.[1] The interaction between interplanetary shocks and the Earth's magnetosphere manifests in many important space physics phenomena including particle acceleration. We investigated the response of the inner magnetospheric hydrogen and oxygen ions to a strong interplanetary shock impinging on the Earth's magnetosphere. Both hydrogen and oxygen ions are found to be heated/accelerated significantly with their temperature enhanced by a factor of two and three immediately after $1 min and $12 min of the shock arrival respectively. Multiple energy dispersion signatures of ions were found in the parallel and anti-parallel direction to the magnetic field immediately after the interplanetary shock impact. The energy dispersions in the anti-parallel direction preceded those in the parallel direction. Multiple dispersion signatures can be explained by the flux modulations of local ions (rather than the ions from the Earth's ionosphere) by ULF waves. It is found that the energy spectrum from 10 eV to $40 keV are highly correlated with the cross product of observed ULF wave electric and magnetic field (V = (E Â B)/B2 ), which indicate that both cold plasmaspheric plasma and hot thermal ions (10 eV to $40 keV) are accelerated and decelerated with the various phases of ULF wave electric field. We then demonstrate that ion acceleration due to the interplanetary shock compression on the Earth's magnetic field is rather limited, whereas the major contribution to acceleration comes from the electric field carried by ULF waves via drift-bounce resonance for both the hydrogen and oxygen ions. The integrated hydrogen and oxygen ion flux with the poloidal mode ULF waves are highly coherent (>0.9) whereas the coherence with the toroidal mode ULF waves is negligible, implying that the poloidal mode ULF waves are much more efficient in accelerating hydrogen and oxygen ions in the inner magnetosphere than the toroidal mode ULF waves. The duration of high coherence for oxygen ions with the poloidal mode ULF wave is longer than that for hydrogen ions, indicating that oxygen ions can be heated/accelerated more efficiently by the poloidal mode ULF wave induced by the interplanetary shock.

1] When a solar wind dynamic pressure impulse impinges on the magnetophere, ultralow-frequency (ULF) waves can be excited in the magnetosphere and the solar wind energy can be transported from interplanetary space into the inner magnetosphere. In this paper, we have systematically studied ULF waves excited at geosynchronous orbit by both positive and negative solar wind dynamic pressure pulses. We have identified 270 ULF events excited by positive solar wind dynamic pressure pulses and 254 ULF events excited by negative pulses from 1 January 2001 to 31 March 2009. We have found that the poloidal and toroidal waves excited by positive and negative pressure pulses oscillate in a similar manner of phase near 06:00 local time (LT) and 18:00 LT, but in antiphase near 12:00 LT and 0:00 LT. Furthermore, it is shown that excited ULF oscillations are in general stronger around local noon than those in the dawn and dusk flanks. It is demonstrated that disturbances induced by negative impulses are weaker than those by positive ones, and the poloidal wave amplitudes are stronger than the toroidal wave amplitudes both in positive and negative events. The potential impact of these excited waves on energetic electrons at geosynchronous orbit has also been discussed.

[1] Interplanetary (IP) shocks can greatly disturb the Earth's magnetosphere, causing the global dynamic changes in the electromagnetic fields and the plasma. In order to investigate this, we have systematically analyzed 106 IP shock events based on OMNI data, GOES, and Los Alamos National Laboratory satellite observations during 1997 −2007. It is revealed that the median value of IMF B z keeps negative/positive prior to shock arrival and becomes more negative/positive following the shock arrival. The statistical analysis shows that IP shocks with southward interplanetary magnetic field (IMF) (46%) are likely to increase AE (AL, AU) and PC indices significantly. The amplitude of AE index increases from 200 to 600 nT, AU from 100 to 200 nT, AL from 50 to 400 nT, and PC from 1.5 to 3 approximately in 10 min, which could be a signature of geomagnetic activity/substorms onset (or substorm further intensification). Meanwhile, there is a strong injection of energetic electrons in the dawn region following the shock arrival and a strong depletion in the dusk region 30 min later, showing a clear dawn-dusk asymmetry. On the other hand, there is only the typical shock compression effect for IP shocks with northward IMF (54%). The median value of AE index increased from 80 to 150 nT, AU from 50 to 90 nT, AL index decreased from −30 to −40 nT, and PC index increased from 0.6 to 1.2 in ∼10 min following the shock arrival. Both individual cases and statistical studies indicate that the magnetosphere-ionosphere system must be preconditioned for a substorm-like geomagnetic activity to be triggered by an IP shock with southward IMF impact, whereas IP shock with northward IMF precondition shows only compression effect.

The existence of planetary radiation belts with relativistic electron components means that powerful acceleration mechanisms are operating within their volume. Mechanisms that bring charged particles planetward toward stronger magnetic fields can cause their heating. On the basis that electron fluxes in Saturn’s radiation belts are enhanced over discrete energy intervals, previous studies have suggested that rapid inward plasma flows may be controlling the production of their most energetic electrons. However, rapid plasma inflows languish in the planet’s inner magnetosphere, and they are not spatially appealing as a mechanism to form the belts. Here we show that slow, global-scale flows resulting from transient noon-to-midnight electric fields successfully explain the discretized flux spectra at quasi- and fully relativistic energies, and that they are ultimately responsible for the bulk of the highest energy electrons trapped at Saturn. This finding is surprising, given that plasma flows at Saturn are dominated by the planetary rotation; these weak electric field perturbations were previously considered impactful only over a very narrow electron energy range where the magnetic drifts of electrons cancel out with corotation. We also find quantitative evidence that ultrarelativistic electrons in Jupiter's radiation belts are accelerated by the same mechanism. Given that similar processes at Earth drive a less efficient electron transport compared to Saturn and Jupiter, the conclusion is emerging that global-scale electric fields can provide powerful relativistic electron acceleration, especially at strongly magnetized and fast-rotating astrophysical objects.