What Mechanisms are Responsible for TINa Difference between Boulder and McMurdo?

Direct lidar measurements of thermosphere-ionosphere metal (TIMt) layers provide a unique way to study plasma-neutral coupling in the critical space-atmosphere interaction region (100–200 km). Since the first discovery of TIMt layers through lidar observations at McMurdo in 2011, these layers have been reported across a wide range of latitudes, though most exhibit intermittent occurrences. Two notable exceptions are the regular occurrence of thermosphere-ionosphere Na (TINa) layers at Boulder, Colorado (40.13°N, 105.24°W), and the “continuous presence” of TINa at McMurdo, Antarctica (77.83°S, 166.66°E). The primary formation mechanism is believed to be the neutralization of converged TINa⁺ ions via recombination with electrons (TINa⁺ + e⁻ → TINa + hν). TINa⁺ ions are strongly influenced by neutral winds and electric fields in both midlatitude and polar regions, though with some key differences.

This study focuses on TINa observations at these two locations. The regular occurrence of Boulder TINa layers has shown great potential for closing the “thermospheric gap” via providing new tracers to study tides and long-lifetime ion transport. Several new discoveries have been made based on Boulder TINa since the first report in 2021. What’s interesting is that McMurdo TINa shows unique features compared to Boulder TINa. TINa layers in Antarctica exist in extremely long hours during nighttime showing diffusive patterns. More interestingly, despite the distinct characteristics of TINa layers at McMurdo and Boulder, the turning points occur at similar altitudes around 105–110 km for both locations. This suggests that additional driving factors may influence TINa formation at McMurdo. The comparison of TINa layers at these sites will not only enhance our understanding of TINa formation mechanisms but also assess the potential of lidar measurements of TIMt layers in studying the global ion transport through numerical modelling studies.