Can High-Sensitivity Doppler Lidar Measurements of TIMt Turning Points Contribute to the Studies of Turbopause?

The turbopause represents the transition from strong turbulent mixing in the middle atmosphere to molecular diffusion dominating in the upper atmosphere. Despite extensive studies of the turbopause with a variety of techniques, there had not been a single contribution from lidar techniques due to challenges in making measurements at such high altitudes (~105 km and above). Development of high-sensitivity resonance-fluorescence lidar technologies has enabled the routine measurements of thermosphere-ionosphere metal (TIMt) layers at such high altitudes over Boulder, Colorado and at McMurdo, Antarctica. These unique data reveal clear turning points in the metal density and mixing ratio profiles of TIMt layers at both locations representing the midlatitudes and polar regions. These TIMt turning points locate right around 105–110 km, basically overlapping the turbopause altitudes. Furthermore, we report for the first time in this paper that the turning point altitudes exhibit annual variations with the winter turning points located ~5 km higher than the other seasons. Such variations resemble the turbopause annual variations nicely, inspiring us to ask whether lidar measurements of TIMt layers can help the studies of turbopause on Earth and Mars. This paper explores this question after characterizing the turning points over Boulder.