Large plasma density enhancements occurring in the northern polar region during the 6 April 2000 superstorm

Abstract

AbstractWe focus on the ionospheric response of northern high‐latitude region to the 6 April 2000 superstorm and aim to investigate how the storm‐enhanced density (SED) plume plasma became distributed in the regions of auroral zone and polar cap plus to study the resultant ionospheric features and their development. Multi‐instrument observational results combined with model‐generated, two‐cell convection maps permitted identifying the high‐density plasma's origin and the underlying plasma transportation processes. Results show the plasma density feature of polar cap enhancement (PCE; ~600 × 103 i+/cm3) appearing for 7 h during the main phase and characterized by increases reaching up to 6 times of the quiet time values. Meanwhile, strong westward convections (~17,500 m/s) created low plasma densities in a wider region of the dusk cell. Oppositely, small (~750 m/s) but rigorous westward drifts drove the SED plume plasma through the auroral zone, wherein plasma densities doubled. As the SED plume plasma traveled along the convection streamlines and entered the polar cap, a continuous enhancement of the tongue of ionization (TOI) developed under steady convection conditions. However, convection changes caused slow convections and flow stagnations and thus segmented the TOI feature by locally depleting the plasma in the affected regions of the auroral zone and polar cap. From the strong correspondence of polar cap potential drop and subauroral polarization stream (SAPS), we conclude that the SAPS E‐field strength remained strong, and under its prolonged influence, the SED plume provided a continuous supply of downward flowing high‐density plasma for the development and maintenance of PCEs.