Ionospheric Conductivity Research Articles

What Controls the Dawn‐Dusk Asymmetry of Dayside Alfvénic Power: Interplanetary Magnetic Field or Ionospheric Conductance?

AbstractAlfvén waves are important carriers of solar wind energy into the Earth's magnetosphere and upper atmosphere. The observed distribution of Alfvénic power at low altitude exhibits significant dawn‐dusk asymmetry with different causes and impacts on the dayside and nighside. The nightside asymmetry has been shown to be controlled by the meridional gradient in the ionospheric Hall conductance. It is not clear what controls the dayside asymmetry. Both the ionospheric conductance gradient and orientation of the y‐component of the interplanetary magnetic field (IMF) are possible factors. We examined both possibilities using global magnetohydrodynamic (MHD) simulations. Our results show: (a) The dayside distribution of Alfvénic power is very sensitive to the orientation of IMF By, with enhanced power in the dawn (dusk) sector of the northern hemisphere for positive (negative) By (and opposite in the southern hemisphere); and (b) gradients in ionospheric conductance exert a weaker influence on the dayside asymmetry.

Inertia of Ionospheric Conductance During Electron Precipitation Events

AbstractUsing the SuperThermal Electron Transport (STET) model coupled with the Super‐thermal Proton Electron Atomic Hydrogen—tRansport in the Ionosphere and Thermosphere (SPEAH‐RIT) codes, we demonstrate that temporal variability of ionospheric conductance is defined by several time scales: the temporal variations of the magnetospheric source, the start time of electron precipitation, and the termination of the corresponding source. In these cases, the time scales are defined by dissipation of energetic electrons and effective recombination processes. The results presented in this paper were applied in the regions of pulsating aurora and polar arcs, demonstrating the fact that ionospheric conductance requires some time to form and decay. These time delays constitute an effective “inertia” in the conductance calculation which is not accounted for in many global models which assume an instantaneous connection between precipitation and conductance. Ionospheric conductance inertia influences the temporal variation in ionospheric and magnetospheric electric fields, and as a result, impacts magnetosphere‐ionosphere (MI) dynamics on a global scale.

Impacts of Extreme Ultraviolet Late Phase of the Solar Flare on Ionospheric Electrodynamics

Previous investigations of ionospheric electrodynamical responses to solar flares primarily focused on the main phases (MPs) of solar flares. Typical solar irradiance models for driving global ionosphere models do not include the extreme ultraviolet (EUV) late phase (ELP) of flares, which was recently observed with new high-quality solar EUV spectra. Thus, it is still unclear how ionospheric electrodynamics respond to the flare ELP. Here, we analyzed the ionospheric electrodynamical response to the MP and ELP of the X9.3 flare on 2017 September 6, using observations from ground magnetometers, along with simulation results from an ionosphere–thermosphere coupled model. Observations indicated an intensification of the dayside eastward equatorial electrojet (EEJ) by approximately 12 nT at the ELP peak as compared to the quiet day reference. Additionally, the dayside eastward electric field increased due to the ELP, which is different from the reduction of dayside electric fields during MP. The upward E × B plasma drifts decreased by 2.5 m s–1 during MP but increased by 0.75 m s–1 during the ELP. Altitude-dependent responses of ionospheric conductivities to the ELP modulated the relative contribution of the E- and F-region wind dynamo to zonal electric fields, resulting in an overall increase in the daytime eastward electric fields. Furthermore, combined effects of electric fields and conductivities enhancements contributed to EEJ intensification during the ELP. This study enhances our understanding of how solar flares with ELP change global ionospheric electric fields and currents.

Modeling Pitch Angle Dependent Electron Precipitation Using Electron Lifetimes

AbstractElectron precipitation, a crucial link between Earth's magnetosphere and atmosphere, profoundly influences the coupled magnetosphere‐ionosphere‐atmosphere system. Existing models of the ring current often rely on electron lifetimes for characterizing the effects of pitch‐angle scattering, thus limiting accurate predictions of loss cone dynamics. This study introduces a method called steady‐state approximation (steady state approximation) utilizing the steady‐state solution of the pitch‐angle diffusion operator to calculate pitch angle resolved flux within the loss cone. The method enables precise comparisons with low‐earth orbit satellite measurements to validate parameterized electron lifetimes. Applying this approach to reevaluate a prior study, we uncover underestimated electron precipitation during geomagnetic storms, particularly in the pre‐midnight sector. This discrepancy reveals a previously overlooked loss process. Our method enhances the fidelity of global magnetospheric simulations, contributing to improved predictions of ionospheric conductance and atmospheric chemistry dynamics.

Условия появления интенсивных потоков энергичных электронов на L<1.2, связанные с солнечной активностью и параметрами солнечного ветра

We present the results of a statistical study of transient enhancements of electrons with energies >30 keV at low drift shells in the quasi-trapped region (forbidden zone) at the geomagnetic equator. Using data from low-altitude NOAA/POES and MetOp satellites, we have compiled a catalog of events with forbidden energetic electron (FEE) enhancements for the period from 1998 to 2023. Statistical analysis of FEE events has revealed solar-cyclic, as well as seasonal and diurnal variations in the occurrence of FEE enhancements. We have examined the correlation of the annual frequency of FEE events with solar activity, solar wind parameters, and geomagnetic activity. Strong correlations have been found with the F10.7 index of solar activity (radio emission flux) as well as with the Alfvén Mach number (solar wind parameter). An interpretation of the obtained results is proposed which is based on the mechanism of electrical drift and radial transport of electrons from Earth’s inner radiation belt to the quasi-trapped region (L<1.2). The key factor for the operation of the mechanism is the effective penetration of the electric field to low latitudes when a significant difference in the conductivity of the high-latitude ionosphere occurs in the illuminated and unilluminated sectors of local time under conditions of weakening auroral activity.

Conditions for the occurrence of intense fluxes of energetic electrons at L<1.2 associated with solar activity and solar wind parameters

We present the results of a statistical study of transient enhancements of electrons with energies >30 keV at low drift shells in the quasi-trapped region (forbidden zone) at the geomagnetic equator. Using data from low-altitude NOAA/POES and MetOp satellites, we have compiled a catalog of events with forbidden energetic electron (FEE) enhancements for the period from 1998 to 2023. Statistical analysis of FEE events has revealed solar-cyclic, as well as seasonal and diurnal variations in the occurrence of FEE enhancements. We have examined the correlation of the annual frequency of FEE events with solar activity, solar wind parameters, and geomagnetic activity. Strong correlations have been found with the F10.7 index of solar activity (radio emission flux) as well as with the Alfvén Mach number (solar wind parameter). An interpretation of the obtained results is proposed which is based on the mechanism of electrical drift and radial transport of electrons from Earth’s inner radiation belt to the quasi-trapped region (L<1.2). The key factor for the operation of the mechanism is the effective penetration of the electric field to low latitudes when a significant difference in the conductivity of the high-latitude ionosphere occurs in the illuminated and unilluminated sectors of local time under conditions of weakening auroral activity.

The Polarity Oscillations of the Equatorial Electrojet in Response to the Geomagnetic Storm on 1 December 2023

AbstractThe moderate geomagnetic storm on 1 December 2023 is interesting that the aurora is unexpectedly observed in Beijing. During this storm, the behaviors of the equatorial electrojet (EEJ) might deserve to be explored. When the polarization of the daytime electric field changes westward, the direction of EEJ turns westward as well, termed the counter electrojet (CEJ). Using the total electron content from Global Navigation Satellite System, observed EEJ from Tatuoca station and low‐orbit Swarm satellites, and the corresponding simulations from the Thermosphere‐Ionosphere Electrodynamic General Circulation Model, the polarization oscillations of EEJ responses (ΔEEJ) during the geomagnetic storm on 1 December 2023 are explored. A significant polarity oscillation is established in the Swarm‐observed ΔEEJ at 9.6 and 12.8 local time (LT). A similar oscillation is also found at 15 LT. The strong polarity oscillations of ΔEEJ are dominated by the electric field, with ignorable effects from the ionospheric Cowling conductivity. The correlation coefficient between ΔEEJ and electric field changes (ΔE) is larger than 0.87, confirming the roles of the electric field. In the pre‐noon sector, the quasi‐oscillations of ΔEEJ are controlled by both the neutral winds and the prompt penetration electric field (PPEF). At noon, ΔEEJ is primarily driven by the PPEF, with minor effects from neutral winds. At afternoon, ΔEEJ is attributed to the PPEF, and the effects of neutral winds are ignorable.

The Influence of Ionospheric Conductance on Magnetospheric Convection During the Southward IMF

The Influence of Ionospheric Conductance on Magnetospheric Convection During the Southward IMF

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.

Quasi‐Diurnal Lunar Tide O1 in Ionospheric Total Electron Content at Solar Minimum

AbstractFor the first time, characteristics of the geographical and seasonal distribution of the quasi‐diurnal lunar O1 tide were derived from a time series of ionospheric total electron content (TEC) maps provided by International Global Navigation Satellite System Service (IGS). The data analysis is focused on solar minimum in 2008 and 2009 where disturbing influences of geomagnetic and solar activity were minimal. We found that the magnitude of the O1 tide is as strong as the “dominant” semidiurnal lunar M2 tide. Relative amplitudes of 10% and larger are observed in some regions for the O1 component in TEC. The O1 component is particularly strong in northern hemispheric winter over the west coast of South America. There, two maxima occur which are northward and southward of the magnetic equator in the Equatorial Ionization Anomaly (EIA) crest regions. Following Yamazaki et al. (2017, https://doi.org/10.1002/2017ja024601), it might be assumed that a longitudinal anomaly of ionospheric conductivities in the Peruvian sector leads to a stronger modulation of the equatorial electrojet by the lunar tides. Electrodynamic lifting of plasma and transport to the EIA crests may explain the variations of the O1 component in TEC. Contrary to many studies, we find the O1 component (period 25.82 hr) more important than the M1 component (period 24.84 hr, a lunar day). We show that the geographical distribution of the O1 component is totally different from that of the M1 component which is smaller. The seasonal variation of O1 shows maximal amplitudes in northern hemispheric winter and minimal amplitudes in southern hemispheric winter.

The Ionospheric Leg of the Substorm Current Wedge: Combining Iridium and Ground Magnetometers

AbstractUtilizing magnetic field measurements made by the Iridium satellites and by ground magnetometers in North America we calculate the full ionospheric current system and investigate the substorm current wedge. The current estimates are independent of ionospheric conductance, and are based on estimates of the divergence‐free (DF) ionospheric current from ground magnetometers and curl‐free (CF) ionospheric currents from Iridium. The DF and CF currents are represented using spherical elementary current systems (SECS), derived using a new inversion scheme that ensures the current systems' spatial scales are consistent. We present 18 substorm events and find a typical substorm current wedge (SCW) in 12 events. Our investigation of these substorms shows that during substorm expansion, equivalent field‐aligned currents (EFACs) derived with ground magnetometers are a poor proxy of the actual FAC. We also find that the intensification of the westward electrojet can occur without an intensification of the FACs. We present theoretical investigations that show that the observed deviation between FACs estimated with satellite measurements and ground‐based EFACs are consistent with the presence of a strong local enhancement of the ionospheric conductance, similar to the substorm bulge. Such enhancements of the auroral conductance can also change the ionospheric closure of pre‐existing FACs such that the ground magnetic field, and in particular the westward electrojet, changes significantly. These results demonstrate that attributing intensification of the westward electrojet to SCW current closure can yield false understanding of the ionospheric and magnetospheric state.

Scintillation Level of Scattered Radio Waves in the Equatorial Ionosphere

Scintillation effects of propagating and scattered radio waves (RWs) are considered analytically and numerically in the equatorial terrestrial ionosphere applying the statistical characteristics. Analytical calculations of the second-order statistical moments of the phase fluctuations of the ordinary and extraordinary RWs in the conductive collision ionospheric magnetoplasma (COCOIMA) are carried out for the first time using the Wentzel-Kramers-Brilluen method and the modified smooth perturbation method in consideration of the diffraction effects. Polarization coefficients of these waves in the equatorial ionosphere have been derived for the first time. The scintillation level includes the variance and the correlation functions of scattered RWs. Statistical moments contain complex refractive index, anisotropy coefficient characterizing irregular plasmonic structures, tilt angle of prolate irregularities concerning to the external magnetic field, permittivity components of the equatorial ionosphere, Hall's, Pedersen and longitudinal conductivities. A new feature of the "Fountain Effect" has been discovered in the equatorial ionosphere at weak and moderate scintillations caused due to anisotropy parameters of electron density fluctuations. Anisotropy parameters of electron density inhomogeneities influence the scintillation index of both the ordinary and extraordinary radio waves shifting maximums of the curves in the opposite directions at weak and moderate scintillations. Numerical calculations are carried out using the hybrid anisotropic correlation function of electron density fluctuations containing both exponential and power-law spectral functions having arbitrary spectral index, applying the experimental data.

Height profile variations of ionospheric conductivity: A case study in Addis Ababa, Ethiopia

Ionospheric conductivity is the ability to conduct ionospheric current and is impacted by a variety of current system flows in height profiles, which increase ionosphere conductivity. In this study, we have analyzed the height profiles of the ionospheric conductivity daily and monthly variations in Addis Ababa, Ethiopia, during a very low solar activity phase in the year 2020. The daily height profile variations of ionospheric conductivity in Addis Ababa with geographic latitude 9o N and longitude 39o E are estimated at midnight (00:00 UT), morning (09:00 UT), mid-day (12:00 UT), and early nighttime (18:00 UT). The monthly variations of ionospheric conductivity (parallel, Pedersen, and Hall conductivity) are also presented for all months, with the highest ionospheric variability occurring after noon (14.00 UT). At midnight (00:00 UT) and early nighttime (18:00 UT), the ionospheric conductivity shows more fluctuation than in the morning (09:00 UT) and midday (12:00 UT) in diurnal variation. The monthly variations of ionospheric conductivity (parallel, Pedersen, and Hall conductivity) in the daytime at 14:00 UT increase steeply to reach their peak values and keep the sharpness of their variability.

Does high-latitude ionospheric electrodynamics exhibit hemispheric mirror symmetry?

Abstract. Ionospheric electrodynamics is a problem of mechanical stress balance mediated by electromagnetic forces. Joule heating (the total rate of frictional heating of thermospheric gases and ionospheric plasma) and ionospheric Hall and Pedersen conductances comprise three of the most basic descriptors of this problem. More than half a century after identification of their central role in ionospheric electrodynamics, several important questions about these quantities, including the degree to which they exhibit hemispheric symmetry under reversal of the sign of dipole tilt and the sign of the y component of the interplanetary magnetic field (so-called “mirror symmetry”), remain unanswered. While global estimates of these key parameters can be obtained by combining existing empirical models, one often encounters some frustrating sources of uncertainty: the measurements from which such models are derived, usually magnetic field and electric field or ion drift measurements, are typically measured separately and do not necessarily align. The models to be combined moreover often use different input parameters, different assumptions about hemispheric symmetry, and/or different coordinate systems. We eliminate these sources of uncertainty in model predictions of electromagnetic work J⋅E (in general not equal to Joule heating ηJ2) and ionospheric conductances by combining two new empirical models of the high-latitude ionospheric electric potential and ionospheric currents that are derived in a mutually consistent fashion: these models do not assume any form of symmetry between the two hemispheres; are based on Apex magnetic coordinates (denoted Apex), spherical harmonics, and the same model input parameters; and are derived exclusively from convection and magnetic field measurements made by the Swarm and CHAMP satellites. The model source code is open source and publicly available. Comparison of high-latitude distributions of electromagnetic work in each hemisphere as functions of dipole tilt and interplanetary magnetic field clock angle indicates that the typical assumption of mirror symmetry is largely justified. Model predictions of ionospheric Hall and Pedersen conductances exhibit a degree of symmetry, but clearly asymmetric responses to dipole tilt and solar wind driving conditions are also identified. The distinction between electromagnetic work and Joule heating allows us to identify where and under what conditions the assumption that the neutral wind corotates with the Earth is not likely to be physically consistent with predicted Hall and Pedersen conductances.

Estimation of Ionospheric Field‐Aligned Currents Using SuperDARN Radar and DMSP Observations

AbstractStudies commonly assumed that variations in ionospheric conductance were insignificant and proposed that vorticities can be a reliable proxy or diagnostic for ionospheric field‐aligned currents (FACs). We propose a complete method for measuring FACs using data from the Super Dual Auroral Radar Network radar and the Defense Meteorological Satellite Program. In our method, the FACs are determined by three terms. The first term is referred to as magnetospheric‐origin FACs, while the second and third terms are known as ionospheric‐origin FACs. This method incorporates height‐integrated conductances based on observational data, thereby addressing the limitation of assuming uniform conductances. Different from previous works, we can calculate FACs at a low altitude of 250 km and obtain high‐resolution measurements within observable areas. Another advantage of this method lies in its ability to directly calculate and analyze the impact of ionospheric vorticity and conductance on FACs. We apply this method to obtain FACs in the Northern Hemisphere from 2010 to 2016 and analyze the distributions of height‐integrated conductances and total FACs. Our analysis reveals that the average FACs clearly exhibit the large‐scale R1 and R2 FAC systems. We conduct statistical analysis on magnetospheric‐origin FACs and ionospheric‐origin FACs. Our findings show that within the auroral oval, ionospheric‐origin FACs reach a comparable level to magnetospheric‐origin FACs. However, ionospheric‐origin FACs are significantly minor and almost negligible in other regions. This implies that height‐integrated conductance gradients and vorticities play equally significant roles within the auroral oval, whereas vorticities dominate in other regions.

Unraveling the Atmospheric Energy Input and Ionization Due To EMIC‐Driven Electron Precipitation From ELFIN Observations

AbstractEnergetic electron precipitation (EEP) from the radiation belts into Earth's atmosphere leads to several profound effects (e.g., enhancement of ionospheric conductivity, possible acceleration of ozone destruction processes). An accurate quantification of the energy input and ionization due to EEP is still lacking due to instrument limitations of low‐Earth‐orbit satellites capable of detecting EEP. The deployment of the Electron Losses and Fields InvestigatioN (ELFIN) CubeSats marks a new era of observations of EEP with an improved pitch‐angle (0°–180°) and energy (50 keV–6 MeV) resolution. Here, we focus on the EEP recorded by ELFIN coincident with electromagnetic ion cyclotron (EMIC) waves, which play a major role in radiation belt electron losses. The EMIC‐driven EEP (∼200 keV–∼2 MeV) exhibits a pitch‐angle distribution (PAD) that flattens with increasing energy, indicating more efficient high‐energy precipitation. Leveraging the combination of unique electron measurements from ELFIN and a comprehensive ionization model known as Boulder Electron Radiation to Ionization (BERI), we quantify the energy input of EMIC‐driven precipitation (on average, ∼3.3 × 10−2 erg/cm2/s), identify its location (any longitude, 50°–70° latitude), and provide the expected range of ion‐electron production rate (on average, 100–200 pairs/cm3/s), peaking in the mesosphere—a region often overlooked. Our findings are crucial for improving our understanding of the magnetosphere‐ionosphere‐atmosphere system as they accurately specify the contribution of EMIC‐driven EEP, which serves as a crucial input to state‐of‐the‐art atmospheric models (e.g., WACCM) to quantify the accurate impact of EMIC waves on both the atmospheric chemistry and dynamics.

Joule Heating rate at high-latitudes by Swarm and ground-based observations compared to MHD simulations

We compare Joule Heating rates as derived from ground-based magnetic field and all-sky camera data, from Low Earth Orbit satellite data (ESA Swarm) and from a MHD simulation (GUMICS-5) with each other in a case study of an auroral arc system. The observational estimates of Joule Heating rates provide information on regional scales and with high spatial resolution (10–100 km). Their comparison with global MHD results is conducted for a quiet time interval of a few minutes, just before a magnetic substorm. Analysis of the ground-based observations yields electric field with dominating North-South component pointing towards the arcs and having maxima values in the range 20–35 V/km. Combining these values with Pedersen conductance estimates from optical data (5–10 S) yields Joule Heating rates in the range 2.5–3.5 mW/m2. Swarm electric field measurements are consistent in their direction and intensity with the ground-based estimates. They also show that heating is increased particularly in the region where the conductance is low. The total amount of Joule heating in the area between the Swarm A and C satellite footprints while crossing the all-sky camera field of view is estimated to be 46 MW and the total amount energy dissipation during the 80 s overflight is around 3.6 GJ (1000 kWh). GUMICS-5 estimate of the peak Joule Heating in the magnetic local time sector of the arc system is smaller than that from the ground-based data with a factor of 2.9. Comparisons of GUMICS-5 results with Space Weather Modeling Framework (SWMF), shows that the latter gives on average larger heating rates being thus more consistent with our regional observations. However, both MHD-codes yield smaller Joule Heating rates around the time of the arcs and during the following substorm than the CTIP-e code. CTIP-e has a more detailed description of ionosphere-thermosphere interactions than the MHD-codes and its convection electric field is enhanced with a randomly varying additional component mimicking small scale structures. GUMICS-SWMF comparisons of global Joule Heating patterns in the Northern polar area reveal that the two simulations have significant differences in their spatial distribution of heating rates. Main cause for these deviations is the difference in the derivation of ionospheric Pedersen conductance. Our results emphasize the fact that future estimates of the global energetics in the magnetosphere–ionosphere–thermosphere system require better knowledge on ionospheric conductivities, both by new measurement concepts and by better understanding on the background physics controlling conductivity variations.

Tidal Composition Analysis of Global Sq Current System

AbstractIn this study, we examine the spatiotemporal variability of the global equivalent ionospheric current system estimated from geomagnetic Solar‐quiet (Sq) variations at 124 mid‐ to low‐latitude ground‐based magnetometer stations during 1–31 May 2020. In this period, geomagnetic activity was particularly low, that is, the hourly geomagnetic activity index Hp60 did not exceed 4o. The spherical harmonic analysis is performed on the Sq variations to estimate the equivalent current function at each universal time hour. Hourly maps of the global Sq current system are used to evaluate, for the first time, the tidal composition of mid‐latitude Sq currents and its temporal evolution. Although tides are known to be an important driver of Sq currents, the tidal composition analysis was difficult in previous studies that focused on Sq currents at particular longitude sectors. Our results show that the migrating tidal components (DW1, SW2, and TW3) are predominant in both hemispheres. This is as expected from the strong day‐night contrast in ionospheric conductivities. The day‐to‐day variations of the migrating tidal components are, however, not strongly correlated between the two hemispheres, suggesting that these variations arise not only from the global effect of solar radiation on ionospheric conductivities but also from the local effect of neutral winds. Variations associated with non‐migrating tides are also found. Especially, eastward‐propagating diurnal and semidiurnal tides with zonal wavenumber 1 (DE1 and SE1) are the largest non‐migrating components. Their production mechanisms remain to be understood.

An Extreme Auroral Electrojet Spike During 2023 April 24th Storm

AbstractAbrupt variations of auroral electrojets can induce geomagnetically induced currents, and the ability to model and forecast them is a pressing goal of space weather research. We report an auroral electrojet spike event that is extreme in magnitude, explosive in nature, and global in spatial extent that occurred on 24 April 2023. The event serves as a fundamental test of our understanding of the response of the geospace system to solar wind dynamics. Our results illustrate new and important characteristics that are drastically different from existing knowledge. Most important findings include (a) the event was only of ∼5‐min duration and was limited to a narrow (2°–3°) band of diffuse aurora; (b) the longitudinal span covered the entire nightside sector, possibly extending to the dayside; (c) the trigger seems to be a transient solar wind dynamic pressure pulse. In comparison, substorms usually last 1–2 hr and span almost the entire latitudinal width of the auroral oval. Magnetic perturbation events (MPEs) span hundreds km in radius. Both substorms and MPEs are mainly driven by disturbances in the magnetotail. A possible explanation is that the pressure pulse compresses the magnetosphere and enhances diffuse precipitation of electrons and protons from the inner plasma sheet, which elevates the ionospheric conductivity and intensifies the auroral electrojet. Therefore, the event exhibits a potentially new type of geomagnetic disturbance and highlights a solar wind driver that is enormously influential in driving extreme space weather events.

On an electromagnetic calculation of ionospheric conductance that seems to override the field line integrated conductivity

The ionospheric conductance is the major quantity that determines the interaction of the magnetosphere with the ionosphere, where the magnetosphere is the large region of space affected by Earth’s geomagnetic field, and the ionosphere is its electrically conducting inner boundary, lying right on the edge of the atmosphere. Storms and substorms in space dissipate their energy through ionospheric currents, which heat the atmosphere and disrupt satellite orbits. The ionospheric conductance has, heretofore, been estimated using the staticized physics known as electrostatic theory, which finds that it can be computed by integrating the zero-frequency conductivity along the lines of Earth’s geomagnetic field. In this work we test this supposition by deriving an electromagnetic solution for collisional plasma, and applying it to obtain a first-ever fully-electromagnetic calculation of ionospheric conductance. We compare the results to the field line integrated conductivity, and find significant differences on all scales investigated. We find short-wavelength, mode-mixing, and wave-admittance effects that were completely unexpected. When this theoretical result is matched with recent observational findings for the scale of the magnetosphere-ionosphere coupling-interaction, there results a situation where small- to intermediate-scale effects really may contribute to global modeling of the Sun-Earth system.