[1] We study ring current evolution during the 10 January 1997 geomagnetic storm, comparing results from two inner magnetospheric convection electric field models: (1) the Kp-dependent Volland-Stern (V-S) model and (2) the high spatial and temporal resolution assimilative mapping of ionospheric electrodynamics (AMIE) model, coupled with our global ring current model. We have added a penetration electric field (driven by partial ring current closure in the ionosphere) to the AMIE model which improves the agreement at low L shells with Polar/EFI measurements, and we mapped the modified AMIE convection electric potentials (MACEP) to the equatorial plane. Both V-S and MACEP convection models predict a very asymmetric local time distribution of ring current energy density during the main and early recovery phase of the storm. However, the peak of the medium energy ions is located during the main phase near midnight when the MACEP model is used, while it is located near dusk using V-S. In both models the energy density peak is located near dusk during the early recovery, and the ring current becomes symmetric during the late recovery phase. Ring current injection is larger, penetrating to lower L shells, and the Dst index is significantly better reproduced using MACEP rather than using V-S model. We compare model results with Polar data and find reasonably good agreement with both models at larger L shells and near dawn. The enhanced storm time distributions at low L shells near dusk are better modeled with MACEP. Electromagnetic ion cyclotron (EMIC) waves are predominantly excited near Dst minimum, have larger wave gain, and cause stronger ion precipitation using the MACEP model. In this case the calculated ion precipitation patterns exhibit features consistent with storm time Polar/IPS observations and show enhancements within the plasmaspheric bulge and along the duskside plasmapause. In the dusk to midnight sector at L > 5, however, there seems to be a need to include the effect of an additional scattering process during highly active conditions.

Owing to satellite and instrumental limitations, in situ magnetospheric electric field measurements are only available at isolated locations during storm time conditions. A global view of the inner magnetospheric convection electric field can be obtained by mapping ionospheric potentials into the equatorial plane. A mapping procedure for assimilative mapping of ionospheric electrodynamics (AMIE) ionospheric potentials (MACEP) is used to obtain convection patterns for the January 10, 1997, magnetic storm. The results are compared with the widely used empirical Volland‐Stern model and the mapping of Weimer ionospheric potentials. While the gross temporal evolution of the large‐scale potential drop across the magnetosphere is similar in all three models, detailed intercomparison shows that the MACEP procedure is capable of resolving highly variable and relatively small scale features of the electric field that are not treated by the Volland‐Stern model nor seen from the Weimer mapping. The MACEP results are in reasonable agreement with limited electric field measurements from the electric field instrument on the Polar spacecraft and LANL measurements of thermal ion velocities at geosynchronous orbit during prestorm and recovery phase conditions. However, the inner boundary condition employed in the current version of AMIE is unable to reproduce the magnitude of the penetrating electric fields observed in the inner magnetosphere during the main phase of a storm. The addition of a penetration electric field associated with an asymmetric ring current in the dusk sector improved MACEP results at the duskside low‐L region.

Polar observations indicate the presence of intense broadband plasma waves nearly all of the time (96% occurrence frequency in this study) near the apogee of the Polar trajectory (∼6–8 RE). The region of wave activity bounds the dayside (0500 to 1800 LT) polar cap magnetic fields, and we thus call these waves polar cap boundary layer (PCBL) waves. The waves are spiky signals spanning a broad frequency range from ∼101 to 2 × 104 Hz. The waves have a rough power law spectral shape. The wave magnetic component has on average a ƒ−2.7 frequency dependence and appears to have an upper frequency cutoff of ∼(6–7) × 103 Hz, which is the electron cyclotron frequency. The electric component has on average a ƒ−2.2 frequency dependence and extends up to ∼2 × 104 Hz. The frequency dependences of the waves and the amplitude ratios of B′/E′ indicate a possible mixture of obliquely propagating electromagnetic whistler mode waves plus electrostatic waves. There are no clear intensity peaks in either the magnetic or electric spectra which can identify the plasma instability responsible for the generation of the PCBL waves. The wave character (spiky nature, frequency dependence and admixture of electromagnetic and electrostatic components) and intensity are quite similar to those of the low‐latitude boundary layer (LLBL) waves detected at and inside the low‐latitude dayside magnetopause. Because of the location of the PCBL waves just inside the polar cap magnetic field lines, it is natural to assume that these waves are occurring on the same magnetic field lines as the LLBL waves, but at lower altitudes. Because of the similar wave intensities at both locations and the occurrence at all local times, we rule out an ionospheric source. We also find a magnetosheath origin improbable. The most likely scenario is that the waves are locally generated by field‐aligned currents or current gradients. We find a strong relationship between the presence of ionospheric and magnetosheath ions and the waves near the noon sector. These waves may thus be responsible for ion heating observed near the cusp region. Antisunward convection of these freshly accelerated oxygen ions over the polar cap during intense wave events (occurring during southward Bz events) might lead to enhanced plasma sheet O+ population. For magnetic storm intervals this mechanism would lead to a natural delay between the main phase onset and the appearance of oxygen ions in the ring‐current.

Recent Polar plasma wave observations indicate that intense wideband waves are always present in the polar cap boundary layer (PCBL) region.