## 1 Introduction
In recent years, the Geostationary Earth Orbit (GEO) satellites of the BeiDou Navigation Satellite System (BDS) have provided a new opportunity to investigate continuous ionospheric TEC variations at a fixed IPP during long-term monitoring. [PERSON] et al. [3] have shown that the BDS-GEO observations, as a powerful data source, can investigate the ionospheric response to geomagnetic storms effectively. [PERSON] et al. [30] have used the BDS-GEO dual-frequency observations to derive the VTEC, and found that the phase-smoothed B1/B2 code observations achieved much higher precision. [PERSON] et al. [31] have demonstrated the strong capability of the BDS-GEO satellites for studying equatorial ionosphere variability from four stations. [PERSON] et al. [32] have focused on the temporal-spatial variation of the ionospheric TEC derived from BDS-GEO satellites over the Asia-pacific area. [PERSON] et al. [33] have focused on the variations of ionospheric irregularities and medium-scale traveling ionospheric disturbances at mid-latitudes over central China by BDS GEO satellite observations. [PERSON] et al. [34] have used the ROTI index calculated from BDS GEO observations to analyze the ionospheric plasma bubble features at low latitudes. [PERSON] et al. [35] have investigated the local time, seasonal and latitudinal variation characteristics of ionospheric TEC perturbation by using a chain of BDS GEO TEC along longitude \(\sim\)110\({}^{\circ}\)E.  
An intense geomagnetic storm caused by intense coronal mass ejections (CME) and a high-speed solar wind stream occurred during 25-26 August 2018 [36]. The large enhancements of daytime TECs, along with positive responses at the Asian-Australian, American and African sectors were detected during the main and recovery phase of the storm on 26-29 August 2018 [37]. In addition, the long-duration daytime TEC enhancements were observed during the recovery phase of the storm in September 2017 [38]. This unique event is quite different from the regular performance of ionospheric TEC during the quiet geomagnetic activity. [PERSON] et al. [39] used multiple observations to study the possible cause of large TEC enhancements during the storm recovery phase on 27-29 August 2018. [PERSON] et al. [40] observed a dramatic positive ionospheric storm in the American sector during the recovery phase on 27-29 August 2018 by investigating the F region behavior of the ionosphere. [PERSON] and [PERSON] [41] have studied variations of ionospheric parameters over the European sector during this magnetic storm, and found some different results that the negative ionospheric responses are observed during the recovery phase. In this work, we have used GEO satellite observations and ionosonde data to investigate the low-latitude ionospheric responses in the eastern hemisphere along longitude sectors during this strong geomagnetic storm. In addition, the electron density Ne of the ionosphere from the Swarm A and C satellites is introduced to analyze the temporal-spatial variation of the electron density Ne over low-latitude regions. The Swarm is a constellation mission for earth observation launched by the European Space Agency (ESA). It consists of two lower pairs of side-by-side satellites A and C at 470 km altitude, and one higher satellite B flying at 520 km altitude. The column density ratio of O to N\({}_{2}\) from the Global Ultraviolet Imager (GUVI) instrument is also used to discuss the possible relationship between ionospheric responses and thermosphere composition changes during the storm period.