C/NOFS observations of the equatorial ionospheric electric field response to the 2009 major sudden stratospheric warming event

[1] We present new observations made by the Coupled Ion Neutral Dynamics Investigation (CINDI) Ion Velocity Meter (IVM) instrument onboard the Communication/Navigation Outage Forecasting System (C/NOFS) satellite that show the effects of the January 2009 sudden stratospheric warming (SSW) event on equatorial electric fields. We have used IVM observations to construct composite curves of mean equatorial vertical plasma drifts as a function of local time and longitude sector. These curves show large upward vertical drifts during morning hours and downward drifts during afternoon. Our analysis indicates that this pattern could be observed over the range of longitudes where adequate IVM measurements were available, from approximately 165°E to about 315°E longitude. A clear day-to-day, quasi-deterministic variability in the drifts is also observed, with the transition from upward to downward drifts occurring at increasing local times from 25 to 30 January 2009. The analysis also suggests some level of longitudinal variability in the magnitude of the drifts. These in-situ observations are in good agreement with previous ground-based measurements of the response of equatorial electric fields to SSW events. In particular, we found that IVM drift measurements centered around 285°E depart significantly from climatological values but agree exceptionally well with ground-based measurements of vertical drifts made by the Jicamarca incoherent backscatter radar. Overall, the results agree well with previous studies of SSW events, demonstrate the usefulness of the IVM observations and motivate further studies of the variability of the equatorial ionosphere using C/NOFS.