TEC spatial gradient resulted from plasma bubbles with ionospheric tomography

Extreme ionospheric disturbances, such as plasma bubbles at low latitudes in China, pose an intact threat to GNSS Ground-based Enhancement System(GBAS) users during severe ionospheric activity. In this paper, the TEC spatial gradient caused by these plasma bubbles is studied, and an ionospheric tomography assisted method is proposed to study the TEC spatial gradient caused by plasma bubbles. Firstly, the multi-resolution ionospheric tomography technology is used to reconstruct the ionospheric tomography results of China and its surrounding middle and low latitudes during the strongest period of 12:00−17:00UT disturbance on September 8, 2017. It is found that the plasma bubble phenomenon of depleted ionospheric electron density occurred in China’s low latitudes during this period. Secondly, the TEC spatial gradient caused by plasma bubble is calculated by short baseline station-pairs method and time step method according to the inversion TEC image. Finally, a comparative study is conducted combining the two to verify that a large TEC spatial gradient often exists around the side wall of the plasma bubble. For example, the maximum TEC spatial gradient near Hong Kong airspace at 14:06UT on September 8th is 133.16 mm/km. It is also found that the inverted images can not only provide 3D electron density distributions of the bubbles, but also help explore the underlying mechanism resulting in large TEC gradients.