Using a coupled EUHFORIA–Gorgon-Space modelling chain, we simulate the magnetosphere–ionosphere coupled response to two coronal mass ejections (CMEs) that impacted Earth on 23 and 28 June 2015. The first CME (CME1), launched on 21 June, triggered a major geomagnetic storm (Kp = 8), driving strong magnetosphere–ionosphere coupling characterised by a cross-polar cap potential of 160 kV and intense field-aligned currents exceeding 23 MA, key indicators of energy transfer from the solar wind into the high-latitude ionosphere. In contrast, the faster CME2 (launched on 25 June) produced only a weak disturbance (Kp ≈ 2) due to the absence of a prolonged southward interplanetary magnetic field (IMF), resulting in minimal magnetospheric driving and ionospheric feedback. These results validate an end-to-end space-weather forecasting framework and demonstrate that CME geoeffectiveness is governed primarily by the IMF orientation and reconnection-driven magnetosphere–ionosphere energy coupling, rather than by kinematic properties such as speed alone.
In many studies of the electrodynamics of the coupled ionosphere-thermosphere (IT) system at high latitudes, the ionosphere is represented as a two-dimensional spherical shell and the height-integrated ionospheric Ohm's law is used to understand IT electrodynamic coupling. Thermospheric winds play a central role in IT electrodynamics, but they are generally ignored in existing empirical models and assimilative methods. While the primary issue is a lack of comprehensive wind measurements, there is also a gap in the literature on how to represent the thermospheric winds – which often exhibit strong variations with altitude – in a height-integrated description of high-latitude IT electrodynamics, and what the associated sources of error might be. Here we highlight that there is in general no single suitable definition of the neutral wind term in high-latitude, height-integrated IT electrodynamics. Instead, two neutral wind terms weighted by Hall and Pedersen conductivities appear in the height-integrated Ohm's law. Using altitude profiles of neutral winds and ionospheric conductivities respectively derived from sounding rocket chemical release experiments near Poker Flat, Alaska, and Poker Flat Incoherent Scatter Radar (PFISR) measurements, we find magnitude differences of order 10–100 m s−1 between the two neutral wind terms. The difference in magnitude increases with increasing geomagnetic activity. We show that a commonly used expression for Joule heating in terms of height-integrated quantities is a lower bound of the actual height-integrated Joule heating. We demonstrate how during geomagnetically quiet periods both the magnitude and direction of the neutral wind may influence total Joule heating, while during active periods the neutral wind influences total Joule heating primarily via its orientation relative to the plasma convection. We also find that measurements of the thermospheric wind at altitudes of ∼100–120 km are a more accurate estimate of the thermospheric wind terms in expressions of height-integrated, high-latitude electrodynamics than simply assuming the neutral winds are zero in Earth's corotating frame of reference. This points to the possible utility of, for example, Fabry–Perot interferometers that measure 557.7-nm (green-line) emissions around this altitude range.
The VISIONS-2 sounding rockets performed in-situ measurements of the active dayside auroral region. Numerous broadband dispersed signatures up to keV energies are visible in the electron electrostatic analyser data, typical of Alfvénic precipitation. In order to characterize the region where the particles are accelerated, we estimate source altitudes based on different fits of the observed energy–time dispersions. Additionally, a method based on pitch-angle–time dispersions is developed, which relaxes the assumption that all electron energies are released simultaneously. Both approaches are found to yield similar source altitudes. For most of the analysed dispersed precipitation structures, these are found to lie between 1000 and 3000 km, and increase in height for larger electron energies. Variations across events suggest differences in the plasma and/or wave conditions in the acceleration region. Finally, a comparison with previous observational studies and theoretical predictions is performed, and our estimated source altitudes are found to be generally consistent with some inertial Alfvén wave velocity profiles, particularly those associated with relatively small O+ scale heights. Overall, the results presented here provide further detail about the Alfvénic auroral acceleration region on the dayside. The developed method also opens the possibility of inferring the plasma density profiles and essential wave parameters above the spacecraft.
Observation-based characteristics of the dayside ionosphere are important for the knowledge of the coupling between the solar wind, magnetosphere and ionosphere. Therefore, this paper presents descriptions and quantitative analyses of characteristics of the polar dayside ionosphere during the winter. We use EISCAT Svalbard radar (ESR) fast elevation scans to obtain both altitudinal and latitudinal information of the ionospheric parameters electron density Ne, electron temperature Te, and ion temperature Ti. We determine the location of the open-closed field line boundary (OCB) and divide the ionosphere into three regions based on their position relative to the OCB: on closed field lines, along the OCB, and in the polar cap. We first show two case examples, illustrative of the method and the dynamic response of the ionosphere to variable solar wind. We then statistically investigate how the parameters vary from closed to open field lines across the OCB and with altitude in the three regions. Finally, we compare the obtained OCB latitudes with the ones obtained in previous studies. Overall, significant differences in the ionospheric parameters can be seen between the three latitude regions. In general, observed enhancements in Te peak in the F-region on open field lines just poleward of the OCB, reaching up to 4 degrees poleward. In particular, Te is highest between 11:00-13:00 MLT where the ESR is most likely below the cusp. During this interval, the gradient in Te from closed to open field lines peaks. Additionally, Ne appears to be slightly enhanced poleward of the OCB at most altitudes and maximizes just below 300 km on open field lines, increasing with a factor 1.2 from closed field lines. In the E-region, Ne decreases with increasing latitude into the polar cap, especially pre-noon. Further, we observe that the ratio between Ne in the E and F regions is larger on closed than on open field lines. In addition, the variability in the ion temperature Ti appears to be larger on open field lines. Together, these result contribute to a quantification of characteristics of the dayside auroral ionosphere with respect to both altitude and latitude.
Solar eclipses are transient atmospheric events that cause rapid localized reduction in solar radiation, which produces complex changes associated with the vertical coupling of the layers. This study investigates how the neutral atmosphere responded vertically to the 14 October 2023 annular solar eclipse over Natal, Brazil (5.79° S, 35.2° W). This event presented a unique setup i.e., the maximum obscuration of ∼ 88.5 % occurred near sunset in a coastal transition between land and ocean. A stratospheric balloon sounding launched immediately before the umbra reached Natal was used. The balloon collected atmospheric profiles (temperature, pressure, relative humidity, and ozone concentration) over 1.45 h, with the umbra passing over the balloon at ∼ 22.35 km altitude for 3 min and 36 s. Comparison with average October profiles, model and reanalysis data revealed clear vertical patterns: (i) A notable cooling of 4–5 K in the tropopause region (14 km altitude); (ii) increased vertical temperature fluctuations, especially above 14 km; (iii) a decrease in atmospheric pressure of 0.2–0.7 hPa above 12 km; (iv) strong vertical oscillation in ozone concentration, with an increase of up to 1.7 ppm above 20 km altitude; (v) higher relative humidity between 5 and 18 km altitude compared to control profiles. These observations of complex, small-scale fluctuations and clear responses in the vertical atmospheric field align with previous reports and theoretical expectations of solar eclipse effects, confirming the importance of an annular eclipse as a significant driver of localized atmospheric dynamics.
The JUpiter ICy moons Explorer (JUICE) mission, launched in April 2023 by the European Space Agency (ESA), is designed to investigate Jupiter and its largest icy moons, Ganymede, Callisto, and Europa, with a focus on assessing their potential habitability and investigating subsurface oceans. During its eight-year interplanetary cruise to the Jovian system, JUICE is scheduled to perform several flybys. The first of these, the combined Lunar-Earth Gravity Assist (LEGA), took place in August 2024. The spacecraft is equipped with a High Accuracy Accelerometer (HAA) that is part of the Gravity and Geophysics of Jupiter and the Galilean Moons (3GM) radio science instrument. During LEGA operations, HAA collected two hours of scientific data centered across the Moon's closest approach. We present here a detailed analysis of the HAA calibrated measurements that show a strong agreement with predicted non-gravitational accelerations, including those related to spacecraft deformation caused by the Moon's gravity gradient and thermoelastic displacements of the solar arrays during penumbra transitions. Additionally, unexpected dynamic responses were observed, including structural vibrations excited by the movement of the steerable telescope of the Submilimetre Wave Instrument (SWI) and a distinct outgassing event detected shortly after crossing the lunar terminator. The outgassing, likely involving sublimated water ice on the spacecraft, resulted in a measurable velocity change of 0.7 ± 0.1 mm s−1 along the -Z spacecraft axis and a consequent mass loss of a few grams. This direction coincides with the normal direction of the spacecraft's most exposed surface to the Moon illuminated surface. The JUICE orbital reconstruction derived from radio tracking data collected by the Deep Space Transponder (DST) confirmed a consistent velocity variation, supporting HAA findings. These in-flight observations are essential for instrument calibration, characterization of the spacecraft's dynamic environment, and refining operational strategies.
In this work we have selected 40 corotating/stream interaction (CIR) driven geomagnetic storms that occurred between 2001 and 2016, and statistically studied their impacts on the magnetotail. The wavelet transform was applied to the interplanetary magnetic field (IMF) Bz component, magnetotail Bx component, and the auroral electrojet (AE) index during geomagnetic storms. The cross-wavelet technique was applied to determine the periods of higher correlation between the IMF Bz× magnetotail Bx, IMF Bz×AE index and magnetotail Bx×AE index. More than 80 % of the most energetic periods in the IMF Bz and magnetotail Bx are found to be shorter than 4 h, independently of the storm phase. The AE index presented the range between 2–4 h as the most common with energetic periods for both storm main and recovery phases. In the recovery phase, periodicities in the AE index are more spread (≤12 h) than for the main phase (≤8 h) probably due to the presence of high-intensity long-duration continuous AE activities (HILDCAAs). From the cross-wavelet analysis (IMF Bz× magnetotail Bx, IMF Bz×AE index and magnetotail Bx× AE index), periods≤4 h are found to be dominant in both storm phases, which coincide with the cyclic substorm periods. The power spectral analysis showed that the IMF Bz and magnetotail Bx time series follow the Kolmogorov (-5/3) power law. Additionally, the mean values of the spectral indices for the magnetotail Bx and AE index are higher during the recovery phase than the main phase.This suggests that turbulence is more pronounced during the recovery phase of geomagnetic storms driven by CIRs.
We present an analysis of four mid-infrared observations of the lunar surface acquired by the MAJIS instrument during the Jupiter Icy Moons Explorer (JUICE) gravity assist in August 2024. The data span 0.49-5.56 & micro;m at sub-kilometre spatial resolution. These data provide a rare opportunity to investigate the challenging spectral regime where reflected solar radiation and thermal emission both contribute to the measured radiance.The study explores three independent approaches to model and retrieve surface temperature and emissivity: (i) a Bayesian inversion framework, (ii) an empirical thermal correction method, and (iii) a roughness-informed thermophysical model. Rather than constituting a formal instrument validation, this paper provides a methodological consistency assessment of thermal retrieval strategies when applied to MAJIS mid-infrared data.Retrieved temperature distributions are compared with expectations from established lunar thermal behaviour, and emissivity spectra are analysed in relation to known compositional contrasts between mare and highland terrains. The analysis highlights the sensitivity of the 3-5 & micro;m crossover regime to modelling assumptions, temperature-emissivity coupling, and surface roughness parameterization.Overall, the results demonstrate that MAJIS mid-infrared observations can be interpreted within physically consistent thermal modelling frameworks, while also revealing limitations and degeneracies inherent to this wavelength range. This workflow is directly transferable to future MAJIS observations of Jovian moons in the reflected-thermal crossover regime.
This study examines the low-latitude ionospheric response to four intense geomagnetic storms during Solar Cycle 25 (March, April, November 2023, and May 2024), focusing on Equatorial Ionization Anomaly (EIA) variations and post-sunset plasma irregularities. We used the model for Joule Heating (J(H)), Madrigal total electron content (TEC) maps, and GNSS-derived ROTI to analyze storm-time changes in EIA structure and equatorial plasma bubbles (EPBs). The May 2024 storm exhibited the strongest post-sunset J(H), particularly near the June solstice, while March and April storms showed moderate J(H) and November the lowest. Equinox storms produced nearly symmetric J(H) patterns, while solstice storms revealed interhemispheric asymmetries. Following J(H) thresholds are used for the classification of storms: weak (20-30 mWm(-2), November), moderate (30-50 mWm(-2), March/April) and strong (>50 mWm(-2), May). J(H), together with storm-time electric fields and equatorial meridional winds, influence the location, strength, hemispheric asymmetry, and the generation or suppression of plasma irregularities of the EIA crest. The generation of ionospheric plasma irregularities and their geographical distribution strongly depend on EIA's density gradients and general structure. Well-developed double-crest EIAs with steep density gradients favor post-sunset irregularities, while single-crest or merged EIAs are less favorable. Fluctuations in the IMF B-z drive east-west prompt penetration electric fields that dynamically modulate the F region, altering the plasma fountain effect, the EIA structure, and the distribution of plasma bubbles after sunset. These results suggest that during geomagnetic storms, the combined effects of storm-driven electrodynamics and neutral winds modulate low-latitude ionospheric variability, influencing EIA dynamics and the formation of plasma irregularities.
The JUpiter ICy moons Explorer spacecraft (JUICE) performed a Lunar-Earth gravity assist maneuver on 20 August 2024, during which the scientific instruments were turned on to test their functionality. In the time of the Earth flyby, the Moon and Jupiter Imaging Spectrometer (MAJIS) on board JUICE acquired a sequence of multispectral images over the Western Pacific Ocean at tropical latitudes. In parallel, an observing campaign was also conducted by the Earth-orbiting PRISMA imaging spectrometer, with the purpose of validating MAJIS spectral observations with independent measurements of the same kind.These two datasets are here exploited to investigate and compare several atmospheric and cloud properties, including composition, temperatures, and atmospheric gravity waves. In the MAJIS spectral range, covering the 500-5560 nm wavelengths, we identified major and minor atmospheric gases, including O2, H2O, CO2, O3, CH4, N2O. Since MAJIS observations mostly covered diffuse cloudiness over the ocean, our analysis mainly focused on the discrimination of clouds' features and altitudes. We verified that ice particles are widespread in the data, allowing for an investigation of their properties (e.g. crystallinity) through different spectral signatures. The only land features identified in MAJIS data are not observed in daylight, hence only a thermal emission analysis is presented. Finally, the coverage of the 4300 nm CO2 band enables the identification of high altitude structures, revealing the presence of several atmospheric wave packets, likely induced by convective events, or lightning strikes known to have occurred at the time of the flyby. The present analysis demonstrates how MAJIS data can contribute to the scientific investigation of an atmospheric environment, and provide the first benchmark in the analysis of water ice, whose characterization in the Jovian system will be of primary importance for the JUICE mission.
The Jupiter Icy Moons Explorer (Juice) embarked in 2023 on a 8-year interplanetary journey to Jupiter and its icy moons. The Submillimetre Wave Instrument (SWI) is one of the ten science instruments aboard the spacecraft. SWI is a sophisticated and first-of-its-kind payload visiting the outer solar system, featuring dual-band tunable receivers, two independent pointing mechanisms, and spectrometers capable of high resolution (up to a resolving power of 107). It is designed to support the diverse science objectives of the Juice mission targeting Jupiter's middle atmosphere, icy-moon's exospheres as well as near sub-surface thermophysical properties. For this purpose the Juice mission adopts a complex trajectory tour within the Jovian system, which further necessitates a sophisticated, mission-driven operations concept for SWI. This presents significant planning, operations and commanding challenges which are described in this paper in the context of the Lunar and Earth Gravity Assist (LEGA). After the development and ground calibration of the instrument, the SWI Team has designed a comprehensive calibration strategy applicable during the Cruise Phase of Juice. Among the various opportunities for calibration, including the Near-Earth Commissioning Phase and more than ten Payload Checkout Windows, the LEGA offers the means not only to improve the calibration of the instrument, but also to validate the operational strategy of future icy moon flybys.
A lightning event was detected by the MAJIS imaging spectrometer onboard the Jupiter Icy Moons Explorer (JUICE) spacecraft during its first Earth gravity assist maneuver. This serendipitous observation represents the first space-based spectroscopic measurement of lightning for any planetary atmosphere. The event, composed of four flashes, was registered on 2024, August, 20th in an area offshore of Sumatra island, during local nighttime, near to optically thick clouds probed by MAJIS thermal wavelengths. No coincident detection has been obtained by ground-based lightning sensor networks, yet MAJIS observations provide unambiguous evidence of neutral atomic oxygen and nitrogen emissions, identified through several diagnostic lines. A faint H alpha signature may also tentatively be associated with lightning flashes.As MAJIS is not optimized for such observations, a number of caveats related to spectral and temporal resolutions have been considered when deriving absolute quantities, such as lightning energy and temperature. Retrieved energies are overall consistent with known emission by lightning of average strength, ranging from (0.7 +/- 0.2) to (1.3 +/- 0.3) MJ in the 777 nm O I line and from (0.5 +/- 0.2) to (1.5 +/- 0.4) MJ in the 870 nm N I line. Estimates of the temperature of the lightning channel yield a broad range of values, spanning between 5000 and 20 000 K, with standard uncertainties of the order of 2000-3000 K depending on the retrieval method. This is ascribed to a higher sensitivity to biases induced by the limited measurement resolutions.Overall, this observation represents a useful benchmark for guiding detection and interpreting possible lightning events on Jupiter, a primary target of the JUICE mission. A preliminary extrapolation of the terrestrial case to the conditions of Jovian atmosphere suggests that H I emissions in the 650 and 1870 nm spectral ranges are the most promising for identifying lightning on Jupiter with the MAJIS instrument.
We investigate how the location, size, and intensity of the auroral oval is affected by the combination of the tilt of the Earth's magnetic dipole axis and a strong, stable dawn/dusk component of the interplanetary magnetic field (IMF By) during northward IMF. Sunlit auroral observations are contaminated by dayglow, and its impact on average intensity estimates remains unclear. Dayglow modelling is also accompanied by significant uncertainties that increase with increasing sunlight intensity. These difficulties motivate us to develop a new technique for isolating the auroral contribution in dayglow-subtracted UV images. This technique assumes the observed distribution of intensities consists of separate contributions from dayglow and aurora, and that the dayglow subtraction process to which the observations are subjected is imperfect and leaves a residual error. By performing a nonlinear fit to dayglow-subtracted count distributions one may extract the best-fit parameters that describe the dayglow residual error and auroral sources separately. We apply this isolation technique to dayglow-subtracted UV images derived from measurements made by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) onboard the Defense Meteorological Satellite Program's F16-19 satellites during 2005-2018. The isolation technique produces 30 %-40 % higher auroral intensities than a simple calculation of the distribution mean. Statistics of the auroral component show a clear and substantial (similar to 500 km in NH, similar to 430 km in SH) dawn-dusk shift in the polar cap location depending on the sign of IMF By during local summer in both Hemispheres. This shift is absent during local winter. We propose that the cause of this seasonally dependent shift in the polar cap location is likely to be related to seasonal differences in lobe reconnection rates. We also demonstrate how the heteroskedasticity of distributions of dayglow residual intensity can influence quantitative estimates of the average auroral intensities.
Anomalous electromagnetic phenomena in the ionosphere before seismic activity have been identified as potential indicators for earthquake early warning. Data from the CSES-01 satellite were analyzed using the STL decomposition method to break down electric field time series into longitudinal, latitudinal, and residual components. To quantify disturbance intensity, we use the C-value, a spectrum-fitting index derived from the power-law relationship between electric-field power spectral density and frequency. The longitudinal and latitudinal components reveal the electric field's double periodicity, characterized by a V-shape from south to north and a bimodal shape from east to west. After isolating conventional periodic disturbances with a strength of 0.87, unconventional disturbances in the residual component were examined to identify seismic precursor anomalies. Electric field power density disturbances associated with the 11 May 2023, Tonga Islands magnitude 7.6 earthquake were extracted. Multiple significant anomalies in the ionospheric electric field were detected within 20 d prior to the earthquake: an initial anomaly with a C-value exceeding 3.5 appeared 20 d before; a persistent anomaly with a peak C-value of 3.9 occurred 13 to 11 d prior; a sharp increase to a peak C-value of 4.4, three times the standard deviation, was observed 7 d prior; disturbances decreased until a resurgence 4 d prior, with a peak C-value of 3.5 lasting 2 d; the C-value returned to baseline 1 d before the earthquake. The STL-C method effectively differentiates various causal disturbances in the ionospheric electric field, offering novel approaches and insights for studying seismic precursors.
This study systematically derives transport coefficients - electrical conductivity, thermoelectric, diffusion, and mobility - for a Lorentz plasma described by a standard Kappa distribution function. Within the five-moment transport framework, the standard Kappa distribution serves as the zeroth-order function. Momentum and energy collision terms are obtained via the Boltzmann collision integral for Coulomb, hard-sphere, and Maxwell molecule interactions, and incorporated into the momentum equation to formulate generalized Ohm's and extended Fick's laws, yielding the transport coefficients. This study also compares the standard Kappa, modified Kappa, and Maxwellian distributions in terms of their influence on plasma behavior. The results show that for velocity-dependent collisions, such as Coulomb collisions, significant differences arise between the standard and modified Kappa distributions. For low kappa parameter kappa values, the standard Kappa distribution reduces collision frequency and thermalization, making it suitable for collisionless or weakly collisional plasmas. In contrast, the modified Kappa distribution increases these effects, indicating its relevance for more collisional environments. Consequently, in Coulomb collisions, the standard distribution weakens momentum and energy exchange compared to the Maxwellian case, while the modified distribution enhances them. Transport properties are also affected differently: as kappa decreases, the standard distribution enhances conductivity, mobility, diffusion, and thermoelectric effects, whereas the modified distribution reduces conductivity, mobility, and diffusion, with no change in the thermoelectric coefficient.
A transatlantic scientific balloon flight (TRANSAT) was conducted between 22 and 26 June 2024. The TRANSAT balloon, operated by the French Space Agency (CNES), floated in the stratosphere at approximately 40 km altitude between Esrange (Sweden) and Baffin Island (Canada) for about 3.8 d. The scientific payload comprised nine instruments, including an optical imager for noctilucent cloud (NLC) studies from the Swedish Institute of Space Physics. The NLC imager consisted of three identical visible-range optical cameras, one of which operated successfully throughout the entire flight, capturing thousands of NLC images. The TRANSAT balloon campaign was supported by ground-based lidar measurements and spaceborne observations from the Swedish MATS satellite. Here, we describe the technical characteristics of the balloon experiment and present early results. Nearly continuous observations of NLC were obtained during the entire flight. A localized warm region in the mesopause was identified as the cause of temporary NLC disappearance, while complex NLC structures exhibiting different motions were found to probably result from horizontal wind rotation with altitude within the mesopause region.
Dynamic loads in planetary mantles have the potential to deform the core-mantle boundary (CMB). On Earth, subducting slabs primarily induce a degree 2-order 2 deformation of the CMB in the spherical harmonic (SH) reference system. On Mars, the presence of the dichotomy and of the Tharsis region could produce loading across multiple degrees and orders, including degree-1, degree 2-order 2, degree 2-order 0, and degree 3-order 3 components. Thanks to the InSight (Interior exploration using Seismic Investigations, Geodesy, and Heat Transport) mission's radio science experiment, observations of Mars' nutations are now available. Periodic length-of-day (LOD) variations of Mars have been detected first by radio tracking the Viking landers, and InSight data have indicated the presence of a secular trend in LOD. In the case of nutations, the Martian core's non-hydrostatic flattening plays a first-order role in determining nutation amplitudes. In this study, we explore second-order effects arising from dynamic topography at the CMB. We compute the pressure exerted on the CMB topography inside Mars' liquid core and evaluate the resulting topographic pressure torque acting on the boundary, which can influence both nutations and LOD variations. Our results show that, albeit at microarcsecond (& micro;arcsec) level - well below current observational thresholds, the most significant contribution to nutations arises from degree 2-order 2 component. As for LOD variations, while Earth exhibits notable contributions from inertial wave resonances, the situation on Mars is different. The planet's tidal LOD variations have periods that are either too long or too far apart from those of inertial waves. Consequently, the associated contributions fall below the level of detectability.
The Next-generation Ionospheric Model for Operations (NIMO) is an assimilative geospace model developed to address the space weather operational needs in the ionosphere. NIMO harnesses contributions from both near real-time data and state-of-the-art implementation of ionospheric theory to provide hindcasts, nowcasts, and forecasts for operational or research purposes. NIMO is currently configured to assimilate various types of electron density measurements through the Ionospheric Data Assimilation Four-Dimensional (IDA-4D) data assimilation schema. Information from the neutral atmosphere is provided by empirical models. The ionospheric chemistry and transport calculations are handled within NIMO using a version of SAMI3 is also a Model of the Ionosphere (SAMI3) designed to have a realistic geomagnetic field and work effectively on a parallel processing system. NIMO was designed to be more adaptive than previous systems that couple first-principle and assimilative models. This article discusses how NIMO is configured, demonstrates potential use cases for the research community, and validates hindcast runs using a new suite of metrics designed to allow repeatable, quantitative, model-independent evaluations against publicly available observations that may be adopted by any ionospheric global circulation or regional space weather model. Future versions of NIMO and other empirical, first-principle, or assimilative models may compare their performance against these results.
Particle measurements from the Polar Operational Environmental Satellites (POES) and the Meteorological Operational (Metop) satellite program, are widely used for various scientific applications. While most studies focus on the Medium Energy Proton and Electron Detector (MEPED), the low-energy (eV and keV) counterpart, the Total Energy Detector (TED), has received comparatively less attention. However, the recent rise in the altitudes considered in ionization and climate models has increased interest in low-energy particle measurements as inputs for atmospheric ionization models. This study analyzes TED particle data (together with selected MEPED channels) from 2001 to 2025 and shows that the TED 0 degrees proton channels, in particular, are contaminated by energetic electrons at L <6, with weaker contamination observed in other TED channels. In some cases, the contaminated fluxes exceed typical auroral flux levels. The affected regions were cross-validated using auroral UV emissions and occurrences of GNSS derived S4 index to rule out the possibility that the observed fluxes correspond to real particle precipitation. As correction approach, we provide a simple Kp-and channel-dependent latitude boundary that may serve as preliminary cut-off criterion for the contaminated regions. In a more advanced step, we identified the contamination characteristics of each particle channel on each satellite. The outcome is a list of problematic channels that should be neglected and a correction method based on background counts for the other channels. The corrected fluxes are in good agreement with UV emissions and the method is available in the additional material.
