[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.

Observations of the low‐latitude boundary layer in the subsolar region when the interplanetary magnetic field (IMF) is strongly northward indicate that the boundary layer consists of steplike multiple layers rather than a single diffusive layer. These sublayers can be formed by spatially limited, temporally varying reconnection near the polar cusp. In this model when the interplanetary magnetic field is strongly northward a magnetosheath flux tube reconnects in the north and south beyond the cusp. The tube shortens itself and reorients to align itself with other magnetospheric field lines and eventually be assimilated with other magnetospheric field lines. Energy from the shortening of the flux tube and the reduction of magnetic energy is transferred into the magnetosphere and increases the pressure above its initial equilibrium value while the reconnected flux tube sinks into the magnetosphere. The interchange instability is one of the possible mechanisms to disperse and expand the newly captured magnetosheath flux tube azimuthally along the magnetopause current layer and to lead the system back to equilibrium. It is stable to radial interchanges and unstable to azimuthal interchanges. Thus the newly formed flux tube becomes a boundary layer. The interchange instability converts the thermal energy of the plasma into dynamic energy. The interchange front moves with a fraction of the sound speed and accelerates toward the terminator. Subsequent reconnection forms a new layer before the last one is completely dispersed. In this model, different sublayers represent different ages after reconnection.

[1] We present a newly developed empirical model of the plasma density in the plasmasphere. It is based on more than 700 density profiles along field lines derived from active sounding measurements made by the radio plasma imager on IMAGE between June 2000 and July 2005. The measurements cover all magnetic local times and vary from L = 1.6 to L = 4 spatially, with every case manually confirmed to be within the plasmasphere by studying the corresponding dynamic spectrogram. The resulting model depends not only on L-shell but also on magnetic latitude and can be applied to specify the electron densities in the plasmasphere between 2000 km altitude and the plasmapause (the plasmapause location itself is not included in this model). It consists of two parts: the equatorial density, which falls off exponentially as a function of L-shell; and the field-aligned dependence on magnetic latitude and L-shell (in the form of invariant magnetic latitude). The fluctuations of density appear to be greater than what could be explained by a possible dependence on magnetic local time or season, and the dependence on geomagnetic activity is weak and cannot be discerned. The solar cycle effect is not included because the database covers only a fraction of a solar cycle. The performance of the model is evaluated by comparison to four previously developed plasmaspheric models and is further tested against the in situ passive IMAGE RPI measurements of the upper hybrid resonance frequency. While the equatorial densities of different models are mostly within the statistical uncertainties (especially at distances greater than L = 3), the clear latitudinal dependence of the RPI model presents an improvement over previous models. The model shows that the field-aligned density distribution can be treated neither as constant nor as a simple diffusive equilibrium distribution profile. This electron density model combined with an assumed model of the ion composition can be used to estimate the time for an Alfven wave to propagate from one hemisphere to the other, to determine the plasma frequencies along a field line, and to calculate the raypaths for high frequency waves propagating in the plasmasphere.Citation: Ozhogin, P., J. Tu, P. Song, and B. W. Reinisch (2012), Field-aligned distribution of the plasmaspheric electron density: An empirical model derived from the IMAGE RPI measurements,

Energetic electron and ion (electrons: 30 keV to 500 keV, protons: 30 keV to 1.5 MeV) flux variations associated with ultralow frequency (ULF) waves in the dayside magnetosphere were observed during the CLUSTER's perigee pass near 0900 MLT on Oct. 31, 2003. The ULF modulation terminated where higher frequency fluctuations appeared, as the CLUSTER spacecraft entered the plasmasphere boundary layer (PBL) where the plasma ion density was elevated. In the region from L ∼ 5.0 to 10, the periods of the ion flux modulation and the electron flux modulation are same but out‐of‐phase. The observed magnetic ULF pulsations are dominated by the toroidal mode, along with a relatively weaker poloidal wave. A 90° phase shift between the radial electric field and the azimuthal magnetic field indicates that dominating toroidal standing waves observed at the southern hemisphere are a fundamental harmonic. This study shows that the modulation of the electron flux is dominated by the toroidal mode in the region of L > 7.5. The observations made in this analysis suggest the excitation of the energetic electron drift resonance at around 127 keV.

Three magnetosheath passes with density enhancements in front of the magnetopause are studied with data from ISEE 1,2, and 3. The density structure appears to be locally generated and slow mode in nature. In one pass when ISEE 1 and 2 were well separated, the motion of the density structure can be determined. The density structure appears to stand in the magnetosheath flow. Thus it propagates upstream in the rest frame of the flow. The flow in and near the density structure appears to be closer to isothermal than adiabatic. The flow velocity decreases from super‐slow to being close to the intermediate and slow mode velocities at the outer edge of the density structure. This study provides additional evidence that the density structure in front of the magnetopause is a slow mode transition in which the flow velocity decreases to the MHD slow mode velocity. The slow mode transition may consist of two waves fronts and a region with strong slow mode waves. This slow mode transition may play an important role in establishing the flow and field pattern near the magnetopause.