Are sawtooth oscillations of energetic plasma particle fluxes caused by periodic substorms or driven by solar wind pressure enhancements?

Abstract

[1] Energetic electron and proton fluxes measured by geosynchronous satellites often show sawtooth-like variations during magnetic storms. We examine whether the sawtooth oscillations and relevant magnetospheric-ionospheric disturbances are caused by periodic substorms or driven by a series of enhancements in the solar wind pressure. We show that there are significant differences between periodic substorms and solar wind-induced variations. The energetic fluxes at geosynchronous orbit may increase by orders of magnitude after each onset of periodic substorms and by 10-50% in response to a large solar wind pressure impulse. The sudden increases of the energetic fluxes during periodic substorms show significant time delays of 30-50 min at different longitudes/local times, indicating that the fluxes are injected on the nightside and then drift to the dayside. In contrast, the small flux increases caused by solar wind pressure enhancements occur almost simultaneously at all local times. The periodic substorms always have a strong spectrum peak at 2-3 hours, no matter whether the solar wind pressure and/or IMF have similar spectrum peaks. The nightside magnetospheric magnetic elevation angle shows a large (30-60°) increase at each onset of periodic substorms through dipolarization and a small (<10°) decrease in response to a solar wind pressure impulse. Each cycle of periodic substorms can cause a deviation of 40-60 nT in the midlatitude geomagnetic field; the midlatitude geomagnetic deviations caused by solar wind pressure enhancements are proportional to the square root of the pressure change. The increase of the polar cap index caused by substorms is $4 times that caused by solar wind pressure enhancements. We conclude that the sawtooth-like flux oscillations represent flux injections during periodic substorms and that the period of substorms is determined by the magnetosphere.Citation: Huang, C.-S., G. D. Reeves, G. Le, and K. Yumoto (2005), Are sawtooth oscillations of energetic plasma particle fluxes caused by periodic substorms or driven by solar wind pressure enhancements?,

Recurrent substorm activity during the passage of a corotating interaction region

“…modulations of the solar wind dynamic pressure (Lee et al, 2004) and northward turnings of the IMF (Lyons et al, 2005). However, the evidence for these hypotheses has been disputed (Huang et al, 2005;. We therefore ask whether the observed periodicities are consistent with an untriggered substorm model, like the MSM.…”

“…So that signatures due to solar wind dynamic pressure increases were excluded the flux increase had to be preceded by a gradual decrease in particle flux-this is indicative of substorm growth phase (e.g. Huang et al, 2005)-and not coincident with a large, abrupt solar wind pressure increase. Further, we required that the injection signature was observed within AE3 h of local magnetic midnight.…”

Electric Fields and Magnetic Fields in the Plasmasphere: A Perspective From CLUSTER and IMAGE

“…These three studies support the response <1 hour. Other work by Huang et al (2005) reported substorm recurrence periods of a few hours during continuous southward IMF, which could be related to the long term (∼hours) effect of IMF. This analysis certainly suggests follow-up analysis to answer significant questions.…”

Augmented Empirical Models of Plasmaspheric Density and Electric Field Using IMAGE and CLUSTER Data

“…Nevertheless, EFW worked well during this orbit. This period corresponds to a major storm with sawtooth signatures (e.g., Huang et al 2005;Ohtani et al 2007). In Fig.…”