Analysis of the Ionospheric Total Electron Content during the Series of September 2017 Solar Flares over the Philippine - Taiwan Region

Abstract

The Sun produced a series of solar flares during the month of September. There were seven solar flares during the period of 4 September 17 to 10 September 2017. It started with an M5.5 solar flare at September 4, 2017, followed by an X2.2 solar flare on September 6, 2017, and at a later time, an X9.3 solar flare. A M7.3 solar flare occured on 7 September 2017, followed by an X1.3 solar flare on the same day. A M8.1 solar flare on 8 September 2017 happened and it ended with an X8.2 solar flare on 10 September 2017. The X9.3 solar flare of September 2017 is the strongest of the seven consecutive flares originating from active sunspot region 2673. Two of these flares produced a G4 Storm. The first to hit is from the X9.3 flare at ~22 UT of 6 September 2017 and the other from a M7.3 flare at ~13 UT of 8 September 2017. The series of continuous bombardment of coronal mass ejections and solar flares caused enhancements in the total electron content (TEC) as observed from ground based International GNSS Service (IGS) receivers. A 15-day observation period from 1 September 2017 to 1 September 2017 is selected such that comparison between the quiet and disturbed periods of the ionosphere can be observed during the series of flares. There are five International GNSS Service (IGS) stations selected over Philippines and Taiwan such that a latitudinal variation over the equatorial regions are highlighted. This storm caused an enhancement of about ~15 TEC units (TECU), (1 TECU = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> electrons / m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) as measured on International GNSS Service (IGS) stations along the Taiwanese and Philippine sectors. This agrees with the TEC observations made by Yasyukevich et al. (2018) at middle latitude regions wherein an increase of ~4 TECU is observed on the X2.2 flare, ~10 TECU during the X9.3 flare, and ~15 TECU at low latitudes.