A Regional 3-D Data Assimilation Model for the Ionospheric Electron Density at Middle-to-High Latitudes in the Northern Hemisphere

In this paper, we developed an efficient regional three-dimensional data assimilation model focused on the middle-to-high latitude ionosphere in the Northern Hemisphere. The model employed the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) as the background, which was specifically optimized for high-latitude applications and has demonstrated exceptional performance in the northern high-latitude regions. Utilizing a three-dimensional variational (3DVAR) method and incorporating extensive slant total electron content (TEC) observations, the model achieves near-real-time computation of the three-dimensional electron density distribution. The spatial-temporal resolution of the reanalyzed three-dimensional electron density product is 2.5° in latitude, 5° in longitude, with altitude intervals of 20 km between 80 and 500 km, 100 km between 500 and 1,000 km, 500 km between 1,000 and 3,000 km, and a temporal resolution of 15 min. To assess the effectiveness and accuracy of the model, we performed extensive comparisons with observational data from various sources, including the GNSS vertical TEC, ionosonde foF2, electron density profile derived from ionosonde measurements and COSMIC radio occultation data. Independent verification confirmed that the data assimilation results align well with these observations. Leveraging on the data assimilation output, we reconstructed critical high-latitude ionospheric structures and phenomena during geomagnetic storms, such as the storm-enhanced density (SED), the tongue of ionization (TOI), boundary blobs, polar cap patches, and the electron density enhancement in the auroral particle precipitation region, and characterized their three-dimensional spatial distributions well.