Global MHD simulation of the geomagnetic sudden commencement on 21 October 1999

Abstract

[1] Recently, Shinbori et al. (2004) examined the electric field variations associated with geomagnetic sudden commencements (SC) by using data from the Akebono satellite in the inner magnetosphere (L < 5) and reported the following characteristics of the SC-associated electric field variations. (1) The electric field shows a bipolar change. (2) The initial excursion of the electric field tends to be directed westward. (3) The electric field amplitude does not show a dependence on magnetic local time. By using a global three-dimensional MHD simulation model, we examine how and where such SC-associated electric field variations are established. In our study, we used the SC event that occurred on 21 October 1999, which was caused by a sudden increase in the solar wind dynamic pressure from $3 to $13 nPa. The solar wind and interplanetary magnetic field conditions observed from the Wind satellite near GSM (x, y, z) $ (22, À62, 20) R E are used as the simulation input parameters. The numerical simulation shows that inward flow is first excited near local noon and then flow vortex is generated near the flankside as the solar wind discontinuity is passing over the magnetosphere. Thus, the convection electric field variations change with local time. The vortical structure has a duration of 3-4 min and propagates with a flow speed of $75% of the solar wind speed. The electric fields associated with flow vortices show a bipolar structure. We suggest that the flow vortex in our simulation is associated with the main impulse of SC and that the SC-associated electric fields observed at Akebono are due to the convection electric field.

Dayside response of the magnetosphere to a small shock compression: Van Allen Probes, Magnetospheric MultiScale, and GOES‐13

“…Simulations by Kim et al . [] examined the local time dependence of the electric field response to a moderate shock with an increase of ~10 nPa. They concluded that the bipolar pulse was not due to a compression followed by rarefaction.…”

Magnetospheric responses to the passage of the interplanetary shock on 24 November 2008

“…Furthermore, we confirmed that a clockwise vortical motion appears in the morningside magnetosphere as the IP shock is passing over the magnetosphere. The clockwise vortical motion generates an upward field‐aligned current in the morningside magnetosphere [ Fujita et al , 2003b; Kim et al , 2009], and this current system is consistent with a MI current system in Araki's SC model. Thus, we suggest that the initial negative perturbation at high‐latitude CHD station is not the PI perturbation but the MI perturbation.…”

“…Thus, the corresponding plasma convection is tailward and duskward. From these THEMIS electric field observations, we suggest that a vortical structure of plasma flow appears on the morningside during the passage of the IP shock [ Fujita et al , 2003b; Kim et al , 2009] as shown in Figure 6.…”

“…The SC onset is clearly marked by a sudden negative change in E y (i.e., the dusk‐to‐dawn electric field) with Δ E y = −4.4 mV/m at THE (MLT = 9.4 and L = 7.3) and Δ E y = −5.8 mV/m at THD (MLT = 10.7 and L = 4.8), respectively, with a small E x perturbation. This strong negative E y perturbation corresponds to the earthward plasma flow caused by the dayside magnetospheric compression during the passage of the IP shock [ Fujita et al , 2003b; Kim et al , 2009]. E y at THE shows a bipolar signature, a negative‐then‐positive polarity, with a peak‐to‐peak amplitude of ∼10 mV/m.…”

Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

“…Global MHD simulations predict that an R2-sense FAC pair during the PI forms equatorward of preexisting DP-2 currents near noon and propagates azimuthally away from noon during its lifetime of a few minutes (Slinker et al 1999;Fujita et al 2003;Kim et al 2009;Samsonov et al 2010;Sun et al 2015). An R1-sense FAC pair follows a similar sequence during the MI.…”