Modulation of the TEC in the Midlatitude Region by ULF Waves: Preliminary Conjunctional Observations between LFWR and GNSS in the Chinese Meridian Project

 

Previous research has established that in geospace, the total electron content (TEC) in the ionosphere can be modulated efficiently by ultralow frequency (ULF) waves in high-latitude regions. However, the correlations between TEC variations and ULF waves in middle-latitude and low-latitude regions remain inadequately explored. In this study, using ground-based magnetometer data from the Chinese Meridian Project, we identified ULF wave events within Pc4 frequency bands in the midlatitude region. During the period from July 1 and December 30, 2023, we identified 438 distinct ULF wave events in the Pc4 band, thereby creating a comprehensive ULF wave database. Statistical analysis indicated that Pc4-band ULF wave events predominantly occurred on the dusk side in midlatitude regions. Notably, on August 24, 2023, simultaneous observations of geomagnetic disturbances and TEC disturbances at the similar frequency were recorded, suggesting a potential correlation between Pc4 ULF waves and TEC variations at midlatitudes. Through quantitative analysis, we infer that ionospheric TEC variations were possibly triggered by Pc4 ULF waves during this event.This result provides direct observational evidence of the modulation of the TEC by Pc4 ULF waves in the midlatitude region. These findings broaden our understanding of the coupling between the solar wind-magnetosphere-ionosphere in midlatitude regions, and have the potential significance on evaluating the effect of space weather of this coupling process.