Low-Latitude Ionospheric and Geomagnetic Disturbances Caused by the X7.13 Solar Flare of 25 February 2014

On 25 February 2014 at around 00:39 UT, a major solar flare (code: SOL2014-02-25T00:39) erupted at sunspot region AR11990. Using the updated science quality data of GOES-15, it has been classified as an X7.13 solar flare. This gave rise to the electron density changes that affected the strengths of ionospheric electric currents. In this work, the difference in total electron content (TEC), between the TEC during a flare day and a quiet, fitted TEC, $\Delta \mathrm{T}\mathrm{E}\mathrm{C}$, and rate of change of TEC, $dTEC/dt$, are determined to observe electron density changes due to the solar flare over a low-latitude region. These stations are at Quezon City (PIMO) and Taguig City (PTAG). Also, responses in the geomagnetic field component, $\Delta H$, are calculated along with the variations in the equatorial electrojet (EEJ) strength. These are observed at equatorial, Davao (DAV) and Cagayan de Oro (CDO), and off-equatorial, Muntinlupa (MUT) and Legazpi (LGZ), stations. The resulting $\Delta \mathrm{T}\mathrm{E}\mathrm{C}$ values were 1.17–1.97 TECU while $dTEC/dt$ maxima were 0.29–0.48 TECU/min. The $dTEC/dt$ maxima were found to concur with the time the solar EUV reached peak intensity at 00:45 UT, 4 min before the flare (i.e., X-ray) peaked. Furthermore, the $\Delta H$ variations exhibited larger enhancements at the equatorial stations. These are mostly attributed to the EEJ contributing to the geomagnetic field variations. The amplification experienced by the EEJ due to the increased ionospheric conductivity is then reflected in the geomagnetic responses. For the CDO-LGZ stations, the EEJ strength reached ~37 nT, while for the DAV-MUT, this was ~60 nT.