Current disruption during November 24, 1996, substorm

Abstract

Abstract. This study uses global magnetohydrodynamic (MHD) simulations driven by solar wind data along with Geotail, Interball, and IMP 8 observations of the magnetotail to investigate the dynamics of the near-Earth plasma sheet during a substorm that occurred on November 24, 1996. The MHD simulation shows that prior to the onset of the substorm, the magnitude of the current density decreases in a small region in the near-Earth plasma sheet. During and after the substorm onset this region of weak current becomes larger and more pronounced, expanding dawnward, duskward, upward, downward, and tailward. Part of the cross-tail current is redirected to the ionosphere via an earthward field-aligned current on the dawnside and a tailward return current on the duskside. The simulation showed that the field-aligned current was associated with velocity shear and flow vortices. IntroductionMagnetospheric substorms constitute one of the most intensively studied and controversial research areas in space physics. The general consensus is that the substorm process is initiated by a region of solar wind that has an interplanetary magnetic field (IMF) with a southward component. When this solar wind reaches the dayside magnetopause, dayside magnetic reconnection couples it to the magnetosphere and transfers energy to the magnetosphere. This energy is stored in the tail lobes in the form of a magnetic field and eventually triggers reconnection in the near-Earth magnetotail. While magnetotail reconnection is included in most substorm models, considerable controversy exists regarding just where in the magnetotail the reconnection occurs and how this location affects the onset of the expansion phase. Some investigators believe that the expansion phase starts as a disruption in the cross-magnetospheric current near the Earth, which later leads to reconnection farther down the tail [Lui et al., 1988, 1992]. (-34, 6, 16) to (-34.6, 4.3, 14.9) Re. The Interball spacecraft was also in the Northern Hemisphere and moved from (-18.8, 1.6, 12.7) to (-20.8, 1.6, 12.3) Re. Notice that Interball moved away from the Earth mainly in the x-direction, while IMP 8 moved toward the plasma sheet in the y-z plane. The Geotail spacecraft, on the other hand, was closer to the equatorial plane and moved from (-20.4, 3.16, -2.26) to (-22, 0.9, -2.53

Comment on “Tail Reconnection Triggering Substorm Onset”

“…2K). This sequence is in agreement with several previous studies and the inside-out model of substorm onset (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15).…”

On the importance of accurate solar wind measurements for studying magnetospheric dynamics

“…Our global magnetosphere‐ionosphere MHD simulation uses solar wind plasma and IMF input from solar wind monitoring spacecraft, including variations in IMF B x [e.g., Raeder et al , 1995, 1998; El‐Alaoui , 2001]. The three‐dimensional global code is based on a one‐fluid description of the interaction between the solar wind and the Earth's magnetosphere [ Raeder et al , 1995; 1998; Berchem et al , 1998; El‐Alaoui , 2001]. The thoroughly benchmarked, parallelized production code uses a conservative finite difference method to solve the gas dynamic part of the MHD equations as an initial value problem.…”

“…The solar wind magnetic field, density, temperature, and velocity are imposed on the inflow boundary of the simulation box. We use a technique developed by El Alaoui [2001] to include IMF B x in the simulation while maintaining ∇ · B = 0.…”

Turbulence in a global magnetohydrodynamic simulation of the Earth's magnetosphere during northward and southward interplanetary magnetic field

“…Vortices at the magnetopause have been found for both northward and southward IMF and have been interpreted as Kelvin-Helmholtz waves (Walker et al, 1998;Nykyri and Otto, 2001;Slinker et al, 2003;Nykyri et al, 2006b;Fairfield et al, 2007;Collado-Vega et al, 2007;Claudepierre et al, 2008). Other simulations have featured vortices within the plasma sheet that were not associated with boundary oscillations (El-Alaoui, 2001;White et al, 2001;Ashour-Abdalla et al, 2002;Walker et al, 2006;El-Alaoui et al, 2009.…”

“…The coupled magnetosphere-ionosphere, three-dimensional global MHD code used for this study is based on a onefluid description of the interaction between the solar wind and Earth's magnetosphere (Raeder et al, , 1998(Raeder et al, , 2001Frank et al, 1995;El-Alaoui, 2001;El-Alaoui et al, 2004). The numerical resistivity in the code is so low that an anomalous resistivity model must be introduced (Raeder et al, 2001).…”