Annual Variation of mesospheric sodium at Arecibo, Puerto Rico

Variety of metals like Mg, Fe, Na, Ca, K and their ions are deposited in the mesospheric region of the Earth's atmosphere through the ablation of meteoroids. These metals act as tracers for studying the chemistry, and dynamics of the least explored region that lies between 80 – 110 km altitudes. A few case studies of the Na metal have been performed from Arecibo using a resonance lidar tuned at 589.0 nm. Most of these studies have focused on individual nights, with the aim of either investigating ion-neutral chemistry, their association with ionization or dynamical processes. This work aims at studying the seasonal variation of different parameters of the Na layer. The analysis procedure involves removal of sporadic layers, which are enhancements in the concentrations. This methodology allows us to evaluate the influence of sporadic layers on the column integrated densities or column abundance determined with and without such events. Our preliminary results show summer time maxima with values close to 4.9 x 109 cm-2, with lowest average values of 3.6 x 109 cm-2 during the winter season. The average abundances during the spring and autumn are similar with 4.0 x 109 cm-2. The layer width peaks during spring, when it is close to 7.2 km while autumn months displays narrow layers with widths ~ 6.3 km. This research intends to investigate this variability in terms of chemistry and dynamics of this region.