On the responses of atomic oxygen at middle thermosphere (~160 km) to the 20-21 November 2003 superstorm

Abstract:

TIMED/GUVI limb measurements and TIEGCM simulation are used to investigate thermospheric atomic oxygen (O) responses on the z = -1.5 pressure surface (~160 km) in middle thermosphere to the 20 and 21 November 2003 superstorm. This height is where O and N₂ number densities make major contribution to column O/column N₂ density ratio (∑O/N₂). The comparison between GUVI data and TIEGCM predictions shows they have good agreement during the storm, which indicate that the physical processes of the O perturbations are well represented in the TIEGCM. Therefore, a diagnostic analysis of TIEGCM results has been carried out to quantify the relative importance of these physical processes responsible for O storm-time changes. Principal conclusions include the following: (1) Horizontal advection, vertical advection and molecular diffusion are the three main processes in determining storm-induced O perturbations on this pressure level. Chemical process and eddy diffusion are negligible. (2) Horizontal and vertical advection dominate the O changes at high latitudes during the storm initial and main phases. Horizontal advection plays a significant role in global O perturbations over the entire course of the storm, including the recovery phase. (3) Molecular diffusion acts to compensate for the O changes caused by horizontal and vertical advection. (4) The temperature changes are not the main cause of the composition perturbations on constant pressure surfaces, though they are relevant to some extent.