RECENT VOLCANIC ERUPTIONS 2021 SERIES

Geomagnetic activities during this period were calm, and the daily Kp index remained within the range 0.7–2.0 ().

RECENT VOLCANIC ERUPTIONS 2021 SERIES

Figure 2 compares the TEC time series 4:30–8:00 UT obtained using the QZSS geostationary satellite (J07) from the 0603 station over five consecutive days, August 11–15, 2021. Basic procedures in the GNSS-TEC studies follow Heki ( 2021). We converted the L1 and L2 carriers into total electron contents (TEC) (we also try L5 as discussed later in this article). This indicates that these satellites are nearly fixed in the sky when viewed from the ground station. SIP trajectories of the QZSS satellites are much shorter than other GNSS, and the SIP of J07 hardly moves. Figure 1c–f shows sub-ionospheric point (SIP) trajectories of these four GNSS as viewed from 0603, Hahajima. Although the two stations in Iwojima track only GPS satellites, the three other stations track GLONASS, Galileo, and QZSS in addition to GPS. Within ~ 300 km from the Fukutoku-Okanoba volcano, there are five GEONET stations on three inhabited islands, P2 on Chihijima, 0603 on Hahajima, and 06 on Iwojima (Fig. We use GNSS raw data files from GEONET (GNSS Earth Observation Network) run by Geospatial Information Authority (GSI), Japan.

A few months later, huge amount of floating pumice reached the coast of the Ryukyu Islands, southwestern Japan, hindering fishing and ferry navigation in that region. The 2021 eruption is one of the largest eruptions in Japan in terms of the total mass of the ejecta. According to Japan Meteorological Agency (JMA), the eruption column as high as ~ 16,000 m lasted from August 13, 00 UT to August 14, 19 UT (JMA 2021).įormation of an island with a diameter of ~ 1 km was confirmed on August 15, but this new island has been shrinking day by day. A strong eruption with Volcanic Explosivity Index (VEI) 4 started on August 13, 2021. The latest volcanic activity started in 2020 February, when the sea water of this area changed its color to yellow-green. In this study, we take this advantage in discussing the frequency content and temporal decay of the oscillation caused by a recent Type-1 ionospheric disturbance case by a volcanic eruption in Japan. This offers a rare opportunity to observe the TEC oscillation caused by a Plinian volcanic eruption lasting for hours without disruptions of data. These satellites stay longer within the view of a station (~ 8 and 24 h a day for J01-03 and J07, respectively). On the other hand, Quasi-Zenith Satellite System (QZSS), the Japanese satellite system for positioning, is composed of three satellites with quasi-zenith orbits (J01, J02, J03) and one geostationary orbit satellite (J07). GPS satellites employ orbits with periods of a half sidereal day and can stay within the view of a ground station only for periods shorter than 4–5 h. Global Positioning System (GPS) has been the main GNSS used to study ionospheric TEC. Type-1 cases have never been found in Japan except the 2009 eruption signal of the Sarychev Peak Volcano, Russia, from stations in northern Japan (Shestakov et al. ( 2021) compiled the recent cases of such Type-1 and Type-2 disturbances, respectively. Both types propagate outward with a speed of 0.8–1.0 km/s, the acoustic wave velocity in the ionospheric F region. Type-2 disturbances occur 8–10 min after Vulcanian explosions of volcanoes as single N-shaped changes of TEC. Type-1 disturbances are caused by continuous Plinian eruptions and often last for hours. 2016), and (Type-2) short pulses of TEC changes (e.g., Heki 2006). Such responses have two distinct types (Type-1) harmonic oscillations of TEC (e.g., Nakashima et al. GNSS-TEC observations enabled us to detect ionospheric responses to large volcanic eruptions worldwide during the last two decades. With arrays of continuous Global Navigation Satellite System (GNSS) stations, we can continuously monitor the Earth’s ionosphere in terms of total electron content (TEC), an integrated number of electrons along line-of-sights connecting satellites and receivers.

Recent volcanic eruptions 2021