GPS observations of ionospheric TEC variations over Nepal during 22 July 2009 solar eclipse

Abstract

As the study of ionospheric behavior during various solar activities is an important task, various studies of ionospheric changes during eclipse events have been widely performed in the different regions of the globe. This paper investigates the ionospheric responses to the solar eclipse on 22 July 2009 over Nepal using the total electron content (TEC) measured by dual-frequency Global Positioning System (GPS) receivers. The time-averaged Vertical TEC (vTEC) of ten GPS stations from Nepal is analyzed and it is found that the value of ionospheric TEC decreases due to the reduction of ionizing radiation. In addition, the deviation in the TEC value on eclipse day from the mean vTEC value of the top five quietest days is found to lie in the range ~1–5 TECu at those regions which were associated with the partial eclipse shadow. On the other hand, the region with the total eclipse (BRN2 and RMTE) faced ~6–7 TECu on average reduction in the TEC value. Considering that the eclipse of 22 July 2009 occurred just at sunrise in the Nepalese zone, a maximum reduction of about 5 TECu is very significant. Higher deviation in TEC is therefore linked with the path of totality and the obscuration rate. This study reveals that the ionospheric TEC over Nepal was altered by wave-like energy and momentum transport, as well as obscuration of the solar disc due to the partial and total solar eclipse. Furthermore, the cross-correlation results presented similar type signatures of the eclipse-induced ionospheric modification over Nepal. This research work serves a crucial future reference for the comparative study of change of ionospheric TEC variability over the Nepal region during Eclipse events

Variation in Total Electron Content Over Ethiopia During the Solar Eclipse Events

“…The STEC between a GPS satellite (S) and a ground‐based receiver (R) can be expressed as (Sun et al., 2017), $$$STEC=\int \nolimits_{R}^{S}Ndl$$$ where l is the direction from the receiver to the satellite, and N is the location‐dependent electron density expressed in electron per meter cube. The STEC also can be computed using pseudo‐range and phase data as (Bagiya et al., 2009; Ghimire et al., 2022; Idosa et al., 2023), $$$STEC=\frac{1}{40.3}\times {\left(\frac{1}{L{1}^{2}}-\frac{1}{L{2}^{2}}\right)}^{-1}\times (P1-P2)+TE{C}_{\mathit{CAL}}$$$ where L1 and L2 are two L‐band frequencies, having respective frequencies of 1,575.42 MHz and 1,227.60 MHz, that are transmitted by each GPS satellite. A dual‐frequency GPS receiver examines the difference in ionospheric delay between the L1 and L2 signals as the GPS signal travels through the ionosphere to estimate the TEC value (Bagiya et al., 2009).…”

“…where l is the direction from the receiver to the satellite, and N is the locationdependent electron density expressed in electron per meter cube. The STEC also can be computed using pseudo-range and phase data as (Bagiya et al, 2009;Ghimire et al, 2022;,…”

“…Observations during the total solar eclipse on 21 August 2017, by Pradipta et al (2018), over North America using global positioning system (GPS) TEC and ionosonde data showed substantial reductions (33%-45%) in TEC and ionospheric plasma densities due to the eclipse. Ghimire et al (2022) studied the ionospheric responses to the solar eclipse on 22 July 2009 over Nepal region. They found that the TEC deviated between 1 and 5 TECU from the mean vertical total electron content (VTEC) value of the five quietest days.…”

On the Dynamic Variability of Global Positioning System (GPS) derived Precipitable Water Vapour (PWV) over three regions of Nepal

“…Although there are many studies of PWV conducted in other countries like India and China, very few to none are done in Nepal. However, study of GPS signals and ionospheric parameters are already conducted and results has been published (Ghimire, Gautam, Chapagain, & Bhatta, 2022;Ghimire, Silwal, et al, 2022). This study intends to expand the study of seasonal PWV trends and explain the rain pattern through it.…”

Variation of Total Electron Content in the Quiet and Disturbed Period and Their Correlation with Solar Wind Parameters

“…Cross-correlation is the measurement to establish the relationship between two time series data. Several early researchers considered it as a robust tool to compare multiple time series and employed it to study Relativistic electron flux [44], solar eclipse [45,46,47], solar wind parameters [48], and now also for seismic activities [49]. Fig.…”