A document by Rezy Pradipta. Click on the document to view its contents.

A document by Deepak Kumar Karan. Click on the document to view its contents.

We simulated the Nov 4, 2021 geomagnetic storm event penetrating electric field using the Multiscale Atmosphere-Geospace Environment (MAGE) and compared with the NASA ICON observation. The ICON observation showed enhancement of the vertical ion drift when the penetrating electric field arrived at the equatorial region. The simulated vertical ion drifts are consistent with ICON observation. Hence, we are able to verify the MAGE simulation with ICON observation. On the dusk side, the MAGE simulation showed strong pre-reversal enhancement (PRE), whereas the ICON observation did not display any sign of the PRE. The MAGE simulation did show that PRE amplitude decreases as altitude increase. Because the ICON orbital height is above the model upper boundary, it could be a factor for the discrepancy. Instrumental issue cannot be ruled out at this moment. GOLD UV image at the same time exhibits multiple plasma bubbles, which seem to suggest the existence of the PRE.

Using the newly developed, Multiscale Atmosphere-Geospace Environment (MAGE) model, we simulated the penetrating electric field in the equatorial region under different interplanetary magnetic field (IMF) Bz conditions during September 2020. Two intervals were selected for detailed analysis with the vertical ion drift data from the NASA ICON. The MAGE simulations show that in southward IMF (S-IMF) cases, the dawn-dusk electric potential drop at the equator is about 14% of the cross polar cap potential difference. The dawn-dusk potential drop at the equator varies instantaneously with the changes in the IMF Bz or interplanetary electric field, which in turn alters the vertical ion drift. The daytime changes of the equatorial vertical ion drift in response to the penetrating electric field related to the IMF Bz are only half of that during the nighttime, due mostly to the E-region dynamo. MAGE simulation shows pre-reversal enhancement (PRE) during southward IMF cases, but the PRE was absent in the ICON IVM observations. Further observations and modeling are needed to resolve this discrepancy.

Strong subauroral plasma flows were observed in the dawnside ionosphere during the 20 November 2003 super geomagnetic storm. They are identified as dawnside subauroral polarization streams (SAPS) in which plasma drift direction is eastward and opposite to the westward SAPS typically found in the dusk sector. Both dawnside and duskside SAPS are driven by the enhanced meridional electric field in the low latitude portion of Region-2 field-aligned currents (FACs) in the subauroral region where ionospheric conductance is relatively low. However, dawnside eastward SAPS were only observed in the main and recovery phases while duskside westward SAPS were found much earlier before the sudden storm commencement. Simulations with the Multiscale Atmosphere-Geospace Environment (MAGE) model demonstrate that the eastward SAPS are associated with dawnside ring current build-up. Unlike the duskside where ring current build-up and SAPS formation can occur under moderate driving conditions, strong magnetospheric convection is required for plasmasheet ions to overcome their energy-dependent drifts to effectively build up the dawnside ring current and upward Region-2 FACs. We further used test particle simulations to show the characteristic drift pattern of energetic protons under strong convection conditions and how they are related to the dawnside SAPS occurrence. This study demonstrates the connection between the level of solar wind driving condition and a rare ionospheric structure, eastward SAPS on the dawnside, which only occur under strong convection typically associated with intense or super storms. Dawnside SAPS are suggested as a unique feature of major geomagnetic storms.