VHF scintillation near the equatorial anomaly crest in the Indian sector

Results of amplitude scintillation measurements of a 136 MHz transionospheric signal made from April 1977 to February 1980 are presented. The signal was recorded at Calcutta (23 deg N, 88.5 deg E) near the northern crest of the equatorial anomaly in the Indian sector. Seasonal variations in scintillation at this location are examined, and it is shown that both the level of scintillation and the seasonal pattern are controlled by solar activity. During the period of low solar activity, the scintillation was found to be an essentially local summer phenomenon with the increase in solar activity, the equinoctial occurrence increases and becomes the dominant phenomenon, while the local summer occurrence shows little change. This pattern is related to the variations of the height of the F2 layer at the magnetic equator with solar activity and the confinement of equatorial irregularities within the magnetic field tubes