C/NOFS measurements of ring current magnetic field in low-latitude ionosphere

The Vector Electric Field Instrument (VEFI) suite onboard the C/NOFS spacecraft includes a sensitive fluxgate magnetometer to measure DC and ULF magnetic fields in the low latitude ionosphere. The instrument includes a DC vector measurement at 1 sample/sec with a range of ± 45,000 nT whose primary objective is to enable both V × B and E × B measurements that are more accurate than those provided when a simple magnetic field model is used instead. The magnetic field data can also be used for scientific research to provide information of large-scale ionospheric and magnetospheric current systems. At low latitudes the magnetic field residuals (data with the internal magnetic field model subtracted) are predominately produced by the stormtime ring current. Since C/NOFS provides a complete coverage of all local times every 97 minutes, magnetic field data allow studies of the temporal evolution and local-time variations of stormtime ring current. The analysis demonstrates the feasibility of using instrumented spacecraft in low-inclination orbits to specify the ring current´s evolution and local time asymmetry. We will present the results of a statistical study of the stormtime ring current.