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The total electron content is an integrated value of ionospheric electron density (Ne) along the satellite-receiver ray path; therefore, it cannot directly resolve ionospheric disturbances in the vertical direction. In this work, to better understand the continuous evolution of co-seismic ionospheric disturbances (CIDs) at different altitudes, we conducted an accurate three-dimensional (3-D) visualization of CIDs associated with the 2011 M9.0 Tohoku-Oki earthquake based on the computerized ionospheric tomography technique. The results clearly revealed the 3-D morphological discrepancies of CIDs caused by Rayleigh waves, acoustic-gravity waves originating from the epicenter, and internal gravity waves induced by the tsunami waves. Further, we investigated the propagation and distribution of Ne disturbances along altitude. It was found that Ne disturbances triggered by different wave patterns exhibited different evolution characteristics in the vertical direction. The application of 3-D ionospheric detection has the potential to enhance the robustness of the earthquake and tsunami early warning systems.

This letter reports first simultaneous detection of F‐region plasma‐depleted structure in O(1D) 630.0 and O(1S) 557.7 nm airglow images on a geomagnetically quiet‐night (Ap = 3) of 26 June 2021 from mid‐latitude station (Hanle, India) due to enhanced thermospheric 557.7 nm emission. Since nighttime thermospheric 557.7 nm emission over mid‐latitudes is predominantly masked by significantly larger mesospheric component, F‐region plasma structures are rarely observed in 557.7 nm images. Interestingly, thermospheric 557.7 nm emission was not significant on the following geomagnetically quiet‐night as bands of medium‐scale traveling ionospheric disturbance were only observed in 630.0 nm images. Poleward wind generated by Equatorial Temperature and Wind Anomaly transported plasma from the boundary of equatorial ionization anomaly, causing significant electron density enhancement around 250 km and descent of F‐layer peak over Hanle on 26 June 2021. This amplified the dissociative recombination enabling the simultaneous detection of plasma‐depleted structure in 557.7 and 630.0 nm images. Plain Language Summary The thermospheric O(1S) 557.7 generated through dissociative recombination of O2+ in the F‐region is significantly lower than its mesospheric counterpart which is generated via the Barth mechanism in the Mesosphere‐Lower‐Thermosphere region. This causes difficulties in the simultaneous detection of mid‐latitude F‐region plasma structures in 630.0 and 557.7 nm airglow images during geomagnetically quiet nights of low solar active years. We report, for the first time, such simultaneous detection of plasma‐depleted structure from mid‐latitude station (Hanle, India) on a geomagnetically quiet night of 26 June 2021. Interestingly, the thermospheric 557.7 nm emission was not significant on the following geomagnetically quiet night as bands of medium‐scale traveling ionospheric disturbance were detected only in the 630.0 nm images. Results from multi‐instrument data sets showed the descent of F‐layer peak and significant electron density enhancement over Hanle. The local poleward wind generated by stronger Equatorial Temperature and Wind Anomaly on 26 June 2021 transported the plasma from the boundary of the equatorial ionization anomaly region to Hanle through geomagnetic field lines. This caused the enhancement of electron density around 250 km and descent of F‐layer peak over Hanle that created suitable condition for the amplification of dissociative recombination reaction. Key Points Simultaneous observation of mid‐latitude F‐region plasma‐depleted structure in O(1D) 630.0 and O(1S) 557.7 nm airglow images Significantly higher electron density is observed over the region on 26 June 2021 than on the following night at airglow emission altitude Thermospheric O(1S) 557.7 nm emission contributed significantly due to the enhancement in the dissociative recombination reaction

Continuous observations at specified locations and chronicling of astronomical phenomena provide a good opportunity to study ancient space weather. There are 248 white, 125 red, and 44 blue color aurora-like descriptions, also known as aurora candidates, recorded in Chinese official historical records during the 1365-year period of 511–1876. Qualitative descriptions of the color, location, and appearance time of these candidates are quantitatively denoted. The red, white, and blue aurora candidates occurred most frequently 34% in autumn, 32% in summer, and 49% in summer, respectively. The white and red aurora as well as the overall candidates tend to appear during high solar activity periods. By contrast, the blue candidates frequently occur during low solar activity periods. Statistical results with 90% confidence intervals further show that the relationship between solar activities and overall/red (white/blue) aurora candidates is significant (insignificant). The red aurora candidates that frequently occurred in autumn during the periods of high solar activity agree well with those of low/middle latitude auroras, while the white aurora candidates might be confounded by noctilucent clouds or other atmospheric optical events, such as airglows, moon halo, etc. The study of ancient space weather/climate based on historical records shows that aurora occurrences are related to solar activities, and in particular, red auroras frequently appear in low/middle latitudes during high solar activity periods.

The ion density and velocity measured by the advanced ionospheric probe (AIP) onboard FORMOSAT‐5 (F5) and ion velocity meter (IVM) onboard FORMOSAT‐7/COSMIC‐2 (F7C2), and the electron density assimilated by the global ionospheric specification (GIS) are employed to study the ionospheric plasma structure and dynamics during the 10 May 2024 Mother's Day storm (Dst −412 nT). The F5/AIP and F7C2/IVM display a large‐scale hole over the magnetic equator in the Atlantic Ocean area (−10° to 25°N, −60° to 20°E) during the local midnight period, with the minimum ion density of 1.7 × 104 #/cm3 and 1.6 × 103 #/cm3, respectively. In the hole area, F5/AIP and F7C2/IVM reveal upward ion velocities at 720 km altitude and downward ones at 550 km altitude, respectively, while GIS profiles show that the electron density yields the lower peak at ∼440 km and upper peak at ∼760 km altitude. This suggests that the downward and upward ion velocities result in the double‐peak feature.

An earthquake of magnitude 9.0 occurred near the east coast of Honshu (Tohoku area), Japan, producing overwhelming Earth surface motions and inducing devastating tsunamis, which then traveled into the ionosphere and significantly disturbed the electron density within it (hereafter referred to as seismotraveling ionospheric disturbances (STIDs)). The total electron content (TEC) derived from nationwide GPS receiving networks in Japan and Taiwan is employed to monitor STIDs triggered by seismic and tsunami waves of the Tohoku earthquake. The STIDs first appear as a disk‐shaped TEC increase about 7 min after the earthquake occurrence centered at about 200 km east of the epicenter, near the west edge of the Japan Trench. Fast propagating disturbances related to Rayleigh waves quickly travel away from the epicenter along the main island of Japan with a speed of 2.3–3.3 km/s, accompanied by sequences of concentric circular TEC wavefronts and followed by circular ripples (close to a tsunami speed of about 720–800 km/h) that travel away from the STID center. These are the most remarkable STIDs ever observed where signatures of Rayleigh waves, tsunami waves, etc., simultaneously appear in the ionosphere. Key Points Ionospheric disturbances generated by earthquake and tsunami Greatest disturbances ever seen containing signatures of following waves Rayleigh, acoustic, and tsunami‐generated waves

Diurnal, monthly, and solar activity variations in L-band signal fluctuations are examined by ROTI (Rate Of Tec Index) derived from measurements of worldwide ground-based GNSS (Global Navigation Satellite System) receivers in 2000, 2009, and 2013. Routine observations of the ionospherically imposed propagation effects upon GNSS satellite signals are available online from IGS (International GNSS Service). With data over 2000 ground-based IGS stations of the globe, ionospheric TEC with the 30-sec time resolution can be derived. The standard deviation of TEC variations every minute in a 5-minute interval is further computed to obtain ROTI around each receiving station. Variations in diurnal, seasonal, solar activity, and geographic distribution of ROTI are examined during the solar maximum year of 2000, solar minimum year of 2009, and solar median year of 2013. ROTIs are proportional to the solar activity, those in the high-latitude ionosphere are much more intense than in the low- and mid-latitude ionosphere. In the low-latitude ionosphere, intense ROTIs frequently occur within ±30° magnetic dip, start at 19:30 LT (Local Time); reach their maximum at 20:00 to 21:00 LT, and vanish by about 02:00 LT; and appear prominently in March and September equinox seasons. The region experiencing the most intense ROTI is the low-latitude ionosphere in South America. The low-latitude ROTIs often exhibit a prominent double-peaked (or crest) structure centering at 20°N and 20°S dip latitude, especially in high/median solar activity years of 2000 and 2013. Monthly-longitude plots of low latitude ROTIs look like a masquerade mask with two eye holes (i.e., ROTI free).

Intense eruptions of the Tonga volcano activated prominent traveling atmospheric disturbances (TADs) at 04:05UT on 15 January 2022. Himawari‐8 satellite images depict that TADs of the tropospheric Lamb wavefront propagate with a speed of 315 m/s and arrive in Taiwan at 11:30UT. Networks of 98 barometers, 28 tide gauges, an ionosonde, and 10 magnetometers are used to study the responses of magnetic fields to TADs in Taiwan. The horizontal components in magnetic field changes of the Taiwan magnetometers all point toward and away from the Tonga volcano at 11:00–12:00UT upon the tropospheric Lamb wavefront arrival and at 22:00–23:00UT when the thermospheric Lamb wavefront with speeds of 487 m/s coming, respectively. Analyses of the raytracing and beamforming techniques on the horizontal components in magnetic field changes of 69 INTERMAGNET magnetometers show that both tropospheric and thermospheric Lamb waves efficiently activate traveling ionospheric disturbances and modify ionospheric currents of the globe. Plain Language Summary At 04:05UT on 15 January 2022, intense Tonga volcanic eruptions induce prominent atmospheric disturbances and tsunami waves. Himawari‐8 meteorological satellite images depict the induced upper‐level tropospheric disturbances with horizontal speeds of about 315 m/s at 8.2 km altitude in the Lamb wave mode travel worldwide. Upon the traveling atmospheric disturbances (TADs) of the tropospheric Lamb wavefront arriving in Taiwan at 11:30UT, 98 ground‐based barometers register increases and reach peaks at about 11:50UT in the atmospheric pressure; 28 tide gauges record enhancements and maximums of sea level fluctuations at about 14:30–17:30UT; and a local ionosonde observes that the ionosphere reaches the highest altitude at 14:30UT. The changes of the horizontal component of the Earth's magnetic fields measured by 10 Taiwan magnetometers almost all point exactly toward the Tonga volcano upon the tropospheric Lamb wavefront arrival at 11:00–12:00UT, and away from the volcano at 22:00–23:00UT, which suggests a 487 m/s TAD (or thermospheric Lamb wavefront) at about 130 km altitude also being activated. The horizontal components in magnetic field changes of 69 INTERMAGNET magnetometers show that both tropospheric and thermospheric Lamb waves triggered by Tonga volcanic eruptions are very powerful, and can induce intense dynamo currents and electric fields on the globe. Key Points Tropospheric and thermospheric Lamb waves of the Tonga volcanic eruption activate dynamo currents and electric fields Traveling atmospheric disturbances of the Tonga volcanic eruption significantly uplift the ionosphere Tropospheric Lamb waves of the Tonga volcanic eruption modulate ground‐based air pressures and sea levels

This study examines the ionosphere response to gravitational forces of the lunar phase and dynamical disturbances of the stratospheric sudden warmings (SSWs). The total electron content (TEC) of global ionosphere maps is employed to examine responses of the equatorial ionization anomaly (EIA) crests to lunar phases and twelve SSW events during 2000–2013. The most prominent feature in the ionosphere is the EIA, characterized by two enhanced TEC crests at low latitudes straddling the magnetic equator, which can be used to observe ionospheric plasma dynamics and structures. Results show that the EIA crest appearance time on new/full moons (first/third quarters) leads (lags) that of the overall 14-year average, which causes a pattern of TEC morning enhancements (suppressions) and afternoon suppressions (enhancements). A statistical analysis shows that SSWs can also significantly cause the early appearance of EIA crests, regardless of the lunar phase. Thus, both lunar phase and SSWs can significantly modulate the appearance time of EIA crest and ionospheric plasma dynamics and structures.

The devastating Hunga Tonga-Hunga Ha’apai underwater volcano erupted at ~04:15 UT on 15 January 2022. We captured the waves that erupted from the volcano propagating in the ionosphere by monitoring total electron content (TEC) perturbations utilizing ground-based global navigation satellite system (GNSS) receivers that receive electromagnetic signals transmitted from the geostationary satellites operated by the BeiDou Navigation Satellite System (BDS). Meanwhile, ground barometers detected unusual enhancements of air pressure traveling in the troposphere. A novel phenomenon shows that the waves can individually propagate with a speed of ~335 m/s in the ionosphere, which is faster than its’ ~305 m/s in the troposphere. We further examined multiple geophysical data at the particular site of the novel instrumental array. Analytical results show that the pressure enhancements traveling in the troposphere not only downward trigger ground vibrations mainly in the horizontal components without obvious time difference, but also upward, leading the secondary TEC perturbations with a ~12-min delay.

The semidiurnal (12.42 h) and semimonthly (14.76 days) lunar tides have been well-known by fishermen for several centuries. The gravitational force of the relative positions between the Sun, the Moon, and the Earth results in two symmetrical tidal bulges (double bulges) appearing at equatorial latitudes directly under and opposite the Moon. We utilize ionospheric GNSS (Global Navigation Satellite System) radio occultation soundings to show the global three-dimensional structures and dynamics of the double bulges of ionospheric lunar tides for the first time. The double-bulge amplitude of ionospheric F2-peak height hmF2, lagging the sublunar or antipodal point by about 2–3 h, is about 3–5 km at the equator and 1.5–2.0 km at ± 35° magnetic latitude. The electron density further depicts global three-dimensional plasma flows in the ionosphere.