Self‐consistent modeling of the large‐scale distortions in the geomagnetic field during the 24–27 September 1998 major magnetic storm

Abstract

[1] A new self-consistent version of a time-dependent magnetospheric paraboloid model is presented and tested on the 24-27 September 1998 magnetic storm interval (minimum Dst = À207 nT). The model uses DMSP satellite data to identify the location of the inner boundary of the magnetotail current sheet and the magnetic flux in the lobes and their variations with time. These inputs plus upstream solar wind dynamic pressure and IMF B z values are used to iteratively model the Earth's field during the storm. Several interesting results with important consequences are obtained: (1) the model tail field strength at the Earth's surface (DT = À134 nT) is a significant fraction of the ring current value (DR = À167 nT); (2) the movement of the tail current sheet inward to L = 3.5-4.0 at storm maximum is consistent with geosynchronous magnetic field data; (3) at the Earth's surface the Chapman-Ferraro magnetopause current field (DCF = 117 nT) is almost equal at storm maximum to the value from the tail current, thus the fields from the two systems nearly cancel; (4) the magnetic flux from the polar cap in the course of the magnetic storm main phase approximately doubles in comparison with the magneto-quiet interval just before the storm onset; this fact shows that the driven processes prevail over dissipation processes throughout the storm main phase; (5) the large-scale internal currents in the magnetosphere (ring current, field-aligned currents, and magnetotail current) have significant influence on the shape and size of the magnetosphere; the location of the magnetopause subsolar point is different from that obtained by extrapolation of empirical results taken during high geomagnetic activity intervals and from magnetospheric models that do not include feedback from internal magnetospheric currents.

Analysis of geomagnetic sudden impulses at low latitudes

“…By contrast, ground observations are in general poorly represented in terms of the global current system (with some interesting exceptions at local midnight) suggesting a contribution of additional currents much smaller (if any) than predicted. It is worth noting in this sense that Feldstein et al [2005], who modeled the geomagnetic field distortions for a case event, clearly determined that the role of the current systems is strongly influenced by the SW conditions during active magnetosphere intervals.…”

“…[2] As discussed in a number of investigations, impulsive variations of the magnetospheric and geomagnetic field (Sudden Impulses, SI; SSC when preceding magnetospheric storms) are caused by the impinging on the Earth's magnetosphere of sudden increases in the dynamic pressure of the solar wind (SW), generally associated with interplanetary shock waves [Nishida, 1978;Smith et al, 1986;Araki, 1994]. SI are important for several aspects of Solar-Terrestrial Physics and Space Weather, such as the compression of the magnetosphere, the acceleration and transport of energetic particles and, eventually, the charged particle precipitation in the dayside auroral zone [Feldstein et al, 1997;Tsurutani et al, 2001;Boudouridis et al, 2003]. In the experimental observations, SI are typically identified by an increase of the magnetospheric and geomagnetic field, approximately between two steady states, over about a two to fifteen minute period.…”

Energetics of magnetic storms driven by corotating interaction regions: A study of geoeffectiveness

“…As many researchers have pointed out, [e.g., Campbell, 1996], the Dst index measures the effects of many key current systems and cannot single out the ring current. Magnetotail currents are among the primary current systems that can perturb the Dst index [see Turner et al, 2000a;Ohtani et al, 2001;Feldstein et al, 2005], as well as induced ground currents. Dst* was corrected to account for these using the relation described in Turner et al [2001].…”

Interstellar-Terrestrial Relations: Variable Cosmic Environments, The Dynamic Heliosphere, and Their Imprints on Terrestrial Archives and Climate

“…The spherical harmonic coefficients for a given period are obtained by interpolating and extrapolating the different IGRF parameters released every five years by the International Association of Geomagnetism and Aeronomy (IAGA). From continuous satellite measurements, different models of the external magnetic field depending on geomagnetic activity and solar wind parameters have also been developed (Olson and Pfitzer, 1982;Tsyganenko, 1989Tsyganenko, , 1995Tsyganenko, , 1996Tsyganenko, , 2002Tsyganenko et al, 2003;Tsyganenko and Sitnov, 2005;Ostapenko and Maltsev, 2000;Alexeev and Feldstein, 2001;Feldstein et al, 2005).…”