Journals
2026 EN
Kajdič Primož · BlancoCano Xochitl · RojasCastillo Diana
+1 more
Abstract Past kinetic simulations and spacecraft observations have shown that traveling foreshocks (TFs) are bounded by either foreshock compressional boundaries (FCBs) or foreshock bubbles (FBs). Here we present four TFs with a different kind of structure appearing at one of their edges. Two of them, observed by the Cluster mission, are bounded by a hot flow anomaly (HFA). In one case, the HFA was observed only by the spacecraft closest to the bow shock, while the other three probes observed an FCB. In addition, two other TFs were observed by the MMS spacecraft to be delimited by a structure that we call HFA‐like FCB. In the spacecraft data, these structures present signatures similar to those of HFAs: dips in magnetic field magnitude and solar wind density, decelerated and deflected plasma flow and increased temperature. However, a detailed inspection of these events reveals the absence of heating of the SW beam. Instead, the beam almost disappears inside these events and the plasma moments are strongly influenced by the suprathermal particles. We suggest that HFA‐like FCBs are related to the evolution and structure of the directional discontinuities of the interplanetary magnetic field whose thickness is larger than the gyroradius of suprathermal ions. We also show that individual TFs may appear together with several different types of transient upstream mesoscale structures, which brings up a question about their combined effect on regions downstream of the bow shock.
Journals
2026 EN
Blüthner G. H. · Volwerk M. · Schmid D.
+5 more
Abstract This study presents a comprehensive statistical comparison of solar wind measurements between the OMNI database which contains data collected at L1 that is shifted to the bow shock nose, and near‐Earth observations from MMS, Cluster, and THEMIS missions near the bow shock nose. Using a threshold‐based classification methodology, the analysis encompasses approximately 353 days (MMS), 283 days (Cluster), and 125 days (THEMIS) of solar wind intervals. Bisector regression analysis reveals that the anti‐sunward flow componentV x${V}_{x}$ demonstrates exceptional agreement across all missions with near‐unity slopes and correlation coefficients of 0.92 for THEMIS and 0.97 for MMS and Cluster. However, perpendicular velocity components show progressively degraded performance:V y${V}_{y}$ exhibits correlation coefficients of 0.63–0.77 with intercepts ranging from 21.57 km/s (MMS) to 47.49 km/s (THEMIS), whileV z${V}_{z}$ shows weaker correlations (0.42–0.72) with intercepts of 4.73–11.94 km/s. Ion density measurements reveal systematic mission‐specific biases: MMS and THEMIS show ion density regression slopes below unity (0.59 and 0.54, respectively), while Cluster shows a slope above unity (1.14) compared to OMNI measurements. Magnetic field measurements show higher consistency, with near‐unity slopes and correlation coefficients exceeding 0.84 for most components. The northward magnetic field componentB z${B}_{z}$ exhibits elevated variance ratios and reduced correlations across all missions, reaching 0.74 for THEMIS. These results quantify inherent uncertainties in cross‐platform solar wind comparisons and assess the accuracy of time‐shifted solar wind measurements in the OMNI database as proxies for actual near‐Earth conditions, with implications for space weather applications, multispacecraft studies, and magnetohydrodynamic simulation validation requiring accurate upstream boundary conditions.
Journals
2026 EN
Samsonov Andrey · Carter Jennifer Alyson · Sembay Steven
+4 more
Abstract Soft X‐rays are emitted in the magnetosheath and cusps because of solar wind charge exchange. The soft X‐ray Imager (SXI) on board Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) will measure these X‐rays. We developed a new method for finding the magnetopause standoff distance from simulations that reproduce the expected X‐ray images using software developed by the SXI instrument team. We consider three points near the SMILE apogee. We apply this method to a three‐hour interval with an interplanetary shock and a southward interplanetary magnetic field turning when the magnetosphere was moderately compressed. The results show that the magnetopause position can be reconstructed with an accuracy better than 0.5R E${R}_{E}$ for a five‐minute integration time, which matches the SMILE scientific requirements. Moreover, we can even determine the magnetopause position using one‐minute integration when the magnetosphere is strongly compressed and the spacecraft's position and SXI's orientation are favorable for magnetopause observations.
Journals
2026 EN
Wharton S. J. · Carter J. A. · Sembay S.
+5 more
Abstract The soft X‐ray imager (SXI) on the SMILE mission promises to revolutionize our understanding of the magnetopause by observing solar wind charge exchange emission from the magnetosheath on a global scale. The primary goal of this instrument is to infer the position and shape of the magnetopause from these images. One method involves devising a 3D X‐ray emissions model through which an image can be simulated and adjusted to match a real image. The magnetopause position can be extracted from the fitted 3D model. Previous work by Wharton et al. (2025b), https://doi.org/10.1029/2025ja033837 showed this method was effective with noisy SXI images if solar wind data was used to initialize their Cusp and Magnetosheath Emissivity Model (CMEM1). This study develops CMEM2, a constrained and simplified model that does not require solar wind data for initialization but uses information in the image instead. It can also be fitted by a range of fitting algorithms, which we thoroughly compare. CMEM2 is shown to perform as accurately as CMEM1. We also test this method for the first time on realistic scenarios with changing solar wind conditions. We find the method struggles during median solar wind conditions when the magnetosheath is dim and largely out of the expected FOV of SMILE‐SXI. However, during active conditions, the method tracks the movement of the magnetopause well and produces errors within the 0.5R E${R}_{E}$ requirement for the SMILE mission, providing that the initialization of CMEM2 is reasonably accurate.
Journals
2026 EN
Teng Shangchun · Yao Zhonghua · Zhang Jian
+4 more
Abstract Enceladus's south polar plumes and their surrounding torus segments (local plasma regions formed by plume material diffusion) are key to understanding its magnetospheric interaction; however, clear observational criteria to distinguish them remain lacking. We analyze data from 23 Cassini flybys (2005–2015), including magnetic field, energetic particle, and wave measurements. Plumes are characterized by localized magnetic perturbations (ΔB > 10 nT), sharp electron and ion density spikes (with n e < n i ), intense energetic particle absorption (exceeding one order of magnitude), and the presence of ice grains and neutral species. The local torus segments show weak ΔB (2–5 nT), gradual density changes ( n e ≈ n i ), and mild particle absorption (less than one order of magnitude). These criteria advanced our understanding of Enceladus' plume‐related material transport. This framework can be adapted to Io/Europa observations by rescaling thresholds to local magnetospheric conditions.
Journals
2026 EN
Hartley D. P. · Christopher I. W. · Argall M. R.
+5 more
Abstract Electric field instruments function by electrically coupling to the surrounding plasma, resulting in a response function that varies depending on local conditions. This variable coupling can complicate quantitative interpretation of wave measurements, yet is rarely considered. While this effect has recently been quantified for the Van Allen Probes, we present the first quantitative analysis for the Magnetospheric MultiScale (MMS) mission. First, MMS observations are evaluated against Faraday's Law, revealing that the angle between the measured whistler‐mode electric and magnetic fields directly depends on the wave propagation direction, a feature consistent with sheath impedance effects. A novel technique for determining electric field observations along each measurement direction is introduced, addressing limitations of previous works. This reveals that, for MMS in low‐density plasma, spin‐plane amplitudes are ∼60% of expected values, with small phase shifts, while spin‐axis measurements are accurate within 5%–10%, with phase shifts up to −20°. At intermediate densities, spin‐plane amplitudes match, or slightly exceed, expected values whereas spin‐axis observations can be overestimated by 70% and experience frequency‐dependent phase shifts. At high‐density, spin‐plane measurements generally agree with expected values, but spin‐axis observations are overestimated by ∼30% and experience ∼30°phase shifts. Accurate measurements are critical, with electric field fluctuations increasingly being used to infer wave‐particle energy exchange rates. If electric field observations can be under or over‐measured depending on the local plasma environment, this directly impacts these computations of energy exchange rates, potentially leading to a misinterpretation of the fundamental physical mechanisms that drive particle dynamics.
Journals
2026 EN
Piasecki June · Saur Joachim · Clark George
+3 more
Abstract Observations made by the Juno spacecraft above Jupiter's polar regions have revealed that electrons accelerated toward Jupiter, which contribute to auroral emissions, are frequently accompanied by electrons accelerated away from Jupiter. These electrons should be observable as narrow electron beams in the middle magnetosphere, in accordance with the principles of adiabatic particle motion. The existence of such beams has been previously reported using data from the Galileo mission, and their relation to auroral processes has been hypothesized. In the present study, we analyze electrons measured by Juno's JEDI instrument in the middle magnetosphere between 13 and 50.5R J$}_}$ radial distance and within energies of 30–1,200 keV. The pitch angle distributions of potential electron beams are fitted with an intensity “beamness” function. The presence of narrow beams is demonstrated throughout the observation range. The energy fluxes of auroral and equatorial electron beams are compared by including pitch angle scattering processes along the magnetospheric field lines. This is achieved by solving the pitch angle diffusion equation for different sets of diffusion coefficients. The statistical occurrence distribution and the energy fluxes of the beams are consistent with auroral upward accelerated electrons observed in studies of the polar space environment. This finding provides further support for the hypothesis that the electron beams observed in the middle magnetosphere originate from the auroral acceleration region.
Journals
2026 EN
Chanyshev Artem · Bondar Dmitry · Wang Lin
+10 more
Abstract Olivine and ahrensite are the primary components of the interiors of Fe‐rich terrestrial planets and meteorites, making their phase relations crucial for planetary science. Moreover, their phase relations can be used for calibrating large‐volume high‐pressure devices such as multi‐anvil apparatus. Here we defined the olivine–ahrensite phase relations in the MgO‐FeO‐SiO 2 system at 7.5–12.0 GPa at 1,530 and 1,950 K using a multi‐anvil apparatus. Combining the current results with our previously determined binary loop at 1,740 K, we re‐estimated the shock parameters of several L5 and L6‐types meteorites. Also, we determined the olivine‐ahrensite phase ratio and compositions along cold and warm Mars aerotherms for Mg/(Mg + Fe) ratios of 0.75 and 0.80. Using this mineralogical model, we estimated and compared seismic wave velocity profiles in Mars' interior to data from the InSight geophysical mission.
Journals
2026 EN
Rolland Robin · BouruetAubertot Pascale · Cuypers Yannis
+13 more
Abstract Near‐inertial waves (NIWs) are an important source of turbulence for the ocean interior. Mesoscale anticyclonic eddies are known to facilitate their propagation at depth while trapping them. However, in situ observations have so far focused on large ( > 50 ${ >} 50$ km radius), energetic eddies, whereas most of the ocean is populated by smaller, moderately energetic fine‐scale structures. Are these smaller structures efficient to trap NIWs and enhance turbulence? Here, we present in situ observations from the BioSWOT‐Med 2023 cruise addressing this issue by surveying a fine‐scale frontal area of the North Balearic front in the Mediterranean Sea, assisted by the first high‐resolution Sea Surface Height images of the new Surface Water and Ocean Topography (SWOT) satellite mission during its Calibration/Validation phase. We explore how fine scales modulate the evolution of turbulence below the mixed layer after experiencing two consecutive strong wind events. We show that turbulence remains low in the front and its cyclonic side, while being greatly enhanced in the anticyclonic side. The latter side is dominated by a fine‐scale anticyclone (12.8 km of radius, Rossby number of 0.5) that trapped NIWs, increasing turbulent dissipation level to several1 0 − 8$1{0}^{-8}$ Wkg − 1${\text{kg -1}$ . The NIW‐induced vertical kinetic energy flux reach up to 5.1 mWm − 2$-2}$ below the pycnocline and represent∼ 20 ${\sim} 20$ % of the wind power input into inertial motions, higher or similar to previous estimations outside and inside mesoscale anticyclones. Future work is needed to investigate whether these results extend to fine scales elsewhere in the world ocean, especially in regions with larger baroclinic Rossby radius of deformation.
Journals
2026 EN
Zaron Edward D. · Waterhouse Amy F. · Wang Jinbo
+2 more
Abstract Sea‐surface topography observations from the Surface Water & Ocean Topography (SWOT) satellite altimeter mission are used to map the baroclinic internal tides in a region off California during the 1‐day calibration/validation orbit phase of the mission. The observations, which cover the period from 30 March through 10 July 2023, reveal a large‐scale internal wave field dominated by waves generated at the Mendocino Fracture zone approximately 500 km north of the region studied. Tidal harmonic constants of baroclinic sea level are derived from mooring observations at four sites within the KaRIn swath and compared with the SWOT data. The harmonic constants from the moorings and altimeter agree qualitatively; however, the SWOT results are significantly uncertain due to long‐wavelength platform errors and non‐astronomical tidal modulations. Spectral analysis of the time series reveal that the phase‐locked tide explains about 75% of the baroclinic sea level variance in the semidiurnal band.