Study on Correlation Between GPS-TEC and Geomagnetic Parameters Over Nepal in The Year of 2016

In recent years, GPS derived TEC has been widely used to study the ionosphere and its behavior. The variability of ionospheric TEC depends on various conditions including the geomagnetic activities. This paper attempts to answer the question of how the TEC generally correlates to various geomagnetic indices. In this presentation, vertical Total Electron Content (VTEC) derived from three different GPS stations from Nepal, namely, Kathmandu (NAST) (27.656°N, 85.327°E), Jomsom (JMSM) (28.805°N, 85.743°E) and Sindhuli (SNDL) (27.384°N, 85.798°E), from December 2015 to November 2016 was used. The geomagnetic storm indices such as disturbance storm time index (DST) and Sigma Bz values were extracted from NASA's OMNIWEB Data Explorer. Then classified according to local seasons, namely, Winter (December 2015-Feburary 2016), Spring (March-May 2016), Summer (June-August 2016) and Autumn (September-November 2016). Two types of correlations were investigated between the TEC and geomagnetic indices: 1) correlation between the maximum TEC value in a day, within a season and the values of DST and Sigma Bz at that time (i.e. amplitude correlation), and 2) the hourly correlation between TEC values in a day and the DST and Sigma Bz values within a season (dynamic correlation). The results showed that generally, the magnitude of the correlation coefficients derived in this manner were below 0.34 for DST index and below 0.24 for Sigma Bz for the amplitude correlation. Most amplitude correlation values were extremely low but autumn season showed moderate correlation values across all stations for DST index. On the other hand, Sigma Bz had much lower amplitude correlation values, but certain spikes were seen during winter season. For dynamic correlation, however a much stronger correlation was seen during certain period. The maximum value for the magnitude of dynamic correlation for DST was seen to be 0.62 and for dynamic correlation for Bz was seen to be 0.4 from Sindhuli station during Autumn season. Generally, a moderately negative correlation was seen between DST and TEC and a very small positive correlation was seen between TEC and Sigma Bz almost in all seasons.