# Effects of Equatorial Plasma Bubbles on Multi-GNSS Signals: A Case Study over South China
[PERSON]  
Zhuhai 519082, China; [EMAIL_ADDRESS] (W.D.) [PERSON]  
1 Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China; [EMAIL_ADDRESS] (X.W. ); [EMAIL_ADDRESS] (X.S. ); [EMAIL_ADDRESS] (W.D.) [PERSON]  
1 Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China; [EMAIL_ADDRESS] (X.W. ); [EMAIL_ADDRESS] (X.S. ); [EMAIL_ADDRESS] (W.D.) [PERSON]  
1 Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China; [EMAIL_ADDRESS] (X.W. ); [EMAIL_ADDRESS] (X.S. ); [EMAIL_ADDRESS] (W.D.) [PERSON]  
1 Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China; [EMAIL_ADDRESS] (X.W. ); [EMAIL_ADDRESS] (X.S. ); [EMAIL_ADDRESS] (W.D.) [PERSON]  
1 Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China; wanzv@mail. The interior of an EPB contains various small-scale irregularities due to a cascade of secondary instability processes and pre-reversal enhancement [8; 11]. Generally, EPBs can extend thousands of kilometers along magnetic field lines in the north-south direction, drift hundreds to thousands of kilometers in the east-west direction, and reach an apex height of 2500 km [12; 13]. The part of the EPB corresponding to the L-band Fresnel scale of 300-400 m will cause enormous degradation in the GNSS signal intensity and loss of lock [14; 15]. As one of the first known effects of space weather, the impact of irregularities on GNSS has been observed worldwide [16; 17]. As early as 1988, [PERSON] et al. [18] analyzed the global distribution of L-band scintillations. Studies on the Brazilian region showed that scintillation follows the seasonal distribution of EPBs [19; 20]. From another perspective, the features of carrier phase cycle slip (CS) and GNSS signals loss of locks (LoLs) over local time, season, spatial distribution, and solar activity dependences closely resemble the characteristics of ionospheric irregularities/EPBs at low latitudes [21; 22; 23; 24; 25; 26]. Many studies have focused on the spatiotemporal relationship between EPBs and GNSS scintillation in the climatological scale. However, how the detailed center and edge parts of the EPB structure affect GNSS signals, and the relationship between the degree of EPB depletion and the GNSS signal quality, are still not well understood. As more GNSS frequencies and ranging signals have become available recently, the response of new frequencies/signal types to the ionosphere has been evaluated to some extent. [PERSON] et al. [27] noted that cycle slips occur more frequently and last longer under strong scintillation (S4 \(>\) 0.6) conditions; moreover, GPS L5 is the most robust, and L2 is the least robust for signal tracking. GPS L2 and L5 are likely to experience deeper signal fading than L1 is [28; 29]. GNSS signals with lower frequencies are more susceptible to strong scintillations, but the S4 index increases linearly with frequency under weak scintillation, which has been verified for both the GPS L1, L2, and L5, and the BDS B1, B2, and B3 frequencies [30; 31]. The type of signal modulation may also affect the scintillation performance, as Galileo E5, which uses Alternative Binary Offset Carrier (AltROC) modulation, has the smallest noise level [32; 33]. Studies have shown that GLONASS L1 is better than L2, and Galileo has the best stability [34; 35]. However, there is still a lack of comprehensive and systematic research about the effects of EPBs on multiple GNSS frequencies/signal types.