Characteristics of equatorial ionization anomaly (EIA) in relation to transionospheric satellite links around the northern crest in the Indian longitude sector

The poleward gradient of the equatorial ionization anomaly (EIA) introduces more intense propagation effects on transionospheric satellite links in comparison to the equatorward gradient. Characterization of the poleward gradient was performed during March-April, August-October 2011 and March-April 2012 using GPS total electron content (TEC) recorded from a chain of stations located more or less along the same meridian (88.5 degrees E) at Calcutta, Baharampore, Farakka and Siliguri. The poleward gradients calculated on magnetically quiet days at elevation in excess of 50 degrees at 14: 00, 15: 00 and 16: 00 LT were found to have a strong correlation with GPS S-4 observed from Calcutta during post-sunset-to-midnight hours. A threshold value of poleward TEC gradient is calculated above which there is a probability of scintillation at Calcutta with S-4 >= 0.4.