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

A Das,A Paul,K S Paul,S Halder,K Basu

doi:10.5194/angeo-32-91-2014

Abstract

Abstract. 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° E) at Calcutta, Baharampore, Farakka and Siliguri. The poleward gradients calculated on magnetically quiet days at elevation in excess of 50° at 14:00, 15:00 and 16:00 LT were found to have a strong correlation with GPS S4 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 S4 ≥ 0.4.

Highlights

The impact of a developed equatorial ionization anomaly (EIA) in the afternoon hours on the subsequent development of equatorial ionization density irregularities during postsunset hours was suggested by Raghavarao et al (1988) and validated by several workers (Valladares et al, 2001, 2004; Ray et al, 2006; Rama Rao et al, 2006; Ram et al, 2006; Nava et al, 2007)
While a lot of emphasis has been given to the adverse effects of the sharp gradient of the EIA from the magnetic equator towards the northern crest on SBAS (Satellite Based Augmentation System) operations, very little work has been done on the sharper gradient of ionization existing beyond the northern crest towards the midlatitudes
The issue that concerns to the SBAS system designers is the steeper gradient of the EIA poleward of the northern crest rather than the equatorward side as estimation of an optimum grid size and group delays will be different on either side of the crest

Summary

Introduction

The impact of a developed equatorial ionization anomaly (EIA) in the afternoon hours on the subsequent development of equatorial ionization density irregularities during postsunset hours was suggested by Raghavarao et al (1988) and validated by several workers (Valladares et al, 2001, 2004; Ray et al, 2006; Rama Rao et al, 2006; Ram et al, 2006; Nava et al, 2007). In order to find a correlation between the poleward gradient of TEC calculated during the afternoon hours with post-sunset occurrence of GPS scintillations at Calcutta, situated at the northern crest of EIA, S4 values measured on GPS links within a subionospheric swath of ±1◦ in latitude and longitude around Calcutta were used.

Results

Conclusion