[1] Strong interplanetary shock interactions with the Earth's magnetosphere have great impacts on energetic particle dynamics in the magnetosphere. An interplanetary shock on 7 November 2004 (with the maximum solar wind dynamic pressure of $70 nPa) was observed by the Cluster constellation to induce significant ULF waves in the plasmasphere boundary, and energetic electrons (up to 2 MeV) were almost simultaneously accelerated when the interplanetary shock impinged upon the magnetosphere. In this paper, the relationship between the energetic electron bursts and the large shock-induced ULF waves is studied. It is shown that the energetic electrons could be accelerated and decelerated by the observed ULF wave electric fields, and the distinct wave number of the poloidal and toroidal waves at different locations also indicates the different energy ranges of electrons resonating with these waves. For comparison, a rather weak interplanetary shock on 30 August 2001 (dynamic pressure $2.7 nPa) is also investigated. It is found that interplanetary shocks or solar wind pressure pulses with even small dynamic pressure change can have a nonnegligible role in the radiation belt dynamics.

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.

We present in situ observations of a shock-induced substorm-like event on 13 April 2013 observed by the newly launched Van Allen twin probes. Substorm-like electron injections with energy of 30-500 keV were observed in the region from L ∼5.2 to 5.5 immediately after the shock arrival (followed by energetic electron drift echoes). Meanwhile, the electron flux was clearly and strongly varying on the ULF wave time scale. It is found that both toroidal and poloidal mode ULF waves with a period of 150 s emerged following the magnetotail magnetic field reconfiguration after the interplanetary (IP) shock passage. The poloidal mode is more intense than the toroidal mode. The 90• phase shift between the poloidal mode B r and E a suggests the standing poloidal waves in the Northern Hemisphere. Furthermore, the energetic electron flux modulations indicate that the azimuthal wave number is ∼14. Direct evidence of drift resonance between the injected electrons and the excited poloidal ULF wave has been obtained. The resonant energy is estimated to be between 150 keV and 230 keV. Two possible scenaria on ULF wave triggering are discussed: vortex-like flow structure-driven field line resonance and ULF wave growth through drift resonance. It is found that the IP shock may trigger intense ULF wave and energetic electron behavior at L ∼3 to 6 on the nightside, while the time profile of the wave is different from dayside cases.

[1] In this study, we report in situ observations on the simultaneous periodic modulations in the drifting energetic electrons (∼100 keV) and in the bouncing thermal ion species (O + at ∼4.5 keV and H + at ∼280 eV) with the same frequency of 3.3 mHz during the storm recovery phase on 21 October 2001. The Cluster fleet was traveling outbound in the inner magnetosphere from the Southern to Northern Hemisphere on the morning sector (0900 MLT). The ultra-low-frequency (ULF) waves from the magnetic field and electric field measurements show a mixture of several dominant wave components in the transverse modes. The poloidal mode at the modulation frequency of 3.3 mHz appears to be a standing wave with an odd harmonic, although other wave components reveal propagating features. The radial extent of this standing wave is around 0.58 R E . The oscillation periods of the energetic electron fluxes (∼100 keV) and the thermal O + (∼4.5 keV) and H + (∼280 eV) fluxes are observed the same as the period of the poloidal standing wave, indicating that the energetic electrons and the thermal ion species are modulating by the same wave. Further, we suggest the simultaneous drift resonances of the energetic electrons around 94 keV and the bounce resonances of the thermal O + around 4.5 keV and H + around 280 eV with the same poloidal standing wave. In addition, the electron energy spectra variations reveal the accelerations of the electrons in the energy range of 50∼110 keV, which are most likely due to the drift resonances. This is the first study to show both energetic particles (radiation belt population, ∼ a few hundred keV) and thermal ions (background plasma population, ∼ a few keV) can be affected by the same ULF wave simultaneously. Furthermore, this study implies that the superdense ionospheric origin O + ions in the inner magnetosphere during storm times can modify the local field line eigenfrequency and result in the energetic electron accelerations by the ULF waves in the deep region of the radiation belt.

[1] We present the first systematic observational study on the pitch angle evolutions of O + ions associated with ULF Pc5 poloidal standing waves excited during geomagnetic storms. The O + ion measurements are made on board the CLUSTER satellites with the Composition Distribution Function (CODIF) instrument, which covers energies from 1 to 40 keV, a low-energy portion of the ring current. We find that the nature of the ion flux oscillation strongly depends on the magnetic latitude of observation. Near the magnetic equator, the flux oscillation appears only around 0°and 180°pitch angles with no phase delay, which can result from wave-particle interactions in a fundamental mode standing wave with a strong poloidal component. Away from the equator, however, the flux oscillation appears in a wide range of pitch angles with strong pitch angle dispersion that reverses sign from the Southern Hemisphere to the Northern Hemisphere. The latitude dependence of the dispersion signature is explained by combining the ion energy modulation near the equator and the time of flight effect of ion bounce motion. The analysis technique shown in this study can be used to diagnose the field line mode structure of ULF waves.