Publications
258 results found
Šafránková J, Němeček Z, Němec F, et al., 2023, Evolution of Magnetic Field Fluctuations and Their Spectral Properties within the Heliosphere: Statistical Approach, Astrophysical Journal Letters, Vol: 946, ISSN: 2041-8205
We present the first comprehensive statistical study of the evolution of compressive and noncompressive magnetic field fluctuations in the inner heliosphere. Based on Parker Solar Probe (PSP) and Solar Orbiter data at various distances from the Sun, we show the general trends and compare them with Wind observations near 1 au. The paper analyzes solar wind power spectra of magnetic field fluctuations in the inertial and kinetic ranges of frequencies. We find a systematic steepening of the spectrum in the inertial range with the spectral index of around −3/2 at closest approach to the Sun toward −5/3 at larger distances (above 0.4 au), the spectrum of the field component perpendicular to the background field being steeper at all distances. In the kinetic range, the spectral indices increase with distance from −4.8 at closest PSP approach to ≈−3 at 0.4 au and this value remains approximately constant toward 1 au. We show that the radial profiles of spectral slopes, fluctuation amplitudes, spectral breaks, and their mutual relations undergo rapid changes near 0.4 au.
Raouafi NE, Stenborg G, Seaton DB, et al., 2023, Magnetic Reconnection as the Driver of the Solar Wind, ASTROPHYSICAL JOURNAL, Vol: 945, ISSN: 0004-637X
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- Citations: 1
Krasnoselskikh V, Tsurutani BT, Dudok de Wit T, et al., 2023, ICARUS: in-situ studies of the solar corona beyond Parker Solar Probe and Solar Orbiter, Experimental Astronomy, Vol: 54, Pages: 277-315, ISSN: 0922-6435
The primary scientific goal of ICARUS (Investigation of Coronal AcceleRation and heating of solar wind Up to the Sun), a mother-daughter satellite mission, proposed in response to the ESA “Voyage 2050” Call, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind, and the entire heliosphere. Reaching this goal will be a Rosetta Stone step, with results that are broadly applicable within the fields of space plasma physics and astrophysics. Within ESA’s Cosmic Vision roadmap, these science goals address Theme 2: “How does the Solar System work?” by investigating basic processes occurring “From the Sun to the edge of the Solar System”. ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution, and flows directly in the regions in which the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion altitude of 1 solar radius and will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow winds are generated. It will probe the local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous, contextual information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosph
Raouafi NE, Matteini L, Squire J, et al., 2023, Parker solar probe: four years of discoveries at solar cycle minimum, Space Science Reviews, Vol: 219, Pages: 1-140, ISSN: 0038-6308
Launched on 12 Aug. 2018, NASA’s Parker Solar Probe had completed 13 of its scheduled 24 orbits around the Sun by Nov. 2022. The mission’s primary science goal is to determine the structure and dynamics of the Sun’s coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Parker Solar Probe returned a treasure trove of science data that far exceeded quality, significance, and quantity expectations, leading to a significant number of discoveries reported in nearly 700 peer-reviewed publications. The first four years of the 7-year primary mission duration have been mostly during solar minimum conditions with few major solar events. Starting with orbit 8 (i.e., 28 Apr. 2021), Parker flew through the magnetically dominated corona, i.e., sub-Alfvénic solar wind, which is one of the mission’s primary objectives. In this paper, we present an overview of the scientific advances made mainly during the first four years of the Parker Solar Probe mission, which go well beyond the three science objectives that are: (1) Trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) Explore mechanisms that accelerate and transport energetic particles.
Trotta D, Hietala H, Horbury T, et al., 2023, Multi-spacecraft observations of shocklets at an interplanetary shock, Monthly Notices of the Royal Astronomical Society, Vol: 520, Pages: 437-445, ISSN: 0035-8711
<jats:title>ABSTRACT</jats:title> <jats:p>Interplanetary (IP) shocks are fundamental building blocks of the heliosphere, and the possibility to observe them in situ is crucial to address important aspects of energy conversion for a variety of astrophysical systems. Steepened waves known as shocklets are known to be important structures of planetary bow shocks, but they are very rarely observed related to IP shocks. We present here the first multi-spacecraft observations of shocklets observed by upstream of an unusually strong IP shock observed on 3 November 2021 by several spacecraft at L1 and near-Earth solar wind. The same shock was detected also by radially aligned Solar Orbiter at 0.8 au from the Sun, but no shocklets were identified from its data, introducing the possibility to study the environment in which shocklets developed. The Wind spacecraft has been used to characterize the shocklets, associated with pre-conditioning of the shock upstream by decelerating incoming plasma in the shock normal direction. Finally, using the Wind observations together with ACE and DSCOVR spacecraft at L1, as well as THEMIS B and THEMIS C in the near-Earth solar wind, the portion of interplanetary space filled with shocklets is addressed, and a lower limit for its extent is estimated to be of about 110RE in the shock normal direction and 25RE in the directions transverse to the shock normal. Using multiple spacecraft also reveals that for this strong IP shock, shocklets are observed for a large range of local obliquity estimates (9º–64º).</jats:p>
De Marco R, Bruno R, Jagarlamudi VK, et al., 2023, Innovative technique for separating proton core, proton beam, and alpha particles in solar wind 3D velocity distribution functions, ASTRONOMY & ASTROPHYSICS, Vol: 669, ISSN: 0004-6361
Sioulas N, Huang Z, Shi C, et al., 2023, Magnetic field spectral evolution in the inner heliosphere, Letters of the Astrophysical Journal, Vol: 943, Pages: 1-7, ISSN: 2041-8205
Parker Solar Probe and Solar Orbiter data are used to investigate the radial evolution of magnetic turbulence between 0.06 ≲ R ≲ 1 au. The spectrum is studied as a function of scale, normalized to the ion inertial scale di. In the vicinity of the Sun, the inertial range is limited to a narrow range of scales and exhibits a power-law exponent of, αB = −3/2, independent of plasma parameters. The inertial range grows with distance, progressively extending to larger spatial scales, while steepening toward a αB = −5/3 scaling. It is observed that spectra for intervals with large magnetic energy excesses and low Alfvénic content steepen significantly with distance, in contrast to highly Alfvénic intervals that retain their near-Sun scaling. The occurrence of steeper spectra in slower wind streams may be attributed to the observed positive correlation between solar wind speed and Alfvénicity.
Brandt PC, Provornikova E, Bale SD, et al., 2023, Future Exploration of the Outer Heliosphere and Very Local Interstellar Medium by Interstellar Probe., Space Sci Rev, Vol: 219, ISSN: 0038-6308
A detailed overview of the knowledge gaps in our understanding of the heliospheric interaction with the largely unexplored Very Local Interstellar Medium (VLISM) are provided along with predictions of with the scientific discoveries that await. The new measurements required to make progress in this expanding frontier of space physics are discussed and include in-situ plasma and pick-up ion measurements throughout the heliosheath, direct sampling of the VLISM properties such as elemental and isotopic composition, densities, flows, and temperatures of neutral gas, dust and plasma, and remote energetic neutral atom (ENA) and Lyman-alpha (LYA) imaging from vantage points that can uniquely discern the heliospheric shape and bring new information on the interaction with interstellar hydrogen. The implementation of a pragmatic Interstellar Probe mission with a nominal design life to reach 375 Astronomical Units (au) with likely operation out to 550 au are reported as a result of a 4-year NASA funded mission study.
Horbury T, Bale S, mcmanus M, et al., 2022, Switchbacks, microstreams and broadband turbulence in the solar wind, Physics of Plasmas, ISSN: 1070-664X
Persson M, Aizawa S, André N, et al., 2022, BepiColombo mission confirms stagnation region of Venus and reveals its large extent., Nat Commun, Vol: 13
The second Venus flyby of the BepiColombo mission offer a unique opportunity to make a complete tour of one of the few gas-dynamics dominated interaction regions between the supersonic solar wind and a Solar System object. The spacecraft pass through the full Venusian magnetosheath following the plasma streamlines, and cross the subsolar stagnation region during very stable solar wind conditions as observed upstream by the neighboring Solar Orbiter mission. These rare multipoint synergistic observations and stable conditions experimentally confirm what was previously predicted for the barely-explored stagnation region close to solar minimum. Here, we show that this region has a large extend, up to an altitude of 1900 km, and the estimated low energy transfer near the subsolar point confirm that the atmosphere of Venus, despite being non-magnetized and less conductive due to lower ultraviolet flux at solar minimum, is capable of withstanding the solar wind under low dynamic pressure.
Matthaeus WH, Adhikari S, Bandyopadhyay R, et al., 2022, The essential role of multi-point measurements in investigations of turbulence, three-dimensional structure, and dynamics: the solar wind beyond single scale and the Taylor Hypothesis
Space plasmas are three-dimensional dynamic entities. Except under veryspecial circumstances, their structure in space and their behavior in time arenot related in any simple way. Therefore, single spacecraft in situmeasurements cannot unambiguously unravel the full space-time structure of theheliospheric plasmas of interest in the inner heliosphere, in the Geospaceenvironment, or the outer heliosphere. This shortcoming leaves numerous centralquestions incompletely answered. Deficiencies remain in at least two importantsubjects, Space Weather and fundamental plasma turbulence theory, due to a lackof a more complete understanding of the space-time structure of dynamicplasmas. Only with multispacecraft measurements over suitable spans of spatialseparation and temporal duration can these ambiguities be resolved. We notethat these characterizations apply to turbulence across a wide range of scales,and also equally well to shocks, flux ropes, magnetic clouds, current sheets,stream interactions, etc. In the following, we will describe the basicrequirements for resolving space-time structure in general, using turbulence'as both an example and a principal target or study. Several types of missionsare suggested to resolve space-time structure throughout the Heliosphere.
Wimmer-Schweingruber RF, Andre N, Barabash S, et al., 2022, STELLA-Potential European contributions to a NASA-led interstellar probe, FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, Vol: 9, ISSN: 2296-987X
Trotta D, Vuorinen L, Hietala H, et al., 2022, Single-spacecraft techniques for shock parameters estimation: a systematic approach, Frontiers in Astronomy and Space Sciences, Vol: 9, Pages: 1-16, ISSN: 2296-987X
Spacecraft missions provide the unique opportunity to study the properties of collisionless shocks utilising in situ measurements. In the past years, several diagnostics have been developed to address key shock parameters using time series of magnetic field (and plasma) data collected by a single spacecraft crossing a shock front. A critical aspect of such diagnostics is the averaging process involved in the evaluation of upstream/downstream quantities. In this work, we discuss several of these techniques, with a particular focus on the shock obliquity (defined as the angle between the upstream magnetic field and the shock normal vector) estimation. We introduce a systematic variation of the upstream/downstream averaging windows, yielding to an ensemble of shock parameters, which is a useful tool to address the robustness of their estimation. This approach is first tested with a synthetic shock dataset compliant with the Rankine-Hugoniot jump conditions for a shock, including the presence of noise and disturbances. We then employ self-consistent, hybrid kinetic shock simulations to apply the diagnostics to virtual spacecraft crossing the shock front at various stages of its evolution, highlighting the role of shock-induced fluctuations in the parameters’ estimation. This approach has the strong advantage of retaining some important properties of collisionless shock (such as, for example, the shock front microstructure) while being able to set a known, nominal set of shock parameters. Finally, two recent observations of interplanetary shocks from the Solar Orbiter spacecraft are presented, to demonstrate the use of this systematic approach to real events of shock crossings. The approach is also tested on an interplanetary shock measured by the four spacecraft of the Magnetospheric Multiscale (MMS) mission. All the Python software developed and used for the diagnostics (SerPyShock) is made available for the public, including an example of parameter estimation fo
Laker R, Horbury TS, Matteini L, et al., 2022, Switchback deflections beyond the early parker solar probe encounters, Monthly Notices of the Royal Astronomical Society, Vol: 517, Pages: 1001-1005, ISSN: 0035-8711
Switchbacks are Aflvénic fluctuations in the solar wind, which exhibit large rotations in the magnetic field direction. Observations from Parker Solar Probe’s (PSP’s) first two solar encounters have formed the basis for many of the described switchback properties and generation mechanisms. However, this early data may not be representative of the typical near-Sun solar wind, biasing our current understanding of these phenomena. One defining switchback property is the magnetic deflection direction. During the first solar encounter, this was primarily in the tangential direction for the longest switchbacks, which has since been discussed as evidence, and a testable prediction, of several switchback generation methods. In this study, we re-examine the deflection direction of switchbacks during the first eight PSP encounters to confirm the existence of a systematic deflection direction. We first identify switchbacks exceeding a threshold deflection in the magnetic field and confirm a previous finding that they are arc-polarized. In agreement with earlier results from PSP’s first encounter, we find that groups of longer switchbacks tend to deflect in the same direction for several hours. However, in contrast to earlier studies, we find that there is no unique direction for these deflections, although several solar encounters showed a non-uniform distribution in deflection direction with a slight preference for the tangential direction. This result suggests a systematic magnetic configuration for switchback generation, which is consistent with interchange reconnection as a source mechanism, although this new evidence does not rule out other mechanisms, such as the expansion of wave modes.
Owen CJ, Abraham JB, Nicolaou G, et al., 2022, Solar Orbiter SWA Observations of Electron Strahl Properties Inside 1 AU, UNIVERSE, Vol: 8
Trotta D, Pecora F, Settino A, et al., 2022, On the Transmission of Turbulent Structures across the Earth's Bow Shock, ASTROPHYSICAL JOURNAL, Vol: 933, ISSN: 0004-637X
Aizawa S, Persson M, Menez T, et al., 2022, LatHyS global hybrid simulation of the BepiColombo second Venus flyby, PLANETARY AND SPACE SCIENCE, Vol: 218, ISSN: 0032-0633
Dimmock AP, Khotyaintsev YV, Lalti A, et al., 2022, Analysis of multiscale structures at the quasi-perpendicular Venus bow shock Results from Solar Orbiter's first Venus flyby, ASTRONOMY & ASTROPHYSICS, Vol: 660, ISSN: 0004-6361
Reville V, Fargette N, Rouillard AP, et al., 2022, Flux rope and dynamics of the heliospheric current sheet Study of the Parker Solar Probe and Solar Orbiter conjunction of June 2020, Astronomy and Astrophysics: a European journal, Vol: 659, Pages: 1-14, ISSN: 0004-6361
Context. Solar Orbiter and Parker Solar Probe jointly observed the solar wind for the first time in June 2020, capturing data from very different solar wind streams: calm, Alfvénic wind and also highly dynamic large-scale structures.Context. Our aim is to understand the origin and characteristics of the highly dynamic solar wind observed by the two probes, particularly in the vicinity of the heliospheric current sheet (HCS).Methods. We analyzed the plasma data obtained by Parker Solar Probe and Solar Orbiter in situ during the month of June 2020. We used the Alfvén-wave turbulence magnetohydrodynamic solar wind model WindPredict-AW and we performed two 3D simulations based on ADAPT solar magnetograms for this period.Results. We show that the dynamic regions measured by both spacecraft are pervaded by flux ropes close to the HCS. These flux ropes are also present in the simulations, forming at the tip of helmet streamers, that is, at the base of the heliospheric current sheet. The formation mechanism involves a pressure-driven instability followed by a fast tearing reconnection process. We further characterize the 3D spatial structure of helmet streamer born flux ropes, which appears in the simulations to be related to the network of quasi-separatrices.
Desai M, Mitchell DG, McComas DJ, et al., 2022, Suprathermal ion energy spectra and anisotropies near the heliospheric current sheet crossing observed by the Parker Solar Probe during encounter 7, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 927, Pages: 1-12, ISSN: 0004-637X
We present observations of ≳10–100 keV nucleon−1 suprathermal (ST) H, He, O, and Fe ions associated with crossings of the heliospheric current sheet (HCS) at radial distances of <0.1 au from the Sun. Our key findings are as follows: (1) very few heavy ions are detected during the first full crossing, the heavy-ion intensities are reduced during the second partial crossing and peak just after the second crossing; (2) ion arrival times exhibit no velocity dispersion; (3) He pitch-angle distributions track the magnetic field polarity reversal and show up to ∼10:1 anti-sunward, field-aligned flows and beams closer to the HCS that become nearly isotropic farther from the HCS; (4) the He spectrum steepens either side of the HCS, and the He, O, and Fe spectra exhibit power laws of the form ∼E−4–E6; and (5) maximum energies EX increase with the ion's charge-to-mass (Q/M) ratio as ${E}_{X}/{E}_{H}\propto {({Q}_{X}/{M}_{X})}^{\delta }$, where δ ∼ 0.65–0.76, assuming that the average Q states are similar to those measured in gradual and impulsive solar energetic particle events at 1 au. The absence of velocity dispersion in combination with strong field-aligned anisotropies closer to the HCS appears to rule out solar flares and near-Sun coronal-mass-ejection-driven shocks. These new observations present challenges not only for mechanisms that employ direct parallel electric fields and organize maximum energies according to E/Q but also for local diffusive and magnetic-reconnection-driven acceleration models. Reevaluation of our current understanding of the production and transport of energetic ions is necessary to understand this near-solar, current-sheet-associated population of ST ions.
Agapitov V, Drake JF, Swisdak M, et al., 2022, Flux Rope Merging and the Structure of Switchbacks in the Solar Wind, ASTROPHYSICAL JOURNAL, Vol: 925, ISSN: 0004-637X
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Moestl C, Weiss AJ, Reiss MA, et al., 2022, Multipoint Interplanetary Coronal Mass Ejections Observed with Solar Orbiter, BepiColombo, Parker Solar Probe, Wind, and STEREO-A, ASTROPHYSICAL JOURNAL LETTERS, Vol: 924, ISSN: 2041-8205
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- Citations: 12
Angelini V, O'Brien H, Horbury T, et al., 2022, Novel magnetic cleaning techniques for Solar Orbiter magnetometer
Solar Orbiter is an ESA mission studying the heliosphere and the Sun. The magnetometer is designed to measure the magnetic field local to the spacecraft and is composed of two sensors located on a boom at different displacement from the spacecraft. This configuration reduces the electromagnetic interference caused by other on-board electrical systems and allows the exploitation of the 'gradiometer technique' to separate spacecraft generated signals from the solar magnetic field. This paper describes the analysis of the magnetometer data to develop a completely novel procedure for removing the magnetic field generated by the spacecraft-controlled heaters, the instruments, and the thrusters on the spacecraft. The difference between the data measured by the two sensors is used to identify this signal, which is then appropriately scaled and removed from the data. This approach produces cleaned magnetic field data which is routinely uploaded to the Solar Orbiter Archive for science exploitation.
Lavraud B, Kieokaew R, Fargette N, et al., 2021, Magnetic reconnection as a mechanism to produce multiple protonpopulations and beams locally in the solar wind, Journal of Astrophysics and Astronomy, Vol: 656, Pages: 1-8, ISSN: 0250-6335
Context. Spacecraft observations early revealed frequent multiple protonpopulations in the solar wind. Decades of research on their origin have focusedon processes such as magnetic reconnection in the low corona and wave-particleinteractions in the corona and locally in the solar wind.Aims.This study aimsto highlight that multiple proton populations and beams are also produced bymagnetic reconnection occurring locally in the solar wind. Methods. We use highresolution Solar Orbiter proton velocity distribution function measurements,complemented by electron and magnetic field data, to analyze the association ofmultiple proton populations and beams with magnetic reconnection during aperiod of slow Alfv\'enic solar wind on 16 July 2020. Results. At least 6reconnecting current sheets with associated multiple proton populations andbeams, including a case of magnetic reconnection at a switchback boundary, arefound during this day. This represents 2% of the measured distributionfunctions. We discuss how this proportion may be underestimated, and how it maydepend on solar wind type and distance from the Sun. Conclusions. Althoughsuggesting a likely small contribution, but which remains to be quantitativelyassessed, Solar Orbiter observations show that magnetic reconnection must beconsidered as one of the mechanisms that produce multiple proton populationsand beams locally in the solar wind.
Adhikari L, Zank GP, Zhao L-L, et al., 2021, Evolution of anisotropic turbulence in the fast and slow solar wind: Theory and Solar Orbiter measurements, ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
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- Citations: 6
Louarn P, Fedorov A, Prech L, et al., 2021, Multiscale views of an Alfvenic slow solar wind: 3D velocity distribution functions observed by the Proton-Alpha Sensor of Solar Orbiter, ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
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- Citations: 6
Aran A, Pacheco D, Laurenza M, et al., 2021, Evidence for local particle acceleration in the first recurrent galactic cosmic ray depression observed by Solar Orbiter The ion event on 19 June 2020, ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
Chust T, Kretzschmar M, Graham DB, et al., 2021, Observations of whistler mode waves by Solar Orbiter's RPW Low Frequency Receiver (LFR): In-flight performance and first results, ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
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- Citations: 5
Fedorov A, Louarn P, Owen CJ, et al., 2021, Switchback-like structures observed by Solar Orbiter, ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
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- Citations: 1
Owen CJ, Foster AC, Bruno R, et al., 2021, Solar Orbiter observations of the structure of reconnection outflow layers in the solar wind, ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
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- Citations: 4
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