Simultaneous sodium airglow and lidar measurements over India: A case study

In order to understand the substantial variation of sodium (Na) airglow intensity from one night to another, a case study is performed using simultaneous, campaign-based measurements of Na airglow and Na lidar during March 2007 from Gadanki (13.5 degrees N, 79.2 degrees E), India, during postmidnight hours. The altitude profiles of mesospheric ozone, temperature, and pressure available for the nearest location during the local postmidnight hours are also obtained from the SABER instrument on board the TIMED satellite and are used in conjunction with the above measurements. The average Na airglow intensity level on 20 March 2007 is found to be less compared to that on the next night despite average Na concentration being larger by at least a factor of three. In order to explain the observation, volume emission rates of Na airglow are calculated for both of the nights using the measured parameters. The enhanced quenching due to the ambient gas is suggested to be responsible for the reduced Na airglow intensity level on 20 March 2007 despite higher Na concentration.