3‐D regional ionosphere imaging and SED reconstruction with a new TEC‐based Ionospheric Data Assimilation System (TIDAS)

A new TEC-based ionospheric data assimilation system (TIDAS) over the continental US and adjacent area (20 degrees-60 degrees N, 60 degrees-130 degrees W, and 100-600 km) has been developed through assimilating heterogeneous ionospheric data, including dense ground-based Global Navigation Satellite System (GNSS) Total Electron Content (TEC) from 2,000+ receivers, Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation data, JASON satellite altimeter TEC, and Millstone Hill incoherent scatter radar measurements. A hybrid Ensemble-Variational scheme is utilized to reconstruct the regional 3-D electron density distribution: a more realistic and location-dependent background error covariance matrix is calculated from an ensemble of corrected NeQuick outputs, and a three-dimensional variational (3DVAR) method is adopted for measurement updates to obtain an optimal state estimation. The spatial-temporal resolution of the reanalyzed 3-D electron density product is as high as 1 degrees x 1 degrees in latitude and longitude, 20 km in altitude, and 5 min in universal time, which is sufficient to reproduce ionospheric fine structure and storm-time disturbances. The accuracy and reliability of data assimilation results are validated using ionosonde and other measurements. TIDAS reanalyzed electron density is able to successfully reconstruct the 3-D morphology and dynamic evolution of the storm-enhanced density (SED) plume observed during the St. Patrick's day geomagnetic storm on 17 March 2013 with high fidelity. Using TIDAS, we found that the 3-D SED plume manifests as a ridge-like high-density channel that predominantly occurred between 300 and 500 km during 19:00-21:00 UT for this event, with the F2 region peak height being raised by 40-60 km and peak density enhancement of 30%-50%.