We report the first lidar observations of regular occurrence of mid‐latitude thermosphere‐ionosphere Na (TINa) layers over Boulder (40.13°N, 105.24°W), Colorado. Detection of tenuous Na layers (∼0.1–1 cm⁻³ from 150 to 130 km) was enabled by high‐sensitivity Na Doppler lidar. TINa layers occur regularly in various months and years, descending from ∼125 km after dusk and from ∼150 km before dawn. The downward‐progression phase speeds are ∼3 m/s above 120 km and ∼1 m/s below 115 km, consistent with semidiurnal tidal phase speeds. One or more layers sometimes occur across local midnight. Elevated volume mixing ratios above the turning point (∼105–110 km) of Na density slope suggest in situ production of the dawn/dusk layers via neutralization of converged Na⁺ layers. Vertical drift velocity of TINa⁺ calculated with the Ionospheric Connection Explorer Hough Mode Extension tidal winds shows convergent ion flow phases aligned well with TINa, supporting this formation hypothesis.

We have discovered that the peak phase time of predawn thermosphere‐ionosphere Na (TINa) layers (∼110–150 km altitude) undergoes clear annual variations with the earliest occurrence in summer and latest in winter over Boulder (40.13°N, 105.24°W), which are closely correlated to annual phase variations of sunrise and tidal winds. Such discoveries were enabled by the first characterization of 12 monthly composites of TINa layers from January through December using 7 years of lidar observations (2011–2017). Despite their tenuous densities, the predawn TINa layers have nearly 100% occurrence rate (160 out of 164 nights of observations). Monthly composites show downward‐phase‐progression TINa descending at similar phase speeds as Climatological Tidal Model of the Thermosphere tidal winds. These TINa layers occur in ion convergence but neutral divergence regions, modeled using tidal winds. These results support the formation mechanism (neutralization of converged TINa⁺ forming TINa) proposed previously and suggest that migrating tidal winds experience annual phase variations.

First characterization of year‐round Na layers from 75 to 150 km is enabled with 7 years (2011–2017) of high‐detection‐sensitivity lidar observations over Boulder (40.13°N, 105.24°W). Clear annual and semiannual oscillations (AO and SAO) are revealed in the nightly‐mean thermosphere‐ionosphere Na (TINa) (∼105–150 km) number density and volume mixing ratio with the summer maximum but spring equinox (March/April) minimum. Such stark contrast to the summer minimum in the main Na layers (∼75–105 km) supports the theory of TINa formed via TINa ⁺ ion neutralization (). The SAO/AO amplitude ratio profiles (75–150 km) exhibit significant changes (∼0.06–2), linking TINa SAO to thermospheric density SAO and the minimal wave/eddy transport around midlatitude equinoxes which hinders TINa ⁺ ion production and upward transport via reduced diffusion of the main Na layer. Stronger TINa in autumn than in spring equinox is explained by the maximal (minimal) meteoric influx occurring in September (April).

Using lidar observations of 12 monthly composites of normalized Na density ratios, we have discovered an Ionosphere‐Thermosphere‐Mesosphere (ITM) Na transition layer from ∼120 to ∼95 km over Boulder, Colorado. The transition layer occurs regularly in all months with a distinct separation from the predawn TINa layer and exhibits coherent downward phase progression. The double‐layer structure in May–July differs from its single layer in other months. Annual oscillations dominate the descending phase speeds (maximizing ∼3.3 km/hr in June) and layer widths, reflecting seasonal variations in tidal wind forcing of Na ⁺ ions. The Na transition layer forms within regions of vertical wind convergence and modeled ion convergence, suggesting both vertical‐wind‐driven neutral convergence that directly concentrates neutral Na, and tidal‐wind‐converged Na ⁺ ions that recombine with electrons, contribute to the transition layer formation. These results establish the Na transition layer as a robust, dynamically‐chemically driven feature coupling the ITM.

First characterization of year-round thermosphere-ionosphere Na (TINa) layers (~105-150 km) is enabled with 7 years (2011–2017) of lidar observations over Boulder. Clear annual and semiannual oscillations (AO and SAO) are discovered in the nightly-mean TINa number density and volume mixing ratio (VMR) with the maximum in summer but minimum around spring equinox (Mar/Apr). The results are in stark contrast to the summer minimum and Nov maximum in the main Na layers (~75–105 km), supporting the theory of TINa formed via TINa+ ion neutralization. SAO in TINa VMR/density is linked to the thermospheric density SAO and the minimal wave/eddy transport around midlatitude equinoxes which hinders TINa+ ion production and upward transport via reduced diffusion of the main Na layer. Stronger TINa in autumn than in spring equinox is explained by the maximal and minimal meteoric input fluxes (MIF) occurring in Sep and Aprl, respectively.

Lidar observations above McMurdo, Antarctica from 2011 to 2024 are used to characterize gravity wave (GWs) potential energies () in the mesosphere and lower thermosphere (MLT). Alongside characterizations in the middle atmosphere (30–70 km), the GW baselines show dissipation at all altitudes from 30 to 110 km. Stronger dissipation occurs for GWs with shorter and in regions of lower , likely driven by convective and shear instabilities, critical level filtering, and viscous damping. Energy baselines are then used to estimate the diffusion‐like transport of constituents and heat induced by non‐breaking GWs. The corresponding wave‐induced constituent and thermal diffusivities and are compared to estimates made at other locations, while this study represents the first such observations in the middle atmosphere. Estimated and are up to 1,000 times typical eddy and molecular diffusion values in the middle atmosphere and 10 times typical values in the MLT.