Sodium lidar observation over full diurnal cycles in Beijing, China.

Abstract

Due to the severe interference from strong solar background light on the received signal, daytime ground-based lidar observation of the sodium (Na) layer is challenging. In this paper, a Na lidar permitting full-diurnal-cycle observation of the metal Na layer over Beijing, China (40.5°N, 116°E) was reported. In order to suppress the skylight background during daytime effectively with less signal losses, a dual-channel Faraday filtering unit was implemented in the lidar receiver. Based on the diurnal Na lidar system, a good number of continuous observational results that lasted more than 120 h with good signal-to-noise ratio were obtained, demonstrating its reliability. Considerable variations within the Na layer during the day were revealed, especially on the layer top and bottom side. In particular, strong sporadic Na layer (Nas) events that occurred during the daytime of 3 consecutive days were also captured with complete evolution process. These observational results showed the advantages of the diurnal Na lidar for investigating the metal layer photochemistry and dynamics in the mesosphere and lower thermosphere region. Na layer observations over the whole diurnal cycle not only benefit the improvements of current theoretical models, but also can allow for a specialized analysis of Nas that occur in the daytime and provide valuable observational support for investigating the rapid production and disappearance mechanisms of Na atoms.