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| Open AccessObservation of a reversal of rotation in a sunspot during a solar flare
Back reaction of coronal magnetic fields on the solar surface may help to understand the coronal reconfiguration during a solar flare. Here the authors report observation of reversal of the rotation of a sunspot during a X1.6 flare with data from HMI.
- Yi Bi
- , Yunchun Jiang
- & Zhe Xu
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Article
| Open AccessDual matter-wave inertial sensors in weightlessness
Atom interferometers in microgravity environments can reach precisions unattainable on Earth. Here the authors report the operation of a dual species interferometer onboard a zero-G aircraft, testing universality of free fall in microgravity and providing a test bed for future moving inertial sensors.
- Brynle Barrett
- , Laura Antoni-Micollier
- & Philippe Bouyer
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| Open AccessNon-thermal hydrogen atoms in the terrestrial upper thermosphere
Model predictions of atomic hydrogen behaviour in the terrestrial atmosphere have long-standing discrepancies with geocoronal observations. Here, using satellite measurements, Qin and Waldrop note the existence of hot hydrogen atoms in the upper thermosphere, reconciling observational modelling differences.
- Jianqi Qin
- & Lara Waldrop
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| Open AccessFlare differentially rotates sunspot on Sun’s surface
Sunspots are concentration of magnetic field visible on the solar surface, which were thought to be unaffected by solar flares that take place in the solar corona. Here the authors report evidence of a flare-induced rotation of a sunspot, showing nonuniform acceleration following the peaks of X-ray emissions.
- Chang Liu
- , Yan Xu
- & Haimin Wang
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| Open AccessEarth’s magnetosphere and outer radiation belt under sub-Alfvénic solar wind
The interaction between the Earth’s magnetic field and the solar wind results in the formation of a collisionless bow shock. Here, the authors study an even in which the solar wind Mach number remained steadily below one, leading to the evanescence of the bow shock and loss of electrons in the outer belts.
- Noé Lugaz
- , Charles J. Farrugia
- & Nathan A. Schwadron
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| Open AccessWave-induced loss of ultra-relativistic electrons in the Van Allen radiation belts
The processes that lead to losses of highly energetic particles from Earth’s radiation belts remain poorly understood. Here the authors compare observations and models of a 2013 event to show that electromagnetic ioncyclotron waves provide the dominant loss mechanism at ultra-relativistic energies.
- Yuri Y. Shprits
- , Alexander Y. Drozdov
- & Nikita A. Aseev
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| Open AccessDetermining solar effects in Neptune’s atmosphere
The causes behind fluctuations in Neptune's brightness as observed from Earth have proved enigmatic. Here, Aplin and Harrison use photometric observations to show that solar ultraviolet radiation and galactic cosmic rays combined are responsible for the fluctuations originating in Neptune’s atmosphere.
- K. L. Aplin
- & R. G. Harrison
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| Open AccessObserving the release of twist by magnetic reconnection in a solar filament eruption
Magnetic reconnection is a fundamental process giving rise to topology change and energy release in plasmas, of particular relevance for the Sun. Here the authors report the observation of fast reconnection in a solar filament eruption, which occurs between a set of ambient fibrils and the filament itself.
- Zhike Xue
- , Xiaoli Yan
- & Li Zhao
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| Open AccessData-driven magnetohydrodynamic modelling of a flux-emerging active region leading to solar eruption
Solar eruptions heavily influence space weather, but what are their causes remains an open question. Here the authors present a magnetohydrodynamic model of a solar eruption directly driven by solar magnetograms, following the transition from pre-eruptive to eruptive state.
- Chaowei Jiang
- , S. T. Wu
- & Qiang Hu
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| Open AccessMultiradionuclide evidence for the solar origin of the cosmic-ray events of AD 774/5 and 993/4
Natural spikes in radiocarbon have been identified at AD 774/5 and 993/4 and attributed to exceptional cosmic-ray events, although the cause remains uncertain. Here, the authors analyse records recovered from ice cores and suggest these spikes originated from extreme solar particle events.
- Florian Mekhaldi
- , Raimund Muscheler
- & Thomas E. Woodruff
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| Open AccessWave-driven butterfly distribution of Van Allen belt relativistic electrons
Relativistic electrons trapped in the Van Allen radiation belts sometimes exhibit a minimum of their pitch angle distribution at 90°. Here, the authors explain the origin of this phenomenon in terms of chorus and magnetosonic waves through simulations and observations of a geomagnetic storm data.
- Fuliang Xiao
- , Chang Yang
- & J. B. Blake
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| Open AccessObservations of discrete harmonics emerging from equatorial noise
Since the 1970s space missions have observed `equatorial noise' — noise-like plasma waves closely confined to the magnetic equatorial region of Earth s magnetosphere. Here, the authors uncover their structured and periodic frequency pattern, revealing that they are generated by proton distributions.
- Michael A. Balikhin
- , Yuri Y. Shprits
- & Benjamin Weiss
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| Open AccessExtreme ultraviolet imaging of three-dimensional magnetic reconnection in a solar eruption
Magnetic reconnection is a fundamental energy release process taking place in various astrophysical environments, but it is difficult to observe it directly. Here, the authors provide evidence of three-dimensional magnetic reconnection in a solar eruption using combined perspectives of two spacecraft.
- J. Q. Sun
- , X. Cheng
- & C. Fang
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| Open AccessRegional climate impacts of a possible future grand solar minimum
Regional surface climate response to a future decline in solar activity remains uncertain. Here, via numerical simulations, the authors show that a return to Maunder Minimum-like lows by 2050 could lead to some areas of significantly reduced surface warming via modulation of the North Atlantic Oscillation.
- Sarah Ineson
- , Amanda C. Maycock
- & Richard A. Wood
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| Open AccessStrong coronal channelling and interplanetary evolution of a solar storm up to Earth and Mars
Coronal mass ejections from the Sun play an important role in space weather, yet a full understanding of their behaviour remains elusive. Towards this aim, Möstl et al. present a suite of observations showing that an ejection was channelled away from its source region, explaining incorrect forecasts.
- Christian Möstl
- , Tanja Rollett
- & Bojan Vršnak
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| Open AccessWave energy budget analysis in the Earth’s radiation belts uncovers a missing energy
Whistler-mode waves regulate trapped electrons in the magnetosphere, but an accurate determination of their energy budget has remained elusive. This study presents a full analysis of their magnetic and electric field contributions and finds that a large amount of energy is stored in oblique waves.
- A.V. Artemyev
- , O.V. Agapitov
- & F.S. Mozer
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| Open AccessUbiquity of Kelvin–Helmholtz waves at Earth’s magnetopause
Although magnetic reconnection is recognized as the dominant mode for solar wind plasma to enter the magnetosphere, Kelvin–Helmholtz waves (KHW) have been suggested to also be involved. Here, the authors use 7 years of THEMIS data to show that KHW occur 19% of the time, and may be important for plasma transport.
- Shiva Kavosi
- & Joachim Raeder
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| Open AccessThe solar magnetic activity band interaction and instabilities that shape quasi-periodic variability
The origins of the Sun’s periodic activity, such as sunspot cycles, are poorly understood. McIntosh et al.posit that the rotational forcing of the activity bands comprising the 22-year magnetic cycle undergoes shorter-term variations, driving magnetic flux surges that impact solar output on those timescales.
- Scott W. McIntosh
- , Robert J. Leamon
- & Roger K. Ulrich
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Formation of lunar swirls by magnetic field standoff of the solar wind
Lunar swirls are high-albedo features on the Moon whose origins are widely debated. Using observations from the Diviner Lunar Radiometer, Glotch et al. present evidence supporting the idea that the swirls arise from abnormal space weathering caused by local magnetic field deflection of solar wind.
- Timothy D. Glotch
- , Joshua L. Bandfield
- & David A. Paige
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| Open AccessFull-Sun observations for identifying the source of the slow solar wind
Both fast and slow solar winds emanate from our Sun, although the source of the slow component remains elusive. Towards identifying this, Brooks et al. present full-Sun spectral images from Hinode, combined with magnetic modelling, to produce a solar wind source map.
- David H. Brooks
- , Ignacio Ugarte-Urra
- & Harry P. Warren
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Modelling the influence of photospheric turbulence on solar flare statistics
Solar flares follow complex statistical patterns, making it hard to understand and model their underlying physical processes. Here, the authors present a model based on reconnection of magnetic flux tubes twisted by turbulent photospheric flow that reproduces flare statistics and energy–time correlations.
- M. Mendoza
- , A. Kaydul
- & H. J. Herrmann
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| Open AccessProbing the solar corona with very long baseline interferometry
Very long baseline interferometry is an astronomical technique that uses radio telescopes on Earth to observe extragalactic radio sources. Here, the authors show that it can be used to measure the electron density of the Sun’s corona and compare their findings to models from spacecraft tracking data.
- B. Soja
- , R. Heinkelmann
- & H. Schuh
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Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections
Coronal mass ejections are large expulsions of plasma from the solar corona into space, and are drivers of major space weather effects. Here, the authors report observations of two successive ejections, whose interaction led to extremely enhanced magnetic fields and high solar wind speeds near 1 AU.
- Ying D. Liu
- , Janet G. Luhmann
- & Antoinette B. Galvin
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| Open AccessSolar wind entry into the high-latitude terrestrial magnetosphere during geomagnetically quiet times
A full understanding of the penetration of solar wind plasma into the Earth’s magnetosphere, during geomagnetically quiet times, remains elusive. Using multi-spacecraft data, Shi et al.find unexpected entry of the solar wind into the high-latitude magnetosphere and suggest a probable entry mechanism.
- Q.Q. Shi
- , Q.-G. Zong
- & E. Lucek
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Observations of ubiquitous compressive waves in the Sun’s chromosphere
A full understanding of the heating and dynamics of the Sun's atmosphere remains elusive, but magnetohydrodynamic waves are believed to be crucial. Using observations from the ROSA imager, this study finds compressive waves in the solar chromosphere, which may provide the energy needed for coronal heating.
- Richard J. Morton
- , Gary Verth
- & Robertus Erdélyi
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Observation of an evolving magnetic flux rope before and during a solar eruption
Explosive energy releases in plasmas, such as in solar eruptions like flares and coronal mass ejections, are thought to be caused by magnetic reconnection in thin current sheets. Zhanget al. observed a magnetic flux rope during a solar eruption, highlighting its role in driving explosive energy releases.
- Jie Zhang
- , Xin Cheng
- & Ming-de Ding
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Mechanism for spectral break in cosmic ray proton spectrum of supernova remnant W44
TheFermispacecraft recently observed gamma-ray emission from supernova remnant W44, however, the mechanism is unclear. Here, the authors show that strong ion-neutral collisions in the remnant surrounding lead to the steepening of the energy spectrum of accelerated particles by one power.
- M. A. Malkov
- , P. H. Diamond
- & R. Z. Sagdeev
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Propagation of an Earth-directed coronal mass ejection in three dimensions
The physics governing the propagation of solar coronal mass ejections (CMEs), an important cause of bad space weather on Earth, is poorly understood. The authors model a CME's three-dimensional propagation and determine accurate arrival times near the Earth's surface.
- Jason P. Byrne
- , Shane A. Maloney
- & Peter T. Gallagher