Simultaneous radar and lidar observations of sporadic E and Na layers at Arecibo

During the early morning of January 16, 1989 the Arecibo 430 MHz incoherent scatter radar and the University of Illinois CEDAR Na lidar were operated simultaneously for several hours at the Arecibo Observatory, Puerto Rico (18°N, 67°W). At approximately 0425 LST a sporadic E (E_s) layer began forming near 101 km altitude and moved steadily downward reaching an altitude of 99 km by 0500 LST. The electron abundance of the E_s layer increased rapidly from approximately 3×10⁹ cm⁻² at 0510 LST to approximately 6×10⁹ cm⁻² by 0530 LST. During this same time period a sporadic Na (Na_s) layer formed at the same altitude as the E_s layer. Both the E_s and Na_s layers moved upwards together between 0530 and 0600 LST before dissipating at an altitude of 101 km. The high correlation between the altitude and abundance variations of the two layers strongly suggests that the Na_s layer formation is related to the E_s layer and may involve Na cluster ion chemistry.