Multi-wavelength (L and S band) study of ionospheric irregularities from an anomaly crest location

This paper reports observation of moderate to intense scintillations, at S band of Indian Regional Navigation Satellite System (IRNSS). During current solar cycle 25, these occurrences are probably being reported for the first time, from a low-latitude station Calcutta (22.58 DEG;N, 88.38 DEG;E geographic; magnetic dip 34.54 DEG;), located near the northern crest of Equatorial Ionization Anomaly. Efforts have been made to analyze irregularity dynamics at IRNSS S band, along with a comparative study at GNSS L1 to characterize occurrence and evolution of multiscale irregularity structures. Power spectral analysis technique has been applied on recorded C/N-O,N- during scintillation patches, to measure east-west zonal drift velocity. Efforts are also made to study intensity of signal perturbation at L5 frequency of IRNSS, compared to S band, when observed simultaneously, during period of ionospheric scintillation. Concurrent irregularity dynamics at L1, L5, and S band, particularly from a low-latitude station, has not been extensively reported earlier. Data is recorded during vernal equinox (February-April 2022) of current solar cycle. Results of this study show occurrence of simultaneous night-time scintillation at L1, L5, and S band. East-west zonal drift velocity of irregularity, obtained from S band observations are found to decrease with the progress of time during 20-23 LT having a maximum value of 125 m/s. At GNSS L1, hourly average value of the velocity, is observed to maximize during 20-21 LT. Simultaneous observation of scintillation effects at L5 and S band of IRNSS led to loss-of-lock at L5, while no such occurrence was noted at S band.