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Ionospheric anomalies related to the Mw 6.5 Samar, Philippines earthquake

Eroglu Emre

Acta Geophysica

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2023

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Vol. 71, no. 2

601--611

EN

Models belonging to the ionosphere that is directly affected by factors such as solar activity, geomagnetic storm, earthquake, seasonal changes, and geographical location need to be considered altogether. In this sense, the cause of the ionospheric anomalies should be meticulously distinguished from each other. Ionospheric anomalies that occur before or (and) after an earthquake have a serious place in earthquake prediction studies. Total electron content (TEC) is one of the significant parameters to be able to discuss the anomalies of the ionosphere. This essay investigates ionospheric anomalies before and after the Mw 6.5 Samar, Philippines (12.025° N, 125.416° E and November 18, 2003, at 17:14 UT) earthquake. The paper analyzes anomalies with the aid of the TEC (TECU) map. In the paper, the time-domain TEC variables are transferred to the frequency-domain for observing some clues-peaks by short-term Fourier transformation spectral analysis. The discussion handles the effect of the solar activity with the F10.7 (sfu) index and the effect of geomagnetic storms with Bz (nT), v (km/s), P (nPa), E (mV/m), Kp (nT), and Dst (nT) parameters (index). The lower and upper boundaries of the TEC map obtained from the International Reference Ionosphere (IRI-2016) are calculated with the help of median and standard deviation. The boundary-setting process is named statistical analysis. TEC data exceeding the boundaries are marked as anomaly data. According to the paper, 11-day anomalies (9-day of which belong to pre-earthquake) are detected. Probably, the anomalies observed on November 6, 7, and 12 belong to the Samar earthquake.

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Seasonal variation of quiet time TEC over West and Central African equatorial/low latitude ionosphere (2011–2014)

Akala Andrew Oke-’Ovie, Oyedokun Oluwole Johnson, Bello Damilola

Acta Geophysica

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2021

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Vol. 69, no. 6

2483--2495

EN

This study investigates seasonal variation of quiet-time total electron content (TEC) over West and Central African equatorial/low-latitude ionosphere during years 2011–2014. We used TEC data obtained at five African equatorial/low-latitude GPS stations, namely; Yamoussoukro (geographic coordinates 6.87° N, 5.24° W; geomagnetic coordinates 2.84°S, 67.41°E) [Ivory Coast], Cotonou (6.37° N, 2.43° E; 3.09° S, 74.52° E) [Benin Republic], Accra (5.55° N, 0.02° W; 3.50°S, 73.13°E) [Ghana], Yaoundé (3.87°N, 11.52°E; 5.29°S, 83.13°E) [Cameroon] and Libreville (0.39°N, 9.45°E; 7.99° S, 80.84°E) [Gabon]. Diurnally, at all the stations, TEC consistently reached maximum at around 1400–1600 LT and minimum at 0600 LT. Surprisingly, contrary to the notion that on season-by-season analysis, TEC over the African equatorial/low-latitude region usually attains maximum during equinoxes, in 2011 and 2013, over West and Central African low-latitude region, TEC attained maximum values in December solstice. In 2012 and 2014, highest TEC values were recorded in equinoxes. Overall, June solstice consistently recorded the lowest values of TEC over West and Central African equatorial/low-latitude region. TEC showed solar activity dependence: highest in 2014 and lowest in 2011. TEC also showed clear evidence of higher electron density at Libreville (inner flank of the southern Equatorial Ionization Anomaly (EIA) crest) than at Yamoussoukro (EIA trough). These results would be helpful in developing new predictive models or validating the existing models for the West and Central African equatorial/low-latitude ionosphere.

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A statistical analysis of seismo‑ionospheric TEC anomalies before 63 Mw ≥ 5.0 earthquakes in Turkey during 2003–2016

Şentürk E., Çepni M. S.

Acta Geophysica

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2018

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Vol. 66, no. 6

1495--1507

EN

In this study, pre-seismic and post-seismic total electron content (TEC) anomalies of 63 Mw ≥ 5.0 earthquakes in Turkey (36°–42°N, 26°–45°E) were statistically investigated. The largest earthquake that occurred in Turkey during 2003–2016 is the Mw 7.1 Van earthquake on October 23, 2011. The TEC data of epicenters is obtained from CODE-GIM using a simple 4-point bivariate interpolation. The anomalies of TEC variations were determined by using a quartile-based running median process. In order to validate GIM results, we used the GPS-TEC data of available four IGS stations within the size of the Van earthquake preparation area. The anomalies that are detected by GIM and GPS-TEC show a similar pattern. Accordingly, the results obtained with CODE-GIM are reliable. The statistical results show that there are not prominent earthquake precursors for Mw ≤ 6.0 earthquakes in Turkey.