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Following the 2022 Tonga Volcano eruption, dramatic suppression and deformation of the equatorial ionization anomaly (EIA) crests occurred in the American sector ∼14,000 km away from the epicenter. The EIA crests variations and associated ionosphere-thermosphere disturbances were investigated using Global Navigation Satellite System total electron content data, Global-scale Observations of the Limb and Disk ultraviolet images, Ionospheric Connection Explorer wind data, and ionosonde observations. The main results are as follows: (a) Following the eastward passage of expected eruption-induced atmospheric disturbances, daytime EIA crests, especially the southern one, showed severe suppression of more than 10 TEC Unit and collapsed equatorward over 10° latitudes, forming a single band of enhanced density near the geomagnetic equator around 14–17 UT, (b) Evening EIA crests experienced a drastic deformation around 22 UT, forming a unique X-pattern in a limited longitudinal area between 20 and 40°W. (c) Thermospheric horizontal winds, especially the zonal winds, showed long-lasting quasi-periodic fluctuations between ±200 m/s for 7–8 hr after the passage of volcano-induced Lamb waves. The EIA suppression and X-pattern merging was consistent with a westward equatorial zonal dynamo electric field induced by the strong zonal wind oscillation with a westward reversal.

This study provides first storm time observations of the westward-propagating medium-scale traveling ionospheric disturbances (MSTIDs), particularly, associated with characteristic subauroral storm time features, storm-enhanced density (SED), subauroral polarization stream (SAPS), and enhanced thermospheric westward winds over the continental US. In the four recent (2017–2019) geomagnetic storm cases examined in this study (i.e., 2018-08-25/26, 2017-09-07/08, 2017-05-27/28, and 2016-02-02/03 with minimum SYM-H index −206, −146, −142, and −58 nT, respectively), MSTIDs were observed from dusk-to-midnight local times predominately during the intervals of interplanetary magnetic field (IMF) Bz stably southward. Multiple wavefronts of the TIDs were elongated NW-SE, 2°–3° longitude apart, and southwestward propagated at a range of zonal phase speeds between 100 and 300 m/s. These TIDs initiated in the northeastern US and intensified or developed in the central US with either the coincident SED structure (especially the SED basis region) or concurrent small electron density patches adjacent to the SED. Observations also indicate coincident intense storm time electric fields associated with the magnetosphere–ionosphere–thermosphere coupling electrodynamics at subauroral latitudes (such as SAPS) as well as enhanced thermospheric westward winds. We speculate that these electric fields trigger plasma instability (with large growth rates) and MSTIDs. These electrified MSTIDs propagated westward along with the background westward ion flow which resulted from the disturbance westward wind dynamo and/or SAPS.

We demonstrate a novel method for observing Large Scale Traveling Ionospheric Disturbances (LSTIDs) using high frequency (HF) amateur radio reporting networks, including the Reverse Beacon Network (RBN), Weak Signal Propagation Reporter Network (WSPRNet), and PSKReporter. LSTIDs are quasi-periodic variations in ionospheric densities with horizontal wavelengths >1,000 km and periods between 30 and 180 min. On Nov 3, 2017, LSTID signatures were observed simultaneously over the continental United States in amateur radio, SuperDARN HF radar, and GNSS Total Electron Content with a period of similar to 2.5 hr, propagation azimuth of similar to 163 degrees, horizontal wavelength of similar to 1680 km, and phase speed of similar to 1,200 km hr(-1). SuperMAG SME index enhancements and Poker Flat Incoherent Scatter Radar measurements suggest the LSTIDs were driven by auroral electrojet intensifications and Joule heating. This novel measurement technique has applications in future scientific studies and for assessing the impact of LSTIDs on HF communications. United States National Science Foundation (NSF) [AGS-2045755, AGS-2002278]; NASA [80NSSC21K0002, 80NSSC21K1772]; NSF [AGS-1952737, AGS-1935110, AGS-1840962, AGS-1853408, AGS-1552269] Published version The authors gratefully acknowledge the support of United States National Science Foundation (NSF) Grants AGS-2045755 and AGS-2002278 and NASA Grants 80NSSC21K0002 and 80NSSC21K1772. We are especially grateful to the amateur radio community who voluntarily produced and provided the HF radio observations used in this presentation, especially the operators of the , , pskreporter.info, and . Blackstone SuperDARN data are made available with support from NSF AGS-1935110. This material is based upon work supported by the Poker Flat Incoherent Scatter Radar which is a major facility funded by the NSF through cooperative agreement AGS-1840962 to SRI International. Algorithms used to calculate the electric field and Joule heating rates were developed under NSF AGS-1853408 and AGS-1552269. GNSS TEC data products and access through the Madrigal distributed data system are provided to the community by the Massachusetts Institute of Technology under support from NSF grant AGS-1952737. Individual contributors of GNSS data are listed in the Open Research section. We gratefully acknowledge the SuperMAG collaborators () who contributed to the SuperMAG database (Gjerloev, 2012) and the SuperMAG SME(r) indices (Newell & Gjerloev, 2011a, 2011b). NAF thanks Rachel Frissell, Bill Liles, Ethan Miller, and Dev Raj Joshi for helpful discussions.

Polar holes were observed in the high-latitude ionosphere during a series of multi-instrument case studies close to the Northern Hemisphere winter solstice in 2014 and 2015. These holes were observed during geomagnetically quiet conditions and under a range of solar activities using the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR) and measurements from Global Navigation Satellite System (GNSS) receivers. Steep electron density gradients have been associated with phase scintillation in previous studies; however, no enhanced scintillation was detected within the electron density gradients at these boundaries. It is suggested that the lack of phase scintillation may be due to low plasma density levels and a lack of intense particle precipitation. It is concluded that both significant electron density gradients and plasma density levels above a certain threshold are required for scintillation to occur.

Simultaneous multi‐instrument observations of the redistribution of cold (, National Aeronautics and Space Administration (NASA) (Contract NAS5-01072)

A plasma density hole was created in the ionosphere by a rocket launch from Cape Canaveral, Florida near local sunset on 30 August 2020, which is called rocket exhaust depletion (RED). The hole persisted for several hours into the night and was observed in total electron content (TEC) maps, the Global-scale Observations of the Limb and Disk (GOLD) imager, and multiple low-earth-orbit satellites. The RED created a nightglow pit in the GOLD 135.6 nm image. Swarm satellites found that the RED exhibited insignificant changes in electron/ion temperature and field-aligned currents. On the other hand, magnetic field strength was enhanced inside the RED by a few tenths of a nanotesla. Assimilation data products of the Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) mission reveal that ionospheric slab thickness increased at the center of the RED, which is supported by combined analyses of the GOLD and TEC data. The RED did not host conspicuous substructures that are stronger and longer-lasting than the ambient plasma did.

Low-latitude plasma blobs have been studied since their first being reported in 1986. However, investigations on temporal evolution of a blob or on continental scale (2,000 km) ionospheric contexts around it are relatively rare. Overcoming these limitations can help elucidate the blob generation mechanisms. On 21 January 2021, the Ionospheric Connection Explorer satellite encountered a typical low-latitude blob near the northeastern coast of South America. The event was collocated with a local enhancement in 135.6 nm nightglow at the poleward edge of an equatorial plasma bubble (EPB), as observed by the Global-scale Observations of the Limb and Disk (GOLD) imager. Total electron content maps from the Global Navigation Satellite System confirm the GOLD observations. Unlike typical medium-scale traveling ionospheric disturbances (MSTIDs), the blob had neither well-organized wavefronts nor moved in the southwest direction. Neither was the blob a monotonically decaying equatorial ionization anomaly crest past sunset. Rather, the blob varied following latitudinal expansion/contraction of EPBs at similar magnetic longitudes. The observational results support that mechanisms other than MSTIDs, such as EPBs, can also contribute to blob generation.

We report on an extreme ionospheric plasma density enhancement and Global Positioning System (GPS) scintillation at dawn, observed within the expanding equatorial ionization anomaly (EIA). The tota...

The role a geospace plume in influencing the efficiency of magnetopause reconnection is an open question with two contrasting theories being debated. A local‐control theory suggests that a plume decreases both local and global reconnection rates, whereas a global‐control theory argues that the global reconnection rate is controlled by the solar wind rather than local physics. Observationally, limited numbers of point measurements from spacecraft cannot reveal whether a local change affects the global reconnection. A distributed observatory is hence needed to assess the validity of the two theories. We use THEMIS and Los Alamos National Laboratory spacecraft to identify the occurrence of a geospace plume and its contact with the magnetopause. Global evolution and morphology of the plume is traced using GPS measurements. SuperDARN is then used to monitor the distribution and the strength of dayside reconnection. Two storm‐time geospace plume events are examined and show that as the plume contacts the magnetopause, the efficiency of reconnection decreases at the contact longitude. The amount of local decrease is 81% and 68% for the two events, and both values are consistent with the mass loading effect of the plume if the plume's atomic mass is ∼4 amu. Reconnection in the surrounding is enhanced, and when the solar wind driving is stable, little variation is seen in the cross polar cap potential. This study illuminates a pathway to resolve the role of cold dense plasma on solar wind‐magnetosphere coupling, and the observations suggest that plumes redistribute magnetopause reconnection activity without changing the global strength substantially., Key Points We strategically coordinate measurements made by THEMIS and Los Alamos National Laboratory spacecraft, GPS network, and SuperDARN to investigate geospace plumesPlumes decrease the local reconnection rate at the plume longitude and increase the reconnection rate in regions adjacent to the plumeWhen the solar wind is stable, the global reconnection remains unchanged in presence of plumes, supporting a global‐control theory

Space weather can cause serious disturbances of global navigation satellite systems (GNSS) used for positioning and navigation purposes. This paper describes a new method to forecast space weather disturbances on GNSS at high latitudes, in which we describe the formation and propagation of polar cap patches and predict their arrival at the nightside auroral oval. The space weather prediction model builds on the expanding/contracting polar cap (ECPC) paradigm and total electron content (TEC) observations from the Global Positioning System (GPS) network. The input parameter is satellite observations of the interplanetary magnetic field at the first Lagrange point. To validate our prediction model, we perform a case study in which we compare the results from our prediction model to observations from the GPS TEC data from the MIT's Madrigal database, convection data from Super Dual Auroral radar network, and scintillation data from Svalbard. Our results show that the ECPC paradigm describes the polar cap patch motion well and can be used to predict scintillations of GPS signals at high latitudes.

Much theoretical and observational work has been devoted to studying the occurrence of F region polar cap patches in the Northern Hemisphere; considerably less work has been applied to the Southern Hemisphere. In recent years, the Madrigal database of mappings of total electron content (TEC) has improved in Southern Hemisphere coverage, to the point that we can now carry out a study of patch frequency and occurrence. We find that Southern Hemisphere patch occurrence is very similar to that of the Northern Hemisphere with a half‐year offset, plus an offset in universal time of approximately 12 hr. This is further supported by running an ionospheric model for both hemispheres and applying the same patch‐to‐background technique. Further, we present a simple physical mechanism involving a sunlit dayside plasma source concurrent with a dark polar cap, which yields a patch‐to‐background pattern very much like that seen in the TEC mappings for both hemispheres.

The Earth's ionosphere/thermosphere (I/T) system exhibits complicated weather variability that can have adverse effects on human operations and systems, and consequently, there is a need for both accurate and reliable specifications and forecasts for this region. As part of the international effort to evaluate and assess the predictive capabilities of space weather models, four working groups for the I/T system have been created with the goal to devise a concerted model validation effort for the I/T environment. This paper presents an overview of the team efforts and reports on the progress made. As a first step, the working teams have selected to limit the validation efforts to critical I/T parameters that include total electron content, the peak density and height of the ionospheric F region, ionospheric scintillations, and thermospheric neutral densities. As part of this effort, initial lists of participating models and events have been constructed and validation data sets have been identified. In the future appropriate metrics will be selected for the various user and scientific needs.

Source at https://doi.org/10.1109/TGRS.2018.2847026. In ionospheric tomography, the atmospheric electron density is reconstructed from different electron density related measurements, most often from ground-based measurements of satellite signals. Typically, ionospheric tomography suffers from two major complications. First, the information provided by measurements is insufficient and additional information is required to obtain a unique solution. Second, with necessary spatial and temporal resolutions, the problem becomes very high dimensional, and hence, computationally infeasible. With Bayesian framework, the required additional information can be given with prior probability distributions. The approach then provides physically quantifiable probabilistic interpretation for all model variables. Here, Gaussian Markov random fields (GMRFs) are used for constructing the prior electron density distribution. The use of GMRF introduces sparsity to the linear system, making the problem computationally feasible. The method is demonstrated over Fennoscandia with measurements from global navigation satellite system (GNSS) and low Earth orbit (LEO) satellite receiver networks, GNSS occultation receivers, LEO satellite Langmuir probes, and ionosonde and incoherent scatter radar measurements.

An edited version of this paper was published by AGU. Copyright 2021 American Geophysical Union. We report new findings of total electron content (TEC) perturbations in the southern hemisphere at conjugate locations to the northern eclipse on August 21, 2017. We identified a persistent conjugate TEC depletion by 10%–15% during the eclipse time, elongating along magnetic latitudes with at least ∼5° latitudinal width. As the Moon's shadow swept southward, this conjugate depletion moved northward and became most pronounced at lower magnetic latitudes (>−20°N). This depletion was coincident with a weakening of the southern crest of the equatorial ionization anomaly (EIA), while the northern EIA crest stayed almost undisturbed or was slightly enhanced. We suggest these conjugate perturbations were associated with dramatic eclipse initiated plasma pressure reductions in the flux tubes, with a large portion of shorter tubes located at low latitudes underneath the Moon's shadow. These short L-shell tubes intersect with the F region ionosphere at low and equatorial latitudes. The plasma pressure gradient was markedly skewed northward in the flux tubes at low and equatorial latitudes, as was the neutral pressure. These effects caused a general northward motion tendency for plasma within the flux tubes, and inhibited normal southward diffusion of equatorial fountain plasma into the southern EIA region. We also identified posteclipse ionospheric disturbances likely associated with the global propagation of eclipse-induced traveling atmospheric disturbances in alignment with the Moon's shadow moving direction.

This work conducts a statistical study of the subauroral polarization stream (SAPS) feature in the North American sector using Millstone Hill incoherent scatter radar measurements from 1979 to 2019...

Trans-coronal radio observations were taken during the 2011 observing campaign of the Akatsuki spacecraft through superior conjunction. The observed X-band (8.4 GHz) signals exhibit frequency fluctuations (FF) that are produced by temporal variations in electron density along the radio ray path. A two-component model for interpretation of the FF is proposed: FF scales largely with acoustic wave amplitude through the inner coronal regions where the sound speed dwarfs the solar wind outflow speed, while FF in the region of solar wind acceleration is dominated by the increased density oscillation frequency on the sensing path that results from bulk advection of the plasma inhomogeneities. An estimate of fractional electron density fluctuation is obtained from the mid-corona. A radial profile of slow solar wind speed is determined in the extended corona using mass-flux continuity principles. The coronal sonic point for slow solar wind is estimated to range from 4 to 5 solar radii from the heliocenter.

The strongest Southern Hemisphere minor sudden stratospheric warming (SSW) in the last 40 years occurred in September 2019 and resulted in unprecedented weakening of the stratospheric polar vortex....

We present a new high resolution empirical model for the ionospheric total electron content (TEC). TEC data are obtained from the global navigation satellite system (GNSS) receivers with a 1 x 1 sp...

We demonstrate scintillation analysis from a network of geodetic Global Positioning System (GPS) receivers which provide data at 1-second resolution. We introduce proxy phase (σ TBC ) and amplitude (SNR 4 ) scintillation indices and validate them against the rate of change of TEC index (ROTI) and S 4 . Additionally, we validate scintillation observations against a Connected Autonomous Space Environment Sensor scintillation receiver. We develop receiver-dependent scintillation event thresholding using hardware-dependent noise variance. We analyze 6 days adjacent to the 7–8 September 2017 geomagnetic storm, using 169 receivers covering magnetic latitudes between 15° and 65° in the American longitude sector. We leverage the available spatial sampling coverage to construct 2-D maps of scintillation and present episodic evolution of scintillation intensifications during the storm. We show that low-latitude and high-latitude scintillation morphology match well-established scintillation climatology patterns. At midlatitudes, spatiotemporal evolution of scintillation partially agrees with known scintillation patterns. Additionally, the results reveal previously undocumented midlatitude scintillation-producing structures. The results provide an unprecedented view into the spatiotemporal development of scintillation-producing plasma irregularities and provide a resource to further exploit scintillation evolution at large spatial scales.

Polar holes were observed in the high-latitude ionosphere during a series of multi-instrument case studies close to the northern hemisphere winter solstice in 2014 and 2015. These holes were observed during geomagnetically quiet conditions and under a range of solar activities using the European Incoherent Scatter Scientific Association (EISCAT) Svalbard Radar (ESR) and measurements from Global Navigational Satellite System (GNSS) satellites. Steep electron density gradients have been associated with phase scintillation in previous studies, however, no enhanced scintillation was detected within the electron density gradients at these boundaries. It is suggested that the lack of phase scintillation may be due to low plasma density levels and a lack of intense particle precipitation. It may be that both significant electron density gradients and that plasma density levels above a certain threshold are required for scintillation to occur.

We report the observation of solar wind‐magnetosphere‐ionosphere interactions using a series of flux transfer events (FTEs) observed by Magnetospheric MultiScale (MMS) mission located near the dayside magnetopause on 18 December 2017. The FTEs were observed to propagate duskward and either southward or slightly northward, as predicted under duskward and southward interplanetary magnetic field (IMF). The Cooling model also predicted a significant dawnward propagation of northward‐moving FTEs. Near the MMS footprint, a series of poleward‐moving auroral forms (PMAFs) occurred almost simultaneously with those FTEs. They propagated poleward and westward, consistent with the modeled FTE propagation. The intervals between FTEs, relatively consistent with those between PMAFs, strongly suggest a one‐to‐one correspondence between the dayside transients and ionospheric responses. The FTEs embedded in continuous reconnection observed by MMS and corresponding PMAFs individually occurred during persistent auroral activity recorded by an all‐sky imager strongly indicate that those FTEs/PMAFs resulted from the temporal modulation of the reconnection rate during continuous reconnection. With the decay of the PMAFs associated with the FTEs, patch‐like plasma density enhancements were detected to form and propagate poleward and then dawnward. Propagation to the dawn was also suggested by the Super Dual Auroral Radar Network (SuperDARN) convection and Global Positioning System (GPS) total electron content data. We relate the temporal variation of the driving solar‐wind and magnetospheric mechanism to that of the high‐latitude and polar ionospheric responses and estimate the response time.