## 1 Introduction  
The ionosphere is an important research subject of the space environment, and its disturbances will have an important impact on the propagation of radio signals in radio communication systems, such as ground-to-air radio communication, satellite navigation and positioning, as well as radar detection. Especially over low-latitude regions, geomagnetic activities are extremely active, which affect satellite communications, and even communication interruptions may occur in severe cases. A geomagnetic storm is a major disturbance of the earth's magnetosphere when there is an exchange of energy from the solar wind into the space environment. The solar wind that produces changes in the currents, plasmas, and fields in Earth's magnetosphere result in these geomagnetic storms [1]. Due to the fact that the thermosphere and ionosphere are coupled system, studies have shown that when a strong geomagnetic storm occurs, it may cause anomaly variations in the ionosphere morphology and the thermosphere composition in different latitudes [2]. Particularly, the column density ratio of O to N\({}_{2}\) (O/N\({}_{2}\)) is an important parameter reflecting the response of the thermosphere composition to geomagnetic storms, mainly deleted in the mid-high latitudes, but enhanced in the low-latitudes during geomagnetic storms [3]. Since geomagnetic storms were first discovered and discussed in the middle of the 20 th century, the study of ionospheric storms has always been an important topic in earth and space science [4]. Therefore, the detection of ionospheric disturbance response during a severe geomagnetic storm will help us understand the temporal-spatial changes of the ionosphere and predict ionospheric activities. The application of the Global Navigation Satellite System (GNSS) in ionospheric research provides a new method for exploring ionospheric disturbances caused by various solar and geophysical processes [5; 6; 7]. At present, many studies have used Global Positioning System (GPS) total electron content (TEC) to investigate the disturbance characteristic of the ionosphere in different space environments [8; 9; 10; 11; 12; 13; 14; 15; 16]. Many researchers have conducted in-depth studies on the response performance of the ionosphere during different geomagnetic storms [17; 18; 19; 20; 21; 22; 23]. [PERSON] et al. [24] have used the ground-based GPS-derived TEC data to analyze the ionospheric response in each longitudinal sector (Asian, African, American, Pacific) during the St Patrick's Day storm in 2015. Moreover, [PERSON] et al. [16] have studied some phenomena of interest over equatorial and low-latitude ionospheric regions in the Brazilian sector through the analysis of vertical TEC maps. [PERSON] et al. [25] have selected the average rate of change in TEC index (ROTI) calculated from GPS data as a proxy for the ionospheric irregularities to investigate the characteristic of quiet and storm time irregularities over the African ionosphere. Additionally, [PERSON] et al. [26] have used the GPS-TEC observations of a low-latitude RASH station in Saudi Arab to investigate the ionospheric response to severe and strong geomagnetic storms. The ionosphere can be assumed to be a single layer model (SLM) at a certain height from the ground, and the intersection of the signal propagation path of the satellite-station and the SLM is named the ionospheric pierce point (IPP) [27]. Due to the moving ionosphere pierce point of GPS satellites, GPS TEC data fail to directly reflect the fine variations of ionospheric TEC at a fixed IPP over a large time scale [28]. [PERSON] et al. [29] have demonstrated that the acquired TEC series from regional or global ionospheric models contain considerable temporal-spatial variation information and have low precision which is about several TEC Units (TECU). The geostationary orbit satellites have the natural advantage of quasi-invariant ionospheric pierce points compared to GPS satellites.