Mapping the conjugate and corotating storm-enhanced density during 17 March 2013 storm through data assimilation

Abstract

The storm-enhanced density (SED) is an electron density enhancement phenomenon extending from the later afternoon at middle latitude to the noontime in high latitude within a narrow band during early stage of geomagnetic storm. Previous investigations were mostly focused on the northern America region due to sparse data coverage in other regions. Recent observational analysis and simulation studies have shown that the SED might be quite complicated both physically and spatial/temporal evolution. In this paper, we obtained the global ionospheric electron density with the spatial/temporal resolution of 5° in latitude, 10° in longitude, ~30 km around F2 peak, and 0.5 h in time, during 17 March 2013 geomagnetic storm through assimilating ground and LEO-based total electron content (TEC) data into the model. A total of ~450 ground-based Global Navigation Satellite Systems stations' and ~10 LEO satellites' observations were applied in the assimilation. Of all the data, six satellites with ionospheric radio occultation profiling capability provided the key altitudinal variation information. The SED associated with the tongue of ionization (TOI) and boundary blob can be well identified from the data assimilation results, although their amplitude of enhancement was only up to ~6 TECU (TEC unit, 1 TECU = 1016 el m−2). All structures show very dynamic and complicated time evolution features. During this storm time, we identified two separate SED/TOI/blob structures corotating from Europe to American with conjugate occurrence. This partly supports the mechanism of convection expansion. Given a significant amount of radio occultation will be available in the near future, this method will help up us to resolve global large-scale ionospheric disturbance down to very small spatial and temporal scale in storm time.