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.
Atmospheric gravity waves can be excited by explosive volcanic eruptions and may reach Earth's upper atmosphere. In this study, we report on mesoscale concentric gravity waves observed in the ...mesopause airglow layer following the La Soufriere volcano eruption in April 2021. A large ash plume observed by the spaceborne Multi-angle Imaging SpectroRadiometer instrument on April 10 reached ∼20 km. Temporal evolution of the volcanic ash plume was provided by the GOES-16 Advanced Baseline Imager. Nightglow gravity waves were observed by the Visible Infrared Imaging Radiometer Suite Day Night Band. These waves had horizontal wavelengths of ∼25–40 km, and took about a half-to-1 hr to travel from the tropopause to the mesopause. Some concentric ionospheric disturbance signatures are also seen in Global Navigation Satellite System-total electron content maps. We found the launch of gravity waves to be highly correlated with the elevated ash plume from explosive eruptions.
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
It is well‐known that equatorial plasma bubbles (EPBs) are highly correlated to the post‐sunset rise of the ionosphere on a climatological basis. However, when proceeding to the daily EPB ...development, what controls the day‐to‐day/longitudinal variability of EPBs remains a puzzle. In this study, we investigate the underlying physics responsible for the day‐to‐day/longitudinal variability of EPBs using the Sami3 is A Model of the Ionosphere (SAMI3) and the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (SD‐WACCM‐X). Simulation results on October 20, 22, and 24, 2020 were presented. SAMI3/SD‐WACCM‐X self‐consistently generated midnight EPBs on October 20 and 24, displaying irregular and regular spatial distributions, respectively. However, EPBs are absent on October 22. We investigate the role of gravity waves on upwelling growth and EPB development and discuss how gravity waves contribute to the distributions of EPBs. We found the westward wind associated with solar terminator waves and gravity waves induces polarization electric fields that map to the equatorial ionosphere from higher latitudes, resulting in midnight vertical drift enhancement and retrograde plasma flow. The upward vertical drift and retrograde flow further lead to shear flow instability and midnight plasma vortex, creating background conditions identical to the post‐sunset ionosphere. This provides conditions favorable for the upwelling growth and EPB development. The converging and diverging winds associated with solar terminator waves and midnight temperature maximum also affect the longitudinal distribution of EPBs. The absence of EPBs on October 22 is related to the weak westward wind associated with solar terminator waves.
Plain Language Summary
Plasma bubbles are a particular space weather phenomenon mainly occurring in the nighttime equatorial region. After sunset, the ionosphere becomes unstable due to the upward motion of vertitical ion drift. Bubbles can develop from the bottomside ionospheric F layere and stretch into the topside ionosphere (above 500 km), like wax bubbles in a lava lamp. Bubbles significantly reduce the plasma density in the ionosphere, displaying turbulent plume structures that can disrupt radio wave communications and GPS navigation. Understanding and predicting the development of plasma bubbles has baffled scientists for more than 80 years, especially in understanding the day‐to‐day variability. In this study, we aim to understand what controls the day‐to‐day variability of plasma bubbles by using the physics‐based SAMI3/SD‐WACCM‐X model. We found that gravity waves are ubiquitous and play a vital role in seeding and determining the spacing between plasma bubbles. The longitudinal distribution of plasma bubbles is affected by meridional wind. The most striking finding is that daily dusk solar terminator waves significantly impact neutral wind and electrodynamics, controlling the presence or absence of plasma bubbles at midnight. This study reveals that the day‐to‐day variability of plasma bubbles is considerably linked to the variations in the lower atmosphere.
Key Points
The regular and irregular spatial distributions of equatorial plasma bubbles (EPBs) are determined by the zonal wavelength and wavefront orientation of gravity waves
Solar terminator/gravity waves contribute to midnight vertical drift enhancement and retrograde flow, creating midnight plasma vortex
The absence of midnight EPBs is related to weak westward winds associated with solar terminator/gravity waves
We report on a new method to derive the on‐orbit electron density using the Tri Global Navigation Satellite System (GNSS) Radio‐occultation System (Tri‐GNSS Radio occultation System (TGRS)) ...differential total electron content data and compare it to the Constellation Observing System for Meteorology Ionosphere and Climate‐2 Ion Velocity Meter (IVM) ion density data. We found that the IVM ion density is about 8%–15% lower than the TGRS derived density at the insertion orbit (∼710 km) and 5% higher at the mission operation orbit (∼540 km) for reasons that are currently unknown. Using a linear coefficient, we scaled the IVM data to remove the offset between TGRS‐derived electron density and the IVM ion density for the two orbital heights. We believe the scaled IVM densities eliminate any inter‐spacecraft discrepancy, making the IVM data suitable for use in high precision multi‐satellite scientific investigations of longitudinal and local time variations of non‐migrating tides, planetary waves and space weather operational applications.
Key Points
A new method is described to derive the on orbit electron density using the differential Global Navigation Satellite System (GNSS) slant data and compared with the FORMOSAT‐7/Constellation Observing System for Meteorology Ionosphere and Climate‐2 ion velocity meter (IVM) ion density data
IVM ion density was smaller (larger) than the GNSS‐derived electron density at high (low) orbits
A linear scaling is applied to the IVM ion density to consistently align the IVM‐derived plasma densities with those derived from the TGRS
This study presents the conjugate ionospheric disturbances triggered by the 2011 Tohoku-Oki
reflected tsunami oceanic waves using the ground-based Global Navigation Satellite System (GNSS) total ...electron content (TEC) observations. We found that the equatorward and westward propagating nighttime medium-scale traveling ionospheric disturbances (MSTIDs) occurred over Japan and Australia simultaneously following the tsunami oceanic waves reflected by the Emperor Seamount Chain in the northern hemisphere. The atmospheric gravity waves driven by reflected tsunami oceanic waves are hypothesized to be the source to trigger the conjugate MSTIDs by transporting the polarization electric fields along the field line to the conjugate hemisphere. Moreover, only the southwestward propagating MSTIDs have this conjugate
effect, which could be due to the wavefront orientation. The Perkins instability could also be involved in the interhemispheric coupling process. This study provides the first observational evidence that the reflected tsunami can induce conjugate ionospheric disturbances through electrodynamic forcing.
Two remarkable typhoon‐induced traveling ionospheric disturbances (TIDs) with concentric and northwest‐southeast (NW‐SE) alignments, respectively, associated with concentric gravity waves (CGWs) and ...ionosphere instabilities possibly seeded by CGWs, were observed in total electron content (TEC) derived from ground‐based Global Navigation Satellite System networks in Taiwan and Japan when the Category 5 Super Typhoon Nepartak approached Taiwan on 7 July 2016. The concentric TIDs (CTIDs) first appear with horizontal phase velocities of ~161–200 m/s, horizontal wavelengths of ~160–270 km, and periods of ~15–22 min during 08:00–11:20 UT. Following the CTIDs, the NW‐SE aligned nighttime medium‐scale TIDs (MSTIDs) are formed on the west edge of the CTIDs over the Taiwan Strait during 11:30–14:00 UT. It is suggested that the MSTIDs are produced by the electrodynamical coupling of Perkins instability and CGW‐induced polarization electric fields. This study proposes connections of typhoon‐induced CTIDs and subsequently occurring MSTIDs in the low‐latitude ionosphere.
Key Points
Concentric and medium‐scale traveling ionosphere disturbances excited by Super Typhoon Nepartak (2016) are observed in GNSS TEC
Nighttime MSTIDs with NW‐SE alignment of wavefronts occurred on the west edge of CTIDs
Electrodynamical coupling of Perkins instability and CGWs‐induced electric fields could explain the typhoon‐induced nighttime MSTID
The FORMOSAT‐3/COSMIC (F3/C) satellites are used to study the climatology of equatorial plasma bubbles (EPBs) during the low to moderate solar flux years (2008–2013). We use the F3/C total electron ...content to identify the presence of EPBs and investigate the background conditions for the initiation of EPBs. The results reveal that the EPB activities have strong solar dependence. The longitudinal and seasonal trends of EPBs are highly correlated to the angle between the dusk solar terminator and magnetic field lines near the magnetic equator. Asymmetries of EPBs between solstices and equinoxes exist and could be due partly to the asymmetry of equatorial ionization anomaly structures, which result in longitudinal differences as well. EPBs extend to higher altitudes and latitudes during the ascending phase of Solar Cycle 24 (2011–2013) due mainly to the increase of background electron density. However, an altitudinal asymmetry of EPBs occurs in moderate solar flux years, which is likely due to the suppression or lower growth and occurrence rates of EPBs. In addition to vertical drift, tidal forcing also contributes to the longitudinal and seasonal distributions of EPBs. Upwellings and precursor waves preceding the EPBs are observed climatologically, which likely play a vital role in initiating the EPBs. This study also reveals a vertical connection between the equatorial ionospheric irregularities and atmospheric forcing on a climatological basis.
Plain Language Summary
Equatorial plasma bubbles (EPBs) are an important space weather phenomenon that are often generated over the magnetic equator around twilight. They are ionospheric irregularities that can cause plasma depletions along the geomagnetic field lines, displaying geomagnetic conjugacy in both hemispheres. Since the ionospheric plasma is one of the significant error sources of the Global Navigation Satellite System (GNSS), EPBs are considered to be a primary disrupter of GNSS communication and navigation. Postsunset rise (PSSR) of the equatorial ionosphere due to vertical ion drift is often used to explain the occurrence of EPBs; however, it cannot fully explain the day‐to‐day variability of EPBs and the features of EPBs in patches and clusters. Mysteries abound around the EPBs and the underlying physics that initiates the EPBs remain unsolved. Here we utilize the FORMOSAT‐3/COSMIC to investigate the underlying background conditions for the generation of EPBs. We find that, in addition to PSSR, symmetric equatorial ionization anomaly, as well as tidal forcing, appears to provide conditions favorable for the initiation of EPBs. Atmospheric tidal waves contribute to the longitudinal and seasonal distribution of EPBs as well. Bottomside ionospheric undulations due to atmospheric forcing are likely playing a vital role in initiating the EPBs.
Key Points
Symmetric EIA provides a condition favorable for the growth of EPBs
Longitudinal three‐ and four‐peak EPB structures related to tidal forcing are identified
Upwellings are observed in the bottomside ionosphere preceding the growth of EPBs
We report the first observation of concentric traveling ionospheric disturbances (CTIDs) triggered by the launch of a SpaceX Falcon 9 rocket on 17 January 2016. The rocket‐triggered ionospheric ...disturbances show shock acoustic wave signature in the time rate change (time derivative) of total electron content (TEC), followed by CTIDs in the 8–15 min band‐pass filtering of TEC. The CTIDs propagated northward with phase velocity of 241–617 m/s and reached distances more than 1000 km away from the source on the rocket trajectory. The wave characteristics of CTIDs with periods of 10.5–12.7 min and wavelength ~ 200–400 km agree well with the gravity wave dispersion relation. The optimal wave source searching and gravity wave ray tracing technique suggested that the CTIDs have multiple sources which are originated from ~38–120 km altitude before and after the ignition of the second‐stage rocket, ~200 s after the rocket was launched.
Key Points
First observation of concentric traveling ionospheric disturbances triggered by CGWs associated with a SpaceX Falcon 9 rocket launch
The horizontal velocities, wavelengths, and periods of CTIDs agree with the gravity wave dispersion relation
The reverse ray tracing shows that multiple concentric waves were most likely generated around and above the mesosphere region
Plain Language Summary
We observed circular ripples in the space plasma 125 mile height above Earth during the SpaceX rocket launch. These ripple disturbances are indicators of the atmospheric gravity waves that are important to altering the winds in the upper atmosphere. The rocket launches could be another anthropogenic source of upper atmosphere disturbances if space travels become widely available.
This study investigates the underlying physics of equatorial plasma bubbles (EPBs) on 11 December 2019, under solar minimum conditions. The Global‐scale Observations of the Limb and Disk (GOLD) ...ultraviolet nightglow images exhibit a periodic distribution of reduced emissions related to EPBs. Remarkably, FORMOSAT‐7/COSMIC‐2 (F7/C2) observes a significant altitudinal difference of ~45 km in the bottomside ionosphere between two nearly collocated electron density profiles before the onset of EPBs, indicating the presence of an upwelling. Distinct ionospheric perturbations are also observed in F7/C2 and ground‐based Global Positioning System observations, suggesting that gravity waves may contribute to the upwelling. Simulations with SAMI3/ESF are further carried out to evaluate the upwelling growth and pre‐reversal enhancement (PRE) effect on EPB development. Simulations reveal that the crests of upwellings show a localized uplift of ~50 km, and EPBs only develop from the crest of upwellings. The uplift altitude of upwellings is comparable to the F7/C2 observations and the post‐sunset rise in moderate solar conditions. The polarization electric field (Ep) developed within the upwellings can drive vertical Ep × B drifts of ~32–35 m/s, which are comparable to the PRE vertical E × B drifts. We find that the PRE alone cannot drive EPBs without upwelling growth, but it can facilitate the upwelling growth. Observations and simulations allow us to conclude that upwelling growth could play a vital role in the formation of EPBs.
Plain Language Summary
Equatorial plasma bubbles (EPBs) are a crucial nighttime space weather phenomenon that can cause severe radio waves scintillations from the Global Navigation Satellite System. Scientists presumed that the post‐sunset rise (PSSR) of the ionosphere due to vertical drift is the primary driver of EPBs. However, the linkage becomes weak on a daily basis; the PSSR cannot explain the morphology and day‐to‐day variability of EPBs. In this study, we used the recently launched FORMOSAT‐7/COSMIC2 (F7/C2) satellite and Global‐scale Observations of the Limb and Disk (GOLD) to investigate the nature behind the EPBs. GOLD observed EPBs with regular spacing over the Atlantic Ocean region on 11 December 2019. We found a distinct local uplift in the bottomside ionosphere between the nearly collocated F7/C2 electron density profiles before the onset of EPBs, indicating an upwelling. Gravity waves likely contribute to the formation of the upwelling and subsequent development of EPBs. A theoretical ionosphere model is further used to evaluate the upwelling growth and post‐sunset vertical drift effect on EPB development. This study reveals the importance of atmospheric waves on the formation of upwelling and subsequent EPB development.
Key Points
Periodic EPBs and an upwelling are observed by GOLD and FORMOSAT‐7/COSMIC2 during solar minimum
The localized upwelling uplifts the bottomside ionosphere by ~45 km
The vertical Ep × B drift generated by upwellings in the bottomside ionosphere are comparable to the pre‐reversal enhancement
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