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
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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).
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FFLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UL, UM, UPUK
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
Equatorial plasma bubbles (EPBs) are plasma depletions that can occur in the nighttime ionospheric F region, causing scintillation in satellite navigation and communications signals. Past research ...has shown that EPB occurrence rates are higher during the equinoxes in most longitude zones. An exception is over the central Pacific and African sectors, where EPB activity has been found to maximize during solstice. Tsunoda et al. (2015) hypothesized that the solstice maxima in these two sectors could be driven by a zonal wavenumber 2 atmospheric tide in the lower thermosphere. In this study, we utilize satellite observations to examine evidence of such a wave‐2 feature preconditioning the nighttime ionosphere to favor higher EPB growth rates over these two regions. We find the postsunset total electron content (TEC) observed by FORMOSAT‐3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) during boreal summer from 2007 to 2012 exhibits a wave‐2 zonal distribution, consistent with elevated vertical plasma gradients favorable for EPB formation. Numerical experiments are also carried out to determine whether such an ionospheric wave‐2 can be produced as a result of vertical coupling from atmospheric tides with zonal wavenumber 2 in the local time frame. We find that forcing from these tidal components produced increases in the Rayleigh‐Taylor growth rate over both sectors during solar maximum and minimum, as well as wave‐2 modulations on vertical ion drift, ion flux convergence, and nighttime TEC. Our results are consistent with the aforementioned hypothesis over both regions with vertical coupling effects from atmospheric tides preconditioning the nighttime ionosphere to favor higher EPB growth rates.
Key Points
Equatorial plasma bubble (EPB) variation over the Central Pacific and African sectors hypothesized to be caused by tidal forcing
Constellation Observing System for Meteorology, Ionosphere, and Climate total electron content (COSMIC TEC) shows recurrent maxima of wave‐2 tidal signatures over both regions during nighttime, favoring higher EPB growth rates
Model results show atmospheric tides can drive increases in Rayleigh‐Taylor growth rates over both regions that vary with solar cycle
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Seismic waves can be detected in the Earth's atmosphere and ionosphere; however, their impacts on ionospheric electron density (Ne) structures near the altitude of peak Ne (hmF2) have not yet been ...fully determined due to the lack of sufficient observations sampled in the vertical direction. Here we apply a ground‐based Global Positioning System (GPS) receiving network in Asia as well as the space‐based GPS occultation experiment on board the FORMOSAT‐3/COSMIC (F3/C) satellite to vertically scan the ionospheric Ne structures, which were perturbed by the magnitude Mw7.8 Nepal earthquake that occurred on 25 April 2015. The F3/C altitudinal Ne profiles show that the Nepal earthquake‐induced air perturbations penetrate into the ionosphere at supersonic speeds of approximately 800 m/s and change the Ne structure by 10% near hmF2. The vertical scale of the Ne perturbation is 150 km, while the hmF2 is uplifted by more than 30 km within 1 min. Those results reveal that the earthquake‐induced ground displacement should be considered as a significant force that perturbs the vertical Ne structure of the ionosphere.
Key Points
Coseismic ionospheric disturbance observed by FORMOSAT‐3/COSMIC
Near‐supersonic uplifting of the ionospheric F2 peak caused by the Nepal earthquake
Vertical scale of the coseismic disturbance is near 150 km in the F2 region
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The coincidental loss of 38 out of 49 SpaceX Starlink satellites during their launch on February 3, 2022, concurrent with two moderate geomagnetic storms, opens a unique window into the study of ...ionospheric irregularities and their potential impacts on Low Earth Orbit assets. This research provides evidence for the first time on the influence of Prompt Penetration Electric (PPE) fields and Disturbance Dynamo (DD) fields on the GNSS S4 amplitude scintillation indices of this particular geomagnetic storm, using observed variations in the distance of Equatorial Ionospheric Anomaly (EIA) crests and the O/N2 density ratio. By examining observations from the F7/C2 (FORMOSAT-7/COSMIC-2) mission, the NASA/GSFC’s OMNI data set, the TIMED/GUVI (Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Imager) O/N2 density ratio, and the GIM-TEC (Global Ionosphere Map of Total Electron Content) data, the study uncovers the complex dynamics of storm-induced irregularities and their correlation with suppressed S4 at low latitudes. It reveals the roles of PPE and DD in augmenting and mitigating S4 occurrences, respectively, during different storm phases. These findings contribute to enhancing the understanding of irregularity occurrence rates, scintillation effects, and geomagnetic storms across various longitudinal sectors, thereby providing a case study of changes to the scintillation environment during this moderate but high-profile geomagnetic event.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study shows that a supersonic moon shadow of a total solar eclipse can steepen the ionospheric total electron content (TEC) wave on August 21, 2017. A data‐adaptive method named Hilbert‐Huang ...transform is employed to examine the nonlinear and non‐stationary evolution of the waves. The results show that the TEC wave behaves as a traveling ionospheric disturbance before the totality appearance, turns later into steepening, and breaks eventually. A TEC wave with a period of ∼40 min and wavelength of ∼1,000 km propagates mainly in an east‐southward direction before the totality appearance. The wave amplitude and scales, respectively, increases and reduce by near ∼50% as the moon shadow approaches the western coast of the continental United States. The short‐period TEC waves (period ∼2 min) reveal that the wave may break eventually when the wave gets steeper. The steepness of the TEC wave is reconstructed according to the constructive interference.
Plain Language Summary
A water wave increasing in height and shortening in wavelength as it propagating is the best‐known example of wave steepening that we often can see near the shore. For the first time, this study shows that a supersonic moon shadow of a total solar eclipse can also steepen the wave of electron density in the Earth's ionosphere over the western coast of the continental United States. The wave propagates in an east‐southward direction over Oregon and California. The evolution of electron density wave (wavelength ∼1,000 km) is similar to a big water wave for surfing in the ionosphere (Movie S1). The results suggest that the dense GNSS arrays developing in the recent decade turn the Earth's ionosphere into one of the best available outdoor laboratories for detecting and examining the wave and dynamics.
Key Points
The TEC wave gets steeper as the supersonic moon shadow approaches the western coast of the continental United States on August 21, 2017
The intense bow‐wave crest ahead of the moon shadow can be attributed to the constructive interference
The data‐adaptive method, Hilbert‐Huang transform, benefits to extract the nonlinear and non‐stationary waves from TEC time series
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
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.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This paper demonstrates the significance of ion‐neutral coupling to ionospheric data assimilation for ionospheric specification and forecast. Ensemble Kalman Filter (EnKF) is used to assimilate ...synthetic electron density profiles sampled according to the Formosa Satellite 3/Constellation Observing System for Meteorology, Ionosphere, and Climate into the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM). The combination of the EnKF and first‐principles TIEGCM allows a self‐consistent treatment of thermosphere and ionosphere coupling in the data assimilation and forecast. Because thermospheric variables affect ionospheric electron densities, different combinations of an observed ionospheric state variable (electron density), and unobserved ionospheric and thermospheric state variables (atomic oxygen ion density, neutral temperature, winds, and composition) are included as part of the EnKF state vector in experiments. In the EnKF, the unobserved state variables are estimated and made dynamically and chemically consistent with the observed state variable, thus improving the performance of the data assimilation system. The impact on ensemble forecast is further examined by initializing the TIEGCM with the assimilation analysis. The main findings are the following: (1) by incorporating ion‐neutral coupling into the EnKF, the ionospheric electron density analysis, and forecast can be considerably improved. (2) Thermospheric composition is the most significant state variable that affects ionospheric analysis and forecast. (3) Thermospheric variables have a much longer impact on ionospheric forecast (>24 h) than ionospheric variables (2 to 3 h). (4) In the TIEGCM, the effect of assimilating electron densities is not completely transmitted to the forecast step unless the densities of ion species are estimated.
Key Points
The impacts of ion‐neutral coupling on ionospheric data assimilation are studiedNeutral composition is very effective to update on ionospheric data assimilationThe adjustment can last longer under the impact of thermospheric variables
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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