JGR:Space physics

Local empirical models of the F2 layer peak electron density (NmF2) are developed for 43 low- middle latitude ionosonde stations using auto-scaled data from Lowell GIRO data center and manually scaled data from World Data Center for Ionosphere and Space Weather. Data coverage at these stations ranges from a few years to up to 6 decades. Flare Irradiance Spectral Model index version 2 (FISM2) and ap3 index are used to parametrize the solar extreme ultraviolet (EUV) flux and geomagnetic activity dependence of NmF2. Learning curves suggest that approximately 8 years of data coverage is required to constrain the solar activity dependence of NmF2. Output of local models altogether captures well known anomalies of the F2 ionospheric layer. Performance metrics demonstrate that the model parametrized using FISM2 has better accuracy than a similarly parametrized model with F10.7, as well as than the IRI-2020 model. Skill score metrics indicate that the FISM2 based model outperforms F10.7 model at all solar activity levels. The improved accuracy of model with FISM2 over F10.7 is due to better representation of solar rotation by FISM2, and due to its performance at solar extremum. Application of singular spectrum analysis to model output reveals that solar rotation contributes to about 2%–3% of the variance in NmF2 data and FISM2 based model, while F10.7 based models overestimate the strength of solar rotation to be at 4%–7%. At solar extremum, both F10.7-based model and IRI-2020 tend to overestimate the NmF2 while FISM2 provides the most accurate prediction out of three.

This work presents an algorithm for automatic detection of anomalous electron heating (AEH) events in the auroral E-region ionosphere using data from the Poker Flat Incoherent Scatter Radar (PFISR). The algorithm considers both E-region electron temperature and magnetically conjugate electric field measurements. Application of this algorithm to 14 years of PFISR data spanning 2010 through 2023 detected 505 AEH events. Measured electron temperatures increase linearly with plasma drift speeds. Statistical trends of AEH occurrence as a function of space weather indices (AE and F10.7) demonstrate correlations with the solar cycle and geomagnetic activity levels. The magnetic local time occurrence rates show preferences for dusk and dawn with most events in the dusk sector. Observed AEH events tend to appear in regions of relatively low electron density and do not appear inside intense auroral arcs with high electron density. Furthermore, AEH detection requires a higher electric field than predicted by the threshold for a positive growth rate of the Farley-Buneman instability (FBI), according to linear fluid theory. The implications of these findings for kinetic theories of FBI and AEH are discussed.

Kelvin Helmholtz Instabilities (KHI) result from interactions between the shocked solar wind and the Earth's magnetosphere. These are formed due to the velocity shear between the plasma in the magnetosphere and magnetosheath. The role of KHI in bringing in the shocked solar wind into the terrestrial magnetosphere has been studied extensively using MHD, Hall-MHD, hybrid and PIC simulations. Such simulations oftentimes make simplifying assumptions of the boundary layer in the magnetopause. To experimentally study the effects of KHI on the boundary layer and its effectiveness in bringing in solar wind, we analyze 43 KHI events. All these events have quasi-constant IMF orientation during its interval, thereby mitigating the effects of variation of IMF in the ongoing transient magnetopause process. In this statistical study of KHIs, we demonstrate that there is a preexisting boundary layer before KHIs begin to develop. As KHI develops to its non-linear state, the ions in the magnetosphere, magnetopause, and magnetosheath are mixed, which is demonstrated using the alpha-to-proton density ratio. As a result of this mixing, the well-defined preexisting boundary layer is replaced by a much more uniformly mixed boundary layer.

In the present work we have modeled diffuse auroral emissions in Jupiter using the recent observations received by JUNO orbiter. Resonant wave-particle interaction by electron-cyclotron harmonic (ECH) waves has been invoked as the mechanism for production of diffuse aurora. Energetic electrons trapped on closed field lines are diffused into the loss-cone via pitch-angle diffusion. Electron precipitation fluxes have been calculated. Electrons entering into the atmosphere undergo collisions with atmospheric constituents atomic H and molecular H2 producing electromagnetic emissions. Four excitations have been considered. These excitations are: HLy-α from excitation of atomic H, HLy-α from dissociative excitation of molecular H2, Lyman and Werner bands of H2. Volume excitation rates have been calculated for these excitations. Height integrated volume excitation rates have been obtained to give auroral intensities. Numerical calculations have been performed at five L-shells; L = 10, 12, 15, 18 and 20. Maximum auroral intensities is obtained at shell L = 10. At higher shell L = 20 the intensity value reduces to a minimum. The intensities in Rayleigh (R) for HLy-α from H, HLy-α from H2, Lyman and Werner bands of H2 are calculated. Comparing these intensities with the diffuse auroral intensities observed at Saturn, it is found that the intensities at Jupiter are higher than the values predicted for Saturn. We have also calculated volume ionization rates for atomic H producing H+, dissociative ionization of H2 producing H+, and ionization of H2 producing H2 +. The continuity equation is solved to obtain the electron density Outcomes are discussed.

The interplanetary magnetic field (IMF) north-south component, B z , plays a crucial role in the interaction between the solar wind and the Earth's magnetosphere. We analyze 98 intervals in which B z changed from >3 nT to <−3 nT in 5 min and for which these rapid southward turnings (STs) were surrounded by consistently northward or southward IMF. We separate out events in proximity of interplanetary coronal mass ejections and corotating interaction regions. We find that IMF magnitude, solar wind dynamic pressure and proton density (but also flow speed in ICME-related events) near the turnings are enhanced above their medians. We analyze the maximum responses of the SML, SMU, SYM-H, and PCN magnetospheric indices and their timescales, along with the occurrence of geomagnetic phenomena. We find that most STs were followed by either substorms (60.20%) or enhanced convection (37.76%). While SML has similar median minima (∼−460 nT) and timescales (∼56 min) for substorm and convection events, SMU has noticeable differences. STs were followed by geomagnetic storms (SYM-H ≤ −50 nT) in 46.94% of events within 12 hr, with more storms following ICME-related turnings. PCN has peaks (median 3.8 mV/m) around 30 min after the turning, and larger ones (median 4.9 mV/m) later. Stronger solar wind driving and magnetospheric responses are observed for ICME-related events. The correlation between the geomagnetic and solar wind parameters around STs reveals a more direct link between solar wind driving and geomagnetic response for STs than at other times.

We study the geomagnetic storm of 9 October 2012, where it had been generally accepted that the resulting prominent outer radiation belt electron acceleration throughout the storm is due to whistler-mode chorus waves. This storm has been studied previously by two-dimensional Fokker–Planck numerical simulations with data-driven quasi-linear (QL) diffusion rates. However, possible nonlinear (NL) resonant interaction effects on electron flux dynamics haven't been looked at yet. This study aims to fill this gap by demonstrating that theory-informed rescaling of QL diffusion rates accounting for contributions of NL resonant interactions helps to reproduce better observed increase of electron fluxes by diffusion simulations. We use machine learning, uncertainty quantification (UQ), physics-perturbed ensemble of VERB simulations and Van Allen Probes observations to identify optimal rescaling of quasi-linear diffusion rates.

We present a unique triangulation measurement of Strong Thermal Emission Velocity Enhancement (STEVE) observed on Sept 3rd, 2022, at Athabasca, Canada. Using two Digital single-lens reflex (DSLR) color cameras with all-sky fish-eye lenses, we show the profile of STEVE altitude variation over time in 1 min resolution for the first time. We estimate the altitude variation of its visible purplish arc and green picket fence structures. We also compare the DLSR camera images with narrowband all-sky images of an Optical Mesosphere Thermosphere Imager (OMTI) to see the correspondence of color camera images with 630 nm and OH-band auroral/airglow emission images. The height of the purplish STEVE arc was stable at 150–170 km while present (∼0,546–0,633 UT), except for a short excursion to ∼200 km at 0,600 UT. The green picket fence structures appeared at 0,549 UT when the intensity of the STEVE arc started to intensify. They presented only for ∼7 min, and their altitude was steady at ∼110 km. The vertical movement of the STEVE arc to ∼200 km was found to be accompanied by the motion across the local magnetic field lines, suggesting a southward E × B drift underlying the westward ion drift. From the comparison with the OMTI images, we find that the purplish STEVE arc moved closer to the 630 nm arc in the all-sky image when it rose to a higher altitude, indicating the occurrence of electron heating at a same or slightly higher altitude than the STEVE.

A detailed analysis is made of horizontal-component geomagnetic-disturbance data acquired at the Colaba observatory in India recording the Carrington magnetic storm of September 1859. Prior to attaining its maximum absolute value, disturbance at Colaba increased with an e-folding timescale of 0.46 hr (28 min). Following its maximum, absolute disturbance at Colaba decreased as a trend having an e-folding timescale of 0.31 hr (19 min). Both of these timescales are much shorter than those characterizing the drift period of ring-current ions. Furthermore, over one 28-min interval when absolute disturbance was increasing, the data indicate an absolute rate of change of ≥2,436 nT/hr. If this is representative of disturbance generated by a symmetric magnetospheric ring current, then, assuming a standard and widely used parameterization, an interplanetary electric field of ≥451 mV/m is indicated. An idealized and extreme solar-wind dynamic pressure could, conceivably, reduce this bound on the interplanetary electric field to ≥202 mV/m. If the parameterization for electric-field extrapolation is accurate, but the field strengths obtained are deemed implausible, then it can be concluded that the Colaba disturbance data were significantly affected by partial-ring, field-aligned, or ionospheric currents. The same conclusion is supported by the shortness of the e-folding timescales characterizing the Colaba data. Several prominent studies of the Carrington event need to be reconsidered.

Utilizing the 8.5-year Venus Express observations, we investigate the effects of solar wind magnetosonic Mach number MMS $\left({M}_{MS}\right)$, solar extreme ultraviolet (EUV) radiation, solar wind dynamic pressure Pd $\left({P}_{d}\right)$ and interplanetary magnetic field (IMF) on the shape of the Venusian bow shock. Our statistical analysis yields several findings: (a) The spatial scale of the Venusian bow shock varies in a nonlinear manner with MMS ${M}_{MS}$ and shows a linear correlation with the EUV flux. (b) After the variance of the bow shock size caused by different MMS ${M}_{MS}$ and EUV are considered, the bow shock size shows no apparent correlation with the IMF intensity, IMF cone angle and solar wind dynamic pressure. (c) The angle between the IMF and the shock normal θBn $\left({\theta }_{Bn}\right)$ emerges as a significant factor shaping the bow shock's local distance. A two-parameter (MMS ${M}_{MS}$ and EUV) dynamic bow shock model is consequently constructed. This dynamic model not only elucidates the typical behavior of the bow shock under normal solar wind conditions but also unveils the anomalously distant bow shock location characterized by extremely low MMS ${M}_{MS}$.

In this study, we investigate the intricate electrodynamics of the Earth's horizontal component of the geomagnetic field (ΔH) in response to two significant solar flares (SF) occurring on 03 July and 28 October 2021. These flares are classified as X1.59 and X1.0, respectively. It is noted that the ΔH follows the X-ray variation during the SF, but there is a time lag of a few minutes between the X-ray and ΔH. A possible explanation for the time lag is the neutral atmosphere and ionosphere coupling, via ion drag.

We study the dynamic evolution of dayside magnetopause reconnection locations and their dependence on the interplanetary magnetic field (IMF) cone angle via 3-D global-scale hybrid simulations. Cases with finite IMF Bx and Bz but IMF By = 0 are investigated. It is shown that the dayside magnetopause reconnection is unsteady under quasi-steady solar wind conditions. The reconnection lines during the dynamic evolution are not always parallel to the equatorial plane even under purely southward IMF conditions. Magnetopause reconnection locations can be affected by the generation, coalescence, and transport of flux ropes (FRs), reconnection inside the FRs, and the magnetosheath flow. In the presence of an IMF component Bx, the magnetopause reconnection initially occurs in high-latitude regions downstream of the quasi-perpendicular bow shock, followed by the generation of multiple reconnection regions. In the later stages of the simulation, a dominant reconnection region is present in low-latitude regions, which can also affect reconnection in other regions. The global distribution of reconnection lines under a finite IMF Bx is found to not be limited to the region with maximum magnetic shear angle.

In this study, we presented a detailed analysis of ultralow frequency compressional waves with frequencies ranging from 16 to 100 mHz by using magnetic measurements of Swarm A and B, when the two spacecraft were flying in a counter-rotating configuration. These waves are assumed to be driven by processes in the fore-shock region and subsequently termed as upstream waves (UWs). An automatic detection algorithm for identifying UW events has been developed and applied to the Swarm magnetic measurements. Different to previous studies we take advantage of the counter-rotating Swarm constellation to investigate the large-scale homogeneous wavefield. Only B-field oscillations from both Swarm A and B satellites satisfy the following criteria are accepted for UWs analysis: (a) highly correlated with normalized correlation coefficient (Cc) larger than 0.9; (b) shifted by less than 3 s between observations; (c) separated up to 90° in latitude and/or longitude. By this procedure we have identified from the years 2018–2023 in total 577 orbits containing UWs in the magnetic recordings of both spacecraft. In the first step, we checked phase shifts between UW detections at large latitudinal separation. The two counter-rotating spacecraft allowed to make use of the Doppler effect to check the possible propagation of UWs at ionospheric altitude. Although individual events show signs of north-south wave propagation, on average no systematic motion could be found. Similarly, possible wave motions toward or away from noon hours have been checked. By analyzing the simultaneous observations at larger longitudinal separation, also hardly any phase differences are identified in the east-west direction. Further by evaluating the statistical results, a mean tiny local time effect seems to emerge, indicating on average an earlier arrival of the waves in the morning and later in the evening hours.

Joule heating is a major energy sink in the solar wind-magnetosphere-ionosphere system and modeling it is key to understanding the impact of space weather on the neutral atmosphere. Ion drifts and neutral wind velocities are key parameters when modeling Joule heating, however there is limited validation of the modeled ion and neutral velocities at mid-latitudes. We use the Blackstone Super Dual Auroral Radar Network radar and the Michigan North American Thermosphere Ionosphere Observing Network Fabry-Perot interferometer to obtain the local nightside ion and neutral velocities at ∼40° geographic latitude during the nighttime of 16 July 2014. Despite being a geomagnetically quiet period, we observe significant sub-auroral ion flows in excess of 200 ms−1. We calculate an enhancement to the local Joule heating rate due to these ion flows and find that the neutrals impart a significant increase or decrease to the total Joule heating rate of >75% depending on their direction. We compare our observations to outputs from the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). At such a low geomagnetic activity however, TIEGCM was not able to model significant sub-auroral ion flows and any resulting Joule heating enhancements equivalent to our observations. We found that the neutral winds were the primary contributor to the Joule heating rates modeled by TIEGCM rather than the ions as suggested by our observations.

This paper conducts a multi-instrument and data assimilation analysis of the three-dimensional ionospheric electron density responses to the total solar eclipse on 08 April 2024. The altitude-resolved electron density variations over the continental US and adjacent regions are analyzed using the Millstone Hill incoherent scatter radar data, ionosonde observations, Swarm in situ measurements, and a novel TEC-based ionospheric data assimilation system (TIDAS) with SAMI3 model as the background. The principal findings are summarized as follows: (a) The ionospheric hmF2 exhibited a slight enhancement in the initial phase of the eclipse, followed by a distinct reduction of 20–30 km in the recovery phase of the eclipse. The hmF2 in the umbra region showed a post-eclipse fluctuation, characterized by wavelike perturbations of 10–25 km in magnitude and a period of ∼ ${\sim} $30 min. (b) There was a substantial reduction in ionospheric electron density of 20%–50% during the eclipse, with the maximum depletion observed in the F-region around 200–250 km. The ionospheric electron density variation exhibited a significant altitude-dependent feature, wherein the response time gradually delayed with increasing altitude. (c) The bottomside ionospheric electron density displayed an immediate reduction after local eclipse began, reaching maximum depletion 5–10 min after the maximum obscuration. In contrast, the topside ionospheric electron density showed a significantly delayed response, with maximum depletion occurring 1–2.5 hr after the peak obscuration.

The harmonic structure of lower hybrid waves (LHWs) driven by energetic ions can be generated through non-linear wave-wave coupling. We investigate the parameter dependence of the excitation and time evolution of this structure, using one-dimensional electromagnetic particle-in-cell (PIC) simulations. Focusing on two parameters, ωpe/Ωe ${\omega }_{pe}/{{\Omega }}_{e}$ (ratio of the electron plasma to electron gyro frequencies) and u⊥/vA<1 ${u}_{\perp }/{v}_{A}< 1$ (ratio of energetic-ion to Alfvén velocities), we analyze the fluctuation spectra in the wavenumber-frequency plane and demonstrate that the harmonic structure can be excited across wide parameter ranges of 0.25≤ωpe/Ωe≤4 $0.25\le {\omega }_{pe}/{{\Omega }}_{e}\le 4$ and u⊥/vA<1 ${u}_{\perp }/{v}_{A}< 1$, indicating a weak parameter dependence. However, the excitation region and time evolution of the harmonic structure can be significantly affected by these parameters. We find that conditions of low ωpe/Ωe ${\omega }_{pe}/{{\Omega }}_{e}$ and intermediate u⊥/vA ${u}_{\perp }/{v}_{A}$ are preferable for the excitation and survival of the harmonic structure. Previous observations have reported the harmonic structure of LHWs in the polar region at 4,000 km altitude and in the plasma sheet at XGSM ∼ ${\sim} $ 17 RE ${R}_{\mathrm{E}}$. Nevertheless, this study predicts that the harmonic structure can also be excited in other regions of the magnetosphere where energetic ions are present.

Increasing carbon dioxide concentrations in the mesosphere and lower thermosphere are increasing radiative cooling in the upper atmosphere, leading to thermospheric contraction and decreased neutral mass densities at fixed altitudes. Previous studies of the historic neutral density trend have shown a dependence upon solar activity, with larger F10.7 values resulting in lower neutral density reductions. To investigate the impact on the future thermosphere, the Whole Atmosphere Community Climate Model with ionosphere and thermosphere extension has been used to simulate the thermosphere under increasing carbon dioxide concentrations and varying solar activity conditions. These neutral density reductions have then been mapped onto the Shared Socioeconomic Pathways published by the Intergovernmental Panel on Climate Change. The neutral density reductions can also be used as a scaling factor, allowing commonly used empirical models to account for CO2 trends. Under the “best case” SSP1-2.6 scenario, neutral densities reductions at 400 km altitude peak (when CO2 = 474 ppm) at a reduction of 13%–30% (under high and low solar activity respectively) compared to the year 2000. Higher CO2 concentrations lead to greater density reductions, with the largest modeled concentration of 890 ppm resulting in a 50%–77% reduction at 400 km, under high and low solar activity respectively.

Electromagnetic ion cyclotron (EMIC) waves and fast magnetosonic (MS) waves were previously reported to be simultaneously generated by ring current protons (10s keV) within the magnetic dip. In this work, we present a distinct physical scenario of concurrent high-frequency EMIC (HFEMIC) and MS waves within a magnetic dip where low-energy (10s–100s eV) and hot (10s keV) protons facilitate the local growth of HFEMIC and MS waves, respectively. Moreover, the low-energy protons exhibit remarkable perpendicular flux enhancements, which are well modulated by MS waves as evidenced by their significant correlation coefficient (∼0.78). Consequently, the concurrent two wave modes should arise from the complicated coupling between HFEMIC and MS waves, marking a departure from previous studies. Our observations demonstrate that the magnetic dip can provide favorable conditions for such intricate coupling processes, offering novel insights into its impact on magnetospheric dynamics.

The Earth's ionosphere undergoes regular intra-annual variations (IAVs) characterized by two peaks and troughs around the equinoxes and solstices. This phenomenon is crucial for analyzing the ionospheric response to geomagnetic storms. This study presents a comprehensive analysis of the IAVs contributed by diurnal and semidiurnal migrating tides (DW1 and SW2) using Global Ionospheric Maps (GIMs) data from 2017 to 2021. Through data stacking techniques, the seasonal variability and splitting phenomenon of DW1 and SW2 across different latitudes are examined. The findings indicate that the splitting of these tides can be attributed to their quasi-periodic variations, predominantly composed of annual oscillation (AO) and semiannual oscillation (SAO). The combination of DW1, SW2, and their side-band harmonics results in beats with annual and semiannual periodicities, enabling the restoration of the seasonal variations in DW1 and SW2. The ionospheric day-to-day variations were reconstructed by superimposing DW1 and SW2, and their IAVs were evaluated using the envelope method. Comparison with IAVs driven by Earth's orbital geometry reveals that tide-driven IAVs are more significant, and both exhibit solar activity dependence. The results advance the understanding of ionospheric variability, emphasizing the critical role of tidal contributions.

In this study, we investigate the impacts of the 17 March 2013 strong geomagnetic storm on the wholly coupled Solar Wind-Magnetosphere-Ionosphere-Thermosphere system-of-systems. Obtained from multipoint observations, our new results show (1) the solar-wind Alfven waves propagating antisunward in the sheath region and (2) oscillating solar wind interplanetary magnetic field (IMF) and electric (E) field (IEF EY) that powered (3) rigorous dayside and nightside flux transfer events (FTEs) when (4) the nightside-reconnection-related short circuiting led to fast-time Subauroral Ion Drifts (SAID) and Subauroral Polarization Streams (SAPS) E field development across the inner-magnetosphere plasmapause where the solar-wind Alfven waves (4) transitioned into kinetic Alfven waves (5) fueling the hot zone. Also, the antisunward solar-wind Alfven waves (6) drove enhanced large-scale region-1 field-aligned currents creating (7) undershielding conditions (8) allowing the dawn-to-dusk convection E field's earthward penetration, and (9) generated increased solar-wind kinetic energy, which became deposited (10) to the ionosphere increasing the ionospheric electron temperature (by the downward flowing suprathermal electron fluxes) and (11) to the thermosphere oscillating the neutral winds and increasing the neutral temperature, and finally leading to (12) the development of bright stable auroral red (SAR) arcs in (13) the enhanced SAID/SAPS flow channels (FCs) developed during FTEs, (14) demonstrated with FC-2 and FC-3 events, in the enhanced polar convection that (15) the Rice Convection Model could reproduce. Finally, we conclude the antisunward-propagating large-amplitude solar-wind Alfven waves' ultimate significant role in creating the favorable conditions for the various phenomena documented with the new observational results (1–14).

No abstract is available for this article.