Auroral Precipitation Research Articles

Intercomparison of Model Determinations of Auroral Electrodynamic Parameters

AbstractContributing to the objectives of the Committee on Space Research (COSPAR) International Space Weather Action Teams (ISWAT) Auroral Precipitation and High Latitude Electrodynamics (AuroraPHILE) group, various methods and models are compared for determining the auroral electrodynamic parameters during geomagnetically active conditions. Parameters used for comparisons include Cross Polar Cap Potential (CPCP), Hemispherically Integrated Joule Heating (HIJH), and Hemispheric Power Input (HPI). Models tested include Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) Derived Electrodynamics of the High Latitude Ionosphere (ADELPHI), Lyon‐Fedder‐Mobarry (LFM) ‐ Magnetosphere Ionosphere Coupler/Solver (MIX), Space Weather Modeling Framework (SWMF), Open Geospace General Circulation Model (OpenGGCM), and Ovation Prime. Modeled CPCP values are compared with the observations from the Super Dual Auroral Radar Network (SuperDARN) and the Defense Meteorological Satellite Program (DMSP). The performance of OpenGGCM is further scrutinized by varying model resolutions. The effects of coupling with the Rice Convection Model (RCM) are also observed. The results showed large and inconsistent differences in the auroral parameters across models. In particular, LFM‐MIX and higher‐resolution OpenGGCM without RCM generally showed higher CPCP and HIJH than the other models. Low‐resolution OpenGGCM with RCM, ADELPHI, and SWMF provided more accurate CPCP. The inclusion of RCM generally improves OpenGGCM model performance. HPI values from ADELPHI were usually higher than those from Ovation Prime and DMSP data. The modeled auroral parameters were moderately correlated with the observations. Modeled HIJH values were also moderately correlated with Auroral Electrojet (AE). Solstitial interhemispheric asymmetries in CPCP and HIJH were observed and explained by varying ionospheric conductances.

Conditions for the Kelvin‐Helmholtz Instability in the Polar Ionosphere

AbstractThe Kelvin‐Helmholtz instability can be excited by a velocity shear in a fluid. Inhomogeneous flows are frequently observed in regions with polar cap patches, reversed flow events and auroral arcs, that is, regions with irregularities that disturb navigation satellite signals. Understanding the driving conditions and the evolution of the instability is therefore important. In this work, we simulate a flow shear and analyze the non‐linear instability development for a range of velocity shear strengths, shear widths and electron densities. The simulations show that Kelvin‐Helmholtz instability structures can form within 2 minutes for high‐velocity shears ( km/s) and low shear widths ( km), while auroral precipitation dampens instability development. We propose an empirical function for the relationship between instability growth and initial conditions. These results can be used to interpret observations of turbulent flow shear conditions.

A Statistical Analysis of Auroral‐Enhanced Plasma Lines Observed by EISCAT During One Solar Cycle

AbstractEnhanced plasma lines (PLs) obtained from incoherent scatter radars can be utilized to estimate multiple parameters of the ionosphere. The occurrence rates of these PLs, intensified by auroral precipitations, depend on the magnetic local time (MLT) according to the source regions of the precipitated electrons. To comprehensively understand how both nightside and dayside PLs respond to the solar‐wind‐magnetosphere‐ionosphere coupling interactions, we present the first‐ever 11‐year statistical analysis of PLs data. This analysis is based on the European Incoherent Scatter Scientific Association (EISCAT) incoherent scatter radar data set, spanning from 2009 to 2019. Our statistical analysis reveals distinctive characteristics in the behavior of enhanced PLs. The occurrence rates of PL enhancements in the E‐region peak during nighttime (19:00–07:00 MLT), aligning with the activity of secondary electrons from the magnetotail, while in the F‐region peaks occur during daytime (07:00–19:00 MLT), consistent with electron beams from the cusp. A clear seasonal preference emerges, with higher occurrence rates of PL enhancements in the E‐region during winter and in the F‐region during summer. This observation may be attributed to heightened auroral activity during equinoctial months. Additionally, the PL enhancements demonstrate a correlation with intervals of heightened solar‐geomagnetic activity, providing further evidence for a robust connection to auroral precipitation. These findings offer valuable insights into the excitation mechanisms of enhanced PLs and present a novel tool for advancing research in particle precipitation.

Association of structured continuum emission with dynamic aurora

Patterns of ionospheric luminosity provide a unique window into our complex, coupled space environment. The aurora, for example, indicates plasma processes occurring thousands of km away, depositing immense amounts of energy into our polar ionospheres. Here we show observations of structured continuum emission associated with the dynamic aurora. The presence of weak ambient continuum emission has long been recognized. However, studies of its relationship to aurora are scarce and limited by observational constraints. We use spectrally resolved measurements to analyze these previously unexplained emissions, adding critical information about spatial structure, characteristic spectra, and location within auroral dynamics. Our findings demonstrate that the coupling among auroral processes, the plasma, and the neutral atmosphere can unfold at meso-scales and is more complex than previously reported. We suggest that the meso-scale auroral precipitation may, under certain circumstances, effectively couple to atmospheric chemistry and conditions to produce the continuum structure.

Spatial distribution of auroral precipitation and failures in railway automatics at the north of European Russia

We study the relationship between space weather disturbances and spatial distribution of failures in railway automatics at segments of Northern and October railways in 2001–2006. During the most intensive magnetic storms that caused numerous failures, latitude distribution of auroral electron precipitation and local geomagnetic disturbance, determined as mean absolute value of time derivative of the geomagnetic field horizontal component |dBH/dt|, are examined. We show that in magnetic storm main and recovery phases the segments, where the failures were recorded, correspond to the region of intense auroral precipitation and |dBH/dt| exceeded 5 nT/s. The relationship between position of auroral oval equatorial boundary and spatial distribution of failures is analyzed for individual magnetic storms and statistically for five years of observations. Both individual cases and statistic tests show that southward displacement of the auroral oval equatorial boundary correlates with increase in the proportion of failures at lower latitude railway segments.

Пространственное распределение авроральных высыпаний и сбоев в работе железнодорожной автоматики на севере европейской части России

We study the relationship between space weather disturbances and spatial distribution of failures in railway automatics at segments of Northern and October railways in 2001–2006. During the most intensive magnetic storms that caused numerous failures, latitude distribution of auroral electron precipitation and local geomagnetic disturbance, determined as mean absolute value of time derivative of the geomagnetic field horizontal component |dBH/dt|, are examined. We show that in magnetic storm main and recovery phases the segments, where the failures were recorded, correspond to the region of intense auroral precipitation and |dBH/dt| exceeded 5 nT/s. The relationship between position of auroral oval equatorial boundary and spatial distribution of failures is analyzed for individual magnetic storms and statistically for five years of observations. Both individual cases and statistic tests show that southward displacement of the auroral oval equatorial boundary correlates with increase in the proportion of failures at lower latitude railway segments.

Stratospheric aerosols and C6H6 in Jupiter’s south polar region from JWST/MIRI observations

Context. The polar atmosphere of Jupiter is significantly affected by auroral activity, which can induce both thermal and chemical differences compared to the rest of the atmosphere. In particular, auroral activity enhances the production of various hydrocarbons, including benzene. Benzene could be a potential precursor to the formation of the stratospheric hazes. Aims. We investigated the spatial distribution of the benzene abundance across latitudes ranging from 50°S to 81°S and 17°S to 25°S. Additionally, we examined the chemical origin of polar aerosols and their latitudinal distribution. Methods. We employed James Webb Space Telescope (JWST) Mid InfraRed Instrument (MIRI) observations to measure the benzene abundance based on its emission at 674 cm−1. Additionally, we examined the spectral dependence of the aerosol opacity within the 680–760 and 1380–1500 cm−1 spectral ranges, and mapped their distribution from 80°S–50°S. Results. At latitudes lower than 60°S, benzene is found to be up to ten times more abundant compared to lower latitudes. This enhancement of C6H6 is well mixed longitudinally and not particularly concentrated inside the auroral oval. Photochemical models predict a decrease in the abundance as we approach the mid latitudes, but fail at polar latitudes as they do not include ion-neutral chemistry. Moreover, we find that the southern polar atmosphere is enriched with aerosols at ~10 mbar. The optical depth of the aerosols increases at latitudes poleward of ~60°S, similar to the enhancement of C6H6. These aerosols have spectral features similar to the aerosols of Titan and Saturn, and the mass loading is of ~1.2 ± 0.2 × 10−4 g cm−2. Finally, we quantified the impact of these aerosols on the retrieved temperature structure, causing a decrease in the temperature at pressure levels deeper than 10 mbar. Conclusions. We find that the auroral precipitation produces abundant stratospheric aerosols, which must play an important role in the chemistry and dynamics of the planet.

Deriving the Ionospheric Electric Field From the Bulk Motion of Radar Aurora in the E‐Region

AbstractIn the auroral E‐region strong electric fields can create an environment characterized by fast plasma drifts. These fields lead to strong Hall currents which trigger small‐scale plasma instabilities that evolve into turbulence. Radio waves transmitted by radars are scattered off of this turbulence, giving rise to the ‘radar aurora’. However, the Doppler shift from the scattered signal does not describe the F‐region plasma flow, the drift imposed by the magnetosphere. Instead, the radar aurora Doppler shift is typically limited by nonlinear processes to not exceed the local ion‐acoustic speed of the E‐region. This being stated, recent advances in radar interferometry enable the tracking of the bulk motion of the radar aurora, which can be quite different and is typically larger than the motion inferred from the Doppler shift retrieved from turbulence scatter. We argue that the bulk motion inferred from the radar aurora tracks the motion of turbulent source regions (provided by auroras). This allows us to retrieve the electric field responsible for the motion of field tubes involved in auroral particle precipitation, since the precipitating electrons must drift. Through a number of case studies, as well as a statistical analysis, we demonstrate that, as a result, the radar aurora bulk motion is closely associated with the high‐latitude convection electric field. We conclude that, while still in need of further refinement, the method of tracking structures in the radar aurora has the potential to provide reliable estimates of the ionospheric electric field that are consistent with nature.

Ionospheric plasma irregularities over Dronning Maud Land in Antarctica and associated space weather effects

Ionospheric plasma irregularities over Dronning Maud Land in Antarctica and associated space weather effects

Investigation of Thermospheric Response to Geomagnetic Storms Using GITM‐OVATION Prime and ‐FTA Model With Comparison to GOLD and SABER Observations

AbstractGlobal Ionosphere Thermosphere Model (GITM) results have been compared with measurements from Global‐scale observations of the limb and disk (GOLD) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). For the first time, GOLD‐derived exospheric temperature and column‐integrated ratio measurements have been used to validate GITM model results. We examine two geomagnetic storm events for which we drive GITM with space weather conditions to understand how well the model reproduces the thermospheric responses to geomagnetic activity. In this paper, a recently developed auroral model, the Feature Tracking of Aurora (FTA) model, has been employed to calculate auroral electron precipitation in GITM (GITM w/FTA), and results are compared with the OVATION prime (OP) driven GITM model (GITM w/OP). GITM w/FTA simulated temperature, neutral density, and nitric oxide (NO) density are generally higher compared to the GITM w/OP model. During the geomagnetic storm, the GITM model and GOLD‐derived exospheric temperature agree between and N latitude in the equatorial region. GOLD measurements show strong peaks on either side of the equator during the geomagnetic storm period, which is also observed in our model results. The NO cooling peaks estimated by GITM models are 20 km lower than SABER observations during geomagnetic storms. GITM w/FTA better matches SABER observations than GITM w/OP except at low latitudes during storm time. Our model‐model/data comparisons show that improved auroral models are needed to better capture the thermospheric variations during geomagnetic storms.

Comprehensive Pattern of the Ionospheric Troughs Localization in the Winter Southern Hemisphere

AbstractA comprehensive pattern of localization of ionization troughs has been constructed for all local time hours. It includes high‐latitude troughs (HLT), main (or sub‐auroral) troughs (MIT), mid‐latitude ring ionospheric troughs (RIT), low‐latitude troughs (LLT), and quasi‐troughs. The CHAMP satellite data recorded in the southern hemisphere for quiet geomagnetic conditions under high solar activity were used. The separation of HLT and MIT was based on the model of auroral diffuse precipitation (Vorobjev et al., 2013). This model describes zone I of diffuse precipitation at the equatorward edge of the auroral oval and zone II of diffuse precipitation at its poleward edge. To distinguish between MIT and RIT the dynamics of both troughs during geomagnetic disturbances was examined. Because the position of all ionospheric structures, including the auroral oval, depends on longitude, the analysis in each local time sector was conducted within the framework of the longitudinal effect. Each local time sector exhibits specificity. (a) The noon sunlit ionosphere is strongly influenced by the dayside cusp; MIT occurs only at shadow longitudes. (b) In the daytime, strong plasma peaks are observed at latitudes of diffuse precipitation in zone I. (c) In the afternoon/evening sector, the plasma peaks are often observed equatorward of the auroral oval. Both peaks are sometimes accompanied by a quasi‐trough. (d) In the evening, HLT sometimes appears slightly equatorward of auroral oval. (e) In the nighttime, at longitudes of America and the Atlantic, a wide electron density minimum is formed near the Polar circle, which masks the MIT minimum.

Different Origin Field‐Aligned Currents and Their Relationship With Auroral Intensity

AbstractThe ionospheric field‐aligned current (FAC) consists of three components related to ionospheric vortices and gradients of Pedersen and Hall conductances, with the first term being of magnetospheric origin and the latter two being of ionospheric origin (Eq. 1). We calculate each of them between 2010 and 2016 using line‐of‐sight velocity data from the Super Dual Auroral Radar Network radar and auroral electron precipitation data from the Defense Meteorological Satellite Program. Then, we investigate the contribution of each FAC component, as well as the relationship between each FAC component and auroral activity. Our result shows that ionospheric‐origin FACs contribute up to 54% (dawn) and 42% (dusk) within the auroral oval. Both magnetospheric‐origin FACs and ionospheric‐origin FACs initially increase and then stabilize as the SuperMAG electrojet (SME) index increases. After stabilization, these two currents have almost equally important roles, with an average contribution rate of 56% and 44%, respectively. Additionally, the ionospheric‐origin FACs are found to have a higher dependency on auroral intensity. We also find that magnetospheric‐origin FACs exhibit distribution patterns similar to the R1/R2 FAC systems because their directions are determined by vorticities. When the SME index exceeds 200 nT, the contribution from the Pedersen conductance gradient consistently exhibits downward currents near 70° magnetic latitude in the dusk and predawn sectors due to the combined effects of velocities and Pedersen conductance gradients. However, the distribution pattern from the Hall conductance gradient is not so clear due to the uncertainty in the angle between velocity and Hall conductance gradient.

Dependence of the main ionospheric trough position on local time, longitude and geomagnetic activity in the southern winter hemisphere

Dependence of the main ionospheric trough position on local time, longitude and geomagnetic activity in the southern winter hemisphere

The Polarity of IMF By Strongly Modulates Particle Precipitation During High‐Speed Streams

AbstractRecent studies have suggested that the interplanetary magnetic field (IMF) component modulates particle precipitation during solstices, or periods of high dipole tilt . So far this explicit IMF ‐effect has only been shown in statistical studies. Here we analyzed a sequence of high‐speed stream (HSS) driven events of auroral ( keV) and medium energy ( keV and keV) particle precipitation. We show that when HSSs are comparable in terms of IMF and solar wind parameters, they can lead to systematically stronger particle precipitation in individual events when the signs of and are opposite. We also perform a superposed epoch analysis of 485 HSSs giving further evidence that the ‐effect is especially significant during HSSs. This is likely due to the persistent IMF polarity during HSSs. We show evidence that the dependence in particle precipitation is caused by a similar dependence in substorm occurrence.

Extended metric validation of a semi-physical Space Weather Modeling Framework conductance model on field-aligned current estimations

In this study, a detailed metric survey on the “Galaxy 15” (April 2010) space weather event is conducted to validate MAGNetosphere–Ionosphere–Thermosphere (MAGNIT), a semi-physical auroral ionospheric conductance model characterizing four precipitation sources, against AMPERE measurements via field-aligned current (FAC) characteristics. As part of this study, the comparative performance of three ionosphere electrodynamic specifications involving auroral conductance models, MAGNIT, Ridley Legacy Model (RLM) (empirical), and Conductance Model for Extreme Events (CMEE) (empirical), within the Space Weather Modeling Framework (SWMF), is demonstrated. Overall, MAGNIT exhibits marginally improved predictions; root mean square error values in upward and downward FACs of MAGNIT predictions compared to AMPERE data are smaller than those of CMEE and Ridley Ionosphere Model (RIM) by ∼12.7% and ∼6.24% before the storm, ∼4.52% and ∼2.13% better during the main phase, ∼1.98% and ∼1.27% worse during the second minimum, and better by ∼1.84% and ∼1.49% by the beginning of the recovery, respectively. In all three model configurations, the dusk and night magnetic local time (MLT) sectors over-predict throughout the storm, while the day and dawn MLT sectors under-predict in response to interplanetary magnetic field (IMF) conditions. In addition to accuracy and bias, similar results and conclusions are drawn from additional metrics, including in the categories of correlation, precision, extremes, and skill, and recommendations are made for the best-performing model configuration in each metric category. Visual data–model comparisons conducted by studying the FAC location and latitude/MLT spread throughout various phases of the storm suggest that the spatial extent of the FACs is captured relatively well in the night-side auroral oval, unlike in the day-side oval. The spread in latitude of the FACs matches that in the previous literature on other model performances. This information on auroral precipitation sources and their weight on FACs, along with metrics from model–data comparisons, can be used to modify MAGNIT settings to optimize SWMF model performance.

Single‐Hemisphere Oxygen Outflow From Earth's Subauroral Zone

AbstractBesides the cusp, polar cap, and auroral oval, the nightside subauroral zone has also recently been reported as a source region of the ionospheric oxygen outflows. However, the detailed mass and energy sources of these ions remain open questions. Here, we address this issue from the perspective of the response of conjugate hemispheres. Investigation of Van Allen Probes data demonstrates a notable preference of oxygen outflows from the nightside subauroral zone from the sunlit hemisphere. This characteristic eliminates the possibility of nightside auroral precipitation playing a significant role, as it is more prominent in darkness. Instead, it highlights sunlight‐induced ionization as the mass source and enhanced plasma waves from the magnetotail as the energy source. The results presented here further support the nightside subauroral zone as an independent source of magnetospheric oxygen ions.

Temperature and Composition Disturbances in the Southern Auroral Region of Jupiter Revealed by JWST/MIRI

AbstractJupiter's South Polar Region (SPR) was observed by James Webb Space Telescope/Mid‐Infrared Instrument in December 2022. We used the Medium Resolution Spectrometer mode to provide new information about Jupiter's South Polar stratosphere. The southern auroral region was visible and influenced the atmosphere in several ways: (a) In the interior of the southern auroral oval, we retrieved peak temperatures at two distinct pressure levels near 0.01 and 1 mbar, with warmer temperatures with respect to non‐auroral regions of 12 ± 2 K and 37 ± 4 K respectively. A cold polar vortex is centered at 65°S at 10 mbar. (b) We found that the homopause is elevated to km above the 1‐bar pressure level inside the auroral oval compared to km at neighboring latitudes and with an upper altitude of 350 km in regions not affected by auroral precipitation. (c) The retrieved abundance of C2H2 shows an increase within the auroral oval, and it exhibits high abundances throughout the polar region. The retrieved abundance of C2H6 increases toward the pole, without being localized in the auroral oval, in contrast with previous analysis (Sinclair et al., 2018, https://doi.org/10.1016/j.icarus.2017.09.016). We determined that the warming at 0.01 mbar and the elevated homopause might be caused by the flux of charged particles depositing their energy in the SPR. The 1‐mbar hotspot may arise from adiabatic heating resulting from auroral‐driven downwelling. The cold region at 10 mbar may be caused by radiative cooling by stratospheric aerosols. The differences in spatial distribution seem to indicate that the hydrocarbons analyzed are affected differently by auroral precipitation.

Интерактивная геоинформационная система динамической визуализации характеристик аврорального овала на основе паттернов компонентно-ориентированного программирования

The practical need for operational monitoring of the position dynamics of the auroral oval is due to the negative technospheric manifestations of space weather effects observed in this spatial region. However, the well-known software tools for modeling the auroral oval solve this problem inefficiently from the point of view of informativeness and ergonomics. The paper proposes an approach to dynamic visualization of the characteristics of the auroral oval, which is available at the program level in the form of a traditional web application with the ability to render visual elements in the browser, as well as in the format of a standalone service like RESTful-API. The developed solution provides visualization of the following parameters: the probability of observing the glow of the upper layers of the atmosphere with the naked eye, the electric and magnetic potentials of the field in the region of the northern auroral belt, as well as various types of auroral precipitation. It is assumed that the proposed approach will make it possible to significantly increase the efficiency of the study of parameters in the auroral oval region by specialists and scientists in the relevant fields. At the same time, the high internal and low external connectivity of the developed software modules allow them to be integrated into third-party applications of various profiles and purposes.

Lower Band Chorus Wave Scattering Causing the Extensive Morningside Diffuse Auroral Precipitation During Active Geomagnetic Conditions: A Detailed Case Study

AbstractThe diffuse aurora is a natural phenomenon observed over the Earth's polar region. Compared with the nightside diffuse aurora, the brightness of the dayside diffuse aurora (0600–1800 magnetic local time (MLT)) is relatively weak, thus requiring more stringent observation conditions. Therefore, the current understanding of what causes the dayside diffuse aurora is still quite limited. Here, we present an intense morningside diffuse aurora (0600–1000 MLT) event observed on 1 January 2016 during the recovery phase of the substorm, using conjugate observations of wave and particle spectrum from the Radiation Belt Storm Probes and auroral emission from the Special Sensor Ultraviolet Spectrographic Imagers on the Air Force Defense Meteorological Satellite Program (DMSP/SSUSI). We perform calculations of diffusion coefficients and simulations of the electron fluxes for this event. Our results show that the chorus waves are the primary contributors to the formation of the morningside diffuse aurora, with precipitated electron energies ranging from a few keV to tens of keV. The lower band chorus shows significant pitch angle scattering efficiency for electrons with energies from 5 to 20 keV. The upper band chorus waves induce acceleration effects on 1–20 keV electrons. We suggest that the upper band chorus waves accelerate low‐energy electrons to higher energies, enabling them to engage in the scattering process of the lower band chorus waves. Our study makes a contribution to recent research on the formation mechanisms of diffuse aurora and deepens our understanding of wave‐particle interactions leading to dayside electron precipitation.

Impact of Electron Precipitation on Brown Dwarf Atmospheres and the Missing Auroral H3+ Emission

Recent observations have demonstrated that very low-mass stars and brown dwarfs are capable of sustaining strong magnetic fields despite their cool and neutral atmospheres. These kilogauss field strengths are inferred based on strong, highly circularly polarized gigahertz radio emission, a consequence of the electron cyclotron maser instability. Crucially, these observations imply the existence of energetic nonthermal electron populations, associated with strong current systems, as are found in the auroral regions of the magnetized planets of the solar system. Intense auroral electron precipitation will lead to electron collisions with the H2 gas that should generate the ion H3+ . With this motivation, we targeted a sample of ultracool dwarfs, known to exhibit signatures associated with aurorae, in search of the K-band emission features of H3+ using the Keck telescopes on Maunakea. From our sample of nine objects, we found no clear indication of H3+ emission features in our low-to-medium-resolution spectra (R ∼ 3600). We also modeled the impact of an auroral electron beam on a brown dwarf atmosphere, determining the depth at which energetic beams deposit their energy and drive particle impact ionization. We find that the H3+ nondetections can be explained by electron beams of typical energies ≳2–10 keV, which penetrate deeply enough that any H3+ produced is chemically destroyed before radiating energy through its infrared transitions. Strong electron beams could further explain the lack of UV auroral detections and suggest that most or nearly all of the precipitating auroral energy must ultimately emerge as thermal emissions deep in brown dwarf atmospheres.