Reconstruction of 2D/3D ionospheric disturbances in high-latitude and arctic regions during a geomagnetic storm using GNSS carrier TEC: a case study of the 2015 great storm

On 2015 March, aG4-level geomagnetic storm hit the earth and then triggered global ionospheric disturbances. Aconsiderable number of studies have been published showing various ionospheric responses in low- and mid-latitude regions. In contrary, very limited efforts have been made on high-latitude or polar regions. Therefore, this paper reconstructed and investigated the 2D/3D ionospheric disturbances in high-latitude and arctic regions during this great storm using multiprocessing methods. First, four longitudinal global navigation satellite system stations' sectors are selected on Polar area, and the second-order differential of total electron content (dTEC) of each sectors is calculated to detect the ionosphere anomaly during the time of interests. Compared with the "auroral oval" distribution and the precipitating of auroral electrons data from Defense Meteorological Satellite Program, the triggering mechanism of the detected anomaly is discussed. Second, based on the dTEC detection results and the auroral electrojet index series, two disturbances processes have been identified. Then, a new computerized ionospheric tomography (CIT) algorithm called MFCIT (CIT with mapping function) is introduced, and the 3D ionosphere images under daytime (LT06:00-LT06:30) and nighttime (LT21:00-LT22:00) over Alaska are individually inverted at the temporal resolution of 1 min. In contrast with magnetic field lines distribution, the relationship between disturbances and geomagnetic fields has been analyzed. Last, two vertical electron motions are monitored with the CIT images. As the two motions occur at two different steps of the geomagnetic storm, the characteristics and amplitudes of the vertical movements can be distinguished. The physical mechanisms for the vertical motions are discussed. The upward vertical motion during the first disturbance may be induced by the eastward abnormal penetration electric field, while the second disturbance may be the outcome of the combined influences of the abnormal electric field and the precipitating of auroral electrons.