This study reports two different properties of ionospheric perturbations detected to the west and south of the Korean Peninsula after the Hunga-Tonga volcanic eruption on 15 January 2022. Transient wave-like total electron content (TEC) modulations and intense irregular TEC perturbations are detected in the west and south of the Korean Peninsula, respectively, about eight hours after the eruption. The TEC modulations in the west propagate away from the epicenter with a speed of 302 m/s. Their occurrence time, propagation direction and velocity, and alignment with the surface air pressure perturbations indicate the generation of the TEC modulations by Lamb waves generated by the eruption. The strong TEC perturbations and L band scintillations in the south are interpreted in terms of the poleward extension of equatorial plasma bubbles (EPBs). We demonstrate the association of the EPBs with volcanic eruption using the EPB occurrence climatology derived from Swarm satellite data.

The equatorial ionosopheric anomalies (EIA) at night are the slowly recombining remnants of the dayside ionosphere, and charged particle densities slowly decay during the course of the night. Thus the electron density in ionosphere in the early morning (0300-0400 Local time) is usually very low and the ionospheric UV 135.6 nm O+ recombination emission is rarely detectable from current UV remote sensing instruments. However, there are times when the EIA have unusually high density even during these morning times and are observable by the DMSP/SSUSI and TIMED/GUVI instruments. By using other UV ‘colors’ - 130.4 nm (from monatomic Oxygen) and N2 Lyman Birge Hopfield bands - we can establish that this emission is definitely from the ionosphere recombination emission. We will show examples of this phenomenon, and correlate these occurrences to geomagnetic storm events. We estimate the electron density in the early morning EIA and compare with other ionosphere observations and climatological models. In the figure below, we show the 135.6 nm radiance seen by DMSP F16 SSUSI as it crosses the equator around 210 degrees longitude (over the Pacific Ocean) at 03:45 local time. The equatorial anomaly peaks are clearly visible in the SSUSI data. These radiances are background subtracted, which is not perfect and introduces a small (-1 Rayleigh) bias to the resulting radiances. DMSP = Defense Meteorological Satellite Program, SSUSI = Special Sensor Ultraviolet Spectrographic Imager; TIMED = Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics, GUVI = Global UltraViolet Imager

Broad plasma depletions (BPDs) are bubble-like plasma depletions in the equatorial F region whose longitudinal widths (> 4 degree) are greater than those of regular bubbles. Their occurrence in satellite observations is understood in terms of the uplift of the ionosphere; BPDs are observed when satellites pass through the bottomside of bubbles. However, a merger of bubbles is also suggested as the cause of BPDs. We investigate the origin of BPDs by examining the occurrence climatology of BPDs and its association with vertical plasma motion. Our preliminary results derived from the C/NOFS observations in 2008–2012 show that BPDs occur more frequently during lower solar activity, during higher magnetic activity, and at lower altitudes. BPDs during solar maximum and minimum periods show different behavior. BPDs during solar maximum period occur frequently at premidnight and during the equinoxes and December solstices (for highly geomagnetically disturbed periods). On the contrary, BPDs during the solar minimum period occur predominantly at postmidnight and during the June solstices. The occurrence rates of postmidnight BPDs are positively correlated with AE index and are inversely correlated with 10.7 cm solar radio flux. Low solar activity creates favorable conditions for generating BPDs by thinning the F region. At the solar minimum, the density of the F region’s bottomside changes significantly even with slight altitude shifts, which can be recognized as BPDs. When a geomagnetic disturbance occurs, the eastward electric field can be enhanced at the equatorial F region, and the entire F layer can move upward.