GPS TEC fluctuations over Tromsø, Norway, in the solar minimum

  • Author(s): Wei-Sheng Chen, Chien-Chih Lee, Fang-Dar Chu, and Wai-Leong Teh
  • DOI: 10.3319/TAO.2017.04.24.01
  • Keywords: TEC fluctuations, Aurora, High-latitude irregularities
  • Fp ≥ 50 occurs when irregularities distribute in the E region or in the E and F regions
  • Strong irregularities (Fp ≥ 200) almost only occur in the magnetic disturbance period
  • The Fp variation relates to the sunlight and the magnetotail geometry

This study investigated GPS TEC fluctuations over the high-latitude site, Tromsø, Norway (69.66°N, 18.94°E), in the solar minimum 2007-2008. The TEC fluctuation index Fp that defined by Mendillo et al. (Radio Science, 2000) was adopted to quantify TEC fluctuations, in which 50≤Fp<200 and Fp≥200 respectively represent moderate and strong irregularities. The investigations include the seasonal and temporal variation of Fp; the correlation between Fp and the magnetic indices Kp and AE; the comparisons between Fp and the ionospheric electron density observed by the Tromsø incoherent scatter radar and COSMIC. The results are that Fp≥50 occurred frequently in all seasons but Fp≥200 occurred more frequently in the equinoctial months; Fp≥50 mainly occurred in 18-04 LT, and maximized around 22 LT in the equinoctial months; The linear correlation between Fp and Kp was poor but that between Fp and AE was moderate; The maximal Fp and the percentages of Fp≥50 and Fp≥200 increased with Kp and AE; Fp≥200 is nearly negligible when Kp<4; The high electron density structure that resulted from the auroral activity caused Fp≥50 when it located in the E region or extended from the E region to the F region. The findings are that Fp≥50 at auroral region mainly relates to the auroral activity; The Fp seasonal variation can be explained by the effect of sunlight and the geometry of the magnetotail; Occurrence of irregularities and their maximal intensity are increased with Kp and AE; Strong irregularities almost only occur in the magnetic disturbance period; Irregularities in the E region or in the E and F regions both can cause Fp≥50.

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