A semiempirical equatorial mapping of AMIE convection electric potentials (MACEP) for the January 10, 1997, magnetic storm

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.