Ionospheric VTEC variations over Pakistan in the descending phase of solar activity during 2016–17

Abstract

This paper presents the variations of the ionospheric Vertical Total Electron Content (VTEC) observed over Pakistan at the verge of low- to mid-latitude regions during the years 2016–17 of the descending phase of the solar cycle. The study is conducted by considering the ionospheric measurements from dual frequency Global Navigation Satellite System (GNSS) receivers permanently installed at Islamabad (geomagnetic Lat. 25.44°N, Long. 148.83°E), Multan (geomagnetic Lat. 22.13°N, Long. 146.91°E) and Quetta (geomagnetic Lat. 22.50°N, Long. 142.73°E). The diurnal, seasonal and annual variations of VTEC over Pakistan are examined in the context of geomagnetic storm during 2016. This study shows high values during the March and September equinoctial months and lower values during the summer and winter solstices from VTEC estimations. Furthermore, higher, moderate and lower VTEC variations are recorded during the seasonal analysis in the equinoxes, summer solstice and winter solstice, respectively. The maximum seasonal VTEC values are observed during the post-sunrise hours between 11:00–17:00 LT and the minimum values are recorded during the post-midnight hours between 02:00–05:00 LT during each season at all the stations. Moreover, the effect of geomagnetic storm is detected in the ionospheric VTEC of the three different stations, which occurred on 13 October 2016. The initial phase of the storm caused no prominent effect on VTEC, while an enhancement in VTEC is registered in the main and recovery phases of the storm. The recorded VTEC from three different stations is correlated with the indices of the geomagnetic storm.