Solar eclipses offer unique opportunities to study ionospheric responses to sudden changes in solar flux. Numerous studies have explored these effects, but each eclipse presents distinct characteristics (duration, location, time of day, season, atmospheric region) necessitating continued research. Total solar eclipses, caused by the moon completely blocking the sun, lead to near-night conditions, interrupting photoionization and thermospheric heating. This disruption affects the thermosphere and ionosphere, modifying temperature balance, ionization production and loss, and generating atmospheric gravity waves. The production and reduction of ionization are also time-of-day dependent, and ionospheric changes correlate with solar radiation obscuration, exhibiting a delayed response that increases with altitude. Radio remote sensing techniques, particularly GPS-derived Total Electron Content (TEC), are cost-effective tools for monitoring these changes. Previous research using GPS data during solar eclipses has reported TEC decreases; however, this study explores the July 2, 2019, eclipse to examine latitudinal variations in TEC and the role of AGWs.

Previous studies using GPS data during solar eclipses have shown a decrease in TEC. Tsai and Liu (1999) analyzed TEC data from five GPS stations during the October 23, 1999, and March 9, 1999, eclipses over the equatorial region, reporting TEC decreases. Afraimovich et al. (1998) analyzed GPS-derived TEC during the March 11, 1997, eclipse, reporting TEC depression depths of 1–3 TEC units. Liu et al. (1998) observed 40–50% TEC depression during the October 24, 1995, eclipse in the equatorial anomaly region. Beyond TEC decreases, studies have also documented the generation of atmospheric gravity waves (AGWs) during solar eclipses, which can significantly impact satellite-based systems (Jakowski et al., 2005; Nayak & Yiğit, 2018). These previous studies highlight the importance of understanding the complex interplay between the direct effects of solar radiation reduction and the secondary effects of wave generation on ionospheric behavior during a solar eclipse. The current study builds upon this existing research by examining the unique characteristics of the July 2, 2019, eclipse and exploring latitudinal TEC variations in greater detail.

The study utilized data from 24 continuously operating GPS stations managed by the Chilean Centro Sismológico Nacional (CSN). These stations provided dual-frequency (L1 and L2) signals, which were processed to derive TEC values. The July 2, 2019, total solar eclipse's path and obscuration levels were shown using a geographical map, which was helpful in visualization. Eclipse conditions at the ground and 350 km ionospheric height were estimated using the method of Verhulst et al. (2020). The data were processed using the GPS_GOPI software to obtain TEC parameters, and vertical TEC (VTEC) was estimated from line-of-sight TEC (STEC) using a single layer ionosphere model (SLIM) at a peak height of 350 km. Data from July 1st, 2nd, and 3rd, 2019 (18:00–23:00 UTC) were analyzed. Signals with elevation angles >20° were selected to avoid multipath and other non-ionospheric disturbances. VTEC data from all 24 stations were analyzed for PRN 13, focusing on a 3-hour duration (19:00–22:00 UTC) encompassing the eclipse period over the region. Mean (unperturbed) VTEC was calculated from the July 1st and 3rd data to compare with eclipse day values. Wavelet analysis (using the Morlet mother wavelet) was used to analyze high-frequency fluctuations in VTEC after filtering out longer-period variations (greater than 2 hours). Background wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis product were also used. Space weather conditions were also assessed to rule out interference from solar flares or geomagnetic storms.

Analysis of VTEC data from the 24 GPS stations revealed peculiar patterns in TEC variations. At totality stations, changes in VTEC were minimal (~0.39 TECu), but significant decreases (maximum -2.24 TECu) were observed at stations south of the totality path, and significant increases (maximum +3.89 TECu) were observed at stations north of the path. Wavelet analysis indicated the presence of strong AGWs with periods of approximately 30–60 minutes at stations north of the totality path, but not at stations south of the totality path. The observed changes in VTEC started about 30 minutes after the eclipse began and recovered approximately 20 minutes before the eclipse ended, indicating a delayed TEC response to the eclipse. The analysis indicated that there were no solar flares or geomagnetic storms to confound the observations. The background wind data showed a South Westerlies flow in the area of the eclipse during the main phase of the eclipse. This wind was conducive to propagation of AGWs to the North and was likely inhibiting propagation of AGWs to the South. It seems likely that the combination of direct eclipse effects and AGW-induced density variations created the observed VTEC variations. The combination of reduced electron density south of the totality path and enhanced density north of the totality path suggests that the eclipse waves may have been generated like ship wakes.

The observed peculiar VTEC variations—minimal change at totality stations but significant decreases south and increases north of the totality—are novel findings. The study suggests an interplay between the direct effect of the eclipse on ionospheric plasma density and the impact of AGWs generated during the eclipse. The presence of strong AGWs north of the totality path, as revealed by wavelet analysis, coupled with background wind patterns that favored northward propagation, explains the asymmetric TEC variations. The background wind data strongly suggests that the AGWs generated during the solar eclipse propagated more readily towards the north due to the prevailing south-westerlies. The lack of AGWs south of the totality path is likely due to the background wind conditions. These findings underscore the importance of considering both the direct and indirect (AGW-induced) effects of solar eclipses on ionospheric dynamics.

The study presents novel observations of asymmetric TEC variations during the July 2, 2019, total solar eclipse, with significant decreases south and increases north of the totality path. The presence of strong AGWs north of the totality, influenced by background wind patterns, likely played a crucial role in these variations. Future research could investigate the role of eclipse-induced mountain waves, using data from additional sensors (radar/lidar) to confirm this hypothesis.

The study relied on GPS data alone, limiting the ability to independently verify the presence or characteristics of eclipse-induced mountain waves. Further research with complementary datasets from radar or lidar would strengthen the findings and provide a more complete understanding of the observed phenomena. Additionally, the analysis was focused on PRN 13, and utilizing data from additional satellite PRNs could provide further validation of these findings.