Modeling magnetospheric current response to solar wind dynamic pressure enhancements during magnetic storms: 2. Application to different storm phases

[1] Two patterns of ground H perturbation as response to pressure enhancements during different phases of storms are found. One is polarity asymmetry under southward IMF Bz, e.g., 25 September 1998, 29 May 2003, and 10 January 1997 events; the other is positive H perturbation everywhere under northward IMF Bz, e.g., 7 November 2000 event. The polarity asymmetry can be further divided into two categories: dawn-dusk asymmetry with negative H perturbation at dusk extending through noon to late morning (25 September 1998 event) and positive H perturbation elsewhere, and day-night asymmetry with a smaller region of negative H perturbation extending less far toward dusk (29 May 2003 and 10 January 1997 events). The net field-aligned current (FAC) system from the R1, R2, and the partial ring current (PRC) closure FAC, the equatorial portion of the PRC, and Chapman-Ferraro (CF) current are responsible for the polarity asymmetry. The stronger effect of the R1 is primarily responsible for the negative H perturbation at noon and positive at midnight. The PRC strength at the onset of pressure enhancements determines how far the negative H perturbation at noon extends toward dusk and which pattern is most likely. A stronger (weaker) PRC extends negative H perturbation more (less) toward dusk and thus increases the likelihood of dawn-dusk (day-night) asymmetry. Positive H perturbation everywhere results from the dominant contribution of the CF and lack of significant preexisting PRC and R1 and R2.