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An unseasonal equatorial plasma bubble (EPB) event occurred in the East/Southeast Asian sector during the geomagnetic storm on 1 December 2023, causing strong amplitude scintillations from equatorial to middle latitudes. Based on the observations from multiple instruments over a large latitudinal and longitudinal region, the spatial features of the super EPB were investigated. The EPB developed vertically at a fast rising speed ∼470 m/s over the magnetic equator and extended to a very high middle latitude more than 40°N, despite that the storm intensity was not very strong with the minimum SYM‐H index −132 nT. In the zonal direction, the super EPB covered over a specific region ∼95–140°E, where the local sunset roughly coincided with southward turning of interplanetary magnetic field (IMF) Bz component. Before the onset of the super EPB, significant upward plasma drift up to ∼110 m/s was observed over the magnetic equator, which could amplify the growth rate of Rayleigh‐Taylor instability and lead to the generation of the super EPB. The significant drift was likely caused by eastward penetration electric field (PEF) due to sharp southward turning of IMF Bz. The local time of storm onset and duration of IMF Bz southward turning during the storm main phase may partly determine the onset region and zonal coverage of the EPB. Plain Language Summary: Previous studies have reported unexpected generation and development of equatorial plasma bubbles (EPBs) during geomagnetic storms, with different EPB morphology varied from case to case. It is important to figure out potential factors controlling the occurrence or absence of EPBs over a specific region during geomagnetic storms, their latitudinal and longitudinal development. In this study, super EPB extending to middle latitudes more than 40°N was observed over a limited zonal region ∼95–140°E during the main phase of the 1 December 2023 geomagnetic storm. Significant upward plasma drift was observed before the onset of the EPB, which coincided with sharp southward turning of interplanetary magnetic field (IMF) Bz that could induce remarkable penetration electric field. Based on the combination of multiple kinds of observations over a large region, the potential factors controlling the generation and development of the EPB over latitude and longitude were investigated. It was suggested that the onset time, duration and intensity of IMF Bz southward turning during the main phase of geomagnetic storm play an important role in controlling the EPB spatial features, including the onset region, zonal coverage and latitudinal extension. Key Points: Ionospheric super bubble with fast rising speed occurred during storm time, extended to more than 40°N and caused strong midlatitude scintillationThe super bubble occurred over a confined longitudinal sector ∼95–140°E where the local sunset roughly coincided with interplanetary magnetic field (IMF) Bz southward turningSignificant upward plasma drift due to penetration electric field (PEF) could be responsible for the generation of the super bubbles [ABSTRACT FROM AUTHOR]

Simultaneous observations from Defense Meteorological Satellite Program, Swarm, Resolute Bay all‐sky imagers, GPS Total Electron Content and Super Dual Auroral Radar Network, are used to investigate the evolution and key characteristics of the Tongue of Ionization (TOI) being restructured into a polar cap patch. Six satellites crossed the TOI of patch as it moved from the dayside to the nightside. It was initially hot, then a mix of both cold and hot, and finally it became a cold patch. This suggests that cold patch is not only a result of solar extreme ultraviolet radiation, but may also develop when a hot patch cools down. Soft‐electron precipitation and flow shears both contribute to the TOI restructuring and the appearance of polar cap patch. The plasma density of patch at ∼500 km was at least 4 times higher than at ∼800 km. The plasma density enhancement gradually decreased as the patch evolved due to decreased production and transport of cold nightside low‐density plasma. Moreover, the duskward motion of the patch was influenced by changes in the ionospheric convection pattern. Plain Language Summary: The appearance of high‐density plasma is a common phenomenon in the polar ionosphere. High‐density polar cap patches usually form near the dayside sunlit region, and then move from the dayside to the nightside with the ionospheric flow. In the paper, we use multiple instruments including six satellites and ground‐based observations to carefully investigate an event that started out on the dayside. It was initially a hot tongue of ionization (TOI) of high density and high electron temperature, followed by a mix of hot and cold (high vs. low electron temperature), before it finally became a cold patch. Soft‐electron precipitation and flow shears both influenced the dayside high‐density TOI plasma restructuring and the appearance of polar cap patch. The enhanced plasma density gradually weakened as the plasma migrated toward the nightside due to decreased production and transport of cold nightside low‐density plasma. Moreover, the duskward motion of the patch was influenced by changes in the ionospheric convection pattern. Key Points: Cold dense plasma in the polar cap can appear either via transport of solar extreme ultraviolet plasma or after a hot patch cools downSoft‐electron precipitation and flow shears both influence the Tongue of Ionization restructuring and the appearance of polar cap patchesThe enhanced plasma density is reduced due to decreased production and transport of cold nightside low‐density plasma [ABSTRACT FROM AUTHOR]

Space weather adversely affects satellite systems by obstructing the services of global positioning systems (GPSs), delaying the launch of space vehicles, and causing damage to basic infrastructures such as radio-communications and power distribution networks. The spatio-temporal variations of ionospheric total electron content (TEC) during geomagnetic storms can be well examined by extreme value analysis. Statistical assessment and analysis of extreme values are necessary for developing risk assessment and mitigation strategies to the affected communication systems. In this study, extreme TEC events are investigated using 25 years (1997–2021) of long-term Global Navigation Satellite System (GNSS) Earth Observation Network System (GEONET) TEC data over Japan grid point location at 34.95° N and 134.05° E, and global data. In this work, a generalized extreme value (GEV) distribution is applied to the annual maxima TEC to evaluate geomagnetic disturbances that could occur once in 44, 88, 132, and 176 years with a confidence interval of 95%. According to the reference thresholds indicated by International Civil Aviation Organization (ICAO) for safer aviation applications, the moderate and severe levels of threshold for TEC are identified as 125 and 175 TEC Units (TECU), respectively. The results illustrate that the estimated extreme TECs for one in 44, 88, 132, and 176 years are 119, 125, 128, 130 and 215, 220, 222, 225 TECU for grid point and global TEC data respectively. That is, a moderate threshold level of activity is likely to happen over considered grid point for a return period of beyond 88 years and severe threshold level of activity beyond 11 years for global TEC data. [ABSTRACT FROM AUTHOR]