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It is well known that the interaction between interplanetary (IP) shocks and the Earth’s magnetosphere would generate/excite various types of geomagnetic phenomena. Progresses have been made on the Earth’s magnetospheric response to solar wind forcing in recent years in the aspects associated with magnetospheric substorms. Strong substorms and super substorms could be triggered externally by sudden changes of solar wind dynamic pressures. When a strong substorms (AE > 1000 nT) or super substorms (AE > 2000 nT) occurs, singly charged oxygen ions escaped from the Earth’s ionosphere are found to be a dominated ion population in the magnetotail and in the inner magnetosphere—ring current region. The products of a strong substorms or super substorms- plasmoid, burst bulk flows are also found to contain significant oxygen ions, even substorm injections can be dominated by oxygen ions. Thus, the magnetospheric dynamic must consider the contributions from the heavy oxygen ions. Also, the IP shock induced super substorms associated electromagnetic pulses (dB/dt) would shift the energetic particle (injections) inward and accelerate existing population significantly. Extensive attempts have also been made to understand how the solar wind energy couples with the magnetosphere to excite magnetospheric substorms. The statistical analysis shows that strong substorms (AE > 1000 nT) and super substorms (AE > 2000 nT) triggered by interplanetary shocks are most likely to occur under the southward interplanetary magnetic field (IMF) and fast solar wind pre-conditions. In addition, strong substorms after the IP shock arrival are more likely to occur when IMF points toward (away from) the Sun around spring (autumn) equinox, which can be ascribed to the Russell-McPherron effect. Thus, the southward IMF precondition of an interplanetary shock and the Russell-McPherron effect can be considered as precursors of a strong substorm and/or super substorm triggered by IP shocks. Moreover, the average duration of CME sheath region which is just behind the interplanetary shock are found to be about 7 hours. This indicates that southward IMF compressed by shock could last at least 7 hours long in the downstream of the interplanetary shock (sheath region) if a southward IMF pre-condition is present, which explains why the largest substorm often occur in the CME sheath.

Kinetic Alfvén waves (KAWs) are ubiquitous throughout the plasma universe. Although they are broadly believed to provide a potential approach for energy exchange between electromagnetic fields and plasma particles, neither the detail nor the efficiency of the interactions has been well-determined yet. The primary difficulty has been the paucity of knowledge of KAWs’ spatial structure in observation. Here, we apply a particle-sounding technique to Magnetospheric Multiscale mission data to quantitatively determine the perpendicular wavelength of KAWs from ion gyrophase-distribution observations. Our results show that KAWs’ perpendicular wavelength is statistically 2.4 ± 0.7 times proton thermal gyro-radius. This observation yields an upper bound of the energy the majority proton population can reach in coherent interactions with KAWs, that is, roughly 5.76 times proton perpendicular thermal energy. Therefore, the method and results shown here provide a basis for unraveling the effects of KAWs in dissipating energy and accelerating particles in a number of astrophysical systems, e.g., planetary magnetosphere, astrophysical shocks, stellar corona and wind, and the interstellar medium. Kinetic Alfven Waves (KAWs) are ubiquitous in space plasmas. Here, the authors show that application of particle sounding technique to Magnetospheric Multiscale Mission data enables measuring perpendicular wavelength of KAWs.

Identifying how energy transfer proceeds from macroscales down to microscales in collisionless plasmas is at the forefront of astrophysics and space physics. It provides information on the evolution of involved plasma systems and the generation of high-energy particles in the universe. Here we report two cross-scale energy-transfer events observed by NASA’s Magnetospheric Multiscale spacecraft in Earth’s magnetosphere. In these events, hot ions simultaneously undergo interactions with macroscale (~ 10 5 km) ultra-low-frequency waves and microscale ( ~ 10 3 km) electromagnetic-ion-cyclotron (EMIC) waves. The cross-scale interactions cause energy to directly transfer from macroscales to microscales, and finally dissipate at microscales via EMIC-wave-induced ion energization. The direct measurements of the energy transfer rate in the second event confirm the efficiency of this cross-scale transfer process, whose timescale is estimated to be roughly ten EMIC-wave periods about (1 min). Therefore, these observations experimentally demonstrate that simultaneous macroscale and microscale wave-ion interactions provide an efficient mechanism for cross-scale energy transfer and plasma energization in astrophysical and space plasmas. Cross-scale energy transfers in collisionless plasmas help understanding involved mechanisms. Here, the authors show simultaneous macro- and micro-scale wave-ion interactions provide an efficient mechanism for cross-scale energy transfer and plasma energization in astrophysical and space plasmas.

Besides the cusp, polar cap, and auroral oval, the nightside subauroral zone has also recently been reported as a source region of the ionospheric oxygen outflows. However, the detailed mass and energy sources of these ions remain open questions. Here, we address this issue from the perspective of the response of conjugate hemispheres. Investigation of Van Allen Probes data demonstrates a notable preference of oxygen outflows from the nightside subauroral zone from the sunlit hemisphere. This characteristic eliminates the possibility of nightside auroral precipitation playing a significant role, as it is more prominent in darkness. Instead, it highlights sunlight‐induced ionization as the mass source and enhanced plasma waves from the magnetotail as the energy source. The results presented here further support the nightside subauroral zone as an independent source of magnetospheric oxygen ions. Plain Language Summary Single‐charged oxygen ions, believed to ultimately originate from the ionosphere, are the main carriers of the ring current during severe space weather, including super geomagnetic storms and substorms. Therefore, comprehending where and how they come from is crucial for understanding the magnetosphere and space weather. Recent studies have reported the nightside subauroral zone as a source region, besides the usually cited cusp, polar cap, and auroral oval. However, the detailed mechanisms for the subauroral oxygen outflows remain open questions. In this study, we address this issue by studying how opposite hemispheres react simultaneously in subauroral oxygen outflow events observed by the Van Allen Probes. Data analysis reveals that these outflows tend to occur in the local summer hemisphere, where the nightside subauroral ionosphere receives more sunlight compared to the opposite hemisphere. This feature rules out nightside auroral precipitation playing a significant role, as it is more noticeable in the dark. Instead, it points to sunlight‐induced ionization as the source of mass and enhanced plasma waves from the magnetotail as the source of energy. Our findings reinforce the idea that the nightside subauroral zone is an important source of ionospheric oxygen outflows. Key Points The Van Allen Probes have observed oxygen outflows from the nightside subauroral ionosphere in a single hemisphere Statistics reveal a preference for the outflows in sunlit hemisphere, distinguishing them from auroral outflows more prominent in darkness This preference highlights sunlight‐induced ionization and waves from the magnetotail as the source of mass and energy

It is generally believed that long-duration gamma-ray bursts (GRBs) originate from the core collapse of rapidly spinning massive stars, and at least some of them are powered by hyperaccreting black holes (BHs). However, definite proofs about the progenitor and central engine of these GRBs have not been directly observed in the past. Here, we report the existence of a quasiperiodic oscillation (QPO) signature with periodic frequency ∼0.02 Hz in the early X-ray afterglow phase of GRB 220711B. Such a low-frequency QPO likely signals the precession of a relativistic jet launched from a GRB hyperaccreting BH central engine. The energy injection signature from the late X-ray observations (from 5 × 102 s ∼ 1 × 104 s) is consistent with the precession hypothesis. The prompt gamma-ray light curve does not show any QPO signature, suggesting that the X-ray flaring emission in the early afterglow phase and prompt emission likely originate from different accretion processess, indicating that the progenitor stars of GRBs have a core-envelope structure with a stratified angular momentum distribution and the late-time accretion disk likely has a misalignment with respect to the rotation axis of the BH. Such a misalignment is not expected in a canonical collapsar model. As a result, the QPO signature in GRB 220711B may reveal a new formation channel of long GRBs, possibly a stellar-merger-induced core collapse, with the orbital angular momentum of the binary misaligned with the spin axis of the collapsing star.

While Jupiter’s magnetosphere is primarily governed by internal processes, variations in solar wind conditions can significantly modulate magnetospheric energy. Assessing solar wind conditions at Jupiter has been a long-standing challenge in the community. In this study, we investigate multiple datasets, including auroral images captured by the Hubble Space Telescope and in situ measurements obtained by the Juno spacecraft, to characterize Jupiter’s magnetosphere during solar wind compression and quiet conditions. The distinct responses demonstrate that auroral morphologies, lobe magnetic fields, ultra-low-frequency waves, and broadband kilometric radio emissions could serve as effective indicators for magnetospheric states. In particular, we statistically analyze the distribution of lobe magnetic fields, which represent the intensities of the cross-field electrical currents in the magnetodisc, and propose the applicability of the lobe magnetic field as a proxy for solar wind conditions. The results from the four individual methods of determining magnetospheric states are generally consistent, providing further evidence of their robustness. These observational proxies for solar wind conditions could therefore be widely applied in both existing spacecraft datasets and those from future missions to Jupiter.

In the analysis of in-situ space plasma and field data, an establishment of the coordinate system and the frame of reference, helps us greatly simplify a given problem and provides the framework that enables a clear understanding of physical processes by ordering the experimental data. For example, one of the most important tasks of space data analysis is to compare the data with simulations and theory, which is facilitated by an appropriate choice of coordinate system and reference frame. While in simulations and theoretical work the establishment of the coordinate system (generally based on the dimensionality or dimension number of the field quantities being studied) and the reference frame (normally moving with the structure of interest) is often straightforward, in space data analysis these are not defined a priori , and need to be deduced from an analysis of the data itself. Although various ways of building a dimensionality-based (D-based) coordinate system (i.e., one that takes account of the dimensionality, e.g., 1-D, 2-D, or 3-D, of the observed system/field), and a reference frame moving along with the structure have been used in space plasma data analysis for several decades, in recent years some noteworthy approaches have been proposed. In this paper, we will review the past and recent approaches in space data analysis for the determination of a structure’s dimensionality and the building of D-based coordinate system and a proper moving frame, from which one can directly compare with simulations and theory. Along with the determination of such coordinate systems and proper frame, the variant axis/normal of 1-D (or planar) structures, and the invariant axis of 2-D structures are determined and the proper frame velocity for moving structures is found. These are found either directly or indirectly through the definition of dimensionality. We therefore emphasize that the determination of dimensionality of a structure is crucial for choosing the most appropriate analysis approach, and failure to do so might lead to misinterpretation of the data. Ways of building various kinds of coordinate systems and reference frames are summarized and compared here, to provide a comprehensive understanding of these analysis tools. In addition, the method of building these systems and frames is shown not only to be useful in space data analysis, but also may have the potential ability for simulation/laboratory data analysis and some practical applications.

The interaction between interplanetary shocks and the Earth's magnetosphere manifests in many important space physics phenomena including particle acceleration. We investigated the response of the inner magnetospheric hydrogen and oxygen ions to a strong interplanetary shock impinging on the Earth's magnetosphere. Both hydrogen and oxygen ions are found to be heated/accelerated significantly with their temperature enhanced by a factor of two and three immediately after ∼1 min and ∼12 min of the shock arrival respectively. Multiple energy dispersion signatures of ions were found in the parallel and anti‐parallel direction to the magnetic field immediately after the interplanetary shock impact. The energy dispersions in the anti‐parallel direction preceded those in the parallel direction. Multiple dispersion signatures can be explained by the flux modulations of local ions (rather than the ions from the Earth's ionosphere) by ULF waves. It is found that the energy spectrum from 10 eV to ∼40 keV are highly correlated with the cross product of observed ULF wave electric and magnetic field (V = (E × B)/B2), which indicate that both cold plasmaspheric plasma and hot thermal ions (10 eV to ∼40 keV) are accelerated and decelerated with the various phases of ULF wave electric field. We then demonstrate that ion acceleration due to the interplanetary shock compression on the Earth's magnetic field is rather limited, whereas the major contribution to acceleration comes from the electric field carried by ULF waves via drift‐bounce resonance for both the hydrogen and oxygen ions. The integrated hydrogen and oxygen ion flux with the poloidal mode ULF waves are highly coherent (>0.9) whereas the coherence with the toroidal mode ULF waves is negligible, implying that the poloidal mode ULF waves are much more efficient in accelerating hydrogen and oxygen ions in the inner magnetosphere than the toroidal mode ULF waves. The duration of high coherence for oxygen ions with the poloidal mode ULF wave is longer than that for hydrogen ions, indicating that oxygen ions can be heated/accelerated more efficiently by the poloidal mode ULF wave induced by the interplanetary shock. Key Points Oxygen ions can be accelerated more efficiently by the poloidal ULF wave The accelerated ions are found to be exhibiting energy dispersion signatures

When a solar wind dynamic pressure impulse impinges on the magnetophere, ultra‐low‐frequency (ULF) waves can be excited in the magnetosphere and the solar wind energy can be transported from interplanetary space into the inner magnetosphere. In this paper, we have systematically studied ULF waves excited at geosynchronous orbit by both positive and negative solar wind dynamic pressure pulses. We have identified 270 ULF events excited by positive solar wind dynamic pressure pulses and 254 ULF events excited by negative pulses from 1 January 2001 to 31 March 2009. We have found that the poloidal and toroidal waves excited by positive and negative pressure pulses oscillate in a similar manner of phase near 06:00 local time (LT) and 18:00 LT, but in antiphase near 12:00 LT and 0:00 LT. Furthermore, it is shown that excited ULF oscillations are in general stronger around local noon than those in the dawn and dusk flanks. It is demonstrated that disturbances induced by negative impulses are weaker than those by positive ones, and the poloidal wave amplitudes are stronger than the toroidal wave amplitudes both in positive and negative events. The potential impact of these excited waves on energetic electrons at geosynchronous orbit has also been discussed.

Solar wind controls nonthermal escape of planetary atmospheric volatiles, regardless of the strength of planetary magnetic fields. For both Earth with a strong dipole and Mars with weak remnant fields, the oxygen ion (O+) outflow has been separately found to be enhanced during corotating interaction region (CIR) passage. Here we compared the enhancements of O+ outflow on Earth and Mars driven by a CIR in January 2008, when Sun, Earth, and Mars were approximately aligned. The CIR propagation was recorded by STEREO, ACE, Cluster, and Mars Express (MEX). During the CIR passage, Cluster observed enhanced flux of upwelling oxygen ions above the Earth's polar region, while MEX detected an increased escape flux of oxygen ions in the Martian magnetosphere. We found that (1) under a solar wind dynamic pressure increase of 2–3 nPa, the rate of increase in Martian O+ outflow flux was 1 order higher than those on Earth; and (2) as a response to the same part of the CIR body, the rate of increase in Martian O+ outflow flux was on the same order as for Earth. The comparison results imply that the dipole effectively prevents coupling of solar wind kinetic energy to planetary ions, and the distance to the Sun is also crucially important for planetary volatile loss in our inner solar system. Key Points CIR enhances the atmospheric outflow on both Earth and Mars Earth's dipole limits transport of solar wind kinetic energy to planetary ions The distance to the Sun is also important for planetary volatile loss