Observation of ionospheric irregularities around midnight and post-midnight near the northern crest of the Equatorial Ionization Anomaly in the Indian longitude sector: Case studies

Multistation and multi-technique observation of equatorial ionospheric irregularities from locations over the magnetic equator through the northern crest of the Equatorial Ionization Anomaly (EIA) and beyond is one of the important objectives of the Indian CAWSES program. For this purpose, multistation observational campaign was conducted during September 2011, April 2012 and September 2012 involving GPS TEC and S-4 from Calcutta situated virtually underneath the northern crest of the EIA, and GPS S-4 measurements from Siliguri, located beyond the northern crest of the EIA. Intense amplitude scintillation observations have been noted around midnight and post-midnight hours on certain GPS links located north of Siliguri with no scintillation patches during pre-midnight period. Satellite links experiencing scintillations from Siliguri were unaffected at Calcutta. Day-to-day variability has been noted in the maximum northern observation of GPS scintillations at different S-4 levels from both Calcutta and Siliguri. Simultaneous observations from Siliguri and Calcutta indicate that post-midnight GPS amplitude scintillations are possibly associated with interaction of traveling ionospheric disturbances from mid-latitudes towards the equator, with transionospheric GPS links contrary to early evening hours when such movement are usually from over the magnetic equator towards the northern and southern crests of EIA. The present paper reports three cases of ionospheric irregularity tracking using the above stations on September 25, 2012, April 12, 2012 and September 11, 2011, all magnetically quiet days. Information related to the variabilities of latitudinal extent of scintillation observations along 88 degrees E meridian at different times during 13-19 UT and different levels of intensities of scintillation could provide useful information for transionospheric satellite link design and Satellite-based Augmentation System (SBAS). (C) 2014 Elsevier Ltd. All rights reserved.