University of Crete Island of Crete

Redistribution of the low-latitude ionospheric plasma structure during a major magnetic storm

C. H. Lin1, A. D. Richmond2, G. J. Bailey3, J. Y. Liu4
  1. Plasma and Space Sciences Center, National Cheng-Kung University, Tainan, Taiwan
  2. High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA
  3. Department of Applied Mathematics, University of Sheffield, Sheffield, S3 7RH, UK
  4. Institute of Space Science, National Central University, Chung-Li, Taiwan

This study presents theoretical simulation of the mid- and low-latitude ionospheric electron density structures during a major magnetic storm. From the coupled NCAR Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) and Sheffield University Plasmasphere Ionosphere Model (SUPIM) simulation runs, storm-generated ionospheric additional layers (named as F3 or F1.5 layer or G condition) occur in both equatorial and low-latitude ionospheric regions due to two different physical mechanisms. The additional layer occurred at the equatorial region is formed due to a strong uplift of the original F2 layer results from an eastward penetration electric field, and followed by replenishment of the newly produced ionization located at the original F2 layer height. This process requires existence of the sunlight in order to produce fresh plasma through photo-ionization process. On the other hand, the additional layer formed at low-latitude requires the existence of the storm-generated equatorward wind. The storm-generated equatorward wind slows down the downward diffusion of plasma at the equatorial ionization anomaly (EIA) crests. The equatorward wind acts like a funnel letting the plasma at EIA crests drip down to a lower altitude and form a new layer there. The presented results indicates that the ionospheric additional layers may occur in both low-latitude and equatorial regions during magnetic storm periods if preferable storm-generated conditions exist. Meanwhile, the model runs also predict the ionospheric electron density hole, electron density trough, electron density arches during the magnetic storm. The storm-time electron density hole is produced by the same process as the additional layer formed at the magnetic equator. On the other hand, if the F-layer uplift occurred during evening hours, while the photo-ionization process becomes much weaker, an equatorial density trough is then formed. The electron density arches are signature of the downward diffusion of the uplifted plasma at the magnetic equator. These model predictions are also compared with the observations.

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