## 1 Introduction  
The variation of the total electron content (TEC) of earth's ionosphere can be mainly attributed to geomagnetic disturbances, during which magnetosphere electric fields penetrate into the ionosphere, changing the electron density and leading to ionosphere reactions. Linked with the interplanetary magnetic field, the dayside positive ionospheric responses are generated by the eastward prompt penetration electric field and the equator-ward neutral wind, while the negative ionosphere responses are generated by the more complex compositional effects of neutral winds. Moreover, with the energy injection by Joule heating at the polar region, the ionosphere responses for the geomagnetic disturbances usually initiate from the polar region and then propagate to the middle and low latitudes, accompanied with the modification of the local atmosphere conditions, causing ionosphere anomalies which are comprehensively observed and discussed. Generally, ionosphere responses to geomagnetic storms can be concluded into three categories: (1) **TEC variations and the expansion of the aurora oval due to particle precipitation**. TEC and Rate of TEC Index (ROTI) behaviors in high latitudes under long-lasting particle precipitations have been analyzed, indicating enhancements of the ROTI accompanied with TEC variations [1]. Researchers have also gotten similar results by studying the Global Navigation Satellite System (GNSS) data collected in Canada during moderate storms in 2012 [2]. (2) **The expansion of the equatorial ionization anomaly (EIA), further leading to hemisphere asymmetry in response to the storm**. For the case of the 2015 St. Patrick's Day storm, positive storm effects were found and considered to be related to different inputs of energy indicated by the AE magnetic index [3]. The negative storm effects were discovered mainly in the middle and high latitudes and were further verified with BDS observations [4]. For the 2013 October case, ROTI inhibition was discovered during the storm phase [5]. The research in Reference [6] indicated that the prompt penetration of the electric field (PPEF) played an important role at the beginning of the storm in the equatorial and low latitude regions. The vertical TEC (VTEC) behaviors during the storm were both influenced by PPEF and the disturbance dynamo electric field (DDEF). (3) **The redistribution of particle densities above the ionosphere and the reshaping of ionosphere irregularities**. According to [PERSON] criterion, the triggering of the ionosphere irregularities under geomagnetic storms closely depends on the geophysical location, the local time, and the geomagnetic intensity. This indicates that the effects of the geomagnetic storm on the ionosphere irregularities can be double-sided [7;8]. The positive effects trigger plasma bubble generation and severe ionosphere scintillations that are observed during geomagnetic storms. Middle-latitude ionosphere irregularities were investigated in association with the November 2004 storm [9]. A supper bubble was discovered from the June 2015 storm, with evidences of ion density decreasing and ROTI enhancements [10]; the negative effects for the evolutions of the plasma bubble were also discovered during the St. Patrick's Day storm, stating that the force of the storm even blew away existing irregularities [11]. Another study was also conducted on the formation of the equatorial spread F, where irregularities and bubbles usually existed under intensive geomagnetic storms [12]. Based on the above responses, the change of ionosphere due to geomagnetic storms can further generate spatial and temporal ionosphere gradients, presented by the temporal discontinuity and spatial decorrelation of the ionosphere delay. Those consequences have influences on trans-ionosphere satellite ranging and positioning signals, causing ranging errors for ground-based argumentation systems (GBAS) [13; 14; 15].