Nikolai A. Tsyganenko

Recently, Hua et al. (2026, https://doi.org/10.1029/2025GL120881 ) combined observations during a 4‐day storm period with numerical simulations and concluded that the abrupt electron loss in the field‐line‐curvature scattering (FLCS) region played a leading role in shaping the outer boundary of radiation belt (RB); the authors conjectured that the simple yet fundamental FLCS process, neglected in previous global radiation belt models, is sufficient to explain the dynamics of the outer electron belt boundary. In this commentary, we discuss the importance of the FLCS‐induced loss mechanism in the light of (a) existing information about the energetic electron precipitation and (b) contradictory conclusions of another recent study (Huang et al., 2025, https://doi.org/10.1029/2025ja033965 ). While in a qualitative sense we agree with the conjecture by Hua et al. (2026, https://doi.org/10.1029/2025GL120881 ) accurate quantification of the FLCS effects, based on a more realistic field model is still needed. Possible pathways for solving this challenging problem are outlined.

Recently, Stephens et al. (2023), https://doi.org/10.1029/2022ja031066 utilized a data mining (DM) algorithm, applied to 26 years of magnetospheric magnetometer observations coupled with a flexible formulation of the magnetospheric magnetic field, to reconstruct the global configuration of the magnetotail when the Magnetospheric MultiScale (MMS) mission observed tail reconnection in situ. Of the 26 DM‐reconstructed MMS reconnection events, 16 had a isocontour within Earth radii of the observed reconnection location. Another eight had a minimum region, identified using nT isocontours, within . This consistency suggests that the structure of tail reconnection is correlated with the substorm/storm state of the magnetosphere, as reflected by geomagnetic indices and solar wind conditions. We verify these results using new validation methods and by comparing in‐sample (including event data) to out‐of‐sample (excluding event data) reconstructions. We first benchmark the architecture of the reconstructed magnetic field using 100 randomly generated magnetic fields containing tail X‐ and O‐lines, resolving 77 of them with three false positives. Next, we quantify the consistency of the reconstructions in resolving the reconnection location using a skill score relative to random chance. 88% of the in‐sample and 75% of the out‐of‐sample scores are positive, confirming that the reconstructions resolve the location of tail reconnection better than random chance. Last, a bootstrapping analysis, which refits the model architecture to 100 random resamples of data, shows standard deviations in of nT, indicating that the DM approach is not overly sensitive to the particular sampling of magnetometer records.

Global distributions of the dayside magnetosheath proton density and temperature are reconstructed, using a multi‐year pool of satellite observations and empirical data‐constrained models with a flexible architecture. The models are based on data of Themis, Cluster, and MMS satellites and are driven by the upstream solar wind density, speed, proton temperature, and interplanetary magnetic field (IMF). In the simplest case of zero IMF and untilted geodipole, the models reveal the expected peak of plasma density and temperature in the subsolar area, with gradual decrease away from the Sun‐Earth line. In more complex situations with nonzero IMF, the magnetic field draping and associated electromagnetic tensions, combined with the reconnection‐induced plasma energization, streaming, and pile‐up effects at the magnetopause, result in dawn‐dusk and north‐south asymmetries. The north‐south asymmetry is dramatically enhanced during periods with large geodipole tilt to the terminator plane. The asymmetry is especially pronounced around the sunward (local summer) polar cusp, more directly exposed to the solar wind. In this case, the cusp's poleward boundary forms a local magnetic wall that brakes the particle flow and, for parallel orientation between the magnetosheath and magnetosphere tail lobe field, forms a pile‐up area with enhanced density. In the opposite case of antiparallel alignment between the magnetosheath and lobe fields, the inflowing plasma is effectively drained away by reconnection. The obtained results are compared with those of gasdynamic theory and MHD simulations. In particular, a remarkable agreement is found with theoretically predicted density and temperature jumps across the subsolar bow shock.

Reconstruction of the magnetospheric magnetic field using swarms of virtual spacecraft provided by data mining confirms seminal in situ evidence (Angelopoulos et al., 2008, https://doi.org/10.1126/science.1160495 ) that on 26 February 2008 an X‐line emerged in the region between two distant Time History of Events and Macroscale Interactions during Substorms probes at the time of the substorm activation in the magnetotail. It also shows that the X‐line formation was preceded by rapid current decay that happened 15 min earlier. The current was built up earthward of the pre‐existing X‐line formed prior to the previous substorm activation 45 min before. The most pronounced effect of the tail reconfiguration at the moments of two substorm activations and the current disruption is the rapid earthward redistribution of the magnetic flux. Comparison of low‐altitude mapping of the magnetotail structure with all‐sky imager data shows that these rapid reconfigurations might be triggered by plasma flows whose source was farther from the Earth than the resolved X‐lines.

So far, the structure and dynamics of the terrestrial magnetotail have largely been investigated within ( is the Earth's radius) because of the lack of in‐situ observations beyond that distance, as well as limitations of earlier empirical models. Here we reconstruct the global structure of the cislunar tail within using 2011–2023 data from the ARTEMIS mission, the 2010 THEMIS‐ARTEMIS transition orbits and other missions, such as IMP‐8 and Geotail. The reconstruction is made using a new‐generation data mining‐based empirical algorithm with minimal ad hoc assumptions on the structure of the equatorial current sheet and its evolution during storms and substorms. It is found that the cislunar tail has a regular structure, stable in the substorm growth phase and regularly changing during the expansion and recovery phases. Substorms likely involve the formation of an X‐line around and magnetic flux accumulation earthward of it, which persists in the growth phase and flattens out after the substorm onset. Consistent with earlier reconstructions of the shorter tail region, the present ones reveal the near‐Earth dipolarization of the magnetic field earthward of , which is a part of the whole cislunar tail flux redistribution. Thin current sheets embedded into a thicker current halo extend up to 40 and may exist at lunar distances, consistent with in‐situ ARTEMIS observations, near O‐lines of plasmoids/flux ropes.

The storm‐time geomagnetic field and electric currents are reconstructed for extreme storms before 1995: the July 1982 superstorm and the March 1989 Hydro‐Québec grid collapse event. The reconstructions are based on an improved magnetic field data mining method utilizing recently published machine learning‐derived solar wind data. The data mining reconstructions are rescaled using statistics of the nearest neighbor bins to eliminate the bias toward weaker storms. A concurrent reconstruction method provides the combined description of storms and substorms: storm and substorm features are first reconstructed independently for the inner and tail magnetosphere, respectively, and then the data fitting is reiterated using synthetic data generated using the first round of reconstructions. The data fitting procedure is further tuned to better resolve the location of the field‐aligned currents. Testing the updated methods for the November 2003 and 1982 superstorms significantly improves the validation results for in situ observations. The effect of rescaling doubles the peak ring current density (from 81 to 168 for the November 2003 storm) while the tuned fitting procedure shifts the Region‐2 field‐aligned currents equatorward to magnetic latitudes as low as . Rescaling also intensifies the equatorial currents such that X‐line arcs and even an X‐loop are formed within geosynchronous orbit, where reconnection may approach a relativistic regime. Such a change in the field topology limits the peak plasma pressure obtained from the quasi‐static force balance equation.

Reconstruction of the magnetospheric magnetic field using swarms of synthetic probes provided by data mining confirms seminal in-situ evidence (Angelopoulos et al., 2008) that on February 26, 2008 an X-line emerged in the region between two distant THEMIS probes at the moment of the substorm activation in the magnetotail. It also shows that the X-line formation was preceded by a rapid current decay. The current was built up earthward of the pre-existing X-line formed prior to the previous substorm activation. The most pronounced effect of the tail reconfiguration at the moments of two substorm activations and the current disruption is the rapid earthward redistribution of the magnetic flux. Comparison of low-altitude mapping of the magnetotail structure with all-sky images suggests that these rapid reconfigurations were triggered by plasma flows whose source is much farther from the Earth than the resolved X-lines.

Large‐scale patterns of the steady‐state magnetosheath plasma flow and their dependence on the interplanetary magnetic field (IMF) have been reconstructed for the first time on the basis of large multi‐year multi‐mission pool of spacecraft observations, concurrent interplanetary data, and an empirical high‐resolution model. The flow model architecture builds upon a recently developed magnetosheath magnetic field representation by flexible expansions of its toroidal and poloidal components in a coordinate system, naturally conformed with the magnetopause and bow shock shapes. The model includes two physics‐based flow symmetry modes: the first one treats the magnetosphere as an axisymmetric unmagnetized obstacle, whereas the second mode takes into account the geodipole tilt, an important factor in the reconnection effects. The spacecraft data pool includes 1‐min average data by Themis (2007–2024), Cluster (2001–2022), and MMS‐1 (2015–2024) missions, as well as OMNI interplanetary data. The model drivers include the solar wind particle flux, IMF components, and the geodipole tilt angle. The model calculations faithfully reproduce the average plasma flow geometry and substantial effects have been found of the IMF orientation and magnitude, a principal factor that defines electromagnetic forces inside the magnetosheath. A strong dependence of the magnetosheath flow patterns on the Earth's dipole tilt indicates an important contribution of reconnection effects at the magnetopause to the solar wind particle transport around the dayside magnetosphere.