Abstract
Abstract We report on the first lidar observations of the nighttime mesospheric sodium layer from Gadanki (13.5°N, 79.2°E) site in India. The lidar measurements of upper atmospheric sodium made on 6 nights between the 10 and 16 January 2005 are presented in this paper. The Gadanki lidar uses a Nd:YAG pumped dye laser, tuned to the sodium D2 line (589.0 nm), as a transmitter. Using the system, sodium number density profiles have been obtained with a vertical resolution of 300 m, a time sampling of 120 s. During the initial six nights of observation, the peak sodium concentration is found at a height of 95 km, and the top side scale height is usually about 2 km. On three occasions, a secondary peak was observed at heights between 87 and 92 km. Measurements at Gadanki site indicate that the mean sodium abundances appear to decrease after sunset and increase before sunrise. The average nocturnal columnar abundances were in the range 2–8.9 × 109 cm2. The nightly mean centroid heights range between 92.9 and 95.2 km and the rms widths vary between 4.3 and 4.9 km. On some nights, wave like structures in the sodium layer were observed with wavelength of about 3 km and downward phase velocities of about 1 km/hr. Four sporadic layers were observed during the initial 54 h of observation. The formation and decay of an intense sporadic sodium layer was observed on the night of 11 January 2005. The layer was found to develop between 93 and 90 km altitude and appear between 0230 and 0430 LT.
Highlights
It is well known that metallic sodium atoms exist in the neutral state in the upper part of the atmosphere (Slipher, 1929)
The resonance lidar measurements of mesospheric sodium were made at Gadanki on 6 days between the 10 and 16 January 2005
The first broadband resonance lidar observations of the nighttime sodium layer made on six nights between 10 and 16 January 2005 at Gadanki, a low latitude site, in India have been reported in this paper
Summary
It is well known that metallic sodium atoms exist in the neutral state in the upper part of the atmosphere (Slipher, 1929). Number of bins per pulse observations of the mesospheric sodium that have been reported from a few low latitude stations such as Mauna Kea, Hawaii (20◦N) (Kwon et al, 1988) and Arecibo, Puerto Rico (18◦N) (Beatty et al, 1989), Kototabang, Indonesia (0.2◦S) (Shibata et al, 2006), there no measurements at other lower latitudes Another important feature of the sodium layer is the event of sporadic sodium, occurrence of sharp sodium densities in short time, whose formation mechanism is still not understood. The detailed system and method of the mesospheric Na number density computation and the statistical error from the NARL sodium lidar is given elsewhere by Bhavani Kumar et al (2007)
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