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We report the first simultaneous observations of total electron content (TEC), radio signal scintillation, and precise point positioning (PPP) variation associated with Strong Thermal Emission Velocity Enhancement (STEVE) emissions during a 26 March 2008 storm‐time substorm. Despite that the mid‐latitude trough TEC decreases during the substorm overall, interestingly, we found an unexpected TEC enhancement (by ∼2 TECU) during STEVE. Enhancement of vertical TEC and phase scintillation was highly localized to STEVE within a thin latitudinal band of 1°. As STEVE shifted equatorward, TEC enhancement was found at and slightly poleward of the optical emission. PPP exhibited enhanced variation across a 3° latitudinal range around STEVE and indicated increased GNSS positioning error. We suggest that TEC enhancement during STEVE creates local TEC structures in the ionosphere that degrade Global Navigation Satellite Systems (GNSS) signals and PPP performance. The TEC enhancement may be created by particle precipitation, Pedersen drift across STEVE, neutral wind, or plasma instability. Plain Language Summary: Global Navigation Satellite Systems (GNSS) signals experience phase and amplitude fluctuations known as scintillation when traveling through density irregularities in the ionosphere. The ionospheric density structures created during Strong Thermal Emission Velocity Enhancement (STEVE) have not yet been characterized in the literature. We combine ground‐based imaging and measurements of ionospheric density to show that STEVE creates unusually steep density gradients and small‐scale density irregularities. We find enhanced phase scintillation and increased GNSS positioning error in GNSS receiver stations where STEVE transects the line of sight between the receiver and satellite. The ionospheric density irregularities associated with STEVE are highly localized and suspected to be connected to particle precipitation and plasma drift during STEVE. These results quantify STEVE's impact on ionospheric dynamics and GNSS navigation for the first time. Key Points: A distinct TEC enhancement was found in the subauroral ionosphere during STEVEThe scintillation indices show significant GNSS phase and amplitude fluctuations during the TEC gradientsPrecise point positioning variations show enhanced GNSS positioning error during STEVE [ABSTRACT FROM AUTHOR]

We examined evolution of Global Positioning System (GPS) scintillation during a substorm in the nightside high latitude ionosphere, using 1‐s phase and amplitude scintillation indices from the Canadian High Arctic Ionospheric Network (CHAIN) network. The traditional 1‐min scintillation indices showed that the phase scintillation was dominant, while the amplitude scintillation was weak. However, the 1‐s amplitude scintillation occurred more often in association with major auroral structures (polar cap arc, growth phase arc, onset arc, poleward expanding arc, poleward boundary intensification, and diffuse aurora) that were detected by the THEMIS all‐sky imagers (ASIs). The 1‐min index missed much of the amplitude fluctuations because they only lasted ∼10 s near a local peak or at the gradients of the auroral structures. The 1‐s phase scintillation was concurrent with the amplitude scintillation but was much weaker than the 1‐min phase scintillation. The frequency spectral analysis showed that the spectral power above ∼1 Hz was diffractive and below ∼1 Hz was refractive. We suggest that the amplitude scintillation in the high‐latitude ionosphere is much more common than previously considered, and that a short time window of the order of 1 s should be used to detect the scintillation. The 1‐min phase scintillation index is largely influenced by refractive effects due to total electron content (TEC) variations, and the spectral power below ∼1 Hz should be removed to identify diffractive scintillation. Plain Language Summary: The Global Positioning System (GPS) is widely used in the society for navigation. The GPS radio signal is disturbed by aurora due to modulation of ionospheric plasma density, and the signal disturbance is called scintillation. The scintillation indices are widely used to quantify the level of scintillation. We show that the conventional scintillation indices often miss the scintillation, because the indices assume that aurora is steady for a minute but aurora evolves rapidly in ∼10 s. We use a modified version of the indices and show that the scintillation of GPS signal amplitude occurs more commonly than previously considered. In addition, we show that the conventional phase scintillation index overestimates the scintillation of GPS signal phase, because it is sensitive to variation of the ionospheric plasma density. Our modified indices remove this effect and characterize the scintillation more accurately. We find that the scintillation is closely related to active auroral forms during an auroral substorm. Key Points: The 1‐s amplitude scintillation index shows much more frequent occurrence of diffractive scintillation than the 1‐min indexThe 1‐s phase scintillation index is smaller than the 1‐min index but is better correlated with the amplitude scintillationThe higher cutoff frequency and shorter time window are important for removing refractive effects and identifying diffractive scintillation [ABSTRACT FROM AUTHOR]

Evolution of large‐scale and fine‐scale plasmaspheric plume density structures was examined using space‐ground coordinated observations of a plume during the 7–8 September 2015 storm. The large‐scale plasmaspheric plume density at Van Allen Probes A was roughly proportional to the total electron content (TEC) along the satellite footprint, indicating that TEC distribution represents the large‐scale plume density distribution in the magnetosphere. The plasmaspheric plume contained fine‐scale density structures and subauroral polarization streams (SAPS) velocity fluctuations. High‐resolution TEC data support the interpretation that the fine‐scale plume structures were blobs with ∼300 km size and ∼500–800 m/s in the ionosphere (∼3,000 km size and ∼5–8 km/s speed in the magnetosphere), emerging at the plume base and drifting to the plume. The short‐baseline Global Navigation Satellite System receivers detected smaller‐scale (∼10 km in the ionosphere, ∼100 km in the magnetosphere) TEC gradients and their sunward drift. Fine‐scale density structures were associated with enhanced phase scintillation index. Velocity fluctuations were found to be spatial structures of fine‐scale SAPS flows that drifted sunward with density irregularities down to ∼10 s of meter‐scale. Fine‐scale density structures followed a power law with a slope of ∼−5/3, and smaller‐scale density structures developed slower than the larger‐scale structures. We suggest that turbulent SAPS flows created fine‐scale density structures and their cascading to smaller scales. We also found that the plume fine‐scale density structures were associated with whistler‐mode intensity modulation, and localized electron precipitation in the plume. Structured precipitation in the plume may contribute to ionospheric heating, SAPS velocity reduction, and conductance enhancements. Plain Language Summary: A plume of cold plasma circulates in the system during geomagnetic storms, and it is important for global positioning system (GPS) signal scintillation at mid‐latitudes of the Earth. We show that the plume contains fine‐scale density structures across multiple‐scales, and reveal their 2‐d structure and motion using GPS remote sensing and multiple satellites. The network of GPS receivers showed that the fine‐scale plume structures were blobs with hundreds of km size in the ionosphere, and GPS signal scintillation was highly correlated with the fine‐scale density structures. Radar observations identified a close relation between the fine‐scale density and fast plasma streams. The plume density structures formed first at large‐scales and then small‐scale density structures emerged near the peak of the geomagnetic storm. We suggest that fast plasma streams created fine‐scale density structures and their turbulent cascading to smaller scales. Key Points: Two dimensional structure and motion of fine‐scale plume density has been revealed by Van Allen Probes‐defense meteorological satellite program‐Swarm‐global positioning system conjunctionFine‐scale subauroral polarization streams flows are related to fine‐scale density and are suggested to create turbulent density cascadingFine‐scale density contributes to waves, precipitation, heating, and scintillation [ABSTRACT FROM AUTHOR]

Using the University Navstar Consortium (UNAVCO) Global Positioning System (GPS) receiver network in North America, we present 2-D distributions of GPS radio signal scintillation in the mid-latitude ionosphere during the 7-8 September 2017 storm. The mid-latitude ionosphere showed a variety of density structures such as the storm enhanced density (SED) base and plume, main trough, secondary plume, and secondary trough during the storm main and early recovery phases. Enhanced phase and amplitude scintillation indices were observed at the density gradients of those structures. SuperDARN radar echoes were also enhanced at the density gradients. The collocation of the scintillation and HF radar echoes indicates that density irregularities developed across a wide range of wavelengths (tens of meters to tens of kilometers) in the mid-latitude density structures. The density gradients and irregularities were also detected by Swarm and DMSP as in-situ density structures that disturbed the GPS signals. The irregularities were a substantial fraction (~10%-50%) of the background density. The density irregularity had a power law spectrum with slope of ~ -1.8, suggesting that gradient drift instability (GDI) contributed to turbulence formation. Both high-latitude and low-latitude processes likely contributed to forming the mid-latitude density structures, and the mid-latitude scintillation occurred at the interface of high-latitude and low-latitude forcing. [ABSTRACT FROM AUTHOR]

On 26 March 2008, simultaneous measurements of a large substorm were made using the Poker Flat Incoherent Scatter Radar, Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft, and all sky cameras. After the onset, electron precipitation reached energies ≳100 keV leading to intense D region ionization. Identifying the source of energetic precipitation has been a challenge because of lack of quantitative and magnetically conjugate measurements of loss cone electrons. In this study, we use the maximum entropy inversion technique to invert altitude profiles of ionization measured by the radar to estimate the loss cone energy spectra of primary electrons. By comparing them with magnetically conjugate measurements from THEMIS-D spacecraft in the nightside plasma sheet, we constrain the source location and acceleration mechanism of precipitating electrons of different energy ranges. Our analysis suggests that the observed electrons ≳100 keV are a result of pitch angle scattering of electrons originating from or tailward of the inner plasma sheet at ~9 RE, possibly through interaction with electromagnetic ion cyclotron waves. The electrons of energy 10-100 keV are produced by pitch angle scattering due to a potential drop of ≲10 kV in the auroral acceleration region (AAR) as well as wave-particle interactions in and tailward of the AAR. This work demonstrates the utility of magnetically conjugate ground- and space-based measurements in constraining the source of energetic electron precipitation. Unlike in situ spacecraft measurements, ground-based incoherent scatter radars combined with an appropriate inversion technique can be used to provide remote and continuous-time estimates of loss cone electrons in the plasma sheet. [ABSTRACT FROM AUTHOR]

Extremely elevated ion temperatures observed with the Poker Flat and Resolute Bay incoherent scatter radars in the E and F regions of the polar ionosphere are discussed. Our observations include one-dimensional, line-of-sight ion temperatures ( T i,1 d) that at times can rise to up to ∼8000°K. While examining the accuracy of the derived temperatures is difficult due to the several potential sources of error and uncertainty, we find that at altitudes of ∼130-250 km the line-of-sight ion temperatures obtained at relatively small aspect angles (for instance, at 22.5° away from the magnetic field direction) are below the expected values for the average or three-dimensional ion temperatures ( T i). We find that this difference matches well with the theoretical expectation from anisotropic ion velocity distributions that emerge from polarization elastic scattering collisions between NO+ and N2. These results are therefore the clearest detection of anisotropic ion velocity distributions with the Poker Flat Incoherent Scatter Radar and Resolute Bay Incoherent Scatter Radar facilities. Moreover, at higher altitudes (>∼300 km), where the resonant charge exchange collisions prevail, and for a very high ion temperature event ( T i∼8000°K), we observe that the incoherent scatter radar (ISR) spectra obtained at large aspect angles (e.g., 55°) look like those expected from non-Maxwellian plasma. At similar altitudes, the measured one-dimensional temperatures at an aspect angle of 22.5° are found to exceed the expected values from the frictional heating and resonant charge exchange collisions by about 1000°K. A portion of this offset is thought to reflect the role of Coulomb collisions. [ABSTRACT FROM AUTHOR]

The beam-plasma mechanism, based on the Langmuir decay process, has been proposed to explain naturally enhanced ion-acoustic lines (NEIALs), which are spectral distortions in incoherent scatter radar (ISR) data frequently observed in the vicinity of auroral arcs. In this work the effect of the Langmuir decay process on the ISR spectrum is studied and compared with an analytical model for different plasma parameters by using an electrostatic parallel particle-in-cell (EPPIC) code. Simulations show that the code is working in accordance with theory for a wide range of beam and plasma values and that the features of the spectrum are sensitive to changes of those values. These results suggest that the EPPIC code might be used to build a spectrum-plasma parameter model which will allow estimation of beam and plasma parameters from observed spectra. Simulations also confirm that background electron density (ne) plays an important role in determining the maximum detectable wavenumber of the enhancement. Specifically, results demonstrate that an increase in ne makes the enhancements of the ion acoustic more likely line at large wavenumbers, a finding consistent with statistical studies showing more frequent NEIAL occurrence near solar maximum. Finally, the simulations expose some inaccuracies of the current theoretical model in quantifying the energy passed from the beam to the Langmuir waves as well as with the range of enhanced wavenumbers. These differences may be attributable to the weak Langmuir turbulent regime assumption used in the theory [ABSTRACT FROM AUTHOR]

Naturally Enhanced Ion Acoustic Lines (NEIALs) detected with Incoherent Scatter Radars (ISRs) can be produced by a Langmuir decay mechanism, triggered by a bump on tail instability. A recent model of the beam-plasma instability suggests that weak-warm beams, such those associated with NEIAL events, might produce Langmuir harmonics which could be detected by a properly configured ISR. The analysis performed in this work shows that such a beamdriven wave may be simultaneously detected with NEIALs within the baseband signal of a single ISR. The analysis shows that simultaneous detection of NEIALs and the first Langmuir harmonic is more likely than simultaneous detection of NEIALs and enhanced plasma line. This detection not only would help to discriminate between current NEIAL models, but could also aid in the parameter estimation of soft precipitating electrons. [ABSTRACT FROM AUTHOR]

The work presents a data-model synthesis examining the response of the auroral F-region ion temperature, composition, and density to short time scale (<1 min) electric field disturbances associated with auroral arcs. Ion temperature profiles recorded by the Sondrestrom incoherent scatter radar (ISR) are critically analyzed with the aid of theoretical calculations to infer ion composition variability. The analyses presented include a partial accounting for the effects of neutral winds on frictional heating and show promise as the groundwork for future attempts to address ion temperature-mass ambiguities in short-integration ISR data sets. Results indicate that large NO+ enchancements in the F-region can occur in as little as 20 s in response to impulsive changes in ion frictional heating. Enhancements in molecular ion density result in recombination and a depletion in plasma, which is shown to occur on time scales of several minutes. This depletion process, thus, appears to be of comparable importance to electrodynamic evacuation processes in producing auroral arc-related plasma depletions. Furthermore, the potential of ionospheric composition in regulating the amounts and types of ions supplied to the magnetosphere is outlined. [ABSTRACT FROM AUTHOR]

Optical observations of the aurora have traditionally focused on the structure, intensity, and wavelength of the emissions. But the apparent motion of auroral forms offers another important diagnostic tool for investigating this poorly understood phenomenon. Prior analyses of auroral motion have focused on tracing individual features. In this letter, we investigate the feasibility of deriving the entire two-dimensional velocity field automatically using robust optical flow estimation. The analysis is applied to two narrow-field video sequences. Both examples are rich in small-scale structure and motion, but appear very different to the eye. The robust optical flow estimator performed well for regions of dense turbulent motion, while sheared flow and flow which is perpendicular to image intensity gradients, was poorly resolved. The relative magnitude of the outliers provides a quantitative measure of the validity of the underlying flow model and, hence, a means of automatically differentiating among auroral forms with differing physical origins. The technique can be used to deduce ionospheric electric fields and neutral winds, and the flow fields yield important physical information about the generation mechanism. [ABSTRACT FROM PUBLISHER]

Global circulation models (GCMs) for the ionosphere‐thermosphere system traditionally use empirical models to specify upper boundary conditions to represent solar wind and magnetospheric drivers. However, the magnetosphere, ionosphere, and thermosphere systems are coupled on different spatial and temporal scales. During increased levels of geomagnetic activity, these empirical models can't resolve dynamic electric field variability (<500 km, <15 min) because of their statistical nature and/or low spatial and temporal resolutions. This results in an underestimation of energy input to the ionosphere, causing disagreements between model results and observations. This paper introduces a new framework to incorporate dynamic electric fields into GCMs: High‐latitude Input for Mesoscale Electrodynamics (HIME). As a demonstration HIME uses the Poker Flat Incoherent Scatter Radar (PFISR) electric field estimates during an experiment on 2 March 2017. The electric potentials were calculated using the PFISR estimates and merged with a global empirical model of electric potential. A set of high‐latitude electric potential drivers were used to drive the University of Michigan Global Ionosphere Thermosphere Model (GITM) to understand the effects of driving at different scales. Data versus model comparisons for ion temperature, electron temperature, and electron density are provided along the PFISR beams. The ion convection velocities and neutral winds at the PFISR location are compared with the PFISR and Scanning Doppler Imager data. The effects of different multiscale drivers are investigated. The results showed that energy deposited by HIME‐driven simulations was locally larger by approximately an order of magnitude compared to the empirical model‐driven results. Key Points: For the first time local, dynamic, 2‐D electric field estimates are merged with a global empirical modelLocal mesoscale electric field variability is successfully communicated to GITMThe energy deposited locally in HIME‐driven simulations is higher compared to Weimer‐driven simulations [ABSTRACT FROM AUTHOR]

Objective: Early identification of individuals who are at risk for suicide is crucial in supporting suicide prevention. Machine learning is emerging as a promising approach to support this objective. Machine learning is broadly defined as a set of mathematical models and computational algorithms designed to automatically learn complex patterns between predictors and outcomes from example data, without being explicitly programmed to do so. The model's performance continuously improves over time by learning from newly available data. Method: This concept paper explores how machine learning approaches applied to healthcare data obtained from electronic health records, including billing and claims data, can advance our ability to accurately predict future suicidal behavior. Results: We provide a general overview of machine learning concepts, summarize exemplar studies, describe continued challenges, and propose innovative research directions. Conclusion: Machine learning has potential for improving estimation of suicide risk, yet important challenges and opportunities remain. Further research can focus on incorporating evolving methods for addressing data imbalances, understanding factors that affect generalizability across samples and healthcare systems, expanding the richness of the data, leveraging newer machine learning approaches, and developing automatic learning systems., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Boudreaux, Rundensteiner, Liu, Wang, Larkin, Agu, Ghosh, Semeter, Simon and Davis-Martin.)

Small-scale dynamic auroras have spatial scales of a few km or less, and temporal scales of a few seconds or less, which visualize the complex interplay among charged particles, Alfvén waves, and plasma instabilities working in the magnetosphere-ionosphere coupled regions. We summarize the observed properties of flickering auroras, vortex motions, and filamentary structures. We also summarize the development of fundamental theories, such as dispersive Alfvén waves (DAWs), plasma instabilities in the auroral acceleration region, ionospheric feedback instabilities (IFI), and the ionospheric Alfvén resonator (IAR)., Supplementary Information: The online version contains supplementary material available at 10.1007/s11214-021-00796-w., (© The Author(s) 2021, corrected publication 2021.)

In this paper, we present a technique for dimensionality reduction in hyperspectral imaging during the data collection process. A four-channel hyperspectral imager using liquid crystal Fabry-Perot etalons has been built and used to verify this method for four applications: auroral imaging, plant study, landscape classification, and anomaly detection. This imager is capable of making measurements simultaneously in four wavelength ranges while being tunable within those ranges, and thus can be used to measure narrow contiguous bands in four spectral domains. In this paper, we describe the design, concept of operation, and deployment of this instrument. The results from preliminary testing of this instrument are discussed and are promising and demonstrate this instrument as a good candidate for hyperspectral imaging.

A four channel hyperspectral imager using Liquid Crystal Fabry-Perot (LCFP) etalons has been built and tested. This imager is capable of making measurements simultaneously in four wavelength ranges in the visible spectrum. The instrument was designed to make measurements of natural airglow and auroral emissions in the upper atmosphere of the Earth and was installed and tested at the Poker Flat Research Range in Fairbanks, Alaska from February to April 2014. The results demonstrate the capabilities and challenges this instrument presents as a sensor for aeronomical studies.