Abstract
Enhancements of aurora and auroral electrojets in response to sudden compression of the magnetosphere by shocks/ pressure pulses are well known and have been attributed by some to compression-enhanced magnetic field reconnection. To examine such a view, we analyze a fortuitous event that is comprised of a series of pressure pulses (< 20 min) on November 8, 2000. These pressure pulses were preceded by a large, northward interplanetary magnetic field (IMF) that lasted more than 15 hours such that effects from reconnection can be minimized. Auroral images acquired by ultraviolet imager on board the Polar satellite clearly show intensifications of the aurora that occurred first near local noon and progressively extended from dayside to nightside. The area-integrated global auroral power reached ~30 gigawatts (GW). It is also found that the global auroral power is well correlated with the solar wind dynamic pressure (correlation coefficient r ~0.90), rather than the change in the solar wind dynamic pressure. In-situ measurements of particle data from the Defense Meteorological Satellite Program satellite indicate that the magnetospheric source for the pressure-enhanced auroras is most likely the central plasma sheet. Other ionospheric parameters such as the auroral electrojet (AE index), magnetic storm index (Sym-H), and the cross polarcap potential drop also show a one-to-one correspondence to the pressure pulses. In one instance the auroral electrojets AE index reached more than 200 nT, the cross polar-cap potential drop (φpc) inferred from the SuperDARN radar network ionospheric plasma convection increased to ~60 kV. The observed increases in the auroral emissions, AE, and polar cap potential were not associated with substorms. Our result strongly suggests that solar wind pressure pulses are an important source of geomagnetic activity during northward IMF periods.
Highlights
The response of the magnetosphere-ionosphere system to variations in the solar wind plasma and interplanetary magnetic field (IMF) constitutes a fundamental element in magnetospheric physics
The intensive studies of the 6 - 11 January 1997, coronal mass ejection (CME)/magnetic cloud (MC) event clearly demonstrated global auroral enhancements associated with the crossing of interplanetary shocks and pressure pulses (e.g., Spann et al 1998; Zhou and Tsurutani 1999; Tsurutani et al 2001)
We have identified a fortuitous event involving a series of large pressure pulses over an extended period of strongly northward IMF to minimize the effects of magnetic reconnection
Summary
The response of the magnetosphere-ionosphere system to variations in the solar wind plasma and interplanetary magnetic field (IMF) constitutes a fundamental element in magnetospheric physics. The effect of magnetospheric compression on geomagnetic and auroral activity depends on the sign of IMF Bz. Previous study results suggest that the compression effect is more pronounced during southward than during northward IMF conditions (e.g., Liou et al 1998; Zhou and Tsurutani 2001; Boudouridis et al 2003, 2005). Previous study results suggest that the compression effect is more pronounced during southward than during northward IMF conditions (e.g., Liou et al 1998; Zhou and Tsurutani 2001; Boudouridis et al 2003, 2005) These works suggest that enhanced solar wind-magnetosphere coupling occurs after a sudden increase in dynamic pressure under a southward IMF. We study the magnetospheric source and provide a possible mechanism for the compression aurora
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