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Journal articleWang S, Toumi R, Ye Q, et al., 2021,
Is the tropical cyclone surge in Shanghai more sensitive to landfall location or intensity change?
, ATMOSPHERIC SCIENCE LETTERS, Vol: 22, ISSN: 1530-261X -
Journal articleMalaspina DM, Wilson LB, Ergun RE, et al., 2021,
Electron Bernstein waves and narrowband plasma waves near the electron cyclotron frequency in the near-Sun solar wind
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 11
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Journal articleHarra L, Brooks DH, Bale SD, et al., 2021,
The active region source of a type III radio storm observed by Parker Solar Probe during encounter 2
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 13
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Journal articleSchwadron NA, Joyce CJ, Aly A, et al., 2021,
A new view of energetic particles from stream interaction regions observed by Parker Solar Probe
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 8
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Journal articleQuaas J, Gryspeerdt E, Vautard R, et al., 2021,
Climate impact of aircraft-induced cirrus assessed from satellite observations before and during COVID-19
, Environmental Research Letters, Vol: 16, Pages: 1-6, ISSN: 1748-9326Aircraft 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 articlePhan TD, Lavraud B S J, Halekas, et al., 2021,
Prevalence of magnetic reconnection in the near-Sun heliospheric current sheet
, Astronomy & Astrophysics, Vol: 650, Pages: 1-14, ISSN: 0004-6361During three of its first five orbits around the Sun, Parker Solar Probe (PSP) crossed the large-scale Heliospheric Current Sheet (HCS)multiple times and provided unprecedented detailed plasma and field observations of the near-Sun HCS. We report the commondetections by PSP of reconnection exhaust signatures in the HCS at heliocentric distances of 29.5-107 solar radii during Encounters1, 4 and 5. Both sunward and antisunward-directed reconnection exhausts were observed. In the sunward reconnection exhausts,PSP detected counterstreaming strahl electrons, indicating that HCS reconnection resulted in the formation of closed magnetic fieldlines with both ends connected to the Sun. In the antisunward exhausts, PSP observed dropouts of strahl electrons, consistent withthe reconnected HCS field lines being disconnected from the Sun. The common detection of reconnection in the HCS suggests thatreconnection is almost always active in the HCS near the Sun. Furthermore, the occurrence of multiple long-duration partial crossingsof the HCS suggests that HCS reconnection could produce chains of large bulges with spatial dimensions of up to several solarradii. The finding of the prevalence of reconnection in the HCS is somewhat surprising since PSP has revealed that the HCS is muchthicker than the kinetic scales required for reconnection onset. The observations are also in stark contrast with the apparent absenceof reconnection in most of the small-scale and much more intense current sheets encountered near perihelia, many of which areassociated with ‘switchbacks’. Thus, the PSP findings suggest that large-scale dynamics either locally in the solar wind or within thecoronal source of the HCS (at the tip of helmet streamers) plays a critical role in triggering reconnection onset.
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Journal articleFargette N, Lavraud B, Rouillard A, et al., 2021,
Magnetic increases with central current sheets: Observations with Parker Solar Probe
, Astronomy & Astrophysics, Vol: 650, Pages: 1-12, ISSN: 0004-6361Aims. We report the observation by Parker Solar Probe (PSP) of magnetic structures in the solar wind that present a strong peak intheir magnetic field magnitude with an embedded central current sheet. Similar structures have been observed, either at the Earth’smagnetopause and called interlinked flux tubes, or in the solar wind and called interplanetary field enhancements.Methods. In this work, we first investigate two striking events in detail; one occurred in the regular slow solar wind on November 2,2018 and the other was observed during a heliospheric current sheet crossing on November 13, 2018. They both show the presenceof a central current sheet with a visible ion jet and general characteristics consistent with the occurrence of magnetic reconnection.We then performed a survey of PSP data from encounters 1 to 4 and find 18 additional events presenting an increase in the magneticfield magnitude of over 30% and a central current sheet. We performed a statistical study on the 20 "magnetic increases with centralcurrent sheet" (MICCS), with 13 observed in the regular slow solar wind with a constant polarity (i.e., identical strahl direction), and7 which were specifically observed near a heliospheric current sheet (HCS) crossing.Results. We analyze and discuss the general properties of the structures, including the duration, location, amplitude, and magnetictopology, as well as the characteristics of their central current sheet. We find that the latter has a preferential orientation in the TNplane of the RTN frame. We also find no significant change in the dust impact rate in the vicinity of the MICCS under study, leadingus to conclude that dust probably plays no role in the MICCS formation and evolution. Our findings are overall consistent with adouble flux tube-configuration that would result from initially distinct flux tubes which interact during solar wind propagation.
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Journal articleFinley AJ, McManus MD, Matt SP, et al., 2021,
The contribution of alpha particles to the solar wind angular momentum flux in the inner heliosphere
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 11
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Journal articleCattell C, Short B, Breneman A, et al., 2021,
Narrowband oblique whistler-mode waves: comparing properties observed by Parker Solar Probe at <0.3 AU and STEREO at 1 AU
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 17
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Journal articleAkhavan-Tafti M, Kasper J, Huang J, et al., 2021,
Discontinuity analysis of the leading switchback transition regions
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 9
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Journal articleCohen CMS, Christian ER, Cummings AC, et al., 2021,
Parker Solar Probe observations of He/H abundance variations in SEP events inside 0.5 au
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 11
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Journal articleVech D, Martinovic MM, Klein KG, et al., 2021,
Wave-particle energy transfer directly observed in an ion cyclotron wave
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 10
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Journal articleAllen RC, Ho GC, Jian LK, et al., 2021,
A living catalog of stream interaction regions in the Parker Solar Probe era
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 17
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Journal articleCattell C, Glesener L, Leiran B, et al., 2021,
Periodicities in an active region correlated with Type Ill radio bursts observed by Parker Solar Probe
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 6
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Journal articleChen CHK, Chandran BDG, Woodham LD, et al., 2021,
The near-Sun streamer belt solar wind: turbulence and solar wind acceleration
, Astronomy & Astrophysics, Vol: 650, Pages: 1-6, ISSN: 0004-6361The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances down to 27.9 R⊙, allowing solar wind turbulence and acceleration mechanisms to be studied in situ closer to the Sun than previously possible. The turbulence properties were found to be significantly different in the inbound and outbound portions of PSP’s fourth solar encounter, which was likely due to the proximity to the heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the streamer belt wind, the turbulence was found to have lower amplitudes, higher magnetic compressibility, a steeper magnetic field spectrum (with a spectral index close to –5/3 rather than –3/2), a lower Alfvénicity, and a ‘1∕f’ break at much lower frequencies. These are also features of slow wind at 1 au, suggesting the near-Sun streamer belt wind to be the prototypical slow solar wind. The transition in properties occurs at a predicted angular distance of ≈4° from the HCS, suggesting ≈8° as the full-width of the streamer belt wind at these distances. While the majority of the Alfvénic turbulence energy fluxes measured by PSP are consistent with those required for reflection-driven turbulence models of solar wind acceleration, the fluxes in the streamer belt are significantly lower than the model predictions, suggesting that additional mechanisms are necessary to explain the acceleration of the streamer belt solar wind.
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Journal articleLaker R, Horbury TS, Bale SD, et al., 2021,
Statistical analysis of orientation, shape, and size of solar wind switchbacks
, Astronomy & Astrophysics, Vol: 650, Pages: 1-7, ISSN: 0004-6361One 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 articleWoodham L, Horbury T, Matteini L, et al., 2021,
Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere
, Astronomy and Astrophysics: a European journal, Vol: 650, Pages: 1-7, ISSN: 0004-6361Context. 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,‖, 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,‖, 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,‖that 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 articleDrake JF, Agapitov O, Swisdak M, et al., 2021,
Are switchbacks signatures of magnetic flux ropes generated by interchange reconnection in the corona?
, Astronomy and Astrophysics: a European journal, Vol: 650, Pages: 1-8, ISSN: 0004-6361The 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 articleHalekas JS, Whittlesey PL, Larson DE, et al., 2021,
Electron heat flux in the near-Sun environment
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 21
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Journal articleShi C, Velli M, Panasenco O, et al., 2021,
Alfvenic versus non-Alfvenic turbulence in the inner heliosphere as observed by Parker Solar Probe
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 23
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Journal articleJagarlamudi VK, de Wit TD, Froment C, et al., 2021,
Whistler wave occurrence and the interaction with strahl electrons during the first encounter of Parker Solar Probe
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 20
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Journal articleFroment C, Krasnoselskikh V, de Wit TD, et al., 2021,
Direct evidence for magnetic reconnection at the boundaries of magnetic switchbacks with Parker Solar Probe
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 24
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Journal articleLiu M, Issautier K, Meyer-Vernet N, et al., 2021,
Solar wind energy flux observations in the inner heliosphere: first results from Parker Solar Probe
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 10
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Journal articleZhao L-L, Zank GP, Hu Q, et al., 2021,
Detection of small magnetic flux ropes from the third and fourth Parker Solar Probe encounters
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 29
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Journal articleLarosa A, Krasnoselskikh V, de Wit TD, et al., 2021,
Switchbacks: statistical properties and deviations from Alfvenicity
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 29
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Journal articleBadman ST, Bale SD, Rouillard AP, et al., 2021,
Measurement of the open magnetic flux in the inner heliosphere down to 0.13 AU
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 20
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Journal articleBandyopadhyay R, Matthaeus WH, McComas DJ, et al., 2021,
Energetic particle behavior in near-Sun magnetic field switchbacks from PSP
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 11
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Journal articleJoyce CJ, McComas DJ, Schwadron NA, et al., 2021,
Time evolution of stream interaction region energetic particle spectra in the inner heliosphere
, ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361- Author Web Link
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- Citations: 10
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Journal articleQuijia P, Fraternale F, Stawarz J, et al., 2021,
Comparing turbulence in a Kelvin-Helmholtz instability region across the terrestrial magnetopause
, Monthly Notices of the Royal Astronomical Society, Vol: 503, Pages: 4815-4827, ISSN: 0035-8711The properties of turbulence observed within the plasma originating from the magnetosheath and the magnetospheric boundary layer, which have been entrained within vortices driven by the Kelvin–Helmholtz Instability (KHI), are compared. The goal of such a study is to determine similarities and differences between the two different regions. In particular, we study spectra, intermittency and the third-order moment scaling, as well as the distribution of a local energy transfer rate proxy. The analysis is performed using the Magnetospheric Multiscale data from a single satellite that crosses longitudinally the KHI. Two sets of regions, one set containing predominantly magnetosheath plasma and the other containing predominantly magnetospheric plasma, are analysed separately, thus allowing us to explore turbulence properties in two portions of very different plasma samples. Results show that the dynamics in the two regions is different, with the boundary layer plasma presenting a shallower spectra and larger energy transfer rate, indicating an early stage of turbulence. In both regions, the effect of the KHI is evidenced.
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Journal articleZhang Z, Desai R, Miyake Y, et al., 2021,
Particle-in-cell simulations of the Cassini spacecraft’s interaction with Saturn’s ionosphere during the Grand Finale
, Monthly Notices of the Royal Astronomical Society, Vol: 504, Pages: 964-973, ISSN: 0035-8711A 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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