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Journal articleVuorinen L, LaMoury AT, Hietala H, et al., 2023, , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380
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- Citations: 8
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Journal articleAdhikari S, Shay M, Parashar T, et al., 2023,
Effect of a guide field on the turbulence like properties of magnetic reconnection
, Physics of Plasmas, Vol: 30, Pages: 1-14, ISSN: 1070-664XThe effect of an external guide field on the turbulence-like properties of magneticreconnection is studied using five different 2.5D kinetic particle-in-cell (PIC) simulations. The magnetic energy spectrum is found to exhibit a slope of approximately−5/3 in the inertial range, independent of the guide field. On the contrary, theelectric field spectrum, in the inertial range steepens more with the guide field andapproaches a slope of −5/3. In addition, spectral analysis of the different terms ofthe generalized Ohm’s law is performed and found to be consistent with PIC simulations of turbulence and MMS observations. Finally, the guide field effect on theenergy transfer behavior is examined using von-K´arm´an Howarth (vKH) equationbased on incompressible Hall-MHD. The general characteristics of the vKH equationwith constant rate of energy transfer in the inertial range, is consistent in all the simulations. This suggests that the qualitative behavior of energy spectrum, and energytransfer in reconnection is similar to that of turbulence, indicating that reconnectionfundamentally involves an energy cascade.
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Journal articleKilpua E, Vainio R, Cohen C, et al., 2023, , ASTROPHYSICS AND SPACE SCIENCE, Vol: 368, ISSN: 0004-640X
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- Citations: 7
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Journal articleGrimmich N, Plaschke F, Archer MO, et al., 2023, , JGR: Space Physics, Vol: 128, Pages: 1-22, ISSN: 2169-9402
To first order, the magnetopause (MP) is defined by a pressure balance between the solar wind and the magnetosphere. The boundary moves under the influence of varying solar wind conditions and transient foreshock phenomena, reaching unusually large and small distances from the Earth. We investigate under which solar wind conditions such extreme MP distortions occur. Therefore, we construct a database of magnetopause crossings (MPCs) observed by the THEMIS spacecraft in the years 2007 to mid-2022 using a simple Random Forest Classifier. Roughly 7% of the found crossing events deviate beyond reported errors in the stand-off distance from the Shue et al. (1998, https://doi.org/10.1029/98JA01103) MP model and thus are termed extreme distortions. We find the occurrence of these extreme events in terms of expansion or compression of the MP to be linked to different solar wind parameters, most notably to the IMF magnitude, cone angle, velocity, Alfvén Mach number and temperature. Foreshock transients like hot-flow anomalies and foreshock bubbles could be responsible for extreme magnetospheric expansions. The results should be incorporated into future magnetopause models and may be helpful for the reconstruction of the MP locations out of soft x-ray images, relevant for the upcoming SMILE mission.
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Journal articleKlein K, Spence H, Kunz M, et al., 2023, , Bulletin of the AAS
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Journal articleChen L-J, Spence H, Klein K, et al., 2023, , Bulletin of the AAS
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Journal articleWimmer-Schweingruber RF, Andr茅 N, Barabash S, et al., 2023, , Bulletin of the AAS
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Journal articleGoodrich K, Schwartz S, III LW, et al., 2023, , Bulletin of the AAS
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Journal articleWilson L, Goodrich K, Turner D, et al., 2023, , Bulletin of the AAS
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Journal articleArridge CS, Xystouris G, Cochrane C, et al., 2023, , Bulletin of the AAS
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Journal articleMontgomery J, Ebert R, Allegrini F, et al., 2023, , Geophysical Research Letters, Vol: 50, ISSN: 0094-8276
We use the Kelvin-Helmholtz instability (KHI) condition with particle and magnetic field observations from Jovian Auroral Distributions Experiment and MAG on Juno along the dawn flank of Jupiter's magnetosphere. We identify the occurrence of magnetopause crossings that show evidence of being KH (Kelvin-Helmholtz) unstable. When estimating the k vector to be parallel to the velocity shear, we find that 25 of 62 (40%) magnetopause crossings satisfy the KHI condition. When considering the k vector of the maximum growth rate through a solid angle approach, we find that 60 of 62 (97%) events are KH unstable. This study shows evidence of KH waves at Jupiter's dawn flank, including primary drivers such as high velocity shears and changes in plasma pressure. Signatures of magnetic reconnection were also observed in ∼25% of the KH unstable crossings. We discuss these results and their implication for the prevalence of KHI at Juno's dawn magnetopause as measured by Juno.
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Journal articleKang SM, Yu Y, Deser C, et al., 2023, , Proceedings of the National Academy of Sciences, Vol: 120, Pages: 1-10, ISSN: 0027-8424
Since the beginning of the satellite era, Southern Ocean sea surface temperatures (SSTs) have cooled, despite global warming. While observed Southern Ocean cooling has previously been reported to have minimal impact on the tropical Pacific, the efficiency of this teleconnection has recently shown to be mediated by subtropical cloud feedbacks that are highly model-dependent. Here, we conduct a coupled model intercomparison of paired ensemble simulations under historical radiative forcing: one with freely evolving SSTs and the other with Southern Ocean SST anomalies constrained to follow observations. We reveal a global impact of observed Southern Ocean cooling in the model with stronger (and more realistic) cloud feedbacks, including Antarctic sea–ice expansion, southeastern tropical Pacific cooling, northward-shifted Hadley circulation, Aleutian low weakening, and North Pacific warming. Our results therefore suggest that observed Southern Ocean SST decrease might have contributed to cooler conditions in the eastern tropical Pacific in recent decades.
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Journal articleKhabarova O, Balasis G, Bu膷铆k R, et al., 2023, , Frontiers in Astronomy and Space Sciences, Vol: 10, Pages: 1-3, ISSN: 2296-987X
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Journal articleSuen GHH, Owen CJ, Verscharen D, et al., 2023, , ASTRONOMY & ASTROPHYSICS, Vol: 675, ISSN: 0004-6361
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- Citations: 2
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Journal articleHuang J, Kasper JC, Fisk LA, et al., 2023, , ASTROPHYSICAL JOURNAL, Vol: 952, ISSN: 0004-637X
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- Citations: 17
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Journal articleYardley SL, Owen CJ, Long DM, et al., 2023, , ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 267, ISSN: 0067-0049
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- Citations: 8
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Journal articleLiu W, Zhao J, Wang T, et al., 2023, , ASTROPHYSICAL JOURNAL, Vol: 951, ISSN: 0004-637X
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- Citations: 18
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Journal articleSioulas N, Velli M, Huang Z, et al., 2023, , ASTROPHYSICAL JOURNAL, Vol: 951, ISSN: 0004-637X
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- Citations: 14
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Journal articleHalekas JS, Bale SD, Berthomier M, et al., 2023, , ASTROPHYSICAL JOURNAL, Vol: 952, ISSN: 0004-637X
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- Citations: 24
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Journal articleLeblanc F, Roth L, Chaufray JY, et al., 2023, , Icarus, Vol: 399, ISSN: 0019-1035
A new analysis of aurora observations of Ganymede's atmosphere on the orbital leading and trailing hemispheres has been recently published by Roth et al. (2021), suggesting that water is its main constituent near noon. Here, we present two additional aurora observations of Ganymede's sub-Jovian and anti-Jovian hemispheres, which suggest a modulation of the atmospheric H2O/O2 ratio on the moon's orbital period, and analyze the orbital evolution of the atmosphere. For this, we propose a reconstruction of aurora observations based on a physical modelling of the exosphere taking into account its orbital variability (the Exospheric Global Model; Leblanc et al., 2017). The solution described in this paper agrees with Roth et al. (2021) that Ganymede's exosphere should be dominantly composed of water molecules. From Ganymede's position when its leading hemisphere is illuminated to when it is its trailing hemisphere, the column density of O2 may vary between 4.3 × 1014 and 3.6 × 1014 cm−2 whereas the H2O column density should vary between 5.6 × 1014 and 1.3 × 1015 cm−2. The water content of Ganymede's atmosphere is essentially constrained by its sublimation rate whereas the O2 component of Ganymede's atmosphere is controlled by the radiolytic yield. The other species, products of the water molecules, vary in a more complex way depending on their sources, either as ejecta from the surface and/or as product of the dissociation of the other atmospheric constituents. Electron impact on H2O and H2 molecules is shown to likely produce H Lyman-alpha emissions close to Ganymede, in addition to the observed extended Lyman-alpha corona from H resonant scattering. All these conclusions being highly dependent on our capability to accurately model the origins of the observed Ganymede auroral emissions, modelling these emissions remains poorly constrained without an accurate knowledge of the Jovian magnetospheric and Ganymede ionospheric electron popul
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Journal articleDuan D, He J, Zhu X, et al., 2023, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 952, ISSN: 2041-8205
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- Citations: 3
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Journal articleNowack P, Ceppi P, Davis SM, et al., 2023, , Nature Geoscience, Vol: 16, Pages: 577-583, ISSN: 1752-0894
Future increases in stratospheric water vapour risk amplifying climate change and slowing down the recovery of the ozone layer. However, state-of-the-art climate models strongly disagree on the magnitude of these increases under global warming. Uncertainty primarily arises from the complex processes leading to dehydration of air during its tropical ascent into the stratosphere. Here we derive an observational constraint on this longstanding uncertainty. We use a statistical-learning approach to infer historical co-variations between the atmospheric temperature structure and tropical lower stratospheric water vapour concentrations. For climate models, we demonstrate that these historically constrained relationships are highly predictive of the water vapour response to increased atmospheric carbon dioxide. We obtain an observationally constrained range for stratospheric water vapour changes per degree of global warming of 0.31 ± 0.39 ppmv K-1. Across 61 climate models, we find that a large fraction of future model projections are inconsistent with observational evidence. In particular, frequently projected strong increases (>1 ppmv K-1) are highly unlikely. Our constraint represents a 50% decrease in the 95th percentile of the climate model uncertainty distribution, which has implications for surface warming, ozone recovery and the tropospheric circulation response under climate change.
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Journal articleMilan SE, Mooney MK, Bower GE, et al., 2023, , JGR: Space Physics, Vol: 128, Pages: 1-17, ISSN: 2169-9402
We investigate a 15-day period in October 2011. Auroral observations by the Special Sensor Ultraviolet Spectrographic Imager instrument onboard the Defense Meteorological Satellite Program F16, F17, and F18 spacecraft indicate that the polar regions were covered by weak cusp-aligned arc (CAA) emissions whenever the interplanetary magnetic field (IMF) clock angle was small, |θ| < 45°, which amounted to 30% of the time. Simultaneous observations of ions and electrons in the tail by the Cluster C4 and Geotail spacecraft showed that during these intervals dense (≈1 cm−3) plasma was observed, even as far from the equatorial plane of the tail as |ZGSE| ≈ 13 RE. The ions had a pitch angle distribution peaking parallel and antiparallel to the magnetic field and the electrons had pitch angles that peaked perpendicular to the field. We interpret the counter-streaming ions and double loss-cone electrons as evidence that the plasma was trapped on closed field lines, and acted as a source for the CAA emission across the polar regions. This suggests that the magnetosphere was almost entirely closed during these periods. We further argue that the closure occurred as a consequence of dual-lobe reconnection. Our finding forces a significant re-evaluation of the magnetic topology of the magnetosphere during periods of northwards IMF.
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Journal articleWilliams RG, Ceppi P, Roussenov V, et al., 2023, , Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 381, ISSN: 1364-503X
<jats:p> The effect of the Southern Ocean on global climate change is assessed using Earth system model projections following an idealized 1% annual rise in atmospheric CO <jats:sub>2</jats:sub> . For this scenario, the Southern Ocean plays a significant role in sequestering heat and anthropogenic carbon, accounting for 40% ± 5% of heat uptake and 44% ± 2% of anthropogenic carbon uptake over the global ocean (with the Southern Ocean defined as south of 36°S). This Southern Ocean fraction of global heat uptake is however less than in historical scenarios with marked hemispheric contrasts in radiative forcing. For this idealized scenario, inter-model differences in global and Southern Ocean heat uptake are strongly affected by physical feedbacks, especially cloud feedbacks over the globe and surface albedo feedbacks from sea-ice loss in high latitudes, through the top-of-the-atmosphere energy balance. The ocean carbon response is similar in most models with carbon storage increasing from rising atmospheric CO <jats:sub>2</jats:sub> , but weakly decreasing from climate change with competing ventilation and biological contributions over the Southern Ocean. The Southern Ocean affects a global climate metric, the transient climate response to emissions, accounting for 28% of its thermal contribution through its physical climate feedbacks and heat uptake, and so affects inter-model differences in meeting warming targets. </jats:p> <jats:p>This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.</jats:p>
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Journal articleDesai R, Zhang Z, 2023, , The Planetary Science Journal, Vol: 4, ISSN: 2632-3338
The Cassini spacecraft's Grand Finale flybys through Saturn's ionosphere provided unprecedented insight into the composition and dynamics of the gas giant's upper atmosphere and a novel and complex spacecraft-plasma interaction. In this article, we further study Cassini's interaction with Saturn's ionosphere using three dimensional Particle-in-Cell simulations. We focus on understanding how electrons and ions, emitted from spacecraft surfaces due to the high-velocity impact of atmospheric water molecules, could have affected the spacecraft potential and low-energy plasma measurements. The simulations show emitted electrons extend upstream along the magnetic field and, for sufficiently high emission rates, charge the spacecraft to positive potentials. The lack of accurate emission rates and characteristics, however, makes differentiation between the prominence of secondary electron emission and ionospheric charged dust populations, which induce similar charging effects, difficult for Cassini. These results provide further context for Cassini's final measurements and highlight the need for future laboratory studies to support high-velocity flyby missions through planetary and cometary ionospheres.
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Journal articleBale SD, Drake JF, McManus MD, et al., 2023, , NATURE, Vol: 618, Pages: 252-+, ISSN: 0028-0836
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- Citations: 81
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Journal articleMalaspina DMM, Toma A, Szalay JRR, et al., 2023, , ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 266, ISSN: 0067-0049
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- Citations: 8
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Journal articleBaker D, Demoulin P, Yardley SL, et al., 2023, , ASTROPHYSICAL JOURNAL, Vol: 950, ISSN: 0004-637X
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- Citations: 21
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Journal articleQi Y, Ergun R, Pathak N, et al., 2023, , ASTROPHYSICAL JOURNAL, Vol: 950, ISSN: 0004-637X
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- Citations: 5
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Journal articleBowler S, Desai R, 2023, , Astronomy and Geophysics, Vol: 64, ISSN: 1366-8781
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