An effort to derive an empirically based, inner-magnetospheric electric field model: Merging Cluster EDI and EFW data

A key ingredient for modelling many inner-magnetospheric processes is the realistic representation of the spatio-temporal dynamics of the inner-magnetospheric electric field, or, IMEF. The Cluster Mission provides a unique opportunity to construct an IMEF model using electric field measurements from both the electron drift instrument (EDI) and the electric fields and waves instrument (EFW). A superset of IMEF data is formed by merging EDI and EFW data. Challenges presented by the merging process include the handling of compromised perpendicular electric field (E⊥)(E⊥) calculations, electric field offsets, scaling problems, and spurious fields. The present goal is to produce the highest quality merged IMEF data set possible which is minimally affected by these issues. Preliminary investigation of the merging process on Cluster 1 for the years 2001–2003 has revealed that merging is a worthwhile exercise. The data sets are shown to be complementary, and the IMEF merged data set is superior to either data set alone in terms of improved spatial coverage, and coverage of a wider range of geomagnetic activity levels. Preliminary use of the merged IMEF data set to construct a parameterized, equatorial, electric field model for the inner magnetosphere, the UNH-IMEF model, is also presented. The electric field morphology produced by this preliminary version of the UNH-IMEF model shows the expected sensitivity to IMF orientation.