Imperial College London

Dr Lorenzo Matteini

Faculty of Natural SciencesDepartment of Physics

Lecturer in Space Plasma Physics
 
 
 
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l.matteini

 
 
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Location

 

Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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89 results found

Laker R, Horbury TS, Matteini L, Bale SD, Stawarz JE, Woodham LD, Woolley Tet al., 2022, Switchback deflections beyond the early parker solar probe encounters, Monthly Notices of the Royal Astronomical Society, ISSN: 0035-8711

<jats:title>Abstract</jats:title> <jats:p>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.</jats:p>

Journal article

Franci L, Papini E, Del Sarto D, Hellinger P, Burgess D, Matteini L, Landi S, Montagud-Camps Vet al., 2022, Plasma Turbulence in the Near-Sun and Near-Earth Solar Wind: A Comparison via Observation-Driven 2D Hybrid Simulations, Universe, Vol: 8, Pages: 453-453

<jats:p>We analyse two high-resolution 2D hybrid simulations of plasma turbulence with observation-driven initial conditions that are representative of the near-Sun and the near-Earth solar wind. The former employs values of some fundamental parameters that have been measured by the Parker Solar Probe at 0.17 au from the Sun, while, in the latter, they are set to average values typically observed at 1 au. We compare the spatial and spectral properties of the magnetic, ion velocity, and density fluctuations, as well as the time evolution of magnetic reconnection events that occur spontaneously as the result of the development of turbulence. Despite some differences due to the different plasma conditions, some key features are observed in both simulations: elongated ion-scale Alfvénic structures form in between vortices whenever the orientation of the magnetic field lines is the same, i.e., magnetic reconnection via the formation of an X point cannot occur; the magnetic and density fluctuations at sub-ion scales are governed by force balance; the magnetic compressibility at sub-ion scales is compatible with isotropic magnetic field components; the characteristic time of the formation of current sheets is the eddy turnover at the energy injection scale, while the characteristic time for their disruption via reconnection is compatible with the Alfvén time of the background turbulence.</jats:p>

Journal article

McManus MD, Verniero J, Bale SD, Bowen TA, Larson DE, Kasper JC, Livi R, Matteini L, Rahmati A, Romeo O, Whittlesey P, Woolley Tet al., 2022, Density and Velocity Fluctuations of Alpha Particles in Magnetic Switchbacks, ASTROPHYSICAL JOURNAL, Vol: 933, ISSN: 0004-637X

Journal article

Hellinger P, Montagud-Camps V, Franci L, Matteini L, Papini E, Verdini A, Landi Set al., 2022, Ion-scale Transition of Plasma Turbulence: Pressure-Strain Effect, ASTROPHYSICAL JOURNAL, Vol: 930, ISSN: 0004-637X

Journal article

D'Amicis R, Bruno R, Panasenco O, Telloni D, Perrone D, Marcucci MF, Woodham L, Velli M, De Marco R, Jagarlamudi V, Coco I, Owen C, Louarn P, Livi S, Horbury T, Andre N, Angelini V, Evans V, Fedorov A, Genot V, Lavraud B, Matteini L, Muller D, O'Brien H, Pezzi O, Rouillard AP, Sorriso-Valvo L, Tenerani A, Verscharen D, Zouganelis Iet al., 2021, First Solar Orbiter observation of the Alfvenic slow wind and identification of its solar source, ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361

Journal article

Maksimovic M, Soucek J, Chust T, Khotyaintsev Y, Kretzschmar M, Bonnin X, Vecchio A, Alexandrova O, Bale SD, Berard D, Brochot J-Y, Edberg NJT, Eriksson A, Hadid LZ, Johansson EPG, Karlsson T, Katra B, Krasnoselskikh V, Krupar V, Lion S, Lorfevre E, Matteini L, Nguyen QN, Pisa D, Piberne R, Plettemeier D, Rucker HO, Santolik O, Steinvall K, Steller M, Stverak S, Travnicek P, Vaivads A, Zaslavsky A, Chaintreuil S, Dekkali M, Astier P-A, Barbary G, Boughedada K, Cecconi B, Chapron F, Collin C, Dias D, Gueguen L, Lamy L, Leray V, Malac-Allain LR, Pantellini F, Parisot J, Plasson P, Thijs S, Fratter I, Bellouard E, Danto P, Julien S, Guilhem E, Fiachetti C, Sanisidro J, Laffaye C, Gonzalez F, Pontet B, Queruel N, Jannet G, Fergeau P, de Wit TD, Vincent T, Agrapart C, Pragout J, Bergerard-Timofeeva M, Delory GT, Turin P, Jeandet A, Leroy P, Pellion J-C, Bouzid V, Recart W, Kolmasova I, Kruparova O, Uhlir L, Lan R, Base J, Andre M, Bylander L, Cripps V, Cully C, Jansson S-E, Puccio W, Brinek J, Ottacher H, Angelini V, Berthomier M, Evans V, Goetz K, Hellinger P, Horbury TS, Issautier K, Kontar E, Le Contel O, Louarn P, Martinovic M, Mueller D, O'Brien H, Owen CJ, Retino A, Rodriguez-Pacheco J, Sahraoui F, Sanchez L, Walsh AP, Wimmer-Schweingruber RF, Zouganelis Iet al., 2021, First observations and performance of the RPW instrument on board the Solar Orbiter mission, ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361

Journal article

Matteini L, Laker R, Horbury T, Woodham L, Bale SD, Stawarz JE, Woolley T, Steinvall K, Jones GH, Grant SR, Afghan Q, Galand M, O'Brien H, Evans V, Angelini V, Maksimovic M, Chust T, Khotyaintsev Y, Krasnoselskikh V, Kretzschmar M, Lorfevre E, Plettemeier D, Soucek J, Steller M, Stverak S, Travnicek P, Vaivads A, Vecchio A, Wimmer-Schweingruber RF, Ho GC, Gomez-Herrero R, Rodriguez-Pacheco J, Louarn P, Fedorov A, Owen CJ, Bruno R, Livi S, Zouganelis I, Muller Det al., 2021, Solar Orbiter's encounter with the tail of comet C/2019 Y4 (ATLAS): Magnetic field draping and cometary pick-up ion waves, Astronomy and Astrophysics: a European journal, Vol: 656, ISSN: 0004-6361

ontext. Solar Orbiter is expected to have flown close to the tail of comet C/2019 Y4 (ATLAS) during the spacecraft’s first perihelion in June 2020. Models predict a possible crossing of the comet tails by the spacecraft at a distance from the Sun of approximately 0.5 AU.Aims. This study is aimed at identifying possible signatures of the interaction of the solar wind plasma with material released by comet ATLAS, including the detection of draped magnetic field as well as the presence of cometary pick-up ions and of ion-scale waves excited by associated instabilities. This encounter provides us with the first opportunity of addressing such dynamics in the inner Heliosphere and improving our understanding of the plasma interaction between comets and the solar wind.Methods. We analysed data from all in situ instruments on board Solar Orbiter and compared their independent measurements in order to identify and characterize the nature of structures and waves observed in the plasma when the encounter was predicted.Results. We identified a magnetic field structure observed at the start of 4 June, associated with a full magnetic reversal, a local deceleration of the flow and large plasma density, and enhanced dust and energetic ions events. The cross-comparison of all these observations support a possible cometary origin for this structure and suggests the presence of magnetic field draping around some low-field and high-density object. Inside and around this large scale structure, several ion-scale wave-forms are detected that are consistent with small-scale waves and structures generated by cometary pick-up ion instabilities.Conclusions. Solar Orbiter measurements are consistent with the crossing through a magnetic and plasma structure of cometary origin embedded in the ambient solar wind. We suggest that this corresponds to the magnetotail of one of the fragments of comet ATLAS or to a portion of the tail that was previously disconnected and advected past the spacec

Journal article

Bale SD, Horbury TS, Velli M, Desai MI, Halekas JS, McManus MD, Panasenco O, Badman ST, Bowen TA, Chandran BDG, Drake JF, Kasper JC, Laker R, Mallet A, Matteini L, Phan TD, Raouafi NE, Squire J, Woodham LD, Woolley Tet al., 2021, A solar source of alfvenic magnetic field switchbacks: in situ remnants of magnetic funnels on supergranulation scales, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 923, Pages: 1-12, ISSN: 0004-637X

One of the striking observations from the Parker Solar Probe (PSP) spacecraft is the prevalence in the inner heliosphere of large amplitude, Alfvénic magnetic field reversals termed switchbacks. These $\delta {B}_{R}/B\sim { \mathcal O }(1$) fluctuations occur over a range of timescales and in patches separated by intervals of quiet, radial magnetic field. We use measurements from PSP to demonstrate that patches of switchbacks are localized within the extensions of plasma structures originating at the base of the corona. These structures are characterized by an increase in alpha particle abundance, Mach number, plasma β and pressure, and by depletions in the magnetic field magnitude and electron temperature. These intervals are in pressure balance, implying stationary spatial structure, and the field depressions are consistent with overexpanded flux tubes. The structures are asymmetric in Carrington longitude with a steeper leading edge and a small (∼1°) edge of hotter plasma and enhanced magnetic field fluctuations. Some structures contain suprathermal ions to ∼85 keV that we argue are the energetic tail of the solar wind alpha population. The structures are separated in longitude by angular scales associated with supergranulation. This suggests that these switchbacks originate near the leading edge of the diverging magnetic field funnels associated with the network magnetic field—the primary wind sources. We propose an origin of the magnetic field switchbacks, hot plasma and suprathermals, alpha particles in interchange reconnection events just above the solar transition region and our measurements represent the extended regions of a turbulent outflow exhaust.

Journal article

Papini E, Hellinger P, Verdini A, Landi S, Franci L, Montagud-Camps V, Matteini Let al., 2021, Properties of Hall-MHD Turbulence at Sub-Ion Scales: Spectral Transfer Analysis, ATMOSPHERE, Vol: 12

Journal article

Woolley T, Matteini L, McManus MD, Bercic L, Badman ST, Woodham LD, Horbury TS, Bale SD, Laker R, Stawarz JE, Larson DEet al., 2021, Plasma properties, switchback patches, and low alpha-particle abundance in slow Alfvenic coronal hole wind at 0.13 au, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 508, Pages: 236-244, ISSN: 0035-8711

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 (∼0.13 au) 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 per cent) 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 per cent in this low-velocity wind could correspond to an abundance of ∼0.9 per cent 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.

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, Dudok de Wit T, 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, ottacher 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., 2021, The Solar Orbiter Radio and Plasma Waves (RPW) instrument (vol 642, A12, 2020), ASTRONOMY & ASTROPHYSICS, Vol: 654, ISSN: 0004-6361

Journal article

Tenerani A, Sioulas N, Matteini L, Panasenco O, Shi C, Velli Met al., 2021, Evolution of switchbacks in the inner heliosphere, Letters of the Astrophysical Journal, Vol: 919, Pages: 1-7, ISSN: 2041-8205

We analyze magnetic field data from the first six encounters of Parker Solar Probe, three Helios fast streams and two Ulysses south polar passes covering heliocentric distances 0.1 ≲ R ≲ 3 au. We use this data set to statistically determine the evolution of switchbacks of different periods and amplitudes with distance from the Sun. We compare the radial evolution of magnetic field variances with that of the mean square amplitudes of switchbacks, and quantify the radial evolution of the cumulative counts of switchbacks per kilometer. We find that the amplitudes of switchbacks decrease faster than the overall turbulent fluctuations, in a way consistent with the radial decrease of the mean magnetic field. This could be the result of a saturation of amplitudes and may be a signature of decay processes of large amplitude Alfvénic fluctuations in the solar wind. We find that the evolution of switchback occurrence in the solar wind is scale dependent: the fraction of longer-duration switchbacks increases with radial distance, whereas it decreases for shorter switchbacks. This implies that switchback dynamics is a complex process involving both decay and in situ generation in the inner heliosphere. We confirm that switchbacks can be generated by the expansion, although other types of switchbacks generated closer to the Sun cannot be ruled out.

Journal article

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 and Astrophysics: a European journal, Vol: 652, Pages: 1-10, ISSN: 0004-6361

Context. 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.Aims. 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.Methods. 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.Results. 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.Conclusions. 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 measurements provide an accurate representation of the solar wind within ±10° latitude, which could be used as a more rigorous constraint on solar wind models and space weather predictions. In the future, this range of latitudes will increase as SO’s orbit becomes more inclined.

Journal article

Hellinger P, Papini E, Verdini A, Landi S, Franci L, Matteini L, Montagud-Camps Vet al., 2021, Spectral Transfer and Karman-Howarth-Monin Equations for Compressible Hall Magnetohydrodynamics, ASTROPHYSICAL JOURNAL, Vol: 917, ISSN: 0004-637X

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

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

Gonzalez CA, Tenerani A, Matteini L, Hellinger P, Velli Met al., 2021, Proton Energization by Phase Steepening of Parallel-propagating Alfvenic Fluctuations, ASTROPHYSICAL JOURNAL LETTERS, Vol: 914, ISSN: 2041-8205

Journal article

Martinovic MM, Klein KG, Huang J, Chandran BDG, Kasper JC, Lichko E, Bowen T, Chen CHK, Matteini L, Stevens M, Case AW, Bale SDet al., 2021, Multiscale Solar Wind Turbulence Properties inside and near Switchbacks Measured by the Parker Solar Probe, ASTROPHYSICAL JOURNAL, Vol: 912, ISSN: 0004-637X

Journal article

Hellinger P, Verdini A, Landi S, Papini E, Franci L, Matteini Let al., 2021, Scale dependence and cross-scale transfer of kinetic energy in compressible hydrodynamic turbulence at moderate Reynolds numbers, PHYSICAL REVIEW FLUIDS, Vol: 6, ISSN: 2469-990X

Journal article

Stawarz JE, Matteini L, Parashar TN, Franci L, Eastwood JP, Gonzalez CA, Gingell IL, Burch JL, Ergun RE, Ahmadi N, Giles BL, Gershman DJ, Le Contel O, Lindqvist P, Russell CT, Strangeway RJ, Torbert RBet al., 2021, Comparative analysis of the various generalized Ohm's law terms in magnetosheath turbulence as observed by magnetospheric multiscale, Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-14, ISSN: 2169-9380

Decomposing the electric field (E) into the contributions from generalized Ohm's law provides key insight into both nonlinear and dissipative dynamics across the full range of scales within a plasma. Using high‐resolution, multi‐spacecraft measurements of three intervals in Earth's magnetosheath from the Magnetospheric Multiscale mission, the influence of the magnetohydrodynamic, Hall, electron pressure, and electron inertia terms from Ohm's law, as well as the impact of a finite electron mass, on the turbulent E spectrum are examined observationally for the first time. The magnetohydrodynamic, Hall, and electron pressure terms are the dominant contributions to E over the accessible length scales, which extend to scales smaller than the electron inertial length at the greatest extent, with the Hall and electron pressure terms dominating at sub‐ion scales. The strength of the non‐ideal electron pressure contribution is stronger than expected from linear kinetic Alfvén waves and a partial anti‐alignment with the Hall electric field is present, linked to the relative importance of electron diamagnetic currents in the turbulence. The relative contribution of linear and nonlinear electric fields scale with the turbulent fluctuation amplitude, with nonlinear contributions playing the dominant role in shaping E for the intervals examined in this study. Overall, the sum of the Ohm's law terms and measured E agree to within ∼ 20% across the observable scales. These results both confirm general expectations about the behavior of E in turbulent plasmas and highlight features that should be explored further theoretically.

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

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

Matteini L, Franci L, Alexandrova O, Lacombe C, Landi S, Hellinger P, Papini E, Verdini Aet al., 2020, Magnetic field turbulence in the solar wind at sub-ion scales: in situ observations and numerical simulations, Frontiers in Astronomy and Space Sciences, ISSN: 2296-987X

We investigate the transition of the solar wind turbulent cascade from MHD tosub-ion range by means of a detail comparison between in situ observations andhybrid numerical simulations. In particular we focus on the properties of themagnetic field and its component anisotropy in Cluster measurements and hybrid2D simulations. First, we address the angular distribution of wave-vectors inthe kinetic range between ion and electron scales by studying the varianceanisotropy of the magnetic field components. When taking into account thesingle-direction sampling performed by spacecraft in the solar wind, the mainproperties of the fluctuations observed in situ are also recovered in ournumerical description. This result confirms that solar wind turbulence in thesub-ion range is characterized by a quasi-2D gyrotropic distribution ofk-vectors around the mean field. We then consider the magnetic compressibilityassociated with the turbulent cascade and its evolution from large-MHD tosub-ion scales. The ratio of field-aligned to perpendicular fluctuations,typically low in the MHD inertial range, increases significantly when crossingion scales and its value in the sub-ion range is a function of the total plasmabeta only, as expected from theoretical predictions, with higher magneticcompressibility for higher beta. Moreover, we observe that this increase has agradual trend from low to high beta values in the in situ data; this behaviouris well captured by the numerical simulations. The level of magnetic fieldcompressibility that is observed in situ and in the simulations is in fairlygood agreement with theoretical predictions, especially at high beta,suggesting that in the kinetic range explored the turbulence is supported bylow-frequency and highly-oblique fluctuations in pressure balance, like kineticAlfv\'en waves or other slowly evolving coherent structures.

Journal article

Franci L, Stawarz JE, Papini E, Hellinger P, Nakamura T, Burgess D, Landi S, Verdini A, Matteini L, Ergun R, Contel OL, Lindqvist P-Aet al., 2020, Modeling MMS observations at the Earth's magnetopause with hybrid simulations of Alfvénic turbulence, The Astrophysical Journal, Vol: 898, ISSN: 0004-637X

Magnetospheric Multiscale (MMS) observations of plasma turbulence generated by a Kelvin–Helmholtz (KH) event at the Earth's magnetopause are compared with a high-resolution two-dimensional (2D) hybrid direct numerical simulation of decaying plasma turbulence driven by large-scale balanced Alfvénic fluctuations. The simulation, set up with four observation-driven physical parameters (ion and electron betas, turbulence strength, and injection scale), exhibits a quantitative agreement on the spectral, intermittency, and cascade-rate properties with in situ observations, despite the different driving mechanisms. Such agreement demonstrates a certain universality of the turbulent cascade from magnetohydrodynamic to sub-ion scales, whose properties are mainly determined by the selected parameters, also indicating that the KH instability-driven turbulence has a quasi-2D nature. The fact that our results are compatible with the validity of the Taylor hypothesis, in the whole range of scales investigated numerically, suggests that the fluctuations at sub-ion scales might have predominantly low frequencies. This would be consistent with a kinetic Alfvén wave-like nature and/or with the presence of quasi-static structures. Finally, the third-order structure function analysis indicates that the cascade rate of the turbulence generated by a KH event at the magnetopause is an order of magnitude larger than in the ambient magnetosheath.

Journal article

Bandyopadhyay R, Sorriso-Valvo L, Chasapis A, Hellinger P, Matthaeus WH, Verdini A, Landi S, Franci L, Matteini L, Giles BL, Gershman DJ, Moore TE, Pollock CJ, Russell CT, Strangeway RJ, Torbert RB, Burch JLet al., 2020, In situ observation of hall magnetohydrodynamic cascade in space plasma, Physical Review Letters, Vol: 124, Pages: 225101 – 1-225101 – 7, ISSN: 0031-9007

We present estimates of the turbulent energy-cascade rate derived from a Hall-magnetohydrodynamic (MHD) third-order law. We compute the contribution from the Hall term and the MHD term to the energy flux. Magnetospheric Multiscale (MMS) data accumulated in the magnetosheath and the solar wind are compared with previously established simulation results. Consistent with the simulations, we find that at large (MHD) scales, the MMS observations exhibit a clear inertial range dominated by the MHD flux. In the subion range, the cascade continues at a diminished level via the Hall term, and the change becomes more pronounced as the plasma beta increases. Additionally, the MHD contribution to interscale energy transfer remains important at smaller scales than previously thought. Possible reasons are offered for this unanticipated result.

Journal article

Bercic L, Larson D, Whittlesey P, Maksimovic M, Badman ST, Landi S, Matteini L, Bale SD, Bonnell JW, Case AW, de Wit TD, Goetz K, Harvey PR, Kasper JC, Korreck KE, Livi R, MacDowall RJ, Malaspina DM, Pulupa M, Stevens MLet al., 2020, Coronal electron temperature inferred from the strahl electrons in the inner heliosphere: parker solar probe and helios observations, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 892, Pages: 1-14, ISSN: 0004-637X

The shape of the electron velocity distribution function plays an important role in the dynamics of the solar wind acceleration. Electrons are normally modeled with three components, the core, the halo, and the strahl. We investigate how well the fast strahl electrons in the inner heliosphere preserve the information about the coronal electron temperature at their origin. We analyzed the data obtained by two missions, Helios, spanning the distances between 65 and 215 R S, and Parker Solar Probe (PSP), reaching down to 35 R S during its first two orbits around the Sun. The electron strahl was characterized with two parameters: pitch-angle width (PAW) and the strahl parallel temperature (T s∥). PSP observations confirm the already reported dependence of strahl PAW on core parallel plasma beta (${\beta }_{\mathrm{ec}\parallel }$). Most of the strahl measured by PSP appear narrow with PAW reaching down to 30°. The portion of the strahl velocity distribution function aligned with the magnetic field is for the measured energy range well described by a Maxwellian distribution function. T s∥ was found to be anticorrelated with the solar wind velocity and independent of radial distance. These observations imply that T s∥ carries the information about the coronal electron temperature. The obtained values are in agreement with coronal temperatures measured using spectroscopy, and the inferred solar wind source regions during the first orbit of PSP agree with the predictions using a PFSS model.

Journal article

DAmicis R, Matteini L, Bruno R, Velli Met al., 2020, Large amplitude fluctuations in the alfvénic solar wind, Solar Physics, Vol: 295, Pages: 1-12, ISSN: 0038-0938

Large amplitude fluctuations, often with characteristics reminiscent of large amplitude Alfvén waves propagating away from the Sun, are ubiquitous in the solar wind. Such features are most frequently found within fast solar wind streams and most often at solar minimum. The fluctuations found in slow solar wind streams usually have a smaller relative amplitude, are less Alfvénic in character and present more variability. However, intervals of slow wind displaying Alfvénic correlations have been recently identified in different solar cycle phases. In the present paper we report Alfvénic slow solar wind streams seen during the maximum of solar activity that are characterized not only by a very high correlation between velocity and magnetic field fluctuations (as required by outwardly propagating Alfvén modes) – comparable to that seen in fast wind streams – but also by higher amplitude relative fluctuations comparable to those seen in fast wind. Our results suggest that the Alfvénic slow wind has a different origin from the slow wind found near the boundary of coronal holes, where the amplitude of the Alfvénic fluctuations decreases together with decreasing the wind speed.

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

Nemecek Z, Durovcova T, Safrankova J, Nemec F, Matteini L, Stansby D, Janitzek N, Berger L, Wimmer-Schweingruber RFet al., 2020, What is the solar wind frame of reference?, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 889, Pages: 1-14, ISSN: 0004-637X

Various solar wind ion species move with different speeds and theoretical considerations as well as limited observations in a region close to the Sun show that heavy solar wind ions tend to flow faster than protons, at least in less-aged fast solar wind streams. The solar wind flow carries the frozen-in interplanetary magnetic field (IMF) and this situation evokes three related questions: (i) what is the proper solar wind speed, (ii) is this speed equal to the speed of the dominant component, whatever that may be, and (iii) what is the speed of the magnetic field? We show that simple theoretical considerations based on the MHD approximation as well as on the dynamics of charged particles in electric and magnetic fields suggest that the IMF velocity of motion (de Hoffmann–Teller (HT) velocity) would be deliberated as the velocity appropriate for solar wind studies. Our analysis based on the Wind, Helios, ACE, and SOHO observations of differential streaming of solar wind populations shows that their energy is conserved in the HT frame. On the other hand, the noise and temporal resolution of the data do not allow us to decide whether the total momentum is also conserved in this frame.

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

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