Ionospheric scintillation characteristics over Indian region from latitudinally-aligned geodetic GPS observations

Abstract

Ionospheric scintillations pose one of the biggest threats to Satellite-Earth communication links in the communication and navigation systems services whose occurrence characteristics could be explained through the strength of fading (amplitude scintillation index; S4) and the rapidity of the fades (decorrelation time; \U0001d70f0). In the present work, we analyzed the S4 index from a latitudinal array of three geodetic global positioning system (GPS) stations along the Indian longitude sector during the descending phase of the 24th solar cycle. The results show predominant occurrences of scintillations during the post-sunset and nighttime periods indicating the level of scintillations close to equatorial, beyond anomaly crest, and near mid-latitude locations. The strong amplitude scintillations during 2014 and 2015 and their lowest magnitudes during 2016 and 2017 reflect the solar activity dependence of the scintillation occurrences. The directional distribution and 2-dimensional surface sky plots of the S4 index substantiate the occurrence of intense scintillation being more prevalent towards the equatorial location, whereas the weak and moderate scintillations are perceived towards the higher low latitude stations. The occurrences of intense scintillations are confirmed in high solar active years and equinox season at all stations, while the equatorial station presents relatively higher occurrences in winter followed by summer. The summer season witnessed intense occurrences even under moderate to low solar activity years (2016–2017), reflecting the post-midnight occurrences due to meridional thermospheric winds. Moreover, maximum percentage occurrences of weak scintillations in all seasons are evident towards the poleward side, far away from the anomaly crest. The amplitude scintillation frequency during the period is further compared with the solar and geomagnetic indices to substantiate the analysis drawn from the variations. The correlation coefficients between the scintillation index occurrence rate with the solar and geomagnetic in-dices at three GNSS stations provide valuable insights into the relationship between solar activity and scintillation. The results show that the strength and direction of the correlation can vary significantly depending on the specific solar index and location. Thus, emphasize further studies on scintillation occurrences for developing effective forecasting and mitigation models over the Indian low-latitude region.