7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Ionospheric Plasma Anomaly Using GPS TEC Measurements Over Nepal
Narayan P. Chapagain1 and Basu Dev Ghimire2
1Department of Physics, Amrit Campus, Tribhuvan University, Kathmandu, Nepal
2
St. Xavier’s College, Maitighar, Kathmandu, Nepal
e-mail (speaker): npchapagain@gmail.com
Ionospheric concentration can be measured as the total
electron content (TEC) i.e. the total number of electronspresent per square meter along a path between a radiotransmitter from a satellite and a receiver. The TEC datafor this study are acquired from the UNAVCO GPSnetwork, which is widely distributed across Nepal. Theionospheric TEC fluctuation is primarily influenced byterrestrial, geomagnetic, and solar activities. This talkcovers such ionospheric variabilities using the GPS TEC
measurements over Nepal [1]. The TEC data from 53 GPSstations from Nepal are extracted for the long period (19years) from 2000 to 2019 to study the trend of theionospheric variability over Nepal with the comparison
study with other ionospheric models. We have also
developed Artificial Neural Network (ANN) models topredict ionospheric behaviour over Nepal. We compared
the ANN model with existing models IRI-2016 andNeQuick- 2 models and found good agreements with theIRI-2016 model than the NeQuick-2 model as illustrated
in Figure 1.
Moreover, the ionospheric anomalies using the TEC data
during solar eclipse as well as before and after the great
Gorkha Earthquake in Nepal (28.23°N, 84.73°E) with amagnitude of 7.8 on April 25, 2015 have been analyzed.
The eclipse-triggered consequences on TEC and hence
metrological parameters in response to the solar eclipse inFigure 1. Percentage deviation of NeQuick, IRI-2016
and NN from GPS-TEC.

different eclipses have been investigated at different solareclipse events [2]. Similarly, diurnal VTEC variations(blue solid line) from a station nearby earthquake
epicentre, upper bound, (UB) (dot-dash blue line), Lowerbound (LB) (dot-dash red line), and the vertical pinkdashed line as earthquake day (o day) are shown in Figure
2. The arrows represent the anomalous TEC variation. Asignificant positive anomaly penetrating the upperboundary layer was seen on April 16th, 23rd, and 24th,
which correspond to the ninth, second, and first days
before the earthquake, respectively [3].
Keywords: Total electron content, Ionospheric anomaly,Superstorms, Earthquake.
References[1] Ghimire, B. D., Gautam, B., Chapagain, N. P., &Bhatta, K. (2022). Annual and semi-annualvariations of TEC over Nepal during the period of
2007–2017
andpossibledrivers. Acta
Geophysica, 70(2), 929-942.
[2] Ghimire, B. D., Silwal, A., Chapagain, N. P., Gautam,S. P., Poudel, P., & Khadka, B. (2022). GPS
observations of ionospheric TEC variations overNepal during 22 July 2009 solar eclipse. EUREKA:
Physics and Engineering (2), 3-1.
[3] Ghimire, B. D., & Chapagain, N. P. (2022).
IonosphericAnomalies
DuetoNepal
Earthquake-2015 as Observed from GPS-TEC
Data. Geomagnetism
andAeronomy, 62(4),460-473.

Figure 2. VTEC observed for the period of one month April 10(-15) to May 11 (16),) 2015 from a station nearby epicenter ofGorkha Earthquake.