85 km to −0.1 Km s⁻¹ at 100 km, with a local maximum of −0.6 Km s⁻¹ at 93 km. The derived mean turbulence thermal diffusivity and energy dissipation rate are 43 m² s⁻¹ and 37 mW kg⁻¹, respectively. The mean net cooling resulted from the heat transport and energy dissipation is −4.9 ± 1.5 K d⁻¹, comparable to that due to gravity wave transport at −7.9 ± 1.9 K d⁻¹. Turbulence key parameters show consistency with turbulence theories.