Comparative analysis of ionosonde spread F and GPS ionospheric scintillations over Hyderabad

Abstract

Investigation of the relationship between ionospheric scintillations and equatorial spread F (ESF) during adverse space weather conditions is of paramount significance for developing ionospheric scintillation mitigation strategies for Global Navigation Satellite System (GNSS) receivers. In this paper, we present correlation analysis between equatorial spread F (ESF) and L-band amplitude scintillations conducted at low-latitude Hyderabad station (17.47° N, 78.57° E) during the severe geomagnetic storm event of 17 March 2015 (St. Patrick's Day). Hyderabad location comes under the region between the magnetic equator and the northern crest of equatorial ionization anomaly (EIA). ESF information is derived from ionograms of ionosonde located at the Tata Institute of Fundamental Research (TIFR) Balloon Facility, Hyderabad, whereas amplitude scintillation index (S4) data have been obtained from the GPS receiver at Hyderabad (GAGAN network). Intense spread F (SSF) signatures were observed during post-sunset hours of 16 March (pre-storm day) and 17 March (storm day), 2015, where the spread F (SF) index is higher than 1 MHz. GPS satellite vehicle with pseudo-random noise code (PRN) 24 experienced strong scintillation (S4 = 1.06) at 18:53 UT on the pre-storm day of 16 March 2015. GPS PRN 30 satellite was affected severely on 17 March (storm day), when the observed S4 index is 0.99. Development of ESF and subsequent scintillations are due to the strong eastward prompt penetration electric fields over the Indian region. The inhibition of spread F and scintillations noticed on 18 March 2015 are because of disturbance dynamo electric fields and disturbance winds. The SSF occurrences were well correlated with scintillation index values at Hyderabad station, India. Variations of the virtual height of the F layer (h′F) and drift velocity (Vd) are related to the S4 values during the period of interest. The outcome of the preliminary results would be useful for development of ionospheric scintillation prediction algorithms for GPS users.