Occurrence of ionospheric scintillations under different solar and geomagnetic conditions over low latitude station Varanasi

Abstract

In the present study, occurrences of amplitude scintillations during the ascending phase of the 25th solar cycle from November 2020 to March 2023 are studied over the equatorial anomaly region Varanasi (latitude 25.31 N, longitude 82.97 E, magnetic dip Lat. 16.2 N). Multi-frequency Global navigation satellite system (GNSS) receiver is used to study the occurrence of amplitude scintillation index S4. Diurnal, monthly, and seasonal occurrence characteristics of the S4 index are presented. The scintillation occurrence is observed during nighttime and daytime but is more probable during nighttime. It is observed that maximum scintillation occurred during the equinox season for the solar moderate period whereas the highest occurrence is in summer during the low solar activity period. The highest scintillation occurrences during the summer solstice for a period of low solar activity condition is rare and could be attributed to the gravity waves (GWs) generation due to the weather phenomena in the lower atmosphere. GWs could act as a seeding perturbation in electron density, affecting the growth of ionospheric irregularities through Rayleigh-Taylor instability. The solar flux index (F10.7) is compared with the percentage occurrence of scintillation for the low and moderate solar activity periods to observe the effect of solar activity on scintillation occurrences. Overall, the scintillation occurrence increases with increasing solar activity. To study the effect of geomagnetic storms on scintillations, we have considered seven moderate and intense geomagnetic storms grouped in three categories that occurred during solar cycle 25. It is observed that the occurrence of scintillations is enhanced for the storms with the recovery phase starting at post-midnight. The probability of occurrence of scintillation during the night hours is decreased when the geomagnetic storm occurs during the daytime.