The two‐dimensional concentric traveling ionospheric disturbances (TIDs) over Japan on the landfall day of Typhoon Faxai in 2019 were detected in total electron content by the ground‐based Global ...Navigation Satellite System observations. They propagated in the radial direction away from the typhoon eye with a horizontal velocity of ∼190 m/s, a period of ∼24 min, and a horizontal wavelength of ∼180 km. Then, we systematically investigated the corresponding three‐dimensional ionospheric responses for the first time. Remarkable wavelike structures of ionospheric electron density (Ne) and inverted conic‐like structures concerning the disturbed Ne (dNe) were visualized in the F region. Furthermore, the descending phase progression of dNe with increasing time was detected at 220–550 km altitudes, which powerfully revealed that the typhoon‐related TIDs were dominated by the upward atmospheric gravity waves (AGWs) propagating from the troposphere into the ionospheric F2 layer. By analyzing the spatial and temporal evolutions of Ne and dNe, we postulated that the transport process of neutral wind fluctuations associated with the upward AGWs were likely responsible for generating TIDs during Typhoon Faxai. In the end, the background wind velocity was estimated based on the recovered vertical wavelength of ∼460 km and the dispersion equation of AGWs. Our results also demonstrated that the weak background wind condition is essential for gravity waves propagating in the ionosphere.
Key Points
The wavelike structures of Ne in concentric traveling ionospheric disturbances (TIDs) caused by Typhoon Faxai are detected in the F region
The distributions of dNe exhibit oblique alignments and downward phase progression in the vertical direction
The neutral wind fluctuations due to the upward atmospheric gravity waves are likely responsible for generating typhoon‐related TIDs
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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 waves propagating around ...the globe in Lamb mode. In space, concentric traveling ionosphere disturbances (CTIDs) are also observed as a manifestation of air pressure waves in New Zealand ∼0500UT and Australia ∼0630UT. As soon as the air pressure waves reached central Australia ∼0800UT, conjugate CTIDs appeared almost simultaneously in the northern hemispheres through interhemispheric coupling, much earlier than the arrival of the surface air pressure waves to Japan after 1100UT. Combining observations over Australia and Japan between 0800 and 1000UT, both direct and conjugate CTIDs show similar horizontal phase velocities of 320–390 m/s, 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 conjugate CTIDs.
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The FORMOSAT‐7/COSMIC‐2 (F7/C2) satellite mission was launched on 25 June 2019 with six low‐Earth‐orbit satellites and can provide thousands of daily radio occultation (RO) soundings in the ...low‐latitude and midlatitude regions. This study shows the preliminary results of space weather data products based on F7/C2 RO sounding: global ionospheric specification (GIS) electron density and Ne‐aided Abel and Abel electron density profiles. GIS is the ionospheric data assimilation product based on the Gauss‐Markov Kalman filter, assimilating the ground‐based Global Positioning System and space‐based F7/C2 RO slant total electron content, providing continuous global three‐dimensional electron density distribution. The Ne‐aided Abel inversion implements four‐dimensional climatological electron density constructed from previous RO observations, which has the advantage of providing altitudinal information on the horizontal gradient to reduce the retrieval error due to the spherical symmetry assumption of the Abel inversion. The comparisons show that climatological structures are consistent with each other above 300 km altitude. Both the Abel electron density profiles and GIS detect electron density variations during a minor geomagnetic storm that occurred within the study period. Moreover, GIS is further capable of reconstructing the variation of equatorial ionization anomaly crests. Detailed validations of all the three products are carried out using manually scaled digisonde NmF2 (hmF2), yielding correlation coefficients of 0.885 (0.885) for both Abel inversions and 0.903 (0.862) for GIS. The results show that both GIS and Ne‐aided Abel are reliable products in studying ionosphere climatology, with the additional advantage of GIS for space weather research and day‐to‐day variations.
Plain Language Summary
This study presents two ionosphere products from the innovative satellite constellation mission launched recently. Global ionospheric specification is an ionospheric data product that assimilates ground‐based Global Positioning System and FORMOSAT‐7/COSMIC‐2 radio occultation observation of total electron content, to generate hourly global three‐dimensional electron density for monitoring space weather condition. Ne‐aided Abel electron density profile is an improved retrieval product of FORMOSAT‐7/COSMIC‐2 radio occultation observations by imposing asymmetry information of ionosphere to mitigate the error introduced by the assumption of spherical symmetry in the Abel inversion. The comparisons and validations confirm that these two data products are reliable for the study of ionosphere climatology and weather. They are operationally produced and released at Taiwan Analysis Center for COSMIC.
Key Points
All the three F7/C2 products capture similar climatological structure of ionosphere in longitudes (Wave 4) and latitudes (EIA crests)
Abel electron density profiles detect responses to geomagnetic storm, but GIS performs better in reconstructing the EIA crests variations
Digisonde validations demonstrate that the GIS NmF2 has excellent performance when there are RO observations available for assimilation
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In this study, a three‐dimensional (3‐D) ionospheric tomography was developed in Japan using the constraint least‐square fitting algorithm, a model‐free method. Moreover, to make enough room for ...electron density (Ne) variations in the horizontal direction, only constraints on height were adopted. Slant total electron content data sets detected by 800 Global Positioning System (GPS) ground‐based receivers in 25°–50°N, 125°–150°E were selected. The spatial resolution was 1°, 1°, and 30 km in latitude, longitude, and altitude, respectively. The reconstructed performances concerning the quiet ionosphere, large‐scale traveling ionospheric disturbances on July 27, 2004, and nighttime medium‐scale traveling ionospheric disturbances on June 23, 2012, were verified successively. By comparing with Ne distributions from the International Reference Ionosphere model and GPS‐TEC mapping, the reconstructed results in both horizontal and vertical directions show good performance in imaging the ionospheric background and disturbed characteristics. The finding strongly indicates that retrieving Ne distributions by the improved constraint least‐square algorithm is promising for ionospheric studies and practical applications.
Key Points
An ionospheric tomography was developed in Japan, utilizing the improved constraint least‐square fitting algorithm
The 3‐D disturbance structures concerning large‐scale traveling ionospheric disturbances and medium‐scale traveling ionospheric disturbances were successfully reconstructed
The vertical profiles were evaluated by comparing with foF2 and hmF2 measured by ionosondes
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This study examined the FORMOSAT‐3/COSMIC radio occultation soundings of total electron content in the ionosphere (from 150 to 550 km) and refractivity index in the lower atmosphere (from 0 to 60 km) ...after/during the 2011 Mw9.0 Tohoku earthquake/tsunami. The refractivity index observations show the first evidence of the Tohoku earthquake/tsunami‐induced vertical oscillations in the lower atmosphere. The atmospheric oscillations with vertical wavelength ranging from 0.5 to 8 km and from 10 to 40 km, respectively, appear in the stratosphere and ionosphere after the earthquake onset. The short vertical wavelengths suggest that the oscillations are the atmospheric oscillatory tail due to the wavefront of the earthquake/tsunami. The radio occultation technique is a tool for detecting the atmospheric waves induced by earthquake or some other sources.
Plain Language Summary
It has been well known that the sudden uplift of the Earth's surface due to earthquake/tsunami significantly disturbs the upper atmosphere and ionosphere. However, the evidence of earthquake/tsunami‐induced waves in the lower atmosphere is insufficient due to the lack of observation supporting. Here the FORMOSAT‐3/COSMIC (F3/C) radio occultation refractivity index is for the first time to capture the Tohoku earthquake‐induced vertical oscillations at the stratosphere altitudes from 30 to 40 km. The results in this study not only shed lights on understanding of earthquake/tsunami waves perturbing the whole atmosphere but also suggest that the radio occultation technique can benefit to the earthquake/tsunami warning system.
Key Points
The study shows the first evidence of the Tohoku earthquake/tsunami‐induced vertical oscillations in the stratosphere
Atmospheric oscillations with vertical scale range from 10 to 40 km and from 0.5 to 8 km, respectively, in the ionosphere and stratosphere
The oscillations are mainly the atmospheric oscillatory tail due to the tsunami
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To clarify and verify the ultralow frequency (ULF) seismomagnetic phenomena, we have performed statistical studies on the geomagnetic data observed at the Kakioka (KAK) station, Japan, during ...2001–2010. We investigated the energy of ULF geomagnetic signals of the frequency around 0.01 Hz using wavelet transform analysis. To minimize the influences of artificial noises and global geomagnetic perturbations, we used only the geomagnetic data observed at nighttime (LT 2:30 A.M. to 4:00 A.M.) and utilized observations from a remote station, Kanoya, as a reference. Statistical results of superposed epoch analysis have indicated that ULF magnetic anomalies are more likely to appear before sizable earthquake events (Es > 108) rather than after them, especially 6–15 days before the events. Further statistical investigations show clearly that the ULF geomagnetic anomalies at KAK station are more sensitive to larger and closer events. Finally, we have evaluated the precursory information of ULF geomagnetic signals for local sizable earthquakes using Molchan's error diagram. The probability gain is around 1.6 against a Poisson model. The above results have indicated that the ULF seismomagnetic phenomena at KAK clearly contain precursory information and have a possibility of improving the forecasting of large earthquakes.
Key Points
Verify existence of ULF electromagnetic phenomena preceding large earthquakes
ULF geomagnetic anomalies are more sensitive to larger and closer events
ULF seismomagnetic phenomena obtained at KAK do contain precursory information
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Solar eclipse is a daytime phenomenon that significantly disturbs the ionosphere, but whether the eclipse induces ionospheric irregularities in the nighttime remains unknown. In this study, we ...analyzed the dense total electron content (TEC) observations from the ground‐based Global Navigation Satellite System receivers over East and South Asia to examine the development of the irregularities in the nighttime on the day of the 21 June 2020 annular solar eclipse. The rate of TEC index (period <5 min) indicates the occurrence of the irregularities that evolve from the large or coarse structures with a period ranging from hours to dozens of minutes in the nighttime due to the eclipse. We take advantage of the data‐adaptive analysis method, Hilbert‐Huang transform, to derive the instantaneous amplitude and frequency of the TEC time series, which exposes the temporal and spatial evolutions of the irregularities from larger structures continuously.
Plain Language Summary
The moon obscuration of a solar eclipse suddenly reduces solar irradiation in the daytime, which generates large atmospheric and ionospheric perturbations. The massive total electron content observations from the dense ground‐based Global Navigation Satellite System network recorded the occurrence of the large‐scale ionospheric perturbations and plasma irregularities in the nighttime on 21 June 2020. The occurrence of nighttime irregularities due to a solar eclipse was never known. This study further shows that the Hilbert‐Huang transform is an efficient technique to sift out the structures with large, coarse, or fine scales (Figure S1 in Supporting Information S1) from the total electron content time series. This data‐adaptive method benefits capturing the transient evolution of the ionospheric weather.
Key Points
Development of ionospheric plasma irregularities after the solar eclipse in postsunset hours
Evolution of the irregularities from the convergence of large enhancements
Hilbert‐Huang transform analysis sifts out the density structures with scales from coarse to fine
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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.
Graphical Abstract
The strength, appearance time, and latitudinal location of the equatorial ionization anomaly (EIA) crest response to the lunar phase are examined using the total electron content of global ionosphere ...maps during the 18‐year period of 2000–2017. The total electron content of the EIA crest reveals semidiurnal tides with 12.42‐hr period, while the appearance time and latitude of the EIA crests present prominent semimonthly lunar tides of 14.77‐day period. The EIA crests on new/full moon (first/third quarter) lead (lag) those of the overall 18‐year average by about 20–40 min, while the EIA crests move the furthest poleward and equatorward 2–5 days after new/full moon and first/third quarter, respectively. Amplitudes of the semimonthly lunar tide in the EIA crest appearance times and latitudes yield the greatest value around perihelion and the smallest value around aphelion, which shows that the solar declination and seasonal effects are important.
Plain Language Summary
The most prominent feature in the ionosphere is the equatorial ionization anomaly (EIA), which is characterized by two enhanced plasma crests at low latitudes straddling the magnetic equator. Global ionosphere maps of total electron content are analyzed to see how the ionospheric EIA crests respond to changes in lunar phases and solar declinations. The results show that the EIA crests exhibit prominent semimonthly lunar tides with 14.77‐day period. Appearance times of the EIA crests on new/full moon (first/third quarter) lead (lag) those on the associated overall 18‐year average by about 20–40 min, while the EIA crests move the furthest poleward during new/full moon and equatorward during first/third quarter with the delays of about 2–5 days. These indicate that the lunar phase can significantly modulate the ionospheric EIA. The semimonthly lunar tide in the crest appearance times and latitudes become most prominent around perihelion but the least around aphelion, which shows that the solar declination and seasonal effects are important.
Key Points
Appearance times of the EIA crests on new/full moon lead those on first/third quarter
The EIA crests move most poleward (equatorward) 2–5 days after new/full moon (first/third quarter)
The semimonthly lunar tide of the EIA crest becomes most prominent around perihelion
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Abstract 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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