Variability of ionospheric scintillation near the equatorial anomaly crest of the Indian zone

Multistation observations of ionosphere scintillation at VHF (250 MHz) and GNSS L1 frequency from three locations - (i) Bokkhali (BOK) (geographic 21.6 degrees N, 88.2 degrees E, dip 31.48 degrees), (ii) Raja Peary Mohan College Centre (RPMC) (geographic 22.66 degrees N, 88.4 degrees E, dip 33.5 degrees) and (iii) Krishnath College Centre (KNC), Berhampore (geographic 24.1 degrees N, 88.3 degrees E, dip 35.9 degrees) - at similar to 1 degrees latitudinal separations near the northern crest of the equatorial ionization anomaly (EIA) of the Indian longitude sector are investigated in conjunction with total electron content (TEC) data and available ionosonde data near the magnetic equator to study fine structure in spatial and temporal variability patterns of scintillation occurrences. The observations are carried out in the autumnal equinoctial months of a high solar activity year (2011). In spite of smaller latitudinal/spatial separation among the observing stations, conspicuous differences are reflected in the onset time, duration, fade rate and fade depth of VHF scintillations as well as in spectral features. Scintillations are mostly associated with depletion in TEC around the anomaly crest and occurrence of ESF near the magnetic equator at an earlier time. Not only the strength of EIA, but also the locations of observing stations with respect to the post-sunset resurgence peak of EIA seem to play dominant role in dictating the severity of scintillation activity. A secondary enhancement in diurnal TEC in the post-sunset period seems to accentuate the irregularity activities near the anomaly crest, and a threshold value of the same may fruitfully be utilized for the prediction of scintillation around the locations. An idea regarding latitudinal extent of scintillation is developed by considering observations at L1 frequency from the GPS and GLONASS constellation of satellites. A critical value of h'F near the magnetic equator for the occurrence of simultaneous scintillation at the three centres is suggested. The observations are discussed considering electrodynamical aspect of equatorial irregularities.