Imperial College London

ProfessorTimothyHorbury

Faculty of Natural SciencesDepartment of Physics

Professor of Physics
 
 
 
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Contact

 

+44 (0)20 7594 7676t.horbury Website

 
 
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Location

 

6M72Huxley BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

213 results found

Laker R, Horbury TS, Bale SD, Matteini L, Woolley T, Woodham LD, Stawarz JE, Davies EE, Eastwood JP, Owens MJ, O'Brien H, Evans V, Angelini V, Richter I, Heyner D, Owen CJ, Louarn P, Fedorov Aet al., 2021, Multi-spacecraft study of the solar wind at solar minimum: Dependence on latitude and transient outflows, ASTRONOMY & ASTROPHYSICS, Vol: 652, ISSN: 0004-6361

Journal article

Woolley T, Matteini L, McManus MD, Berčič L, Badman ST, Woodham LD, Horbury TS, Bale SD, Laker R, Stawarz JE, Larson DEet al., 2021, Plasma Properties, Switchback Patches and Low α-Particle Abundance in Slow Alfvénic Coronal Hole Wind at 0.13 au, Monthly Notices of the Royal Astronomical Society, ISSN: 0035-8711

<jats:title>Abstract</jats:title> <jats:p>The Parker Solar Probe (PSP) mission presents a unique opportunity to study the near-Sun solar wind closer than any previous spacecraft. During its fourth and fifth solar encounters, PSP had the same orbital trajectory, meaning that solar wind was measured at the same latitudes and radial distances. We identify two streams measured at the same heliocentric distance (∼0.13au) and latitude (∼-3.5○) across these encounters to reduce spatial evolution effects. By comparing the plasma of each stream, we confirm that they are not dominated by variable transient events, despite PSP’s proximity to the heliospheric current sheet. Both streams are consistent with a previous slow Alfvénic solar wind study once radial effects are considered, and appear to originate at the Southern polar coronal hole boundary. We also show that the switchback properties are not distinctly different between these two streams. Low α-particle abundance (∼ 0.6 %) is observed in the encounter 5 stream, suggesting that some physical mechanism must act on coronal hole boundary wind to cause α-particle depletion. Possible explanations for our observations are discussed, but it remains unclear whether the depletion occurs during the release or the acceleration of the wind. Using a flux tube argument, we note that an α-particle abundance of ∼ 0.6 % in this low velocity wind could correspond to an abundance of ∼ 0.9 % at 1 au. Finally, as the two streams roughly correspond to the spatial extent of a switchback patch, we suggest that patches are distinct features of coronal hole wind.</jats:p>

Journal article

Stansby D, Green LM, van Driel-Gesztelyi L, Horbury TSet al., 2021, Active Region Contributions to the Solar Wind over Multiple Solar Cycles, SOLAR PHYSICS, Vol: 296, ISSN: 0038-0938

Journal article

Laker R, Horbury TS, Bale SD, Matteini L, Woolley T, Woodham LD, Stawarz JE, Davies EE, Eastwood JP, Owens MJ, OBrien H, Evans V, Angelini V, Richter I, Heyner D, Owen CJ, Louarn P, Fedorov Aet al., 2021, Multi-spacecraft study of the solar wind at solar minimum: Dependence on latitude and transient outflows, Astronomy & Astrophysics, Vol: 652, Pages: A105-A105, ISSN: 0004-6361

<jats:p><jats:italic>Context.</jats:italic> The recent launches of Parker Solar Probe, Solar Orbiter (SO), and BepiColombo, along with several older spacecraft, have provided the opportunity to study the solar wind at multiple latitudes and distances from the Sun simultaneously.</jats:p><jats:p><jats:italic>Aims.</jats:italic> We take advantage of this unique spacecraft constellation, along with low solar activity across two solar rotations between May and July 2020, to investigate how the solar wind structure, including the heliospheric current sheet (HCS), varies with latitude.</jats:p><jats:p><jats:italic>Methods.</jats:italic> We visualise the sector structure of the inner heliosphere by ballistically mapping the polarity and solar wind speed from several spacecraft onto the Sun’s source surface. We then assess the HCS morphology and orientation with the in situ data and compare this with a predicted HCS shape.</jats:p><jats:p><jats:italic>Results.</jats:italic> We resolve ripples in the HCS on scales of a few degrees in longitude and latitude, finding that the local orientations of sector boundaries were broadly consistent with the shape of the HCS but were steepened with respect to a modelled HCS at the Sun. We investigate how several CIRs varied with latitude, finding evidence for the compression region affecting slow solar wind outside the latitude extent of the faster stream. We also identified several transient structures associated with HCS crossings and speculate that one such transient may have disrupted the local HCS orientation up to five days after its passage.</jats:p><jats:p><jats:italic>Conclusions.</jats:italic> We have shown that the solar wind structure varies significantly with latitude, with this constellation providing context for solar wind measurements that would not be possible with a single spacecraft. These measurement

Journal article

Drake JF, Agapitov O, Swisdak M, Badman ST, Bale SD, Horbury TS, Kasper JC, MacDowall RJ, Mozer FS, Phan TD, Pulupa M, Szabo A, Velli Met 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: 0004-6361

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.

Journal article

Woodham L, Horbury T, Matteini L, Woolley T, Laker R, Bale S, Nicolaou G, Stawarz J, Stansby D, Hietala H, Larson D, Livi R, Verniero J, McManus M, Kasper J, Korreck K, Raouafi N, Moncuquet M, Pulupa Met 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: 0004-6361

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,‖, 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.

Journal article

Laker R, Horbury TS, Bale SD, Matteini L, Woolley T, Woodham LD, Badman ST, Pulupa M, Kasper JC, Stevens M, Case AW, Korreck KEet al., 2021, Statistical analysis of orientation, shape, and size of solar wind switchbacks, 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.

Journal article

Telloni D, Sorriso-Valvo L, Woodham LD, Panasenco O, Velli M, Carbone F, Zank GP, Bruno R, Perrone D, Nakanotani M, Shi C, D'Amicis R, De Marco R, Jagarlamudi VK, Steinvall K, Marino R, Adhikari L, Zhao L, Liang H, Tenerani A, Laker R, Horbury TS, Bale SD, Pulupa M, Malaspina DM, MacDowall RJ, Goetz K, de Wit TD, Harvey PR, Kasper JC, Korreck KE, Larson D, Case AW, Stevens ML, Whittlesey P, Livi R, Owen CJ, Livi S, Louarn P, Antonucci E, Romoli M, O'Brien H, Evans V, Angelini Vet al., 2021, Evolution of solar wind turbulence from 0.1 to 1 au during the first parker solar probe-solar orbiter radial alignment, 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.

Journal article

Heyner, Auster, Fornacon, Carr C, Richter, Mieth, Kolhey, Exner, Motschmann, Baumjohann, Matsuoka, Magnes, Berghofer, Fischer, Plaschke, Nakamura, Narita, Delta, Volwerk, Balogh A, Dougherty M, Horbury T, Langlais, Mandea, Masters A, Oliveira, Sanchez-Cano, Slavin, Vennerstrøm, Vogt, Wicht, Glassmeieret al., 2021, The BepiColombo Planetary Magnetometer MPO-MAG: what can we Learn from the Hermean magnetic field?, Space Science Reviews, Vol: 217, ISSN: 0038-6308

The magnetometer instrument MPO-MAG on-board the Mercury Planetary Orbiter (MPO) of the BepiColombo mission en-route to Mercury is introduced, with its instrument design, its calibration and scientific targets. The instrument is comprised of two tri-axial fluxgate magnetometers mounted on a 2.9 m boom and are 0.8 m apart. They monitor the magnetic field with up to 128 Hz in a ±2048 nT range. The MPO will be injected into an initial 480×1500 km polar orbit (2.3 h orbital period). At Mercury, we will map the planetary magnetic field and determine the dynamo generated field and constrain the secular variation. In this paper, we also discuss the effect of the instrument calibration on the ability to improve the knowledge on the internal field. Furthermore, the study of induced magnetic fields and field-aligned currents will help to constrain the interior structure in concert with other geophysical instruments. The orbit is also well-suited to study dynamical phenomena at the Hermean magnetopause and magnetospheric cusps. Together with its sister instrument Mio-MGF on-board the second satellite of the BepiColombo mission, the magnetometers at Mercury will study the reaction of the highly dynamic magnetosphere to changes in the solar wind. In the extreme case, the solar wind might even collapse the entire dayside magnetosphere. During cruise, MPO-MAG will contribute to studies of solar wind turbulence and transient phenomena.

Journal article

Freiherr von Forstner JL, Dumbović M, Möstl C, Guo J, Papaioannou A, Elftmann R, Xu Z, Terasa JC, Kollhoff A, Wimmer-Schweingruber RF, Rodríguez-Pacheco J, Weiss AJ, Hinterreiter J, Amerstorfer T, Bauer M, Belov AV, alet al., 2021, Radial evolution of the April 2020 stealth coronal mass ejection between 0.8 and 1 AU. Comparison of Forbush decreases at Solar Orbiter and near the Earth, Astronomy & Astrophysics, ISSN: 0004-6361

Journal article

Davies EE, Möstl C, Owens MJ, Weiss AJ, Amerstorfer T, Hinterreiter J, Bauer M, Bailey RLet al., 2021, In situ multi-spacecraft and remote imaging observations of the first CME detected by Solar Orbiter and BepiColombo, Astronomy & Astrophysics, ISSN: 0004-6361

Journal article

Woolley T, Matteini L, Horbury TS, Bale SD, Woodham LD, Laker R, Alterman BL, Bonnell JW, Case AW, Kasper JC, Klein KG, Martinović MM, Stevens Met al., 2020, Proton core behaviour inside magnetic field switchbacks, Monthly Notices of the Royal Astronomical Society, Vol: 498, Pages: 5524-5531, ISSN: 0035-8711

During Parker Solar Probe’s first two orbits there are widespread observations of rapid magnetic field reversals known as switchbacks. These switchbacks are extensively found in the near-Sun solar wind, appear to occur in patches, and have possible links to various phenomena such as magnetic reconnection near the solar surface. As switchbacks are associated with faster plasma flows, we questioned whether they are hotter than the background plasma and whether the microphysics inside a switchback is different to its surroundings. We have studied the reduced distribution functions from the Solar Probe Cup instrument and considered time periods with markedly large angular deflections, to compare parallel temperatures inside and outside switchbacks. We have shown that the reduced distribution functions inside switchbacks are consistent with a rigid velocity space rotation of the background plasma. As such, we conclude that the proton core parallel temperature is very similar inside and outside of switchbacks, implying that a T-V relationship does not hold for the proton core parallel temperature inside magnetic field switchbacks. We further conclude that switchbacks are consistent with Alfvénic pulses travelling along open magnetic field lines. The origin of these pulses, however, remains unknown. We also found that there is no obvious link between radial Poynting flux and kinetic energy enhancements suggesting that the radial Poynting flux is not important for the dynamics of switchbacks.

Journal article

Baumjohann W, Matsuoka A, Narita Y, Magnes W, Heyner D, Glassmeier K-H, Nakamura R, Fischer D, Plaschke F, Volwerk M, Zhang TL, Auster H-U, Richter I, Balogh A, Carr CM, Dougherty M, Horbury TS, Tsunakawa H, Matsushima M, Shinohara M, Shibuya H, Nakagawa T, Hoshino M, Tanaka Y, Anderson BJ, Russell CT, Motschmann U, Takahashi F, Fujimoto Aet al., 2020, The BepiColombo-Mio magnetometer en route to Mercury, Space Science Reviews, Vol: 216, Pages: 1-33, ISSN: 0038-6308

The fluxgate magnetometer MGF on board the Mio spacecraft of the BepiColombo mission is introduced with its science targets, instrument design, calibration report, and scientific expectations. The MGF instrument consists of two tri-axial fluxgate magnetometers. Both sensors are mounted on a 4.8-m long mast to measure the magnetic field around Mercury at distances from near surface (initial peri-center altitude is 590 km) to 6 planetary radii (11640 km). The two sensors of MGF are operated in a fully redundant way, each with its own electronics, data processing and power supply units. The MGF instrument samples the magnetic field at a rate of up to 128 Hz to reveal rapidly-evolving magnetospheric dynamics, among them magnetic reconnection causing substorm-like disturbances, field-aligned currents, and ultra-low-frequency waves. The high time resolution of MGF is also helpful to study solar wind processes (through measurements of the interplanetary magnetic field) in the inner heliosphere. The MGF instrument firmly corroborates measurements of its companion, the MPO magnetometer, by performing multi-point observations to determine the planetary internal field at higher multi-pole orders and to separate temporal fluctuations from spatial variations.

Journal article

Horbury TS, OBrien H, Carrasco Blazquez I, Bendyk M, Brown P, Hudson R, Evans V, Oddy TM, Carr CM, Beek TJ, Cupido E, Bhattacharya S, Dominguez J-A, Matthews L, Myklebust VR, Whiteside B, Bale SD, Baumjohann W, Burgess D, Carbone V, Cargill P, Eastwood J, Erdös G, Fletcher L, Forsyth R, Giacalone J, Glassmeier K-H, Goldstein ML, Hoeksema T, Lockwood M, Magnes W, Maksimovic M, Marsch E, Matthaeus WH, Murphy N, Nakariakov VM, Owen CJ, Owens M, Rodriguez-Pacheco J, Richter I, Riley P, Russell CT, Schwartz S, Vainio R, Velli M, Vennerstrom S, Walsh R, Wimmer-Schweingruber RF, Zank G, Müller D, Zouganelis I, Walsh APet al., 2020, The Solar Orbiter magnetometer, Astronomy & Astrophysics, Vol: 642, Pages: A9-A9, ISSN: 0004-6361

The magnetometer instrument on the Solar Orbiter mission is designed to measure the magnetic field local to the spacecraft continuously for the entire mission duration. The need to characterise not only the background magnetic field but also its variations on scales from far above to well below the proton gyroscale result in challenging requirements on stability, precision, and noise, as well as magnetic and operational limitations on both the spacecraft and other instruments. The challenging vibration and thermal environment has led to significant development of the mechanical sensor design. The overall instrument design, performance, data products, and operational strategy are described.

Journal article

Zouganelis I, 2020, The Solar Orbiter Science Activity Plan: translating solar and heliospheric physics questions into action, Astronomy & Astrophysics, Vol: 642, Pages: 1-19, ISSN: 0004-6361

Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate?; (2) How do solar transients drive heliospheric variability?; (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere?; (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission’s science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit’s science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans, resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime. This allows for all four mission goals to be addressed. In this paper, w

Journal article

Müller D, Cyr OCS, Zouganelis I, Gilbert HR, Marsden R, Nieves-Chinchilla Tet al., 2020, The solar orbiter mission. science overview, Astronomy & Astrophysics, Vol: 642, Pages: 1-31, ISSN: 0004-6361

Aims. Solar Orbiter, the first mission of ESA’s Cosmic Vision 2015–2025 programme and a mission of international collaboration between ESA and NASA, will explore the Sun and heliosphere from close up and out of the ecliptic plane. It was launched on 10 February 2020 04:03 UTC from Cape Canaveral and aims to address key questions of solar and heliospheric physics pertaining to how the Sun creates and controls the Heliosphere, and why solar activity changes with time. To answer these, the mission carries six remote-sensing instruments to observe the Sun and the solar corona, and four in-situ instruments to measure the solar wind, energetic particles, and electromagnetic fields. In this paper, we describe the science objectives of the mission, and how these will be addressed by the joint observations of the instruments onboard.Methods. The paper first summarises the mission-level science objectives, followed by an overview of the spacecraft and payload. We report the observables and performance figures of each instrument, as well as the trajectory design. This is followed by a summary of the science operations concept. The paper concludes with a more detailed description of the science objectives.Results. Solar Orbiter will combine in-situ measurements in the heliosphere with high-resolution remote-sensing observations of the Sun to address fundamental questions of solar and heliospheric physics. The performance of the Solar Orbiter payload meets the requirements derived from the mission’s science objectives. Its science return will be augmented further by coordinated observations with other space missions and ground-based observatories.

Journal article

Owen CJ, Bruno R, Livi S, Louarn P, Al Janabi K, Allegrini F, Amoros C, Baruah R, Barthe A, Berthomier M, Bordon S, Brockley-Blatt C, Brysbaert C, Capuano G, Collier M, DeMarco R, Fedorov A, Ford J, Fortunato V, Fratter I, Galvin AB, Hancock B, Heirtzler D, Kataria D, Kistler L, Lepri ST, Lewis G, Loeffler C, Marty W, Mathon R, Mayall A, Mele G, Ogasawara K, Orlandi M, Pacros A, Penou E, Persyn S, Petiot M, Phillips M, Prech L, Raines JM, Reden M, Rouillard AP, Rousseau A, Rubiella J, Seran H, Spencer A, Thomas JW, Trevino J, Verscharen D, Wurz P, Alapide A, Amoruso L, Andre N, Anekallu C, Arciuli V, Arnett KL, Ascolese R, Bancroft C, Bland P, Brysch M, Calvanese R, Castronuovo M, Cermak I, Chornay D, Clemens S, Coker J, Collinson G, D'Amicis R, Dandouras I, Darnley R, Davies D, Davison G, De Los Santos A, Devoto P, Dirks G, Edlund E, Fazakerley A, Ferris M, Frost C, Fruit G, Garat C, Genot V, Gibson W, Gilbert JA, de Giosa V, Gradone S, Hailey M, Horbury TS, Hunt T, Jacquey C, Johnson M, Lavraud B, Lawrenson A, Leblanc F, Lockhart W, Maksimovic M, Malpus A, Marcucci F, Mazelle C, Monti F, Myers S, Nguyen T, Rodriguez-Pacheco J, Phillips I, Popecki M, Rees K, Rogacki SA, Ruane K, Rust D, Salatti M, Sauvaud JA, Stakhiv MO, Stange J, Stubbs T, Taylor T, Techer J-D, Terrier G, Thibodeaux R, Urdiales C, Varsani A, Walsh AP, Watson G, Wheeler P, Willis G, Wimmer-Schweingruber RF, Winter B, Yardley J, Zouganelis Iet al., 2020, The Solar Orbiter Solar Wind Analyser (SWA) suite, ASTRONOMY & ASTROPHYSICS, Vol: 642, ISSN: 0004-6361

Journal article

Walsh AP, Horbury TS, Maksimovic M, Owen CJ, Rodriguez-Pacheco J, Wimmer-Schweingruber RF, Zouganelis I, Anekallu C, Bonnin X, Bruno R, Carrasco Blazquez I, Cernuda I, Chust T, De Groof A, Espinosa Lara F, Fazakerley AN, Gilbert HR, Gomez-Herrero R, Ho GC, Krucker S, Lepri ST, Lewis GR, Livi S, Louarn P, Mueller D, Nieves-Chinchilla T, O'Brien H, Osuna P, Plasson P, Raines JM, Rouillard AP, St Cyr OC, Sanchez L, Soucek J, Varsani A, Verscharen D, Watson CJ, Watson G, Williams DRet al., 2020, Coordination of the in situ payload of Solar Orbiter, Astronomy and Astrophysics: a European journal, Vol: 642, Pages: 1-7, ISSN: 0004-6361

Solar Orbiter’s in situ coordination working group met frequently during the development of the mission with the goal of ensuring that its in situ payload has the necessary level of coordination to maximise science return. Here we present the results of that work, namely how the design of each of the in situ instruments (EPD, MAG, RPW, SWA) was guided by the need for coordination, the importance of time synchronisation, and how science operations will be conducted in a coordinated way. We discuss the mechanisms by which instrument sampling schemes are aligned such that complementary measurements will be made simultaneously by different instruments, and how burst modes are scheduled to allow a maximum overlap of burst intervals between the four instruments (telemetry constraints mean different instruments can spend different amounts of time in burst mode). We also explain how onboard autonomy, inter-instrument communication, and selective data downlink will be used to maximise the number of transient events that will be studied using high-resolution modes of all the instruments. Finally, we briefly address coordination between Solar Orbiter’s in situ payload and other missions.

Journal article

Rouillard AP, Pinto RF, Vourlidas A, De Groof A, Thompson WT, Bemporad A, Dolei S, Indurain M, Buchlin E, Sasso C, Spadaro D, Dalmasse K, Hirzberger J, Zouganelis I, Strugarek A, Brun AS, Alexandre M, Berghmans D, Raouafi NE, Wiegelmann T, Pagano P, Arge CN, Nieves-Chinchilla T, Lavarra M, Poirier N, Amari T, Aran A, Andretta V, Antonucci E, Anastasiadis A, Auchere F, Bellot Rubio L, Nicula B, Bonnin X, Bouchemit M, Budnik E, Caminade S, Cecconi B, Carlyle J, Cernuda I, Davila JM, Etesi L, Espinosa Lara F, Fedorov A, Fineschi S, Fludra A, Genot V, Georgoulis MK, Gilbert HR, Giunta A, Gomez-Herrero R, Guest S, Haberreiter M, Hassler D, Henney CJ, Howard RA, Horbury TS, Janvier M, Jones SI, Kozarev K, Kraaikamp E, Kouloumvakos A, Krucker S, Lagg A, Linker J, Lavraud B, Louarn P, Maksimovic M, Maloney S, Mann G, Masson A, Mueller D, Onel H, Osuna P, Orozco Suarez D, Owen CJ, Papaioannou A, Perez-Suarez D, Rodriguez-Pacheco J, Parenti S, Pariat E, Peter H, Plunkett S, Pomoell J, Raines JM, Riethmueller TL, Rich N, Rodriguez L, Romoli M, Sanchez L, Solanki SK, St Cyr OC, Straus T, Susino R, Teriaca L, del Toro Iniesta JC, Ventura R, Verbeeck C, Vilmer N, Warmuth A, Walsh AP, Watson C, Williams D, Wu Y, Zhukov ANet al., 2020, Models and data analysis tools for the Solar Orbiter mission, ASTRONOMY & ASTROPHYSICS, Vol: 642, ISSN: 0004-6361

Journal article

Velli M, Harra LK, Vourlidas A, Schwadron N, Panasenco O, Liewer PC, Mueller D, Zouganelis I, St Cyr OC, Gilbert H, Nieves-Chinchilla T, Auchere F, Berghmans D, Fludra A, Horbury TS, Howard RA, Krucker S, Maksimovic M, Owen CJ, Rodriguez-Pacheco J, Romoli M, Solanki SK, Wimmer-Schweingruber RF, Bale S, Kasper J, McComas DJ, Raouafi N, Martinez-Pillet V, Walsh AP, De Groof A, Williams Det al., 2020, Understanding the origins of the heliosphere: integrating observations and measurements from Parker Solar Probe, Solar Orbiter, and other space- and ground-based observatories, Astronomy and Astrophysics: a European journal, Vol: 642, Pages: 1-13, ISSN: 0004-6361

Context. The launch of Parker Solar Probe (PSP) in 2018, followed by Solar Orbiter (SO) in February 2020, has opened a new window in the exploration of solar magnetic activity and the origin of the heliosphere. These missions, together with other space observatories dedicated to solar observations, such as the Solar Dynamics Observatory, Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations from WIND and ACE, and ground based multi-wavelength observations including the DKIST observatory that has just seen first light, promise to revolutionize our understanding of the solar atmosphere and of solar activity, from the generation and emergence of the Sun’s magnetic field to the creation of the solar wind and the acceleration of solar energetic particles.Aims. Here we describe the scientific objectives of the PSP and SO missions, and highlight the potential for discovery arising from synergistic observations. Here we put particular emphasis on how the combined remote sensing and in situ observations of SO, that bracket the outer coronal and inner heliospheric observations by PSP, may provide a reconstruction of the solar wind and magnetic field expansion from the Sun out to beyond the orbit of Mercury in the first phases of the mission. In the later, out-of-ecliptic portions of the SO mission, the solar surface magnetic field measurements from SO and the multi-point white-light observations from both PSP and SO will shed light on the dynamic, intermittent solar wind escaping from helmet streamers, pseudo-streamers, and the confined coronal plasma, and on solar energetic particle transport.Methods. Joint measurements during PSP–SO alignments, and magnetic connections along the same flux tube complemented by alignments with Earth, dual PSP–Earth, and SO-Earth, as well as with STEREO-A, SOHO, and BepiColumbo will allow a better understanding of the in situ evolution of solar-wind plasma flows and the full three-dimensional distribution of

Journal article

Rodriguez-Pacheco J, Wimmer-Schweingruber RF, Mason GM, Ho GC, Sanchez-Prieto S, Prieto M, Martin C, Seifert H, Andrews GB, Kulkarni SR, Panitzsch L, Boden S, Boettcher SI, Cernuda I, Elftmann R, Espinosa Lara F, Gomez-Herrero R, Terasa C, Almena J, Begley S, Boehm E, Blanco JJ, Boogaerts W, Carrasco A, Castillo R, da Silva Farina A, de Manuel Gonzalez V, Drews C, Dupont AR, Eldrum S, Gordillo C, Gutierrez O, Haggerty DK, Hayes JR, Heber B, Hill ME, Juengling M, Kerem S, Knierim V, Koehler J, Kolbe S, Kulemzin A, Lario D, Lees WJ, Liang S, Martinez Hellin A, Meziat D, Montalvo A, Nelson KS, Parra P, Paspirgilis R, Ravanbakhsh A, Richards M, Rodriguez-Polo O, Russu A, Sanchez I, Schlemm CE, Schuster B, Seimetz L, Steinhagen J, Tammen J, Tyagi K, Varela T, Yedla M, Yu J, Agueda N, Aran A, Horbury TS, Klecker B, Klein K-L, Kontar E, Krucker S, Maksimovic M, Malandraki O, Owen CJ, Pacheco D, Sanahuja B, Vainio R, Connell JJ, Dalla S, Droege W, Gevin O, Gopalswamy N, Kartavykh YY, Kudela K, Limousin O, Makela P, Mann G, Onel H, Posner A, Ryan JM, Soucek J, Hofmeister S, Vilmer N, Walsh AP, Wang L, Wiedenbeck ME, Wirth K, Zong Qet al., 2020, The energetic particle detector: energetic particle instrument suite for the Solar Orbiter mission, Astronomy and Astrophysics: a European journal, Vol: 642, Pages: 1-35, ISSN: 0004-6361

After decades of observations of solar energetic particles from space-based observatories, relevant questions on particle injection, transport, and acceleration remain open. To address these scientific topics, accurate measurements of the particle properties in the inner heliosphere are needed. In this paper we describe the Energetic Particle Detector (EPD), an instrument suite that is part of the scientific payload aboard the Solar Orbiter mission. Solar Orbiter will approach the Sun as close as 0.28 au and will provide extra-ecliptic measurements beyond ∼30° heliographic latitude during the later stages of the mission. The EPD will measure electrons, protons, and heavy ions with high temporal resolution over a wide energy range, from suprathermal energies up to several hundreds of megaelectronvolts/nucleons. For this purpose, EPD is composed of four units: the SupraThermal Electrons and Protons (STEP), the Electron Proton Telescope (EPT), the Suprathermal Ion Spectrograph (SIS), and the High-Energy Telescope (HET) plus the Instrument Control Unit that serves as power and data interface with the spacecraft. The low-energy population of electrons and ions will be covered by STEP and EPT, while the high-energy range will be measured by HET. Elemental and isotopic ion composition measurements will be performed by SIS and HET, allowing full particle identification from a few kiloelectronvolts up to several hundreds of megaelectronvolts/nucleons. Angular information will be provided by the separate look directions from different sensor heads, on the ecliptic plane along the Parker spiral magnetic field both forward and backwards, and out of the ecliptic plane observing both northern and southern hemispheres. The unparalleled observations of EPD will provide key insights into long-open and crucial questions about the processes that govern energetic particles in the inner heliosphere.

Journal article

Maksimovic M, Bale SD, Chust T, Khotyaintsev Y, Krasnoselskikh V, Kretzschmar M, Plettemeier D, Rucker HO, Soucek J, Steller M, Stverak S, Travnicek P, Vaivads A, Chaintreuil S, Dekkali M, Alexandrova O, Astier P-A, Barbary G, Berard D, Bonnin X, Boughedada K, Cecconi B, Chapron F, Chariet M, Collin C, de Conchy Y, Dias D, Gueguen L, Lamy L, Leray V, Lion S, Malac-Allain LR, Matteini L, Nguyen QN, Pantellini F, Parisot J, Plasson P, Thijs S, Vecchio A, Fratter I, Bellouard E, Lorfevre E, Danto P, Julien S, Guilhem E, Fiachetti C, Sanisidro J, Laffaye C, Gonzalez F, Pontet B, Queruel N, Jannet G, Fergeau P, Brochot J-Y, Cassam-Chenai G, de Wit TD, Timofeeva M, Vincent T, Agrapart C, Delory GT, Turin P, Jeandet A, Leroy P, Pellion J-C, Bouzid V, Katra B, Piberne R, Recart W, Santolik O, Kolmasova I, Krupar V, Kruparova O, Pisa D, Uhlir L, Lan R, Base J, Ahlen L, Andre M, Bylander L, Cripps V, Cully C, Eriksson A, Jansson S-E, Johansson EPG, Karlsson T, Puccio W, Brinek J, Oettacher H, Panchenko M, Berthomier M, Goetz K, Hellinger P, Horbury TS, Issautier K, Kontar E, Krucker S, Le Contel O, Louarn P, Martinovic M, Owen CJ, Retino A, Rodriguez-Pacheco J, Sahraoui F, Wimmer-Schweingruber RF, Zaslavsky A, Zouganelis Iet al., 2020, The Solar Orbiter Radio and Plasma Waves (RPW) instrument, ASTRONOMY & ASTROPHYSICS, Vol: 642, ISSN: 0004-6361

Journal article

Phan TD, Bale SD, Eastwood JP, Lavraud B, Drake JF, Oieroset M, Shay MA, Pulupa M, Stevens M, MacDowall RJ, Case AW, Larson D, Kasper J, Whittlesey P, Szabo A, Korreck KE, Bonnell JW, de Wit TD, Goetz K, Harvey PR, Horbury TS, Livi R, Malaspina D, Paulson K, Raouafi NE, Velli Met al., 2020, Parker solar probe In situ observations of magnetic reconnection exhausts during encounter 1, The Astrophysical Journal Supplement, Vol: 246, Pages: 34-34, ISSN: 0067-0049

Magnetic reconnection in current sheets converts magnetic energy into particle energy. The process may play an important role in the acceleration and heating of the solar wind close to the Sun. Observations from Parker Solar Probe (PSP) provide a new opportunity to study this problem, as it measures the solar wind at unprecedented close distances to the Sun. During the first orbit, PSP encountered a large number of current sheets in the solar wind through perihelion at 35.7 solar radii. We performed a comprehensive survey of these current sheets and found evidence for 21 reconnection exhausts. These exhausts were observed in heliospheric current sheets, coronal mass ejections, and regular solar wind. However, we find that the majority of current sheets encountered around perihelion, where the magnetic field was strongest and plasma β was lowest, were Alfvénic structures associated with bursty radial jets, and these current sheets did not appear to be undergoing local reconnection. We examined conditions around current sheets to address why some current sheets reconnected while others did not. A key difference appears to be the degree of plasma velocity shear across the current sheets: the median velocity shear for the 21 reconnection exhausts was 24% of the Alfvén velocity shear, whereas the median shear across 43 Alfvénic current sheets examined was 71% of the Alfvén velocity shear. This finding could suggest that large, albeit sub-Alfvénic, velocity shears suppress reconnection. An alternative interpretation is that the Alfvénic current sheets are isolated rotational discontinuities that do not undergo local reconnection.

Journal article

Horbury T, Woolley T, Laker R, Matteini L, Eastwood J, Bale SD, Velli M, Chandran BDG, Phan T, Raouafi NE, Goetz K, Harvey PR, Pulupa M, Klein KG, De Wit TD, Kasper JC, Korreck KE, Case AW, Stevens ML, Whittlesey P, Larson D, MacDowall RJ, Malaspina DM, Livi Ret al., 2020, Sharp Alfvenic impulses in the near-Sun solar wind, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 246, Pages: 1-8, ISSN: 0004-637X

Measurements of the near-Sun solar wind by Parker Solar Probe have revealed the presence of largenumbers of discrete Alfv ́enic impulses with an anti-Sunward sense of propagation. These are similarto those previously observed near 1 AU, in high speed streams over the Sun’s poles and at 60 solarradii. At 35 solar radii, however, they are typically shorter and sharper than seen elsewhere. Inaddition, these spikes occur in “patches” and there are also clear periods within the same stream whenthey do not occur; the timescale of these patches might be related to the rate at which the spacecraftmagnetic footpoint tracks across the coronal hole from which the plasma originated. While the velocityfluctuations associated with these spikes are typically under 100 km/s, due to the rather low Alfv ́enspeeds in the streams observed by the spacecraft to date, these are still associated with large angulardeflections of the magnetic field - and these deflections are not isotropic. These deflections do notappear to be related to the recently reported large scale, pro-rotation solar wind flow. Estimates ofthe size and shape of the spikes reveal high aspect ratio flow-aligned structures with a transverse scaleof≈104km. These events might be signatures of near-Sun impulsive reconnection events.

Journal article

Stansby D, Matteini L, Horbury TS, Perrone D, D'Amicis R, Bercic Let al., 2020, The origin of slow Alfvenic solar wind at solar minimum, Monthly Notices of the Royal Astronomical Society, Vol: 492, Pages: 39-44, ISSN: 0035-8711

Although the origins of slow solar wind are unclear, there is increasing evidence that at least some of it is released in a steady state on overexpanded coronal hole magnetic field lines. This type of slow wind has similar properties to the fast solar wind, including strongly Alfvénic fluctuations. In this study, a combination of proton, alpha particle, and electron measurements are used to investigate the kinetic properties of a single interval of slow Alfvénic wind at 0.35 au. It is shown that this slow Alfvénic interval is characterized by high alpha particle abundances, pronounced alpha–proton differential streaming, strong proton beams, and large alpha-to-proton temperature ratios. These are all features observed consistently in the fast solar wind, adding evidence that at least some Alfvénic slow solar wind also originates in coronal holes. Observed differences between speed, mass flux, and electron temperature between slow Alfvénic and fast winds are explained by differing magnetic field geometry in the lower corona.

Journal article

Perrone D, D'Amicis R, De Marco R, Matteini L, Stansby D, Bruno R, Horbury TSet al., 2020, Highly Alfvenic slow solar wind at 0.3 au during a solar minimum: Helios insights for Parker Solar Probe and Solar Orbiter, Astronomy and Astrophysics: a European journal, Vol: 633, Pages: 1-7, ISSN: 0004-6361

Alfvénic fluctuations in solar wind are an intrinsic property of fast streams, while slow intervals typically have a very low degree of Alfvénicity, with much more variable parameters. However, sometimes a slow wind can be highly Alfvénic. Here we compare three different regimes of solar wind, in terms of Alfvénic content and spectral properties, during a minimum phase of the solar activity and at 0.3 au. We show that fast and Alfvénic slow intervals share some common characteristics. This would suggest a similar solar origin, with the latter coming from over-expanded magnetic field lines, in agreement with observations at 1 au and at the maximum of the solar cycle. Due to the Alfvénic nature of the fluctuations in both fast and Alfvénic slow winds, we observe a well-defined correlation between the flow speed and the angle between magnetic field vector and radial direction. The high level of Alfvénicity is also responsible of intermittent enhancements (i.e. spikes), in plasma speed. Moreover, only for the Alfvénic intervals do we observe a break between the inertial range and large scales, on about the timescale typical of the Alfvénic fluctuations and where the magnetic fluctuations saturate, limited by the magnitude of the local magnetic field. In agreement with this, we recover a characteristic low-frequency 1/f scaling, as expected for fluctuations that are scale-independent. This work is directly relevant for the next solar missions, Parker Solar Probe and Solar Orbiter. One of the goals of these two missions is to study the origin and evolution of slow solar wind. In particular, Parker Solar Probe will give information about the Alfvénic slow wind in the unexplored region much closer to the Sun and Solar Orbiter will allow us to connect the observed physics to the source of the plasma.

Journal article

Klein KG, Martinovic M, Stansby D, Horbury TSet al., 2019, Linear Stability in the Inner Heliosphere: Helios Re-evaluated, ASTROPHYSICAL JOURNAL, Vol: 887, ISSN: 0004-637X

Journal article

Kasper JC, Bale SD, Belcher JW, Berthomier M, Case AW, Chandran BDG, Curtis DW, Gallagher D, Gary SP, Golub L, Halekas JS, Ho GC, Horbury TS, Hu Q, Huang J, Klein KG, Korreck KE, Larson DE, Livi R, Maruca B, Lavraud B, Louarn P, Maksimovic M, Martinovic M, McGinnis D, Pogorelov NV, Richardson JD, Skoug RM, Steinberg JT, Stevens ML, Szabo A, Velli M, Whittlesey PL, Wright KH, Zank GP, MacDowall RJ, McComas DJ, McNutt RL, Pulupa M, Raouafi NE, Schwadron NAet al., 2019, Alfvenic velocity spikes and rotational flows in the near-Sun solar wind, Nature, Vol: 576, Pages: 228-233, ISSN: 0028-0836

The prediction of a supersonic solar wind1 was first confirmed by spacecraft near Earth2,3 and later by spacecraft at heliocentric distances as small as 62 solar radii4. These missions showed that plasma accelerates as it emerges from the corona, aided by unidentified processes that transport energy outwards from the Sun before depositing it in the wind. Alfvénic fluctuations are a promising candidate for such a process because they are seen in the corona and solar wind and contain considerable energy5,6,7. Magnetic tension forces the corona to co-rotate with the Sun, but any residual rotation far from the Sun reported until now has been much smaller than the amplitude of waves and deflections from interacting wind streams8. Here we report observations of solar-wind plasma at heliocentric distances of about 35 solar radii9,10,11, well within the distance at which stream interactions become important. We find that Alfvén waves organize into structured velocity spikes with duration of up to minutes, which are associated with propagating S-like bends in the magnetic-field lines. We detect an increasing rotational component to the flow velocity of the solar wind around the Sun, peaking at 35 to 50 kilometres per second—considerably above the amplitude of the waves. These flows exceed classical velocity predictions of a few kilometres per second, challenging models of circulation in the corona and calling into question our understanding of how stars lose angular momentum and spin down as they age12,13,14.

Journal article

Bale SD, Badman ST, Bonnell JW, Bowen TA, Burgess D, Case AW, Cattell CA, Chandran BDG, Chaston CC, Chen CHK, Drake JF, De Wit TD, Eastwood JP, Ergun RE, Farrell WM, Fong C, Goetz K, Goldstein M, Goodrich KA, Harvey PR, Horbury TS, Howes GG, Kasper JC, Kellogg PJ, Klimchuk JA, Korreck KE, Krasnoselskikh VV, Krucker S, Laker R, Larson DE, MacDowall RJ, Maksimovic M, Malaspina DM, Martinez-Oliveros J, McComas DJ, Meyer-Vernet N, Moncuquet M, Mozer FS, Phan TD, Pulupa M, Raouafi NE, Salem C, Stansby D, Stevens M, Szabo A, Velli M, Woolley T, Wygant JRet al., 2019, Highly structured slow solar wind emerging from an equatorial coronal hole, Nature, Vol: 576, Pages: 237-242, ISSN: 0028-0836

During the solar minimum, when the Sun is at its least active, the solar wind1,2 is observed at high latitudes as a predominantly fast (more than 500 kilometres per second), highly Alfvénic rarefied stream of plasma originating from deep within coronal holes. Closer to the ecliptic plane, the solar wind is interspersed with a more variable slow wind3 of less than 500 kilometres per second. The precise origins of the slow wind streams are less certain4; theories and observations suggest that they may originate at the tips of helmet streamers5,6, from interchange reconnection near coronal hole boundaries7,8, or within coronal holes with highly diverging magnetic fields9,10. The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfvén-wave turbulence11,12, heating by reconnection in nanoflares13, ion cyclotron wave heating14 and acceleration by thermal gradients1. At a distance of one astronomical unit, the wind is mixed and evolved, and therefore much of the diagnostic structure of these sources and processes has been lost. Here we present observations from the Parker Solar Probe15 at 36 to 54 solar radii that show evidence of slow Alfvénic solar wind emerging from a small equatorial coronal hole. The measured magnetic field exhibits patches of large, intermittent reversals that are associated with jets of plasma and enhanced Poynting flux and that are interspersed in a smoother and less turbulent flow with a near-radial magnetic field. Furthermore, plasma-wave measurements suggest the existence of electron and ion velocity-space micro-instabilities10,16 that are associated with plasma heating and thermalization processes. Our measurements suggest that there is an impulsive mechanism associated with solar-wind energization and that micro-instabilities play a part in heating, and we provide evidence that low-latitude coronal holes are a key source of the slow solar wind.

Journal article

Matthaeus WH, Bandyopadhyay R, Brown MR, Borovsky J, Carbone V, Caprioli D, Chasapis A, Chhiber R, Dasso S, Dmitruk P, Zanna LD, Dmitruk PA, Franci L, Gary SP, Goldstein ML, Gomez D, Greco A, Horbury TS, Ji H, Kasper JC, Klein KG, Landi S, Li H, Malara F, Maruca BA, Mininni P, Oughton S, Papini E, Parashar TN, Petrosyan A, Pouquet A, Retino A, Roberts O, Ruffolo D, Servidio S, Spence H, Smith CW, Stawarz JE, TenBarge J, Vasquez1 BJ, Vaivads A, Valentini F, Velli M, Verdini A, Verscharen D, Whittlesey P, Wicks R, Bruno R, Zimbardo Get al., 2019, [Plasma 2020 Decadal] The essential role of multi-point measurements in turbulence investigations: the solar wind beyond single scale and beyond the Taylor Hypothesis, Publisher: Arxiv

This paper briefly reviews a number of fundamental measurements that need tobe made in order to characterize turbulence in space plasmas such as the solarwind. It has long been known that many of these quantities require simultaneousmultipoint measurements to attain a proper characterization that would revealthe fundamental physics of plasma turbulence. The solar wind is an ideal plasmafor such an investigation, and it now appears to be technologically feasible tocarry out such an investigation, following the pioneering Cluster and MMSmissions. Quantities that need to be measured using multipoint measurementsinclude the two-point, two-time second correlation function of velocity,magnetic field and density, and higher order statistical objects such as thirdand fourth order structure functions. Some details of these requirements aregiven here, with a eye towards achieving closure on fundamental questionsregarding the cascade rate, spectral anisotropy, characteristic coherentstructures, intermittency, and dissipation mechanisms that describe plasmaturbuelence, as well as its variability with plasma parameters in the solarwind. The motivation for this discussion is the current planning for a proposedHelioswarm mission that would be designed to make these measurements,leading tobreakthrough understanding of the physics of space and astrophysicalturbulence.

Working paper

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