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This paper reports the first high‐resolution 4‐dimensional ionospheric disturbance caused by hurricane Matthew on 7 October 2016. The temporal as well as vertical and horizontal variations of the concentric traveling ionospheric disturbances (CTIDs) were reconstructed using 3‐dimensional computerized ionospheric tomography (3DCIT) technology, based upon the Global Navigation Satellite System data from the dense receiver network over North America. The frequency range of disturbances was determined by spectrum analysis, and a Butterworth band‐pass filter was used to de‐trend the total electron content (TEC) sequences to determine TIDs. A remarkable CTID segment was detected at a distance of 1,000–1,500 km from the hurricane eye at ∼5:40–6:10 UT on 7 October 2016, moving westward with the horizontal phase velocity of ∼153.4 m/s, the period of ∼30 min and the horizontal wavelength of ∼276.1 km. The positive and negative wavefronts dominated the CITD at different times during the event. From 4:00 to 8:00 UT, the altitudinal variation of the CTIDs in electron density exhibited clear downward phase progression predominately in the range of 150–400 km altitudes; however, the percentage of electron density disturbances was larger below 250 km. The inverted cone‐like geometry of CTID wavefronts was presented. The vertical phase velocities of the CTIDs ∼1,100 km away from the hurricane eye in the northwest direction near 88°W, 34°N were ∼203.7–277.8 m/s, and at the same location, the horizontal phase velocities at 300 km altitude were ∼149.1–181.5 m/s, slightly larger than those at 200 km altitude (∼145.1–178.5 m/s). Key Points: The propagation features of concentric traveling ionospheric disturbances (CTID) caused by Hurricane Matthew on 7 October 2016 were analyzedFirst 4‐dimensional CTIDs caused by hurricane were reconstructed using ionospheric tomographyThe horizontal phase velocities at different altitudes and the vertical phase velocities of the ionospheric disturbances were estimated [ABSTRACT FROM AUTHOR]

An accurate description of the state of the ionosphere is crucial for understanding the physics of Earth's coupling to space, including many potentially hazardous space weather phenomena. To support this effort, ground networks of magnetometer stations, optical instruments, and radars have been deployed. However, the spatial coverage of such networks is naturally restricted by the distribution of land mass and access to necessary infrastructure. We present a new technique for local mapping of polar ionospheric electrodynamics, for use in regions with high data density, such as Fennoscandia and North America. The technique is based on spherical elementary current systems (SECS), which were originally developed to map ionospheric currents. We expand their use by linking magnetic field perturbations in space and on ground, convection measurements from space and ground, and conductance measurements, via the ionospheric Ohm's law. The result is a technique that is similar to the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique, but tailored for regional analyses of arbitrary spatial extent and resolution. We demonstrate our technique on synthetic data, and with real data from three different regions. We also discuss limitations of the technique and potential areas for improvement. Plain Language Summary: The ionosphere, where a small but significant fraction of the atmosphere is ionized, forms the edge of space. At only 100‐km altitude, it is the region in space which is by far best monitored by human instruments. Space scientists routinely use measurements that inform about specific aspects of the dynamics in the ionosphere, but not the whole picture. For example, magnetometers on ground measure one part of the electric current system while magnetometers on satellites measure another part. Radars measure the flow of charged particles in the ionosphere, while optical images and particle measurements can be used to estimate electric conductivity. In this paper, we present a technique that combines all these different types of measurements to give a complete picture of what takes place in the ionosphere. The technique is tailored for use in regions where the data density is high, and the spatial resolution and extent of the analysis region are flexible. Key Points: We present a technique to use disparate data types to produce local maps of polar ionospheric electrodynamicsΔB and convection measurements are related via ionospheric Ohm's law and spherical elementary current systemsWe demonstrate the technique on real and synthetic data, and discuss limitations and future development [ABSTRACT FROM AUTHOR]

Medium‐scale Traveling Ionospheric Disturbances (MSTIDs) are prominent and ubiquitous features of the mid‐latitude ionosphere, and are observed in Super Dual Auroral Radar Network (SuperDARN) and high‐resolution Global Navigational Satellite Service (GNSS) Total Electron Content (TEC) data. The mechanisms driving these MSTIDs are an open area of research, especially during geomagnetic storms. Previous studies have demonstrated that nightside MSTIDs are associated with an electrodynamic instability mechanism like Perkins, especially during geomagnetically quiet conditions. However, dayside MSTIDs are often associated with atmospheric gravity waves. Very few studies have analyzed the mechanisms driving MSTIDs during strong geomagnetic storms at mid‐latitudes. In this study, we present mid‐latitude MSTIDs observed in de‐trended GNSS TEC data and SuperDARN radars over the North American sector, during a geomagnetic storm (peak Kp reaching 9) on 7–8 September 2017. In SuperDARN, MSTIDs were observed in ionospheric backscatter with Line of Sight (LOS) velocities exceeding 800 m/s. Additionally, radar LOS velocities oscillated with amplitudes reaching ±500 m/s as the MSTIDs passed through the fields‐of‐view. In detrended TEC, these MSTIDs produced perturbations reaching ∼50 percent of background TEC magnitude. The MSTIDs were observed to propagate in the westward/south‐westward direction with a time period of ∼15 min. Projecting de‐trended GNSS TEC data along SuperDARN beams showed that enhancements in TEC were correlated with enhancements in SuperDARN SNR and positive LOS velocities. Finally, SuperDARN LOS velocities systematically switched polarities between the crests and the troughs of the MSTIDs, indicating the presence of polarization electric fields and an electrodynamic instability process during these MSTIDs. Key Points: Medium‐scale Traveling Ionospheric Disturbance (MSTID) signatures were observed in Global Navigational Satellite Service Total Electron Content and Super Dual Auroral Radar Network (SuperDARN) ionospheric backscatter during a strong geomagnetic stormMSTID characteristics were broadly consistent between the data sets, with periods of 10–20 min and phase speeds of ∼800 m/sSuperDARN Line of Sight velocities systematically switched polarities between MSTID crests and troughs, indicating polarization electric fields [ABSTRACT FROM AUTHOR]

An updated global climatology of blanketing sporadic E (Es) is developed from a combined data set of Global Positioning System (GPS) radio occultation (RO) and ground‐based ionosonde soundings over the period of September 2006–January 2019. A total of 46 sites and 3.2 million total soundings from the Global Ionosphere Radio Observatory network in combination with 3.0 million occultations from the Constellation Observing System for Meteorology, Ionosphere, and Climate constellation are used to calculate global occurrence rates (ORs) for two blanketing frequency thresholds: all blanketing sporadic‐E with no limit on intensity (all‐Es) and moderate‐Es with fbEs ≥ 3 MHz. Following the GPS‐RO to ionosonde comparison by Carmona et al. (2022), https://doi.org/10.3390/rs14030581 the all‐Es rates are calculated using ionosonde data and an amplitude‐based S4 threshold for the GPS‐RO data while the moderate‐Es rates use a primarily phase‐based technique. Occurrence rates are separated by intensity, season, month, and solar local time for quiet geomagnetic conditions. Overall, the general geomagnetic trends agree with previous Es climatologies and the ORs peak near 50% for all‐Es and 25% for moderate‐Es measured in the mid‐latitudes during local summer in the late afternoon. Low ORs are observed near the South Atlantic Anomaly and North America, and a general asymmetry is observed between hemispheres with higher ORs in the Northern Hemisphere. High‐latitude and late morning blanketing Es are found to be stronger but less frequent with rates nearly equal to the moderate‐Es mid‐latitude maximums. Plain Language Summary: A global climatology for sporadic‐E occurrence is developed using a combination of GPS radio occultation and ionosonde measurements for two intensity thresholds. The global OR trends generally follow the results of many previous studies with peaks in the mid‐latitudes of the local summer hemisphere during late afternoon. However, the OR magnitudes differ from previous studies as the inclusion of ionosonde data provides a "ground‐truth" to determine the best Global positioning satellite radio occultation technique for a given intensity threshold. From this, peak occurrence rates of nearly 50% are observed for sporadic‐E with no lower limit on intensity, and 25% for moderate intensity blanketing sporadic‐E. Key Points: An updated global sporadic‐E climatology is presented for two intensity thresholds using a combination of global positioning satellite radio occultation and ionosonde observationsPeak rates of 50% for blanketing Es with no intensity threshold and 25% for moderate‐Es are observed in mid‐latitudes during local summerGlobal trends are similar for both thresholds with high‐latitude sporadic‐E shown to be stronger but less frequent [ABSTRACT FROM AUTHOR]

This study analyzes a simulation of the Arctic winter 2016–2017 with focus on multi‐step vertical coupling (MSVC) by primary, secondary, and higher‐order gravity waves (GWs). We employ the HIgh Altitude Mechanistic general Circulation Model with nudging of the large scales to MERRA‐2 reanalysis. Simulation results confirm the well‐known effects from primary GWs in the winter middle atmosphere regarding strong westward GW drag and a warm winter polar stratopause during the strong‐vortex period in late December 2016, as well as weak eastward GW drag and mesospheric cooling during the sudden stratospheric warming (SSW) in late January and early February 2017. Since the amplitudes of the primary GWs that dissipate in the middle atmosphere are weaker for a reversed or weakened polar vortex, the theory for secondary GW generation predicts reduced MSVC in this case. This is confirmed by strongly reduced secondary and higher‐order GW amplitudes during the SSW and the weak‐vortex period in February. The wintertime higher‐order GWs show partial concentric ring structures above their sources in the lower thermosphere. We find that mostly those higher‐order GWs propagate to higher altitudes that have horizontal propagation directions against the tidal winds. The simulated GWs at 300 km height and observed perturbations of total electron content over Europe and North America during selected days of low geomagnetic activity show very good agreement regarding (a) the wave characteristics and (b) the reduction of amplitudes during the SSW and early February as compared to late December. Plain Language Summary: We analyze the Arctic winter 2016–2017 using a whole atmosphere model with resolved gravity waves (GWs) and nudging of the large scales to MERRA‐2 reanalysis. Model results confirm the well‐known effects from primary GWs in the winter middle atmosphere regarding strong westward GW drag and a warm winter polar stratopause during the strong‐vortex period in late December 2016, as well as weak eastward GW drag and mesospheric cooling during the sudden stratospheric warming (SSW), which started in late January 2017 and was followed by a weak vortex in February. Since secondary and higher‐order GWs are the predominant GWs in the winter mesopause region and thermosphere, the vertical coupling from the lower to the upper atmosphere by GWs is termed multi‐step vertical coupling (MSVC). We find that MSVC is strongly reduced during and after the SSW. The simulated GWs at 300 km height and observed total electron content (TEC) perturbations over Europe and North America during days of low geomagnetic activity show very good agreement regarding the wave characteristics. Furthermore, we find a clear reduction in the TEC perturbation amplitudes during and after the SSW. This agreement between model and observations strongly suggests that quiet‐time TEC perturbations in the winter thermosphere are caused by GWs from MSVC. Key Points: Wintertime thermospheric gravity waves (GWs) simulated by a whole atmosphere model are strongly reduced during the January 2017 sudden stratospheric warming (SSW) and the subsequent weak‐vortex periodObserved quiet‐time total electron content (TEC) perturbations show reduced amplitudes during the SSW and weak‐vortex period as wellPropagation directions, wavelengths, and periods of the simulated thermospheric GWs agree with observed quiet‐time TEC perturbations [ABSTRACT FROM AUTHOR]