Dynamic Properties of a Sporadic Sodium Layer Revealed by Observations Over Zhongshan, Antarctica: A Case Study

摘要

A sodium Doppler lidar system with three-directional measurements of sodium density, atmospheric wind field, and temperature was established at Zhongshan (69.4 degrees S, 76.4 degrees E), Antarctica. On November 14, 2019, a sporadic sodium layer (SSL) was observed at an altitude range of 93-103 km. The temporal/spatial sodium density variations of this SSL are associated with a strong sporadic E (E-s) layer at nearly the same height, which is modulated by the convective electric field. By considering the structures and the time lags of the SSL's growth at three positions, the SSL appears to have a horizontal advection in an approximately westward direction with a velocity of the order of 80 m/s. This is consistent with the zonal wind velocity derived from the lidar system itself. The temporal/spatial sodium density variations strongly indicate that the formation and perturbation of SSLs are related to the evolution of E-S layers due to varied electric fields and atmospheric gravity waves, while it is advected by the horizontal wind. Plain Language Summary A sporadic E layer (E-s) could be formed by metallic ions and then modified or transported by the action of magnetospheric electric fields in the high latitude ionosphere. It has been widely proposed that E-s layers play an important role in the formation of sporadic sodium layers (SSL), but detailed studies of their dynamic process and evolution are still lacking. A three-frequency Sodium (Na) resonance fluorescence Doppler lidar has been recently deployed by the Polar Research Institute of China, which could measure the sodium density, temperature, and wind profiles simultaneously in three directions. To clarify the dynamic properties of E-s/SSL, we have performed observations of an event at Zhongshan Station (69.4 degrees S, 76.4 degrees E), Antarctica, which includes sodium density profiles and wind velocity measured by the multidirectional lidar system, detection of the E-s layer by a collocated Digisonde radar, F region ion velocity, that is, electric field, derived by the SuperDARN HF radar network, as well as gravity wave perturbations determined from the Davis medium frequency radar.