The underlying physical processes of the vortex-like structure over the East Asia region during the recovery phase of the November 2003 superstorm

Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) is used to investigate underlying physical processes of the thermospheric and ionospheric vortex-like structure over East Asia region in November 2003 superstorm. Horizontal neutral winds with a vortex configuration modulate the composition (O/N₂) perturbations, forming the two-dimensional vortex-like structure. Vertical winds also have a positive contribution to the final shape of this structure in the altitude distribution. The ionospheric vortex-like structure below the ionospheric peak height (hmF2) is dominated by chemical effects (O/N₂ enhancements) and neutral wind transport, while it is directly controlled by the neutral wind transport above the hmF2. Decreases of plasma density within the core region of this structure, driven by E×B drifts at all altitudes, also contribute to its formation. Analysis of the forcing terms driving the wind vortex in the middle thermosphere reveals the dominant role of pressure gradients, alongside the combined action from Coriolis force and horizontal momentum advection. In the upper thermosphere, the ion drag becomes significant, but only partially offsets the substantial positive effects of pressure gradients. Furthermore, controlled numerical experiments demonstrate that the storm intensity is not the single trigger mechanism for this structure. Instead, the asymmetrical prevailing circulation is more beneficial to the formation of the vortex-like structure. The storm onset time also affects the formation and location of this structure, although it is more liable to appear near the magnetic poles primarily in the American and East Asia sector.