Ionospheric total electron content response to September-2017 geomagnetic storm and December-2019 annular solar eclipse over Sri Lankan region

The geomagnetic storm and solar eclipse are two important transient phenomena that crucially influence the quiet time ionospheric behavior over the low latitudes. The present study investigates the ionospheric total electron content response to the September-2017 geomagnetic storm and December-2019 annular solar eclipse from global navigation satellite system derived total electron content observations over the Sri Lankan equatorial and low latitude region. Four global navigation satellite system stations at Jaffna (1.21(0) N), Colombo (1.52(0) S), Kegalle (1.20(0) S) and Kalutara (1.84(0) S) within Sri Lanka were used for the study. The results accentuate a noticeable increase/decrease in the ionospheric total electron content during both the events. The results confirm a positive ionospheric storm effect during the solar flare associated severe geomagnetic storm in September 2017 with the total electron content enhancement of about similar to 11 total electron content units during the main phase of the storm with the highest variation at Kegalle. The abrupt vertical total electron content flipping during the storm are attributed to the prompt penetration electric fields followed by the disturbance dynamo electric fields during the recovery phase. Concerning the annular solar eclipse in December 2019, the four major features such as pre-ascension, major depression, sunset ascension, and secondary depression were perceptible in the total electron content variation at all stations. Moreover, the ionosphere experienced a clear vertical total electron content depletion of about similar to 4 total electron content units during the maximum phase of the eclipse with a percentual deviation of 23% over Jaffna and 15% over Colombo than the average quiet day values, indicating an interplay between photoionization production and recombination due to temporary solar interruption. The results would strengthen the understanding of ionospheric variability of the southern hemisphere in the Indian longitude sector.