C-Structures in Mesospheric Na and K Layers and Their Relations with Dynamical and Convective Instabilities

We analyzed the C-structures in the mesospheric metal layers. We used two datasets: one from a narrow band Sodium (Na) Density and Temperature LIDAR and the other from a high-resolution dual band Na and Potassium (K) LIDAR, both operated at São José dos Campos, Brazil (23° S, 46° W). We also investigated the Es layer occurrence and wind shear influences forming these structures. We found three C-type events over 82 analyzed nights in the first data set. They all showed lower temperatures inside C-structures compared to the borders. The squared Brunt-Väissälä frequency analyses showed positive values in the region of C-structures. In two out of three cases, dynamical instability was present (Ri < 0.25). We compared these results with the nine simultaneous C-type events identified in the 185 nights from the second data set. They showed height and time simultaneity correspondence as observed in the Na and K layers. Our results showed a low correlation between Es occurrence and C-structures. Additionally, strong wind shears in the altitude and time where C-structures appeared were always present. The advection of a metal cloud to the LIDAR station and a wind distortion seems to be the plausible mechanism that can explain all the observations