We present the structure and dynamics of the sodium and its characteristics in the mesosphere in the altitude range from 80 to 110 km during 2005 and 2006, a tropical station, using resonance fluorescence lidar system located at the National Atmospheric Research laboratory (NARL), Gadanki. The sodium density is maximum in March and also in October and shows clearly a semi-annual oscillation. There are no clear seasonal variations of the layer width but there is a distinct decrease of the centroid height by about 1km in February and March when the abundance is maximum. The observed nighttime variation could be the manifestation of semidiurnal variation in the sodium layer. The database showing more than 63 Sporadic Sodium Layer (SSL) events makes it clear that we are dealing with a complicated and puzzling phenomenon. The analysis has shown that sporadic sodium layers are observed during 42 % of the time. The most prominent sporadic layer, which formed on 12 February 2005 exhibited a peak density of 64344 Na atoms/cm3 around 92 km and it was nearly twice the peak density reported from elsewhere using ground-based observations. A downward motion of the peaks is observed in the majority of the events.