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Journal articleJoyce CJ, McComas DJ, Schwadron NA, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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- Citations: 16
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Journal articleFroment C, Krasnoselskikh V, de Wit TD, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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- Citations: 36
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Journal articleJagarlamudi VK, de Wit TD, Froment C, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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- Citations: 30
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Journal articleShi C, Velli M, Panasenco O, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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- Citations: 42
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Journal articleHalekas JS, Whittlesey PL, Larson DE, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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- Citations: 32
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Journal articleAllen RC, Ho GC, Jian LK, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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- Citations: 28
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Journal articleDrake JF, Agapitov O, Swisdak M, et al., 2021, , Astronomy and Astrophysics: a European journal, Vol: 650, Pages: 1-8, ISSN: 0004-6361
The structure of magnetic flux ropes injected into the solar wind duringreconnection in the coronal atmosphere is explored with particle-in-cellsimulations and compared with {\it in situ} measurements of magnetic"switchbacks" from the Parker Solar Probe. We suggest that multi-x-linereconnection between open and closed flux in the corona will inject flux ropesinto the solar wind and that these flux ropes can convect outward over longdistances before disintegrating. Simulations that explore the magneticstructure of flux ropes in the solar wind reproduce key features of the"switchback" observations: a rapid rotation of the radial magnetic field intothe transverse direction (a consequence of reconnection with a strong guidefield); and the potential to reverse the radial field component. The potentialimplication of the injection of large numbers of flux ropes in the coronalatmosphere for understanding the generation of the solar wind is discussed.
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Journal articleWoodham L, Horbury T, Matteini L, et al., 2021, , Astronomy and Astrophysics: a European journal, Vol: 650, Pages: 1-7, ISSN: 0004-6361
Context. Switchbacks are discrete angular deflections in the solar wind magnetic field that have been observed throughout the helio-sphere. Recent observations by Parker Solar Probe(PSP) have revealed the presence of patches of switchbacks on the scale of hours to days, separated by ‘quieter’ radial fields. Aims. We aim to further diagnose the origin of these patches using measurements of proton temperature anisotropy that can illuminate possible links to formation processes in the solar corona. Methods. We fit 3D bi-Maxwellian functions to the core of proton velocity distributions measured by the SPAN-Ai instrument onboard PSP to obtain the proton parallel, Tp,鈥, and perpendicular, Tp,⊥, temperature. Results. We show that the presence of patches is highlighted by a transverse deflection in the flow and magnetic field away from the radial direction. These deflections are correlated with enhancements in Tp,鈥, while Tp,⊥remains relatively constant. Patches sometimes exhibit small proton and electron density enhancements. Conclusions. We interpret that patches are not simply a group of switchbacks, but rather switchbacks are embedded within a larger-scale structure identified by enhanced Tp,鈥杢hat is distinct from the surrounding solar wind. We suggest that these observations are consistent with formation by reconnection-associated mechanisms in the corona.
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Journal articleLaker R, Horbury TS, Bale SD, et al., 2021, , Astronomy & Astrophysics, Vol: 650, Pages: 1-7, ISSN: 0004-6361
One of the main discoveries from the first two orbits of Parker Solar Probe(PSP) was the presence of magnetic switchbacks, whose deflections dominated themagnetic field measurements. Determining their shape and size could provideevidence of their origin, which is still unclear. Previous work with a singlesolar wind stream has indicated that these are long, thin structures althoughthe direction of their major axis could not be determined. We investigate ifthis long, thin nature extends to other solar wind streams, while determiningthe direction along which the switchbacks within a stream were aligned. We tryto understand how the size and orientation of the switchbacks, along with theflow velocity and spacecraft trajectory, combine to produce the observedstructure durations for past and future orbits. We searched for the alignmentdirection that produced a combination of a spacecraft cutting direction andswitchback duration that was most consistent with long, thin structures. Theexpected form of a long, thin structure was fitted to the results of the bestalignment direction, which determined the width and aspect ratio of theswitchbacks for that stream. The switchbacks had a mean width of $50,000 \,\rm{km}$, with an aspect ratio of the order of $10$. We find that switchbacksare not aligned along the background flow direction, but instead aligned alongthe local Parker spiral, perhaps suggesting that they propagate along themagnetic field. Since the observed switchback duration depends on how thespacecraft cuts through the structure, the duration alone cannot be used todetermine the size or influence of an individual event. For future PSP orbits,a larger spacecraft transverse component combined with more radially alignedswitchbacks will lead to long duration switchbacks becoming less common.
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Journal articleVech D, Martinovic MM, Klein KG, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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- Citations: 19
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Journal articleQuaas J, Gryspeerdt E, Vautard R, et al., 2021, , Environmental 91桃色 Letters, Vol: 16, Pages: 1-6, ISSN: 1748-9326
Aircraft produce condensation trails, which are thought to increase high-level cloudiness under certain conditions. Howeverthe magnitude of such an effect and whether this contributes substantially to the radiative forcing due to the aviation sectorremain uncertain. The very substantial, near-global reduction in air traffic in response to the COVID-19 outbreak offers anunprecedented opportunity to identify the anthropogenic contribution to the observed cirrus coverage and thickness. Here weshow, using an analysis of satellite observations for the period March-May 2020, that in the 20% of the Northern Hemispheremid-latitudes with the largest air traffic reduction, cirrus fraction was reduced by ~9 ± 1.5% on average, and cirrus emissivitywas reduced by ~2 ±5% relative to what they should have been with normal air traffic. The changes are corroborated by aconsistent estimate based on linear trends over the period 2011 – 2019. The change in cirrus translates to a global radiativeforcing of 61 ±39 mWm-2. This estimate is somewhat smaller than previous assessments.
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Journal articleCattell C, Glesener L, Leiran B, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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- Citations: 9
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Journal articleStansby D, Bercic L, Matteini L, et al., 2021, , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
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Journal articleZhang Z, Desai R, Miyake Y, et al., 2021, , Monthly Notices of the Royal Astronomical Society, Vol: 504, Pages: 964-973, ISSN: 0035-8711
A surprising and unexpected phenomenon observed during Cassini’s Grand Finale was the spacecraft charging to positive potentials in Saturn’s ionosphere. Here, the ionospheric plasma was depleted of free electrons with negatively charged ions and dust accumulating up to over 95 per cent of the negative charge density. To further understand the spacecraft–plasma interaction, we perform a three-dimensional Particle-In-Cell study of a model Cassini spacecraft immersed in plasma representative of Saturn’s ionosphere. The simulations reveal complex interaction features such as electron wings and a highly structured wake containing spacecraft-scale vortices. The results show how a large negative ion concentration combined with a large negative to positive ion mass ratio is able to drive the spacecraft to the observed positive potentials. Despite the high electron depletions, the electron properties are found as a significant controlling factor for the spacecraft potential together with the magnetic field orientation which induces a potential gradient directed across Cassini’s asymmetric body. This study reveals the global spacecraft interaction experienced by Cassini during the Grand Finale and how this is influenced by the unexpected negative ion and dust populations.
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Journal articleDesai RT, Zhang Z, Wu X, et al., 2021, , The Planetary Science Journal, Vol: 2, Pages: 99-99
<jats:title>Abstract</jats:title> <jats:p>Negative ions have been detected in abundance in recent years by spacecraft across the solar system. These detections were, however, made by instruments not designed for this purpose and, as such, significant uncertainties remain regarding the prevalence of these unexpected plasma components. In this article, the phenomenon of photodetachment is examined, and experimentally and theoretically derived cross-sections are used to calculate photodetachment rates for a range of atomic and molecular negative ions subjected to the solar photon spectrum. These rates are applied to negative ions outflowing from Europa, Enceladus, Titan, Dione, and Rhea and their trajectories are traced to constrain source production rates and the extent to which negative ions are able to pervade the surrounding space environments. Predictions are also made for further negative ion populations in the outer solar system with Triton used as an illustrative example. This study demonstrates how, at increased heliocentric distances, negative ions can form stable ambient plasma populations and can be exploited by future missions to the outer solar system.</jats:p>
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Journal articleStarkey MJ, Fuselier SA, Desai MI, et al., 2021, , ASTROPHYSICAL JOURNAL, Vol: 913, ISSN: 0004-637X
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- Citations: 2
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Journal articleWeiss Z, Concepcion-Mairey F, Pickering JC, et al., 2021, , SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY, Vol: 180, ISSN: 0584-8547
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- Citations: 2
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Journal articleJohlander A, Battarbee M, Vaivads A, et al., 2021, , ASTROPHYSICAL JOURNAL, Vol: 914, ISSN: 0004-637X
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- Citations: 3
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Journal articleGonzalez CA, Tenerani A, Matteini L, et al., 2021, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 914, ISSN: 2041-8205
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- Citations: 7
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Journal articleSchwartz SJ, Ergun RE, Harald K, et al., 2021,
<jats:p>Shock waves are common in the heliosphere and beyond. The collisionlessnature of most astrophysical plasmas allows for the energy processed byshocks to be partitioned amongst particle sub-populations andelectromagnetic fields via physical mechanisms that are not wellunderstood. The electrostatic potential across such shocks is framedependent. In a frame where the incident bulk velocity is parallel tothe magnetic field, the deHoffmann-Teller frame, the potential is linkeddirectly to the ambipolar electric field established by the electronpressure gradient. Thus measuring and understanding this potentialsolves the electron partition problem, and gives insight into othercompeting shock processes. Integrating measured electric fields is spaceis problematic since the measurements can have offsets that change withplasma conditions. The offsets, once integrated, can be as large orlarger than the shock potential. Here we exploit the high-quality fieldand plasma measurements from NASA's Magnetospheric Multiscale mission toattempt this calculation. We investigate recent adaptations of thedeHoffmann-Teller frame transformation to include time variability, andconclude that in practise these face difficulties inherent in the 3Dtime-dependent nature of real shocks by comparison to 1D simulations.Potential estimates based on electron fluid and kinetic analyses providethe most robust measures of the deHoffmann-Teller potential, but withsome care direct integration of the electric fields can be made toagree. These results suggest that it will be difficult to independentlyassess the role of other processes, such as scattering by shockturbulence, in accounting for the electron heating.</jats:p>
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Journal articleKuhn-R茅gnier A, Voulgarakis A, Nowack P, et al., 2020, , Biogeosciences, ISSN: 1726-4170
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Journal articleTelloni D, Sorriso-Valvo L, Woodham LD, et al., 2021, , Letters of the Astrophysical Journal, Vol: 912, Pages: 1-8, ISSN: 2041-8205
The first radial alignment between Parker Solar Probe and Solar Orbiter spacecraft is used to investigate the evolution of solar wind turbulence in the inner heliosphere. Assuming ballistic propagation, two 1.5 hr intervals are tentatively identified as providing measurements of the same plasma parcels traveling from 0.1 to 1 au. Using magnetic field measurements from both spacecraft, the properties of turbulence in the two intervals are assessed. Magnetic spectral density, flatness, and high-order moment scaling laws are calculated. The Hilbert–Huang transform is additionally used to mitigate short sample and poor stationarity effects. Results show that the plasma evolves from a highly Alfvénic, less-developed turbulence state near the Sun, to fully developed and intermittent turbulence at 1 au. These observations provide strong evidence for the radial evolution of solar wind turbulence.
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Journal articleGaland M, Feldman PD, Bockelee-Morvan D, et al., 2021, , NATURE ASTRONOMY, ISSN: 2397-3366
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Journal articleCheng IK, Achilleos N, Masters A, et al., 2021, , Journal of Geophysical 91桃色: Space Physics, Vol: 126, ISSN: 2169-9380
Magnetic reconnection at the magnetopause (MP) energizes ambient plasma via the release of magnetic energy and produces an “open” magnetosphere allowing solar wind particles to directly enter the system. At Saturn, the nature of MP reconnection remains unclear. The current study examines electron bulk heating at MP crossings, in order to probe the relationship between observed and predicted reconnection heating proposed by Phan et al. (2013, https://doi.org/10.1002/grl.50917) under open and closed MP, and how this may pertain to the position of the crossings in the Δβ鈥恗agnetic shear parameter space. The electron heating for 70 MP crossings made by the Cassini spacecraft from April 2005 to July 2007 was found using 1d and 3d moment methods. Minimum variance analysis was used on the magnetic field data to help indicate whether the MP is open or closed. We found better agreement between observed and predicted heating for events suggestive of locally “open” MP. For events suggestive of locally “closed” MP, we observed a cluster of points consistent with no electron heating, but also numerous cases with significant heating. Examining the events in the Δβ鈥恗agnetic shear parameter space, we find 83% of events without evidence of energization were situated in the “reconnection suppressed” regime, whilst between 43% to 68% of events with energization lie in the “reconnection possible” regime depending on the threshold used. The discrepancies could be explained by a combination of spatial and temporal variability which makes it possible to observe heated electrons with different conditions from the putative reconnection site.
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Journal articleGibbins G, Haigh JD, 2021, , Journal of Climate, Vol: 34, Pages: 3721-3728, ISSN: 0894-8755
A recent paper by Kato and Rose reports a negative correlation between the annual mean entropy production rate of the climate and the absorption of solar radiation in the CERES SYN1deg dataset, using the simplifying assumption that the system is steady in time. It is shown here, however, that when the nonsteady interannual storage of entropy is accounted for, the dataset instead implies a positive correlation; that is, global entropy production rates increase with solar absorption. Furthermore, this increase is consistent with the response demonstrated by an energy balance model and a radiative–convective model. To motivate this updated analysis, a detailed discussion of the conceptual relationship between entropy production, entropy storage, and entropy flows is provided. The storage-corrected estimate for the mean global rate of entropy production in the CERES dataset from all irreversible transfer processes is 81.9 mW m−2 K−1 and from only nonradiative processes is 55.2 mW m−2 K−1 (observations from March 2000 to February 2018).
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Journal articleLai T-K, Hendricks EA, Yau MK, et al., 2021, , JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 78, Pages: 1411-1428, ISSN: 0022-4928
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Journal articleHoilijoki S, Pucci F, Ergun RE, et al., 2021, , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
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Journal articleMartinovic MM, Klein KG, Huang J, et al., 2021, , ASTROPHYSICAL JOURNAL, Vol: 912, ISSN: 0004-637X
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- Citations: 30
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Journal articleMa B, Chen L, Wu D, et al., 2021, , ASTROPHYSICAL JOURNAL LETTERS, Vol: 913, ISSN: 2041-8205
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- Citations: 6
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Journal articleDiaz-Aguado MF, Bonnell JW, Bale SD, et al., 2021, , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
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- Citations: 3
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