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 ele ctric field measurements are only available at isolated locations during st orm time conditions, A global view of the inner magnetospheric convection e lectric field can be obtained by mapping ionospheric potentials into the eq uatorial plane. A mapping procedure for assimilative mapping of ionospheric electrodynamics (AMIE) ionospheric potentials (MACEP) is used to obtain co nvection patterns for the January 10, 1997, magnetic storm. The results are compared with the widely used empirical Volland-Stern model and the mappin g of Weimer ionospheric potentials. While the gross temporal evolution of t he large-scale potential drop across the magnetosphere is similar in all th ree models, detailed intercomparison shows that the MACEP procedure is capa ble of resolving highly variable and relatively small scale features of the electric field that are not treated by the Volland-Stern model nor seen fr om the Weimer mapping. The MACEP results are in reasonable agreement with l imited electric field measurements from the electric field instrument on th e Polar spacecraft and LANL measurements of thermal ion velocities at geosy nchronous 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 t he dusk sector improved MACEP results at the duskside low-L region.