Tracking tsunami propagation and Island's collapse after the Hunga Tonga Hunga Ha'apai 2022 volcanic eruption from multi-space observations.

The quantity and accuracy of satellite-geodetic measurements have increased over time, revolutionizing the monitoring of tectonic processes. Global Navigation Satellite System (GNSS) and satellite radar signals provide observations beyond ground deformation, including how earthquake and tsunami processes affect variations in the ionosphere. Here, we study the Hunga Tonga Hunga Ha'apai (HTHH) volcanic eruption 2022 and its associated tsunami propagation with the analysis GNSS derived Total Electron Content (TEC), Synthetic Aperture Radar (SAR) Sentinel-1 data, complemented with tide gauge observations. We utilize GNSS sites data within a ~ 5000 km radius from the volcanic eruption for estimating the ionospheric perturbation as Vertical TEC. We give evidence on the detection of acoustic gravity, internal gravity, and atmospheric Lamb waves signatures in the TEC perturbation. In particular, the internal gravity waves that concentrated in the southwest of Tonga, directly correlates with the observed tsunami propagation direction as accounted by the tide gauge measurements. However, the acoustic gravity wave signature in the TEC is dominant in the north direction suggesting a surface deformation, which could be verified using Sentinel-1A SAR amplitude data. The analysis presented herein shows that within 5 h of the volcanic eruption, the central part of the HTHH island landscape disappeared with the biggest explosion. The unprecedented detail resolved by integrating satellite data yields previously unknown details of the deformation of the 2022 HTHH volcano eruption.

Rare observations of sprites and gravity waves supporting D, E, F-regions ionospheric coupling.

We report rare simultaneous observations of columniform sprites and associated gravity waves (GWs) using the Transient Luminous Events (TLEs) camera and All-sky imager at Prayagraj (25.5° N, 81.9° E, geomag. lat. ~ 16.5° N), India. On 30 May 2014, a Mesoscale Convective System generated a group of sprites over the north horizon that reached the upper mesosphere. Just before this event, GWs (period ~ 14 min) were seen in OH broadband airglow (emission peak ~ 87 km) imaging that propagated in the direction of the sprite occurrence and dissipated in the background atmosphere thereby generating turbulence. About 9-14 min after the sprite event, another set of GWs (period ~ 11 min) was observed in OH imaging that arrived from the direction of the TLEs. At this site, we also record Very Low Frequency navigational transmitter signal JJI (22.2 kHz) from Japan. The amplitude of the JJI signal showed the presence of GWs with ~ 12.2 min periodicities and ~ 18 min period. The GWs of similar features were observed in the ionospheric Total Electron Content variations recorded at a nearby GPS site. The results presented here are important to understand the physical coupling of the troposphere with the lower and upper ionosphere through GWs.

Tsunami detection by GPS-derived ionospheric total electron content.

To unravel the relationship between earthquake and tsunami using ionospheric total electron content (TEC) changes, we analyzed two Chilean tsunamigenic subduction earthquakes: the 2014 Pisagua Mw 8.1 and the 2015 Illapel Mw 8.3. During the Pisagua earthquake, the TEC changes were detected at the GPS sites located to the north and south of the earthquake epicenter, whereas during the Illapel earthquake, we registered the changes only in the northward direction. Tide-gauge sites mimicked the propagation direction of tsunami waves similar to the TEC change pattern during both earthquakes. The TEC changes were represented by three signals. The initial weaker signal correlated well with Acoustic Rayleigh wave (AWRayleigh), while the following stronger perturbation was interpreted to be caused by Acoustic Gravity wave (AGWepi) and Internal Gravity wave (IGWtsuna) induced by earthquakes and subsequent tsunamis respectively. Inevitably, TEC changes can be utilized to evaluate earthquake occurrence and tsunami propagation within a framework of multi-parameter early warning systems.

Ionospheric monitoring with the Chilean GPS eyeball during the South American total solar eclipse on 2nd July 2019.

The impact of total solar eclipse of July 2, 2019 on the Ionosphere is studied using 24 Chilean GPS stations north-south of the totality path. The total solar eclipse passed through Coquimbo region from ~ 16:38 CLT (~ 20:38 UTC) to ~ 16:40 CLT (~ 20:40 UTC) and maximum eclipse was observed ~ 16:39 CLT (~ 20:39 UTC). The total electron content (TEC) derived from GPS signals shows peculiar features. At the totality stations TEC variations are small (~ 0.39 TECu), but it shows significant decrease (maximum ~ 2.24 TECu) for stations located south and increase (maximum ~ 3.89 TECu) for the stations located north of totality of the surface. The wavelet analysis of VTEC timeseries shows the presence of strong atmospheric gravity waves (AGWs) of duration ~ 30 to 60 min at the stations located north of totality. Thus, the results suggest an interplay between eclipse effect on the ionosphere plasma density and eclipse generated AGWs induced plasma density perturbation provided the peculiar features.

Anomalous variations of VLF sub-ionospheric signal and Mesospheric Ozone prior to 2015 Gorkha Nepal Earthquake.

The subject of pre-earthquake ionospheric signatures has always been contentious and debatable. Some of the previous reports have documented unforeseen and unusual variations in some of the atmospheric and ionospheric parameters well before an earthquake. Here, we analyze the ionospheric response from the Indian Subcontinent to Nepal Gorkha Earthquakes occurred between April and May 2015, which were the most powerful and disastrous natural calamities in past ~80 years over the Himalayan region left ~9000 causalities and more than ~20000 people injured with the property damage of the order of several billion dollars. In view of severe earthquakes occurrences, their prior information on the shorter time scales are warranted for mitigation of associated disasters. Here, we report for the first time, a case which shows a strong link in anomalous variations between VLF sub-ionospheric signal and mesospheric ozone prior to both April 25, 2015 (Mw = 7.8) earthquake and its biggest aftershock on May 12, 2015 (Mw = 7.3). Observations show an unusual variation in VLF signals amplitude /shift in terminator time (TT) strongly linked with positive (negative) mesospheric ozone anomaly in D-region altitudes prior to the Gorkha Nepal earthquakes. It is surmised that simultaneous continuous observations of both VLF waves and mesospheric ozone can be considered as an important tool to identify the prior earthquake signatures in the vicinity of the extremely earthquake-prone zone such as Himalayan region. In this context, the current report opens up a new dimension in lithosphere-atmosphere-ionosphere coupling during the earthquake preparation processes itself.

Assessment of Unusual Gigantic Jets observed during the Monsoon season: First observations from Indian Subcontinent.

Gigantic Jets are electric discharges from thunderstorm cloud tops to the bottom of ionosphere at ~90 km altitude and electrically connect the troposphere and lower ionosphere. Since their first report in 2002, sporadic observations have been reported from ground and space based observations. Here we report first observations of Gigantic Jets in Indian subcontinent over the Indo-Gangetic plains during the monsoon season. Two storms each produced two jets with characteristics not documented so far. Jets propagated ~37 km up remarkably in ~5 ms with velocity of ~7.4 × 106ms-1 and disappeared within ~40-80 ms, which is faster compared to jets reported earlier. The electromagnetic signatures show that they are of negative polarity, transporting net negative charge of ~17-23 C to the lower ionosphere. One jet had an unusual form observed for the first time, which emerged from the leading edge of a slowly drifting complex convective cloud close to the highest regions at ~17 km altitude. A horizontal displacement of ~10 km developed at ~50 km altitude before connecting to the lower ionosphere. Modeling of these Gigantic jets suggests that Gigantic Jets may bend when initiated at the edge of clouds with misaligned vertical charge distribution.