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  • Journal article
    Lewis ZM, Beth A, Galand M, Henri P, Rubin M, Stephenson Pet al., 2024,

    Constraining ion transport in the diamagnetic cavity of comet 67P

    , Monthly Notices of the Royal Astronomical Society, Vol: 530, Pages: 66-81, ISSN: 0035-8711

    The European Space Agency Rosetta mission escorted comet 67P for a 2-yr section of its six and a half-year orbit around the Sun. By perihelion in 2015 August, the neutral and plasma data obtained by the spacecraft instruments showed the comet had transitioned to a dynamic object with large-scale plasma structures and a rich ion environment. One such plasma structure is the diamagnetic cavity: a magnetic field-free region formed by interaction between the unmagnetized cometary plasma and the impinging solar wind. Within this re gion, une xpectedly high ion bulk velocities have been observed, thought to have been accelerated by an ambipolar electric field. We hav e dev eloped a 1D numerical model of the cometary ionosphere to constrain the impact of various electric field profiles on the ionospheric density profile and ion composition. In the model, we include three ion species: H 2 O + , H 3 O + , and NH + 4 . The latter, not previously considered in ionospheric models including acceleration, is produced through the protonation of NH 3 and only lost through ion-electron dissociative recombination, and thus particularly sensitive to the time-scale of plasma loss through transport. We also assess the importance of including momentum transfer when assessing ion composition and densities in the presence of an electric field. By comparing simulated electron densities to Rosetta Plasma Consortium data sets, we find that to recreate the plasma densities measured inside the diamagnetic cavity near perihelion, the model requires an electric field proportional to r -1 of around 0.5-2 mV m -1 surface strength, leading to bulk ion speeds at Rosetta of 1.2-3.0 km s -1 .

  • Journal article
    De Keyser J, Edberg NJT, Henri P, Auster HU, Galand M, Rubin M, Nilsson H, Soucek J, André N, Corte VD, Rothkaehl H, Funase R, Kasahara S, Van Damme CCet al., 2024,

    In situ plasma and neutral gas observation time windows during a comet flyby: Application to the Comet Interceptor mission

    , Planetary and Space Science, Vol: 244, ISSN: 0032-0633

    A comet flyby, like the one planned for ESA's Comet Interceptor mission, places stringent requirements on spacecraft resources. To plan the time line of in situ plasma and neutral gas observations during the flyby, the size of the comet magnetosphere and neutral coma must be estimated well. For given solar irradiance and solar wind conditions, comet composition, and neutral gas expansion speed, the size of gas coma and magnetosphere during the flyby can be estimated from the gas production rate and the flyby geometry. Combined with flyby velocity, the time spent in these regions can be inferred and a data acquisition plan can be elaborated for each instrument, compatible with the limited data storage capacity. The sizes of magnetosphere and gas coma are found from a statistical analysis based on the probability distributions of gas production rate, flyby velocity, and solar wind conditions. The size of the magnetosphere as measured by bow shock standoff distance is 105–106 km near 1 au in the unlikely case of a Halley-type target comet, down to a nonexistent bow shock for targets with low activity. This translates into durations up to 103–104 seconds. These estimates can be narrowed down when a target is identified far from the Sun, and even more so as its activity can be predicted more reliably closer to the Sun. Plasma and neutral gas instruments on the Comet Interceptor main spacecraft can monitor the entire flyby by using an adaptive data acquisition strategy in the context of a record-and-playback scenario. For probes released from the main spacecraft, the inter-satellite communication link limits the data return. For a slow flyby of an active comet, the probes may not yet be released during the inbound bow shock crossing.

  • Journal article
    Zhou Y, He F, Archer MO, Zhang X, Hao YX, Yao Z, Rong Z, Wei Yet al., 2024,

    Spatial Evolution Characteristics of Plasmapause Surface Wave During a Geomagnetic Storm on 16 July 2017

    , Geophysical Research Letters, Vol: 51, ISSN: 0094-8276

    <jats:title>Abstract</jats:title><jats:p>Boundary dynamics are crucial for the transport of energy, mass, and momentum in geospace. The recently discovered plasmapause surface wave (PSW) plays a key role in the inner magnetosphere dynamics. However, a comprehensive investigation of spatial variations of the PSW remains absent. In this study, we elucidate the spatial characteristics of a PSW through observations from multiple spacecrafts in the magnetosphere. Following the initiation of the PSW, quasi‐periodic injections of energetic ions, rather than electrons, are suggested to serve as energy source of the PSW. Based on the distinct wave and particle signatures, we categorize the PSW into four regions: seed region, growth region, stabilization region and decay region, spanning from nightside to afternoon plasmapause. These findings advance our understanding of universal boundary dynamics and contribute to a deeper comprehension of the pivotal roles of surface waves in the energy couplings within the magnetosphere‐plasmasphere‐ionosphere system.</jats:p>

  • Journal article
    Mitchell DG, Hill ME, McComas DJ, Cohen CMS, Schwadron NA, Mostafavi PS, Matthaeus WH, Raouafi NE, Al-Nussirat ST, Larson DE, Rahmati A, Kasper JC, Whittlesey PL, Livi R, Bale SD, Pulupa M, Giacalone J, McNutt RL, Christian ER, Wiedenbeck ME, Sharma Tet al., 2024,

    Likely Common Coronal Source of Solar Wind and <sup>3</sup>He-enriched Energetic Particles: Uncoupled Transport from the Low Corona to 0.2 au

    , Astrophysical Journal, Vol: 965, ISSN: 0004-637X

    Parker Solar Probe (PSP) observations of a small dispersive event on 2022 February 27 and 28 indicate scatter-free propagation as the dominant transport mechanism between the low corona and greater than 35 solar radii. The event occurred during unique orbital conditions that prevailed along specific flux tubes that PSP encountered repeatedly between 25 and 35 Rs during outbound orbit 11. This segment of the PSP orbit exhibits almost stationary angular motion relative to the rotating solar surface, such that in the rotating frame, PSP’s motion is essentially radial. The time dispersion often observed in impulsive solar energetic particle (SEP) events continues in this case down to velocities including the core solar-wind ion velocities. Especially at the onset of this event, the 3He content is much larger than the usual SEP abundances seen in the energy range from ∼100 keV to several MeV for helium. Later in the event, iron is enhanced. The compositional signatures suggest this to be an example of an acceleration mechanism for generating the seed energetic particles required by shock (or compression) acceleration models in SEP events to account for the enrichment of various species above solar abundances in such events. A preliminary search of similar orbital conditions over the PSP mission has not revealed additional such events, although favorable conditions (isolated impulsive acceleration and well-ordered magnetic field connection with minimal magnetic field fluctuation) that would be required are infrequently realized, given the small fraction of the PSP trajectory that meets these observation conditions.

  • Journal article
    Eriksson S, Swisdak M, Mallet A, Kruparova O, Livi R, Romeo O, Bale SD, Kasper JC, Larson DE, Pulupa Met al., 2024,

    Parker Solar Probe Observations of Magnetic Reconnection Exhausts in Quiescent Plasmas near the Sun

    , Astrophysical Journal, Vol: 965, ISSN: 0004-637X

    Parker Solar Probe observations are analyzed for the presence of reconnection exhausts across current sheets (CSs) within R < 0.26 au during encounters 4-11. Exhausts are observed with nearly equal probability at all radial distances with a preference for quiescent Tp < 0.80 MK plasmas typical of a slow-wind regime. High Tp > 0.80 MK plasmas of a fast wind characterized by significant transverse fluctuations rarely support exhausts irrespective of the CS width. Exhaust observations demonstrate the presence of local temperature gradients across several CSs with a higher-Tp plasma on locally closed fields and a lower-Tp plasma on locally open field lines for an interchange-type reconnection. A CS geometry analysis directly supports the property that X-lines bisect the magnetic field rotation θ-angle, whether the fields and plasmas are asymmetric or not, to maximize reconnection rates and available magnetic energy. The CS normal width d cs distributions suggest that a multiscale reconnection process through nested layers of bifurcated CSs may be responsible for observed power-law distributions beyond the median d cs ∼ 1000 km with an exponential d cs distribution present for ion kinetic dissipation scales below this median. Magnetic field shear θ-angles are essentially identical at R < 0.26 and 1 au with medians at θ ∼ 55° near the Sun and θ ∼ 65° at 1 au. In contrast, the tangential flow shear distributions are different near and far from the Sun. A bimodal flow shear angle distribution is present near the Sun with strong shear flow magnitudes. This distribution is modified with radial distance toward a relatively flat distribution of weaker flow shear magnitudes.

  • Journal article
    Stephenson P, Galand M, Deca J, Henri Pet al., 2024,

    Cold electrons at a weakly outgassing comet

    , Monthly Notices of the Royal Astronomical Society, Vol: 529, Pages: 2854-2865, ISSN: 0035-8711

    Throughout the Rosetta mission, cold electrons (<1 eV) were measured in the coma of comet 67P/Churyumov–Gerasimenko. Cometary electrons are produced at ∼10 eV through photoionization or through electron-impact ionization collisions. The cold electron population is formed by cooling the warm population through inelastic electron–neutral collisions. Assuming radial electron outflow, electrons are collisional with the neutral gas coma below the electron exobase, which only formed above the comet surface in near-perihelion high-outgassing conditions (Q > 3 × 1027 s−1). However, the cold population was identified at low outgassing (Q < 1026 s−1), when the inner coma was not expected to be collisional. We examine cooling of electrons at a weakly outgassing comet, using a 3D collisional model of electrons at a comet. Electron paths are extended by trapping in an ambipolar electric field and by gyration around magnetic field lines. This increases the probability of electrons undergoing inelastic collisions with the coma and becoming cold. We demonstrate that a cold electron population can be formed and sustained, under weak outgassing conditions (Q = 1026 s−1), once 3D electron dynamics are accounted for. Cold electrons are produced in the inner coma through electron–neutral collisions and transported tailwards by an E × B drift We quantify the efficiency of trapping in driving electron cooling, with trajectories typically 100 times longer than expected from ballistic radial outflow. Based on collisional simulations, we define an estimate for a region where a cold electron population can form, bounded by an electron cooling exobase. This estimate agrees well with cold electron measurements from the Rosetta Plasma Consortium.

  • Journal article
    Fiedler S, Naik V, O'Connor FM, Smith CJ, Griffiths P, Kramer RJ, Takemura T, Allen RJ, Im U, Kasoar M, Modak A, Turnock S, Voulgarakis A, Watson-Parris D, Westervelt DM, Wilcox LJ, Zhao A, Collins WJ, Schulz M, Myhre G, Forster PMet al., 2024,

    Interactions between atmospheric composition and climate change - progress in understanding and future opportunities from AerChemMIP, PDRMIP, and RFMIP

    , Geoscientific Model Development, Vol: 17, Pages: 2387-2417, ISSN: 1991-959X

    The climate science community aims to improve our understanding of climate change due to anthropogenic influences on atmospheric composition and the Earth's surface. Yet not all climate interactions are fully understood, and uncertainty in climate model results persists, as assessed in the latest Intergovernmental Panel on Climate Change (IPCC) assessment report. We synthesize current challenges and emphasize opportunities for advancing our understanding of the interactions between atmospheric composition, air quality, and climate change, as well as for quantifying model diversity. Our perspective is based on expert views from three multi-model intercomparison projects (MIPs) - the Precipitation Driver Response MIP (PDRMIP), the Aerosol Chemistry MIP (AerChemMIP), and the Radiative Forcing MIP (RFMIP). While there are many shared interests and specializations across the MIPs, they have their own scientific foci and specific approaches. The partial overlap between the MIPs proved useful for advancing the understanding of the perturbation-response paradigm through multi-model ensembles of Earth system models of varying complexity. We discuss the challenges of gaining insights from Earth system models that face computational and process representation limits and provide guidance from our lessons learned. Promising i

  • Journal article
    Feingold G, Ghate VP, Russell LM, Blossey P, Cantrell W, Christensen MW, Diamond MS, Gettelman A, Glassmeier F, Gryspeerdt E, Haywood J, Hoffmann F, Kaul CM, Lebsock M, McComiskey AC, McCoy DT, Ming Y, Mülmenstädt J, Possner A, Prabhakaran P, Quinn PK, Schmidt KS, Shaw RA, Singer CE, Sorooshian A, Toll V, Wan JS, Wood R, Yang F, Zhang J, Zheng Xet al., 2024,

    Physical science research needed to evaluate the viability and risks of marine cloud brightening.

    , Sci Adv, Vol: 10

    Marine cloud brightening (MCB) is the deliberate injection of aerosol particles into shallow marine clouds to increase their reflection of solar radiation and reduce the amount of energy absorbed by the climate system. From the physical science perspective, the consensus of a broad international group of scientists is that the viability of MCB will ultimately depend on whether observations and models can robustly assess the scale-up of local-to-global brightening in today's climate and identify strategies that will ensure an equitable geographical distribution of the benefits and risks associated with projected regional changes in temperature and precipitation. To address the physical science knowledge gaps required to assess the societal implications of MCB, we propose a substantial and targeted program of research-field and laboratory experiments, monitoring, and numerical modeling across a range of scales.

  • Journal article
    Matteini L, Tenerani A, Landi S, Verdini A, Velli M, Hellinger P, Franci L, Horbury TS, Papini E, Stawarz JEet al., 2024,

    Alfvénic fluctuations in the expanding solar wind: Formation and radial evolution of spherical polarization

    , Physics of Plasmas, Vol: 31, ISSN: 1070-664X

    We investigate properties of large-scale solar wind Alfvénic fluctuations and their evolution during radial expansion. We assume a strictly radial background magnetic field B ∥ R , and we use two-dimensional hybrid (fluid electrons, kinetic ions) simulations of balanced Alfvénic turbulence in the plane orthogonal to B ; the simulated plasma evolves in a system comoving with the solar wind (i.e., in the expanding box approximation). Despite some model limitations, simulations exhibit important properties observed in the solar wind plasma: Magnetic field fluctuations evolve toward a state with low-amplitude variations in the amplitude B = | B | and tend to a spherical polarization. This is achieved in the plasma by spontaneously generating field aligned, radial fluctuations that suppress local variations of B, maintaining B ∼ const. spatially in the plasma. We show that within the constraint of spherical polarization, variations in the radial component of the magnetic field, BR lead to a simple relation between δ B R and δ B = | δ B | as δ B R ∼ δ B 2 / ( 2 B ) , which correctly describes the observed evolution of the rms of radial fluctuations in the solar wind. During expansion, the background magnetic field amplitude decreases faster than that of fluctuations so that their the relative amplitude increases. In the regime of strong fluctuations, δ B ∼ B , this causes local magnetic field reversals, consistent with solar wind switchbacks.

  • Journal article
    Kuhlbrodt T, Swaminathan R, Ceppi P, Wilder Tet al., 2024,

    A Glimpse into the Future The 2023 Ocean Temperature and Sea Ice Extremes in the Context of Longer-Term Climate Change

    , Bulletin of the American Meteorological Society, Vol: 105, Pages: E474-E485, ISSN: 0003-0007

    In the year 2023, we have seen extraordinary extrema in high sea surface temperature (SST) in the North Atlantic and in low sea ice extent in the Southern Ocean, outside the 4σ envelope of the 1982–2011 daily time series. Earth’s net global energy imbalance (12 months up to September 2023) amounts to +1.9 W m−2 as part of a remarkably large upward trend, ensuring further heating of the ocean. However, the regional radiation budget over the North Atlantic does not show signs of a suggested significant step increase from less negative aerosol forcing since 2020. While the temperature in the top 100 m of the global ocean has been rising in all basins since about 1980, specifically the Atlantic basin has continued to further heat up since 2016, potentially contributing to the extreme SST. Similarly, salinity in the top 100 m of the ocean has increased in recent years specifically in the Atlantic basin, and in addition in about 2015 a substantial negative trend for sea ice extent in the Southern Ocean began. Analyzing climate and Earth system model simulations of the future, we find that the extreme SST in the North Atlantic and the extreme in Southern Ocean sea ice extent in 2023 lie at the fringe of the expected mean climate change for a global surface-air temperature warming level (GWL) of 1.5°C, and closer to the average at a 3.0°C GWL. Understanding the regional and global drivers of these extremes is indispensable for assessing frequency and impacts of similar events in the coming years.

  • Journal article
    Kellogg PJ, Mozer FS, Moncuquet M, Malaspina DM, Halekas J, Bale SD, Goetz Ket al., 2024,

    Heating and Acceleration of the Solar Wind by Ion Acoustic Waves—Parker Solar Probe

    , Astrophysical Journal, Vol: 964, ISSN: 0004-637X

    The heating of the solar wind has been shown to be correlated with certain ion acoustic waves. Here calculations of the heating are made, using the methods used previously for STEREO observations, which show that the strong damping of ion acoustic waves rapidly delivers their energy to the plasma of the solar wind. It is shown that heating by the observed waves is not only sufficient to produce the observed heating but can also provide much or all of the outward acceleration of the solar wind.

  • Journal article
    Johnson M, Rivera YJ, Niembro T, Paulson K, Badman ST, Stevens ML, Dieguez I, Case A, Bale SD, Kasper Jet al., 2024,

    Helium Abundance Periods Observed by the Solar Probe Cup on Parker Solar Probe: Encounters 1-14

    , Astrophysical Journal, Vol: 964, ISSN: 0004-637X

    Parker Solar Probe is a mission designed to explore the properties of the solar wind closer than ever before. Detailed particle observations from the Solar Probe Cup (SPC) have primarily focused on examining the proton population in the solar wind. However, several periods throughout the Parker mission have indicated that SPC has observed a pronounced and distinctive population of fully ionized helium, He2+. Minor ions are imprinted with properties of the solar wind’s source region, as well as mechanisms active during outflow, making them sensitive markers of its origin and formation at the Sun. Through a detailed analysis of the He2+ velocity distributions functions, this work examines periods where significant and persistent He2+ peaks are observed with SPC. We compute the helium abundance and examine the stream’s bulk speed, density, temperature, magnetic field topology, and electron strahl properties to identify distinctive solar-wind features that can provide insight to their solar source. We find that nearly all periods exhibit an elevated mean helium composition (8.34%) compared to typical solar wind and a majority (∼87%) of these periods are connected to coronal mass ejections (CMEs), with the highest abundance reaching 23.1%. The helium abundance and number of events increases as the solar cycle approaches maximum, with a weak dependence on speed. Additionally, the events not associated with a CME are clustered near the heliospheric current sheet, suggesting they are connected to streamer belt outflows. However, there are currently no theoretical explanations that fully describe the range of depleted and elevated helium abundances observed.

  • Journal article
    Grimmich N, Prencipe F, Turner DL, Liu TZ, Plaschke F, Archer MO, Nakamura R, Sibeck DG, Mieth JZD, Auster HU, Constantinescu OD, Fischer D, Magnes Wet al., 2024,

    Multi Satellite Observation of a Foreshock Bubble Causing an Extreme Magnetopause Expansion

    , Journal of Geophysical Research: Space Physics, Vol: 129, ISSN: 2169-9380

    The interaction of a solar wind discontinuity with the backstreaming particles of the Earth’s ion foreshock can generate hot, tenuous plasma transients such as foreshock bubbles (FB) and hot flow anomalies (HFA). These transients are known to have strong effects on the magnetosphere, distorting the magnetopause (MP), either locally during HFAs or globally during FBs. However, previous studies on the global impact of FBs have not been able to determine whether the response stems directly from the transverse scale size of the phenomenon or its fast motion over the magnetosphere. Here we present the observation of an FB and its impact on the magnetosphere from different spacecraft scattered over the dayside magnetosphere. We are able to constrain the size of the transverse scale of an FB from direct observations to be about 10 RE. We go on to discuss how the magnetosphere responds to this transient, which seems to have a similar scale across the dayside.

  • Journal article
    Rojo M, Persson M, Sauvaud JA, Aizawa S, Nicolaou G, Penou E, Barthe A, André N, Mazelle C, Fedorov A, Yokota S, Saito Y, Heyner D, Richter I, Auster U, Schmid D, Fischer D, Horbury T, Owen CJ, Maksimovic M, Khotyaintsev Y, Louarn P, Murakami Get al., 2024,

    Electron moments derived from the Mercury Electron Analyzer during the cruise phase of BepiColombo

    , Astronomy and Astrophysics, Vol: 683, ISSN: 0004-6361

    Aims. We derive electron density and temperature from observations obtained by the Mercury Electron Analyzer on board Mio during the cruise phase of BepiColombo while the spacecraft is in a stacked configuration. Methods. In order to remove the secondary electron emission contribution, we first fit the core electron population of the solar wind with a Maxwellian distribution. We then subtract the resulting distribution from the complete electron spectrum, and suppress the residual count rates observed at low energies. Hence, our corrected count rates consist of the sum of the fitted Maxwellian core electron population with a contribution at higher energies. We finally estimate the electron density and temperature from the corrected count rates using a classical integration method. We illustrate the results of our derivation for two case studies, including the second Venus flyby of BepiColombo when the Solar Orbiter spacecraft was located nearby, and for a statistical study using observations obtained to date for distances to the Sun ranging from 0.3 to 0.9 AU. Results. When compared either to measurements of Solar Orbiter or to measurements obtained by HELIOS and Parker Solar Probe, our method leads to a good estimation of the electron density and temperature. Hence, despite the strong limitations arising from the stacked configuration of BepiColombo during its cruise phase, we illustrate how we can retrieve reasonable estimates for the electron density and temperature for timescales from days down to several seconds.

  • Journal article
    Coburn JT, Verscharen D, Owen CJ, Maksimovic M, Horbury TS, Chen CHK, Guo F, Fu X, Liu J, Abraham JB, Nicolaou G, Innocenti ME, Micera A, Jagarlamudi VKet al., 2024,

    The Regulation of the Solar Wind Electron Heat Flux by Wave-Particle Interactions

    , Astrophysical Journal, Vol: 964, ISSN: 0004-637X

    The solar wind electrons carry a significant heat flux into the heliosphere. The weakly collisional state of the solar wind implicates collisionless processes as the primary factor that constrains nonthermal features of the velocity distribution function (VDF), including the heat flux. Previous observational work suggests that the electron VDF sometimes becomes unstable to the whistler wave, but reliance on model VDFs (e.g., drifting bi-Maxwellians) has proven insufficient for an exact description of the behavior of the solar wind electrons—in particular, the regulation of the heat flux. The characterization of these processes requires methods to obtain fine details of the VDF and quantification of the impact of kinetic processes on the VDF. We employ measurements of the electron VDF by Solar Orbiter’s Solar Wind Analyser and of the magnetic field by the Radio and Plasma Waves instrument to study an unstable solar wind electron configuration. Through a Hermite-Laguerre expansion of the VDF, we implement a low-pass filter in velocity space to remove velocity space noise and obtain a VDF suitable for analysis. With our method, we directly measure the instability growth rate and the rate of change of the electron heat flux through wave-particle interactions.

  • Journal article
    Sishtla CP, Pomoell J, Magyar N, Kilpua E, Good Set al., 2024,

    Validity of using Elsässer variables to study the interaction of compressible solar wind fluctuations with a coronal mass ejection

    , Astronomy and Astrophysics, Vol: 683, ISSN: 0004-6361

    Context. Alfvénic fluctuations, as modelled by the non-linear interactions of AlfvÉn waves of various scales, are seen to dominate solar wind turbulence. However, there is also a non-negligible component of non-Alfvénic fluctuations. The Elsässer formalism, which is central to the study of Alfvénic turbulence due to its ability to differentiate between parallel and anti-parallel Alfvén waves, cannot strictly separate wavemodes in the presence of compressive magnetoacoustic waves. In this study, we analyse the deviations generated in the Elsässer formalism as density fluctuations are naturally generated through the propagation of a linearly polarised Alfvén wave. The study was performed in the context of a coronal mass ejection (CME) propagating through the solar wind, which enables the creation of two solar wind regimes, pristine wind and a shocked CME sheath, where the Elsässer formalism can be evaluated. Aims. We studied the deviations of the Elsässer formalism in separating parallel and anti-parallel components of AlfvÉnic solar wind perturbations generated by small-amplitude density fluctuations. Subsequently, we evaluated how the deviations cause a misinterpretation of the composition of waves through the parameters of cross helicity and reflection coeffcient. Methods.We used an ideal 2.5D magnetohydrodynamic model with an adiabatic equation of state. An AlfvÉn pump wave was injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components. This wave subsequently generates density fluctuations through the ponderomotive force. A CME was injected by inserting a flux-rope modelled as a magnetic island into the quasi-steady solar wind. Results. The presence of density perturbations creates a ≈10% deviation in the Elsässer variables and reflection coeffcient for the AlfvÉn waves as well as a deviation of ≈0.1 in the cross helicity

  • Journal article
    Liu YD, Zhu B, Ran H, Hu H, Liu M, Zhao X, Wang R, Stevens ML, Bale SDet al., 2024,

    Direct In Situ Measurements of a Fast Coronal Mass Ejection and Associated Structures in the Corona

    , Astrophysical Journal, Vol: 963, ISSN: 0004-637X

    We report on the first direct in situ measurements of a fast coronal mass ejection (CME) and shock in the corona, which occurred on 2022 September 5. In situ measurements from the Parker Solar Probe spacecraft near perihelion suggest two shocks, with the second one decayed, which is consistent with more than one eruption in coronagraph images. Despite a flank crossing, the measurements indicate unique features of the young ejecta: a plasma much hotter than the ambient medium, suggestive of a hot solar source, and a large plasma β implying a highly non-force-free state and the importance of thermal pressure gradient for CME acceleration and expansion. Reconstruction of the global coronal magnetic fields shows a long-duration change in the heliospheric current sheet (HCS), and the observed field polarity reversals agree with a more warped HCS configuration. Reconnection signatures are observed inside an HCS crossing as deep as the sonic critical point. As the reconnection occurs in the sub-Alfvénic wind, the reconnected flux sunward of the reconnection site can close back to the Sun, which helps balance magnetic flux in the heliosphere. The nature of the sub-Alfvénic wind after the HCS crossing as a low Mach-number boundary layer (LMBL) leads to in situ measurements of the near subsonic plasma at a surprisingly large distance. Specifically, an LMBL may provide favorable conditions for the crossings of the sonic critical point in addition to the Alfvén surface.

  • Journal article
    Heinemann SG, Sishtla C, Good S, Grandin M, Pomoell Jet al., 2024,

    Classification of Enhanced Geoeffectiveness Resulting from High-speed Solar Wind Streams Compressing Slower Interplanetary Coronal Mass Ejections

    , Astrophysical Journal Letters, Vol: 963, ISSN: 2041-8205

    High-speed solar wind streams (HSSs) interact with the preceding ambient solar wind to form stream interaction regions (SIRs), which are a primary source of recurrent geomagnetic storms. However, HSSs may also encounter and subsequently interact with interplanetary coronal mass ejections (ICMEs). In particular, the impact of the interaction between slower ICMEs and faster HSSs represents an unexplored area that requires further in-depth investigation. This specific interaction can give rise to unexpected geomagnetic storm signatures, diverging from the conventional expectations of individual SIR events sharing similar HSS properties. Our study presents a comprehensive analysis of solar wind data spanning from 1996 to 2020, capturing 23 instances where such encounters led to geomagnetic storms (SymH < −30 nT). We determined that interaction events between preceding slower ICMEs and faster HSSs possess the potential to induce substantial storm activity, statistically nearly doubling the geoeffective impact in comparison to SIR storm events. The increase in the amplitude of the SymH index appears to result from heightened dynamic pressure, often coupled with the concurrent amplification of the CMEs rearward |B| and/or Bz components.

  • Journal article
    Blackford K, Kasoar M, Burton C, Burke E, Prentice IC, Voulgarakis Aet al.,

    INFERNO-peat v1.0.0: a representation of northern high latitude peat fires in the JULES-INFERNO global fire model

    , Geoscientific Model Development, ISSN: 1991-959X
  • Journal article
    Trotta D, Larosa A, Nicolaou G, Horbury TS, Matteini L, Hietala H, Blanco-Cano X, Franci L, Chen CHK, Zhao L, Zank GP, Cohen CMS, Bale SD, Laker R, Fargette N, Valentini F, Khotyaintsev Y, Kieokaew R, Raouafi N, Davies E, Vainio R, Dresing N, Kilpua E, Karlsson T, Owen CJ, Wimmer-Schweingruber RFet al., 2024,

    Properties of an Interplanetary Shock Observed at 0.07 and 0.7 au by Parker Solar Probe and Solar Orbiter

    , The Astrophysical Journal, Vol: 962, Pages: 147-147, ISSN: 0004-637X

    <jats:title>Abstract</jats:title> <jats:p>The Parker Solar Probe (PSP) and Solar Orbiter (SolO) missions opened a new observational window in the inner heliosphere, which is finally accessible to direct measurements. On 2022 September 5, a coronal mass ejection (CME)-driven interplanetary (IP) shock was observed as close as 0.07 au by PSP. The CME then reached SolO, which was radially well-aligned at 0.7 au, thus providing us with the opportunity to study the shock properties at different heliocentric distances. We characterize the shock, investigate its typical parameters, and compare its small-scale features at both locations. Using the PSP observations, we investigate how magnetic switchbacks and ion cyclotron waves are processed upon shock crossing. We find that switchbacks preserve their V–B correlation while compressed upon the shock passage, and that the signature of ion cyclotron waves disappears downstream of the shock. By contrast, the SolO observations reveal a very structured shock transition, with a population of shock-accelerated protons of up to about 2 MeV, showing irregularities in the shock downstream, which we correlate with solar wind structures propagating across the shock. At SolO, we also report the presence of low-energy (∼100 eV) electrons scattering due to upstream shocklets. This study elucidates how the local features of IP shocks and their environments can be very different as they propagate through the heliosphere.</jats:p>

  • Journal article
    Mostafavi P, Allen RC, Jagarlamudi VK, Bourouaine S, Badman ST, Ho GC, Raouafi NE, Hill ME, Verniero JL, Larson DE, Kasper JC, Bale SDet al., 2024,

    Parker Solar Probe observations of collisional effects on thermalizing the young solar wind

    , Astronomy and Astrophysics, Vol: 682, ISSN: 0004-6361

    Solar wind ions exhibit distinct kinetic non-thermal features such as preferential heating and acceleration of alpha particles compared to protons. On the other hand, Coulomb collisions in the solar wind act to eliminate these non-thermal features and gradually lead to thermal equilibrium. Previous observations at 1 au have revealed that even though the local Coulomb collisions in the solar wind plasma are rare, the cumulative effect of the collisions during a transit time of a particle can be important in terms of thermalizing the solar wind plasma populations and reducing the ion non-thermal features. Here, we analyze Parker Solar Probe observations to study the effects of Coulomb collisions on the non-thermal features (alpha-to-proton temperature ratio and differential flow) of young solar wind closer to the Sun than previously possible. Our results show that even close to the Sun (~15Rs), these non-thermal features are organized by collisionality. Moreover, observations at these unprecedented distances allow us to investigate the preferential heating of the alpha particles close to the source for both fast and slow wind streams. We show that the alpha-to-proton temperature ratio is positively correlated with the solar wind speed, which is consistent with Wind observations. Solar wind close to the Sun is less collisionally old than when it reaches 1 au. As such, observed differences in the temperature ratio between slow and fast streams near their solar source suggest causes that go beyond different Coulomb numbers. Our results suggest that slow and fast wind streams, originating from different solar regions, may have different mechanisms for the preferential heating of alpha particles compared to protons.

  • Journal article
    Laker R, Horbury TS, OBrien H, Fauchon-Jones EJ, Angelini V, Fargette N, Amerstorfer T, Bauer M, Möstl C, Davies EE, Davies JA, Harrison R, Barnes D, Dumbović Met al., 2024,

    Using Solar Orbiter as an Upstream Solar Wind Monitor for Real Time Space Weather Predictions

    , Space Weather, Vol: 22

    Coronal mass ejections (CMEs) can create significant disruption to human activities and systems on Earth, much of which can be mitigated with prior warning of the upstream solar wind conditions. However, it is currently extremely challenging to accurately predict the arrival time and internal structure of a CME from coronagraph images alone. In this study, we take advantage of a rare opportunity to use Solar Orbiter, at 0.5 au upstream of Earth, as an upstream solar wind monitor. In combination with low-latency images from STEREO-A, we successfully predicted the arrival time of two CME events before they reached Earth. Measurements at Solar Orbiter were used to constrain an ensemble of simulation runs from the ELEvoHI model, reducing the uncertainty in arrival time from 10.4 to 2.5 hr in the first case study. There was also an excellent agreement in the Bz profile between Solar Orbiter and Wind spacecraft for the second case study, despite being separated by 0.5 au and 10° longitude. The opportunity to use Solar Orbiter as an upstream solar wind monitor will repeat once a year, which should further help assess the efficacy upstream in-situ measurements in real time space weather forecasting.

  • Journal article
    Laker R, Horbury TS, Woodham LD, Bale SD, Matteini Let al., 2024,

    Coherent deflection patternãndãssociated temperature enhancements in the near-Sun solar wind

    , Monthly Notices of the Royal Astronomical Society, Vol: 527, Pages: 10440-10447, ISSN: 0035-8711

    Measurements of transverse magnetic fieldãnd velocity components from Parker Solar Probe hav e rev ealedã coherent quasi- periodic pattern in the near-Sun solar wind. As wellãs being Alfvénicãndãrc-polarized, these deflections were characterized byã consistent orientationãndãn increased proton core temperature, which was greater parallel to the magnetic field. We show that switchbacks represent the largest deflections within this underlying structure, which is itself consistent with the expected outflow from interchange reconnection simulations. Additionally, the spatial scale of the deflections was estimated to beãround 1 Mm on the Sun, comparable to the jettingãctivity observedãt coronal bright points within the base of coronal plumes. Therefore, our results could represent the in situ signature of interchange reconnection from coronal bright points within plumes, complementing recent numericalãnd observational studies. Weãlso foundã consistent relationship between the proton core temperatureãnd magnetic fieldãngleãcross the Parker Solar Probe encountersãnd discussed how suchã persistent signature could be more indicative ofãn in situ mechanism creatingã local increase in temperature. In future, observations of minor ions, radio bursts,ãnd remote sensing images could help further establish the connection between reconnection events on the Sunãnd signatures in the solar wind.

  • Journal article
    Louarn P, Fedorov A, Prech L, Owen CJ, D'Amicis R, Bruno R, Livi S, Lavraud B, Rouillard AP, Génot V, André N, Fruit G, Réville V, Kieokaew R, Plotnikov I, Penou E, Barthe A, Lewis G, Berthomier M, Allegrini F, Alterman BL, Lepri ST, Raines JM, Verscharen D, Mele G, Fargette N, Horbury TS, Maksimovic M, Kasper JC, Bale SDet al., 2024,

    Skewness and kurtosis of solar wind proton distribution functions: The normal inverse-Gaussian model and its implications

    , Astronomy and Astrophysics, Vol: 682, ISSN: 0004-6361

    Context. In the solar wind (SW), the particle distribution functions are generally not Gaussian. They present nonthermal features that are related to underlying acceleration and heating processes. These processes are critical in the overall dynamics of this expanding astrophysical fluid. Aims. The Proton Alpha Sensor (PAS) on board Solar Orbiter commonly observes skewed proton distributions, with a more populated high-energy side in the magnetic field direction than the Gaussian distribution. Our objectives are: (1) to identify a theoretical statistical function that adequately models the observed distributions and (2) to use its statistical interpretation to constrain the acceleration and heating processes. Methods. We analyzed the 3D velocity distribution functions (VDFs) measured by PAS and compared them to model statistical functions. Results. We show that the normal inverse Gaussian (NIG), a type of hyperbolic statistical distribution, provides excellent fits of skewed and leptokurtic proton distributions. NIG can model both the core distribution and the beam, if present. We propose an interpretation that is inspired by the mathematical formulation of the NIG. It assumes that the acceleration or heating mechanism can be modeled as a drifting diffusion process in velocity space, controlled (or subordinated) by the time of interaction of the particles with "accelerating structures". The probability function of the interaction time is an inverse Gaussian (IG), obtained by considering a random drift across structures of a given size. The control of the diffusion by interaction times that follow an IG probability function formally defines the NIG distribution. Following this model, we show that skewness and kurtosis can be used to estimate the kinetic and thermal energy gains provided by the interaction with structures. For example, in the case studies presented here, the analyzed populations would have gained kinetic energy representing approximately two

  • Journal article
    Wells CD, Kasoar M, Ezzati M, Voulgarakis Aet al., 2024,

    Significant human health co-benefits of mitigating African emissions

    , Atmospheric Chemistry and Physics, Vol: 24, Pages: 1025-1039, ISSN: 1680-7316

    Future African aerosol emissions, and therefore air pollution levels and health outcomes, are uncertain and understudied. Understanding the future health impacts of pollutant emissions from this region is crucial. Here, this research gap is addressed by studying the range in the future health impacts of aerosol emissions from Africa in the Shared Socioeconomic Pathway (SSP) scenarios, using the UK Earth System Model version 1 (UKESM1), along with human health concentration-response functions. The effects of Africa following a high-pollution aerosol pathway are studied relative to a low-pollution control, with experiments varying aerosol emissions from industry and biomass burning. Using present-day demographics, annual deaths within Africa attributable to ambient particulate matter are estimated to be lower by 150 000 (5th-95th confidence interval of 67 000-234 000) under stronger African aerosol mitigation by 2090, while those attributable to O3 are lower by 15 000 (5th-95th confidence interval of 9000-21 000). The particulate matter health benefits are realised predominantly within Africa, with the O3-driven benefits being more widespread - though still concentrated in Africa - due to the longer atmospheric lifetime of O3. These results demonstrate the important health co-benefits from future emission mitigation in Africa.

  • Journal article
    Smith AW, Rae IJ, Stawarz JE, Sun WJ, Bentley S, Koul Aet al., 2024,

    Automatic Encoding of Unlabeled Two Dimensional Data Enabling Similarity Searches: Electron Diffusion Regions and Auroral Arcs

    , Journal of Geophysical Research: Space Physics, Vol: 129, ISSN: 2169-9380

    Critically important phenomena in Earth’s magnetosphere often occur briefly, or in small spatial regions. These processes are sampled with orbiting spacecraft or by fixed ground observatories and so rarely appear in data. Identifying such intervals can be an incredibly time consuming task. We apply a novel, powerful method by which two dimensional data can be automatically processed and embeddings created that contain key features of the data. The distance between embedding vectors serves as a measure of similarity. We apply the state-of-the-art method to two example datasets: MMS electron velocity distributions and auroral all sky images. We show that the technique creates embeddings that group together visually similar observations. When provided with novel example images the method correctly identifies similar intervals: when provided with an electron distribution sampled during an encounter with an electron diffusion region the method recovers similar distributions obtained during two other known diffusion region encounters. Similarly, when provided with an interesting auroral structure the method highlights the same structure observed from an adjacent location and at other close time intervals. The method promises to be a useful tool to expand interesting case studies to multiple events, without requiring manual data labeling. Further, the models could be fine-tuned with relatively small set of labeled example data to perform tasks such as classification. The embeddings can also be used as input to deep learning models, providing a key intermediary step—capturing the key features within the data.

  • Journal article
    McManus MD, Klein KG, Bale SD, Bowen TA, Huang J, Larson D, Livi R, Rahmati A, Romeo O, Verniero J, Whittlesey Pet al., 2024,

    Proton- and Alpha-driven Instabilities in an Ion Cyclotron Wave Event

    , Astrophysical Journal, Vol: 961, ISSN: 0004-637X

    Ion-scale wave events or wave storms in the solar wind are characterized by enhancements in magnetic field fluctuations as well as coherent magnetic field polarization signatures at or around the local ion cyclotron frequencies. In this paper, we study in detail one such wave event from Parker Solar Probe's (PSP) fourth encounter, consisting of an initial period of left-handed (LH) polarization abruptly transitioning to a strong period of right-handed (RH) polarization, accompanied by a clear core beam structure in both the alpha and proton velocity distribution functions. A linear stability analysis shows that the LH-polarized waves are anti-sunward propagating Alfvén/ion cyclotron waves primarily driven by a proton cyclotron instability in the proton core population, and the RH polarized waves are anti-sunward propagating fast magnetosonic/whistler waves driven by a firehose-like instability in the secondary alpha beam population. The abrupt transition from LH to RH is caused by a drop in the proton core temperature anisotropy. We find very good agreement between the frequencies and polarizations of the unstable wave modes as predicted by linear theory and those observed in the magnetic field spectra. Given the ubiquity of ion-scale wave signatures observed by PSP, this work gives insight into which exact instabilities may be active and mediating energy transfer in wave-particle interactions in the inner heliosphere, as well as highlighting the role a secondary alpha population may play as a rarely considered source of free energy available for producing wave activity.

  • Journal article
    Bowen TA, Bale SD, Chandran BDG, Chasapis A, Chen CHK, Dudok de Wit T, Mallet A, Meyrand R, Squire Jet al., 2024,

    Mediation of collisionless turbulent dissipation through cyclotron resonance

    , Nature Astronomy

    The dissipation of turbulence in astrophysical systems is fundamental to energy transfer and heating in environments ranging from the solar wind and corona to accretion disks and the intracluster medium. Although turbulent dissipation is relatively well understood in fluid dynamics, astrophysical plasmas often exhibit exotic behaviour, arising from the lack of interparticle collisions, which complicates turbulent dissipation and heating in these systems. Recent observations by NASA’s Parker Solar Probe mission in the inner heliosphere have shed new light on the role of ion cyclotron resonance as a potential candidate for turbulent dissipation and plasma heating. Here, using in situ observations of turbulence and wave populations, we show that ion cyclotron waves provide a major pathway for dissipation and plasma heating in the solar wind. Our results support recent theoretical predictions of turbulence in the inner heliosphere, known as the helicity barrier, that suggest a role of cyclotron resonance in ion-scale dissipation. Taken together, these results provide important constraints for turbulent dissipation and acceleration efficiency in astrophysical plasmas.

  • Journal article
    Chen L, Ma B, Wu DJ, Zhou X, Pulupa M, Zhang PJ, Zucca P, Bale SD, Kasper JC, Duan SPet al., 2024,

    Weak Solar Radio Bursts from the Solar Wind Acceleration Region Observed by the Parker Solar Probe and Its Probable Emission Mechanism

    , Astrophysical Journal, Vol: 961, ISSN: 0004-637X

    The Parker Solar Probe (PSP) provides us with an unprecedentedly close approach to the observation of the Sun and hence the possibility of directly understanding the elementary process that occurs on the kinetic scale of particles' collective interaction in solar coronal plasmas. We report a type of weak solar radio burst (SRB) that was detected by PSP when it passed a low-density magnetic channel during its second encounter phase. These weak SRBs have a low starting frequency of ∼20 MHz and a narrow frequency range from a few tens of MHz to a few hundred kHz. Their dynamic spectra display a strongly evolving feature of the intermediate relative drift rate decreasing rapidly from above 0.01 s−1 to below 0.01 s−1. Analyses based on common empirical models of solar coronal plasmas indicate that these weak SRBs originate from a heliocentric distance of ∼1.1-6.1 R S (the solar radius), a typical solar wind acceleration region with a low-β plasma, and that their sources have a typical motion velocity of ∼v A (Alfvén velocity) obviously lower than that of the fast electrons required to effectively excite SRBs. We propose that solitary kinetic Alfvén waves with kinetic scales could be responsible for the generation of these small-scale weak SRBs, called solitary wave radiation.

  • Journal article
    Krupar V, Kruparova O, Szabo A, Nemec F, Maksimovic M, Martinez Oliveros JC, Lario D, Bonnin X, Vecchio A, Pulupa M, Bale SDet al., 2024,

    Comparative Analysis of Type III Radio Bursts and Solar Flares: Spatial Localization and Correlation with Solar Flare Intensity

    , Astrophysical Journal, Vol: 961, ISSN: 0004-637X

    We present a comprehensive study of type III radio bursts and their association with solar flares of magnitude M1.0 and larger, as observed by four widely separated spacecraft (Parker Solar Probe, Solar Orbiter, STEREO-A, and Wind). Our main focus is the introduction and validation of two methods for localizing radio bursts using the available multispacecraft data. The first method utilizes intensity fitting with a circular Gaussian distribution, while the second method is based on the time arrival of radio bursts. We demonstrate the effectiveness of these methods through the analysis of a single type III burst event and compare their results with the traditional radio triangulation technique. Furthermore, we conduct a statistical study of 17 type III bursts associated with M- and X-class solar flares in years 2020-2022. Our findings suggest a possible correlation between solar flare intensities and longitudes, with east limb flares tending to be weaker than west limb flares. We also observe a systematic drift of radio burst longitudes toward the east, potentially explained by a poleward component of the local density gradient. Our results suggest a strong correlation between solar flare intensities and radio burst properties, enhancing our understanding of the relationship between solar flares and type III radio bursts.

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