A unique phenomenon {\textendash} merging of Equatorial Ionization Anomaly (EIA) crests, leading to an X-pattern (EIA-X) around the magnetic equator {\textendash} has been observed in the night-time ionospheric measurements by the Global-scale Observations of the Limb and Disk (GOLD) mission. A whole atmospheric general circulation model simulation reproduces this pattern. The pattern is also produced in an assimilative ionosphere model that assimilates slant Total Electron Content (slant-TEC) from Global Navigation Satellite System (GNSS) and Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2). Due to the observed similarity between measurements and simulations, the latter is used to diagnose this heretofore unexplained phenomenon. The simulation shows that the EIA-X occurs in the afternoon to evening sector at a longitude where the vertical drift is negative, which is a necessary but not sufficient condition. The simulation was performed under constant low-solar and quiescent-geomagnetic forcing conditions, therefore we suggest that one of the drivers of this phenomenon is from lower-atmospheric processes.

The explosive eruption of the Hunga-Tonga volcano in the southwest Pacific at 0415UT on 15 January 2022 triggered gigantic atmospheric disturbances with surface air pressure wave propagating around the globe in Lamb mode. In space, concentric traveling ionosphere disturbances (CTIDs) are also observed as a manifestation of air pressure acoustic waves in New Zealand ~0500UT and Australia ~0630UT. As soon as the wave reached central Australia ~0800UT, CTIDs appeared simultaneously in the northern hemispheres through magnetic field line conjugate effect, which is much earlier than the arrival of the air pressure wave to Japan after 1100UT. Combining observations over Australia and Japan between 0800-1000UT, CTIDs with characteristics of phase velocities of 320-390 m/s are observed, matching with the dispersion relation of Lamb mode. The arrival of atmospheric Lamb wave to Japan later created in situ CTIDs showing the same Lamb mode characteristics as the earlier arriving CTIDs.

The Tonga volcano eruption of 15 January 2022 unleashed a variety of atmospheric perturbations, coinciding with the recovery phase of a geomagnetic storm. The ensuing thermospheric variations created rare display of extreme poleward-expanding conjugate plasma bubbles seen in the rate of total electron content index (ROTI) over 100-150°E. This is associated with fluctuations in FORMOSAT-7/COSMIC-2 (F7/C2) ion-density measurements and spread-F signatures in ionograms, reaching ~40°N geographic latitude. This was preceded by an unusually strong pre-reversal enhancement (PRE) in the global ionospheric specification (GIS) electron density profiles derived from F7/C2 observations. The GIS further revealed a decrease of equatorial ionization anomaly (EIA) crest density due to the storm impact. A sharp decrease of E-region conductivity by volcano-induced waves, combined with enhanced F-region wind over EIA with less ion-drag apparently intensified the PRE. The strong PRE and seed perturbations from the volcano-induced waves likely further triggered super plasma bubble activity.