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  • Journal article
    van der Holst B, Huang J, Sachdeva N, Kasper JC, Manchester WB, Borovikov D, Chandran BDG, Case AW, Korreck KE, Larson D, Livi R, Stevens M, Whittlesey P, Bale SD, Pulupa M, Malaspina DM, Bonnell JW, Harvey PR, Goetz K, MacDowall RJet al., 2022,

    Improving the Alfven Wave Solar Atmosphere Model Based on Parker Solar Probe Data

    , ASTROPHYSICAL JOURNAL, Vol: 925, ISSN: 0004-637X
  • Journal article
    Shebanits O, Wahlund J-E, Waite JH, Dougherty MKet al., 2022,

    Conductivities of Titan's Dusty Ionosphere

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 127, ISSN: 2169-9380
  • Journal article
    Simon Wedlund CL, Volwerk M, Beth A, Mazelle C, Moestl C, Halekas JS, Gruesbeck JR, Rojas-Castillo Det al., 2021,

    A fast bow shock location predictor-estimator from 2D and 3D analytical models: Application to Mars and the MAVEN mission

    , Journal of Geophysical Research: Space Physics, ISSN: 2169-9380
  • Journal article
    Archer M, Waters C, Dewan S, Foster S, Portas Aet al., 2022,

    GC Insights: Space sector careers resources need a greater diversity of roles

    <jats:p>Abstract. Educational research highlights that improved careers education is needed to increase participation in STEM. Current careers resources concerning the space sector, however, are found to perhaps not best reflect the diversity of roles present and may in fact perpetuate misconceptions about the usefulness of science. We, therefore, compile a more diverse set of space-related jobs, which will be used in the development of a new space careers resource. </jats:p>
  • Journal article
    Christensen MW, Gettelman A, Cermak J, Dagan G, Diamond M, Douglas A, Feingold G, Glassmeier F, Goren T, Grosvenor DP, Gryspeerdt E, Kahn R, Li Z, Ma P-L, Malavelle F, McCoy IL, McCoy DT, McFarquhar G, Mulmenstadt J, Pal S, Possner A, Povey A, Quaas J, Rosenfeld D, Schmidt A, Schroedner R, Sorooshian A, Stier P, Toll V, Watson-Parris D, Wood R, Yang M, Yuan Tet al., 2022,

    Opportunistic experiments to constrain aerosol effective radiative forcing

    , Atmospheric Chemistry and Physics, Vol: 22, Pages: 641-674, ISSN: 1680-7316

    Aerosol–cloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The nonlinearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can be challenging when meteorological variability also drives both aerosol and cloud changes independently. Natural and anthropogenic aerosol perturbations from well-defined sources provide “opportunistic experiments” (also known as natural experiments) to investigate ACI in cases where causality may be more confidently inferred. These perturbations cover a wide range of locations and spatiotemporal scales, including point sources such as volcanic eruptions or industrial sources, plumes from biomass burning or forest fires, and tracks from individual ships or shipping corridors. We review the different experimental conditions and conduct a synthesis of the available satellite datasets and field campaigns to place these opportunistic experiments on a common footing, facilitating new insights and a clearer understanding of key uncertainties in aerosol radiative forcing. Cloud albedo perturbations are strongly sensitive to background meteorological conditions. Strong liquid water path increases due to aerosol perturbations are largely ruled out by averaging across experiments. Opportunistic experiments have significantly improved process-level understanding of ACI, but it remains unclear how reliably the relationships found can be scaled to the global level, thus demonstrating a need for deeper investigation in order to improve assessments of aerosol radiative forcing and climate change.
  • Journal article
    Chadney JM, Koskinen TT, Hu X, Galand M, Lavvas P, Unruh Y, Serigano J, Hörst SM, Yelle RVet al., 2022,

    Energy deposition in Saturn's equatorial upper atmosphere

    , Icarus, Vol: 372, Pages: 1-16, ISSN: 0019-1035

    We construct Saturn equatorial neutral temperature and density profiles of H, H2, He, and CH4, between 10−12 and 1 bar using measurements from Cassini’s Ion Neutral Mass Spectrometer (INMS) taken during the spacecraft’s final plunge into Saturn’s atmosphere on 15 September 2017, combined with previous deeper atmospheric measurements from the Cassini Composite InfraRed Spectrometer (CIRS) and from the UltraViolet Imaging Spectrograph (UVIS). These neutral profiles are fed into an energy deposition model employing soft X-ray and Extreme UltraViolet (EUV) solar fluxes at a range of spectral resolutions (∆λ = 4×10−3 nm to 1 nm) assembled from TIMED/SEE, from SOHO/SUMER, and from the Whole Heliosphere Interval (WHI) quiet Sun campaign. Our energy deposition model calculates ion production rate profiles through photo-ionisation and electron-impact ionisation processes, as well as rates of photo-dissociation of CH4. The ion reaction rate profiles we determine are important to obtain accurate ion density profiles, meanwhile methane photo-dissociation is key to initiate complex organic chemical processes. We assess the importance of spectral resolution in the energy deposition model by using a high-resolution H2 photo-absorption cross section, which has the effect of producing additional ionisation peaks near 800 km altitude. We find that these peaks are still formed when using low resolution (∆λ = 1 nm) or mid-resolution (∆λ = 0.1 nm) solar spectra, as long as high-resolution cross sections are included in the model.
  • Journal article
    Stawarz J, Eastwood J, Phan T, Gingell I, Pyakurel P, Shay M, Robertson S, Russell C, Le Contel Oet al., 2022,

    Turbulence-driven magnetic reconnection and the magnetic correlation length: observations from magnetospheric multiscale in Earth's magnetosheath

    , Physics of Plasmas, Vol: 29, Pages: 1-20, ISSN: 1070-664X

    Turbulent plasmas generate a multitude of thin current structures that can be sites for magnetic reconnection. The Magnetospheric Multiscale (MMS) mission has recently enabled the detailed examination of such turbulent current structures in Earth's magnetosheath and revealed that a novel type of reconnection, known as electron-only reconnection, can occur. In electron-only reconnection, ions do not have enough space to couple to the newly reconnected magnetic fields, suppressing ion jet formation and resulting in thinner sub-proton-scale current structures with faster super-Alfvénic electron jets. In this study, MMS observations are used to examine how the magnetic correlation length (λC) of the turbulence, which characterizes the size of the large-scale magnetic structures and constrains the length of the current sheets formed, influences the nature of turbulence-driven reconnection. We systematically identify 256 reconnection events across 60 intervals of magnetosheath turbulence. Most events do not appear to have ion jets; however, 18 events are identified with ion jets that are at least partially coupled to the reconnected magnetic field. The current sheet thickness and electron jet speed have a weak anti-correlation, with faster electron jets at thinner current sheets. When 𝜆𝐶≲20 ion inertial lengths, as is typical near the sub-solar magnetosheath, a tendency for thinner current sheets and potentially faster electron jets is present. The results are consistent with electron-only reconnection being more prevalent for turbulent plasmas with relatively short λC and may be relevant to the nonlinear dynamics and energy dissipation in turbulent plasmas.
  • Journal article
    Moestl C, Weiss AJ, Reiss MA, Amerstorfer T, Bailey RL, Hinterreiter J, Bauer M, Barnes D, Davies JA, Harrison RA, von Forstner JLF, Davies EE, Heyner D, Horbury T, Bale SDet al., 2022,

    Multipoint Interplanetary Coronal Mass Ejections Observed with Solar Orbiter, BepiColombo, Parker Solar Probe, Wind, and STEREO-A

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 924, ISSN: 2041-8205
  • Conference paper
    Eckersley S, Rowe S, Antoniou N, Forsyth C, Wicks R, Eastwood J, Brown P, Dániel V, Gromeš J, Junas M, Ryden K, Heil M, Terzo S, Gonzalo AR, Jiggens Pet al., 2022,

    A Distributed Space-Weather Sensor System using Small Satellites

    , ISSN: 0074-1795

    Space weather is becoming increasingly important for space and terrestrial activities and is likely to transition to an operational service. Small satellites are ideally suited for space-weather measurements given the need for making simultaneous measurements across both small and large volumes of space. The “Nanosatellites for D3S” Phase 0/A study for ESA was initiated in early 2021 with the objective to assess the feasibility of using nanosatellites for future operational space weather monitoring missions in near-Earth space as part of ESA's Distributed Space Weather Sensor System (D3S) - which itself forms part of the wider ESA Enhanced Space Weather Monitoring System. The study team consortium is highly experienced including sub-contractors supporting SSTL from MSSL, Imperial College London, and VZLU. Surrey Space Centre and Northumbria University are also providing expert consultancy. In the first part of the Phase 0 study, a survey of the measurement requirements and potential space weather instruments was carried out, alongside an investigation into recent relevant nanosatellite missions and future nanosatellite technologies. This was followed by an analysis and trade-off of high level mission architecture concepts eventually converging down to two of the most promising mission architecture concepts, which were further analysed in the latter half of the Phase 0 study. The objective of the first Phase 0 mission architecture concept was to provide near-real time measurements of radiation, thermal plasma and Ionospheric neutrals/plasma, via a constellation of 20x SSTL-21 satellites, in a single LEO orbital plane. The objective of the second Phase 0 mission architecture concept was to provide near-real time measurements of radiation, the Ionosphere and the Thermosphere, via a constellation of 6x 16U SSTL-Cube satellites, in a single LEO orbital plane. The orbit selected for both missions was a 500-600km Sun-Synchronous LEO Orbit with an LTAN of 10:30a
  • Conference paper
    Angelini V, O'Brien H, Horbury T, Fauchon-Jones Eet al., 2022,

    Novel magnetic cleaning techniques for Solar Orbiter magnetometer

    Solar Orbiter is an ESA mission studying the heliosphere and the Sun. The magnetometer is designed to measure the magnetic field local to the spacecraft and is composed of two sensors located on a boom at different displacement from the spacecraft. This configuration reduces the electromagnetic interference caused by other on-board electrical systems and allows the exploitation of the 'gradiometer technique' to separate spacecraft generated signals from the solar magnetic field. This paper describes the analysis of the magnetometer data to develop a completely novel procedure for removing the magnetic field generated by the spacecraft-controlled heaters, the instruments, and the thrusters on the spacecraft. The difference between the data measured by the two sensors is used to identify this signal, which is then appropriately scaled and removed from the data. This approach produces cleaned magnetic field data which is routinely uploaded to the Solar Orbiter Archive for science exploitation.
  • Journal article
    Malaspina DM, Stenborg G, Mehoke D, Al-Ghazwi A, Shen MM, Hsu H-W, Iyer K, Bale SD, de Wit TDet al., 2022,

    Clouds of Spacecraft Debris Liberated by Hypervelocity Dust Impacts on Parker Solar Probe

    , ASTROPHYSICAL JOURNAL, Vol: 925, ISSN: 0004-637X
  • Journal article
    Cattell C, Breneman A, Dombeck J, Hanson E, Johnson M, Halekas J, Bale SD, de Wit TD, Goetz K, Goodrich K, Malaspina D, Pulupa M, Case T, Kasper JC, Larson D, Stevens M, Whittlesey Pet al., 2022,

    Parker Solar Probe Evidence for the Absence of Whistlers Close to the Sun to Scatter Strahl and to Regulate Heat Flux

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 924, ISSN: 2041-8205
  • Journal article
    Verniero JL, Chandran BDG, Larson DE, Paulson K, Alterman BL, Badman S, Bale SD, Bonnell JW, Bowen TA, de Wit TD, Kasper JC, Klein KG, Lichko E, Livi R, McManus MD, Rahmati A, Verscharen D, Walters J, Whittlesey PLet al., 2022,

    Strong Perpendicular Velocity-space Diffusion in Proton Beams Observed by Parker Solar Probe

    , ASTROPHYSICAL JOURNAL, Vol: 924, ISSN: 0004-637X
  • Journal article
    Lavergne A, Hemming D, Prentice IC, Guerrieri R, Oliver R, Graven Het al., 2022,

    Global decadal variability of plant carbon isotope discrimination and its link to gross primary production.

    , Global Change Biology, Vol: 28, Pages: 524-541, ISSN: 1354-1013

    Carbon isotope discrimination (Δ13C) in C3 woody plants is a key variable for the study of photosynthesis. Yet how Δ13C varies at decadal scales, and across regions, and how it is related to gross primary production (GPP), are still incompletely understood. Here we address these questions by implementing a new Δ13C modelling capability in the land-surface model JULES incorporating both photorespiratory and mesophyll-conductance fractionations. We test the ability of four leaf-internal CO2 concentration models embedded in JULES to reproduce leaf and tree-ring (TR) carbon isotopic data. We show that all the tested models tend to overestimate average Δ13C values, and to underestimate interannual variability in Δ13C. This is likely because they ignore the effects of soil water stress on stomatal behavior. Variations in post-photosynthetic isotopic fractionations across species, sites and years, may also partly explain the discrepancies between predicted and TR-derived Δ13C values. Nonetheless, the “least-cost” (Prentice) model shows the lowest biases with the isotopic measurements, and lead to improved predictions of canopy-level carbon and water fluxes. Overall, modelled Δ13C trends vary strongly between regions during the recent (1979–2016) historical period but stay nearly constant when averaged over the globe. Photorespiratory and mesophyll effects modulate the simulated global Δ13C trend by 0.0015 ± 0.005‰ and –0.0006 ± 0.001‰ ppm−1, respectively. These predictions contrast with previous findings based on atmospheric carbon isotope measurements. Predicted Δ13C and GPP tend to be negatively correlated in wet-humid and cold regions, and in tropical African forests, but positively related elsewhere. The negative correlation between Δ13C and GPP is partly due to the strong dominant influences of temperature on GPP and vapor pressure deficit on Δ13
  • Journal article
    Nakamura TKM, Blasl KA, Hasegawa H, Umeda T, Liu Y-H, Peery SA, Plaschke F, Nakamura R, Holmes JC, Stawarz JE, Nystrom WDet al., 2022,

    Multi-scale evolution of Kelvin–Helmholtz waves at the earth's magnetopause during southward IMF periods

    , Physics of Plasmas, Vol: 29, Pages: 012901-012901, ISSN: 1070-664X

    At the Earth's low-latitude magnetopause, the Kelvin–Helmholtz instability (KHI), driven by the velocity shear between the magnetosheath and magnetosphere, has been frequently observed during northward interplanetary magnetic field (IMF) periods. However, the signatures of the KHI have been much less frequently observed during southward IMF periods, and how the KHI develops under southward IMF has been less explored. Here, we performed a series of realistic 2D and 3D fully kinetic simulations of a KH wave event observed by the Magnetospheric Multiscale (MMS) mission at the dusk-flank magnetopause during southward IMF on September 23, 2017. The simulations demonstrate that the primary KHI bends the magnetopause current layer and excites the Rayleigh–Taylor instability (RTI), leading to penetration of high-density arms into the magnetospheric side. This arm penetration disturbs the structures of the vortex layer and produces intermittent and irregular variations of the surface waves which significantly reduces the observational probability of the periodic KH waves. The simulations further demonstrate that in the non-linear growth phase of the primary KHI, the lower-hybrid drift instability (LHDI) is induced near the edge of the primary vortices and contributes to an efficient plasma mixing across the magnetopause. The signatures of the large-scale surface waves by the KHI/RTI and the small-scale fluctuations by the LHDI are reasonably consistent with the MMS observations. These results indicate that the multi-scale evolution of the magnetopause KH waves and the resulting plasma transport and mixing as seen in the simulations may occur during southward IMF
  • Journal article
    Blasl KA, Nakamura TKM, Plaschke F, Nakamura R, Hasegawa H, Stawarz JE, Liu Y-H, Peery S, Holmes JC, Hosner M, Schmid D, Roberts OW, Volwerk Met al., 2022,

    Multi-scale observations of the magnetopause Kelvin-Helmholtz waves during southward IMF

    , PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X
  • Journal article
    Jankee P, Oyedokun D, Soltanian M, Chisepo HK, Heyns Met al., 2022,

    Geomagnetically Induced Currents: Frequency Spectra and Threats to Voltage Stability

    , IEEE ACCESS, Vol: 10, Pages: 62484-62501, ISSN: 2169-3536
  • Journal article
    Adhikari S, Parashar TN, Shay MA, Matthaeus WH, Pyakurel PS, Fordin S, Stawarz JE, Eastwood JPet al., 2021,

    Energy transfer in reconnection and turbulence

    , Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, Vol: 104, ISSN: 1539-3755

    Reconnection and turbulence are two of the most commonly observed dynamical processes in plasmas, but their relationship is still not fully understood. Using 2.5D kinetic particle-in-cell simulations of both strong turbulence and reconnection, we compare the cross-scale transfer of energy in the two systems by analyzing the generalization of the von Kármán Howarth equations for Hall magnetohydrodynamics, a formulation that subsumes the third-order law for steady energy transfer rates. Even though the large scale features are quite different, the finding is that the decomposition of the energy transfer is structurally very similar in the two cases. In the reconnection case, the time evolution of the energy transfer also exhibits a correlation with the reconnection rate. These results provide explicit evidence that reconnection dynamics fundamentally involves turbulence-like energy transfer.
  • Journal article
    Wright CJ, Hall RJ, Banyard TP, Hindley NP, Krisch I, Mitchell DM, Seviour WJMet al., 2021,

    Dynamical and surface impacts of the January 2021 sudden stratospheric warming in novel Aeolus wind observations, MLS and ERA5

    , WEATHER AND CLIMATE DYNAMICS, Vol: 2, Pages: 1283-1301
  • Conference paper
    Dipu S, Schwarz M, Ekman A, Gryspeerdt E, Goren T, Sourdeval O, Mülmenstädt J, Quaas Jet al., 2021,

    Exploring satellite-derived relationships between cloud droplet number concentration and liquid water path using a large-domain large-eddy simulation

    <jats:p>&amp;lt;div class=&amp;quot;page&amp;quot; title=&amp;quot;Page 1&amp;quot;&amp;gt;&amp;lt;div class=&amp;quot;layoutArea&amp;quot;&amp;gt;&amp;lt;div class=&amp;quot;column&amp;quot;&amp;gt;&amp;lt;p&amp;gt;Important aspects of the adjustments to aerosol-cloud interactions can be examined using the relationship between cloud droplet number concentration (Nd) and liquid water path (LWP). Specifically, this relation can constrain the role of aerosols in leading to thicker or thinner clouds in response to adjustment mechanisms. This study investigates the satellite retrieved relationship between Nd and LWP for a selected case of mid-latitude continental clouds using high-resolution Large-eddy simulations (LES) over a large domain in weather prediction mode. Since the satellite retrieval uses adiabatic assumption to derive the Nd (NAd), we have also considered NAd from the LES model for comparison. The NAd-LWP relationship in the satellite and the LES model show similar, generally positive, but non-monotonic relations. This case over continent thus behaves differently compared to previously-published analysis of oceanic clouds, and the analysis illustrates a regime dependency (marine and continental) in the NAd-LWP relation in the satellite retrievals. The study further explores the impact of the satellite&amp;amp;#160;retrieval assumptions on the Nd-LWP relationship. When considering the relationship of the actually simulated cloud-top Nd, rather than NAd, with LWP, the result shows a much more nonlinear relationship. The difference is much less pronounced, however, for shallow stratiform than for convective clouds. Comparing local vs large-scale statistics from satellite data shows that continental clouds exhibit only a weak nonlinear Nd-LWP relationship. Hence a regime based Nd-LWP analysis is even more relevant when it comes to continental clouds.&amp;lt;/p&amp;gt;&amp;lt;
  • Journal article
    Cohen CMS, Christian ER, Cummings AC, Davis AJ, Desai M, de Nolfo GA, Giacalone J, Hill ME, Joyce CJ, Labrador AW, Leske RA, Matthaeus WH, McComas DJ, McNutt RL, Mewaldt RA, Mitchell DG, Mitchell JG, Rankin JS, Roelof EC, Schwadron NA, Stone EC, Szalay JR, Wiedenbeck ME, Vourlidas A, Bale SD, Pulupa M, MacDowall RJet al., 2021,

    PSP/IS⊙IS observations of the 29 November 2020 solar energetic particle event

    , ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
  • Journal article
    Zaslavsky A, Mann I, Soucek J, Czechowski A, Pisa D, Vaverka J, Meyer-Vernet N, Maksimovic M, Lorfevre E, Issautier K, Babic KR, Bale SD, Morooka M, Vecchio A, Chust T, Khotyaintsev Y, Krasnoselskikh V, Kretzschmar M, Plettemeier D, Steller M, Stverak S, Travnicek P, Vaivads Aet al., 2021,

    First dust measurements with the Solar Orbiter Radio and Plasma Wave instrument

    , ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
  • Journal article
    Allen RC, Cernuda I, Pacheco D, Berger L, Xu ZG, von Forstner JLF, Rodriguez-Pacheco J, Wimmer-Schweingruber RF, Ho GC, Mason GM, Vines SK, Khotyaintsev Y, Horbury T, Maksimovic M, Hadid LZ, Volwerk M, Dimmock AP, Sorriso-Valvo L, Stergiopoulou K, Andrews GB, Angelini V, Bale SD, Boden S, Boettcher S, Chust T, Eldrum S, Espada PP, Lara FE, Evans V, Gomez-Herrero R, Hayes JR, Hellin AM, Kollhoff A, Krasnoselskikh V, Kretzschmar M, Kuehl P, Kulkarni SR, Lees WJ, Lorfevre E, Martin C, O'Brien H, Plettemeier D, Polo OR, Prieto M, Ravanbakhsh A, Sanchez-Prieto S, Schlemm CE, Seifert H, Soucek J, Steller M, Stverak S, Terasa JC, Travnicek P, Tyagi K, Vaivads A, Vecchio A, Yedla Met al., 2021,

    Energetic ions in the Venusian system: Insights from the first Solar Orbiter flyby

    , ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
  • Journal article
    Zhao L-L, Zank GP, He JS, Telloni D, Hu Q, Li G, Nakanotani M, Adhikari L, Kilpua EKJ, Horbury TS, O'Brien H, Evans V, Angelini Vet al., 2021,

    Turbulence and wave transmission at an ICME-driven shock observed by the Solar Orbiter and Wind

    , ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
  • Journal article
    Davies EE, Mostl C, Owens MJ, Weiss AJ, Amerstorfer T, Hinterreiter J, Bauer M, Bailey RL, Reiss MA, Forsyth RJ, Horbury TS, O'Brien H, Evans V, Angelini V, Heyner D, Richter I, Auster H-U, Magnes W, Baumjohann W, Fischer D, Barnes D, Davies JA, Harrison RAet al., 2021,

    In situ multi-spacecraft and remote imaging observations of the first CME detected by Solar Orbiter and BepiColombo

    , ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
  • Journal article
    Verscharen D, Stansby D, Finley AJ, Owen CJ, Horbury T, Maksimovic M, Velli M, Bale SD, Louarn P, Fedorov A, Bruno R, Livi S, Khotyaintsev Y, Vecchio A, Lewis GR, Anekallu C, Kelly CW, Watson G, Kataria DO, O'Brien H, Evans V, Angelini Vet al., 2021,

    The angular-momentum flux in the solar wind observed during Solar Orbiter's first orbit

    , Astronomy and Astrophysics: a European journal, Vol: 656, Pages: 1-10, ISSN: 0004-6361

    Aims. We present the first measurements of the angular-momentum flux in the solar wind recorded by the Solar Orbiter spacecraft. Our aim is to validate these measurements to support future studies of the Sun’s angular-momentum loss.Methods. We combined 60-min averages of the proton bulk moments and the magnetic field measured by the Solar Wind Analyser and the magnetometer onboard Solar Orbiter. We calculated the angular-momentum flux per solid-angle element using data from the first orbit of the mission’s cruise phase in 2020. We separated the contributions from protons and from magnetic stresses to the total angular-momentum flux.Results. The angular-momentum flux varies significantly over time. The particle contribution typically dominates over the magnetic-field contribution during our measurement interval. The total angular-momentum flux shows the largest variation and is typically anti-correlated with the radial solar-wind speed. We identify a compression region, potentially associated with a co-rotating interaction region or a coronal mass ejection, which leads to a significant localised increase in the angular-momentum flux, albeit without a significant increase in the angular momentum per unit mass. We repeated our analysis using the density estimate from the Radio and Plasma Waves instrument. Using this independent method, we find a decrease in the peaks of positive angular-momentum flux, but otherwise, our results remain consistent.Conclusions. Our results largely agree with previous measurements of the solar wind’s angular-momentum flux in terms of amplitude, variability, and dependence on radial solar-wind bulk speed. Our analysis highlights the potential for more detailed future studies of the solar wind’s angular momentum and its other large-scale properties with data from Solar Orbiter. We emphasise the need for studying the radial evolution and latitudinal dependence of the angular-momentum flux in combination with data from
  • Journal article
    Carbone F, Sorriso-Valvo L, Khotyaintsev Y, Steinvall K, Vecchio A, Telloni D, Yordanova E, Graham DB, Edberg NJT, Eriksson A, Johansson EPG, Vasconez CL, Maksimovic M, Bruno R, D'Amicis R, Bale SD, Chust T, Krasnoselskikh V, Kretzschmar M, Lorfevre E, Plettemeier D, Soucek J, Steller M, Stverak S, Travnicek P, Vaivads A, Horbury TS, O'Brien H, Angelini V, Evans Vet al., 2021,

    Statistical study of electron density turbulence and ion-cyclotron waves in the inner heliosphere: Solar Orbiter observations

    , ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
  • Journal article
    Pisa D, Santolik O, Hanzelka M, Nicolaou G, Maksimovic M, Bale SD, Chust T, Khotyaintsev Y, Krasnoselskikh V, Kretzschmar M, Lorfevre E, Plettemeier D, Steller M, Stverak S, Travnicek P, Vaivads A, Vecchio A, Horbury T, O'Brien H, Evans V, Angelini V, Owen CJ, Louarn Pet al., 2021,

    First-year ion-acoustic wave observations in the solar wind by the RPW/TDS instrument on board Solar Orbiter

    , ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361
  • Journal article
    Steinvall K, Khotyaintsev Y, Cozzani G, Vaivads A, Yordanova E, Eriksson A, Edberg NJT, Maksimovic M, Bale SD, Chust T, Krasnoselskikh V, Kretzschmar M, Lorfevre E, Plettemeier D, Soucek J, Steller M, Stverak S, Vecchio A, Horbury TS, O'Brien H, Evans V, Fedorov A, Louarn P, Genot V, Andre N, Lavraud B, Rouillard AP, Owen CJet al., 2021,

    Solar wind current sheets and deHoffmann-Teller analysis First results from Solar Orbiter's DC electric field measurements

    , Astronomy and Astrophysics: a European journal, Vol: 656, Pages: 1-7, ISSN: 0004-6361

    Context. Solar Orbiter was launched on 10 February 2020 with the purpose of investigating solar and heliospheric physics using a payload of instruments designed for both remote and in situ studies. Similar to the recently launched Parker Solar Probe, and unlike earlier missions, Solar Orbiter carries instruments designed to measure low-frequency DC electric fields.Aims. In this paper, we assess the quality of the low-frequency DC electric field measured by the Radio and Plasma Waves instrument (RPW) on Solar Orbiter. In particular, we investigate the possibility of using Solar Orbiter’s DC electric and magnetic field data to estimate the solar wind speed.Methods. We used a deHoffmann-Teller (HT) analysis, based on measurements of the electric and magnetic fields, to find the velocity of solar wind current sheets, which minimises a single component of the electric field. By comparing the HT velocity to the proton velocity measured by the Proton and Alpha particle Sensor (PAS), we have developed a simple model for the effective antenna length, Leff of the E-field probes. We then used the HT method to estimate the speed of the solar wind.Results. Using the HT method, we find that the observed variations in Ey are often in excellent agreement with the variations in the magnetic field. The magnitude of Ey, however, is uncertain due to the fact that the Leff depends on the plasma environment. Here, we derive an empirical model relating Leff to the Debye length, which we can use to improve the estimate of Ey and, consequently, the estimated solar wind speed.Conclusions. The low-frequency electric field provided by RPW is of high quality. Using the deHoffmann-Teller analysis, Solar Orbiter’s magnetic and electric field measurements can be used to estimate the solar wind speed when plasma data are unavailable.
  • Journal article
    Graham DB, Khotyaintsev Y, Vaivads A, Edberg NJT, Eriksson A, Johansson EPG, Sorriso-Valvo L, Maksimovic M, Soucek J, Pisa D, Bale SD, Chust T, Kretzschmar M, Krasnoselskikh V, Lorfevre E, Plettemeier D, Steller M, Stverak S, Travnicek P, Vecchio A, Horbury TS, O'Brien H, Evans V, Angelini Vet al., 2021,

    Kinetic electrostatic waves and their association with current structures in the solar wind

    , ASTRONOMY & ASTROPHYSICS, Vol: 656, ISSN: 0004-6361

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