Role of vertical ion convection in the highlatitude ionospheric plasma distribution

[1] We use the Global Ionosphere-Thermosphere Model (GITM) to simulate the ionospheric reaction to a simple step change of the high-latitude forcing terms during the first hour of electric field enhancement. In response to the enhanced convection electric field, both the convection velocity and Joule heating increase dramatically. The changes in NmF2 present that the tongue extends across the polar cap and the troughs stretch longitudinally. The calculated total electron content (TEC) can vary by 15 TECU and have a similar pattern to the changes of NmF2. The changes in the vertical ion drift can be upward 100 m/s on the dayside and downward 100 m/s on the nightside as a consequence of the changes in the E B drift. Approximately, hmF2 ascends where ViR is upward and descends where ViR is downward. In general, the response of the ionosphere to the enhanced E-field is that the F2 layer moves upward on the dayside and enhances at all altitudes on the nightside. Below the F2 peak (250 km altitude), the region of decreasing electron density coincides with the upward ViR on the dayside, and the reverse is true on the nightside. Above the F2 peak (450 km altitude), the features related with both horizontal convection and vertical advection are present. The vertical ion drift sets up a vertical circulation in the noon-midnight meridional plane during the early stage of E-field enhancement in addition to the widely accepted horizontal two cell convection. According to the circulation, the significant sources of tongue ionization are not only the plasma from the lower latitudes, but also from the low altitudes on the dayside. While the vertical circulation is not well organized after 6-hour E-field enhancement, the contribution of vertical ion convection is still significant. Although the vertical E B drift in Apex coordinates is more complex and variable than that in a simple dipole magnetic field, the main characteristics are the same, which indicate the significance of the vertical circulation for the electron density distribution in reality during the early stage of E-field enhancement. The Joule heating drives upwelling of the atmosphere and modifies the O/N2 ratio. Meanwhile, the enhanced neutral advection twists the O/N2 ratio pattern a little bit. However, the changes in the O/N2 ratio have relatively poor correlation with the variation of electron density during the first hour of E-field enhanced time.