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  • 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
    Bercic L, Maksimovic M, Halekas JS, Landi S, Owen CJ, Verscharen D, Larson D, Whittlesey P, Badman ST, Bale SD, Case AW, Goetz K, Harvey PR, Kasper JC, Korreck KE, Livi R, MacDowall RJ, Malaspina DM, Pulupa M, Stevens MLet al., 2021,

    Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions

    , ASTROPHYSICAL JOURNAL, Vol: 921, ISSN: 0004-637X
  • Journal article
    Chakravorty S, Perez RC, Anderson BT, Larson SM, Giese BS, Pivotti Vet al., 2021,

    Ocean Dynamics are Key to Extratropical Forcing of El Niño

    , Journal of Climate, Vol: 34, Pages: 8739-8753, ISSN: 0894-8755

    <jats:title>Abstract</jats:title><jats:p>El Niño–Southern Oscillation (ENSO) has been recently linked with extratropical Pacific Ocean atmospheric variability. The two key mechanisms connecting the atmospheric variability of the extratropical Pacific with ENSO are the heat flux–driven “seasonal footprinting mechanism” (SFM) and the ocean dynamics–driven “trade wind charging” (TWC) mechanism. However, their relative contributions to ENSO are still unknown. Here we present modeling evidence that the positive phase of the SFM generates a weaker, short-lived central Pacific El Niño–like warming pattern in the autumn, whereas the TWC positive phase leads to a wintertime eastern Pacific El Niño–like warming. When both mechanisms are active, a strong, persistent El Niño develops. While both mechanisms can trigger equatorial wind anomalies that generate an El Niño, the strength and persistence of the warming depends on the subsurface heat content buildup by the TWC mechanism. These results suggest that while dynamical coupling associated with extratropical forcing is crucial to maintain an El Niño, thermodynamical coupling is an extratropical source of El Niño diversity.</jats:p>
  • Journal article
    Chakravorty S, Perez RC, Gnanaseelan C, Anderson BTet al., 2021,

    Revisiting the Recharge and Discharge Processes for Different Flavors of El Niño

    , Journal of Geophysical Research: Oceans, Vol: 126, ISSN: 2169-9275

    <jats:title>Abstract</jats:title><jats:p>El Niño‐related sea surface temperature (SST) anomalies over the tropical Pacific Ocean impact global climates, but these impacts differ substantially for conventional cold tongue El Niño (CT El Niño) and the central Pacific El Niño (CP El Niño) events. This study is motivated by the need for a better understanding of the recharge/discharge processes associated with these two different flavors of El Niño. Composite analysis based on improved CT and CP El Niño identification methods applied to the Simple Ocean Data Assimilation demonstrates that the recharge/discharge processes are active during CT El Niño events. In contrast, for CP El Niño events, the recharge/discharge processes do not play a significant role. Prior to a CT El Niño, warm water accumulates over the western Pacific due to off‐equatorial anticyclonic wind stress curl. The onset of a CT El Niño is closely associated with the formation of a cyclonic atmospheric circulation over the northwest Pacific in the winter and spring, which induces westerly wind anomalies in the equatorial western Pacific and initiates eastward warm water transport. This leads to peak warming in the eastern equatorial Pacific the following winter, followed by the poleward discharge of warm water. This quasi‐cyclical behavior provides a measure of predictability. In contrast, the CP El Niño events do not show a precursor subsurface warming signal along the tropical Pacific thermocline. Instead, modest warm SST anomalies appear in boreal summer and peak in the fall, with weak subsurface warming mainly in the fall during CP El Niños. Hence, CP El Niños are less predictable in terms of an equatorial thermocline precursor than CT El Niño events.</jats:p>
  • Journal article
    Palmerio, Nieves-Chinchilla, Kilpua, Barnes D, Zhukov, Jian, Witasse, Provan, Tao, Lamy, Bradley, Mays, Mostl, Roussos, Futaana, Masters A, Sanchez-Canoet al., 2021,

    Magnetic structure and propagation of two interacting CMEs from the Sun to Saturn

    , Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-28, ISSN: 2169-9380

    One of the grand challenges in heliophysics is the characterization of coronal mass ejection (CME) magnetic structure and evolution from eruption at the Sun through heliospheric propagation. At present, the main difficulties are related to the lack of direct measurements of the coronal magnetic fields and the lack of 3D in-situ measurements of the CME body in interplanetary space. Nevertheless, the evolution of a CME magnetic structure can be followed using a combination of multi-point remote-sensing observations and multi-spacecraft in-situ measurements as well as modeling. Accordingly, we present in this work the analysis of two CMEs that erupted from the Sun on April 28, 2012. We follow their eruption and early evolution using remote-sensing data, finding indications of CME–CME interaction, and then analyze their interplanetary counterpart(s) using in-situ measurements at Venus, Earth, and Saturn. We observe a seemingly single flux rope at all locations, but find possible signatures of interaction at Earth, where high-cadence plasma data are available. Reconstructions of the in-situ flux ropes provide almost identical results at Venus and Earth but show greater discrepancies at Saturn, suggesting that the CME was highly distorted and/or that further interaction with nearby solar wind structures took place before 10 AU. This work highlights the difficulties in connecting structures from the Sun to the outer heliosphere and demonstrates the importance of multi-spacecraft studies to achieve a deeper understanding of the magnetic configuration of CMEs.
  • Journal article
    Mejnertsen L, Eastwood J, Chittenden J, 2021,

    Control of magnetopause flux rope topology by non-local reconnection

    , Frontiers in Astronomy and Space Sciences, Vol: 8, Pages: 1-15, ISSN: 2296-987X

    Dayside magnetic reconnection between the interplanetary magnetic field and the Earth’s magnetic field is the primary mechanism enabling mass and energy entry into the magnetosphere. During favorable solar wind conditions, multiple reconnection X-lines can form on the dayside magnetopause, potentially forming flux ropes. These flux ropes move tailward, but their evolution and fate in the tail is not fully understood. Whilst flux ropes may constitute a class of flux transfer events, the extent to which they add flux to the tail depends on their topology, which can only be measured in situ by satellites providing local observations. Global simulations allow the entire magnetospheric system to be captured at an instant in time, and thus reveal the interconnection between different plasma regions and dynamics on large scales. Using the Gorgon MHD code, we analyze the formation and evolution of flux ropes on the dayside magnetopause during a simulation of a real solar wind event. With a relatively strong solar wind dynamic pressure and southward interplanetary magnetic field, the dayside region becomes very dynamic with evidence of multiple reconnection events. The resulting flux ropes transit around the flank of the magnetosphere before eventually dissipating due to non-local reconnection. This shows that non-local effects may be important in controlling the topology of flux ropes and is a complicating factor in attempts to establish the overall contribution that flux ropes make in the general circulation of magnetic flux through the magnetosphere.
  • Journal article
    Giacalone J, Burgess D, Bale SD, Desai M, Mitchell JG, Lario D, Chen CHK, Christian ER, de Nolfo GA, Hill ME, Matthaeus WH, McComas DJ, McNutt RL, Mitchell DG, Roelof EC, Schwadron NA, Getachew T, Joyce CJet al., 2021,

    Energetic Particles Associated with a Coronal Mass Ejection Shock Interacting with a Convected Magnetic Structure

    , ASTROPHYSICAL JOURNAL, Vol: 921, ISSN: 0004-637X
  • Journal article
    Vech D, Malaspina DM, Cattell C, Schwartz SJ, Ergun RE, Klein KG, Kromyda L, Chasapis Aet al., 2021,

    Experimental Determination of Ion Acoustic Wave Dispersion Relation With Interferometric Analysis

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
  • Journal article
    Lai, Jia, Russell, Jia X, Masters A, Dougherty M, Cuiet al., 2021,

    Magnetic flux circulation in the Saturnian magnetosphere as constrained by Cassini observations in the inner magnetosphere

    , Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-9, ISSN: 2169-9380

    In steady state, magnetic flux conservation must be maintained in Saturn’s magnetosphere. The Enceladus plumes add mass to magnetic flux tubes in the inner magnetosphere, and centrifugal force pulls the mass-loaded flux tubes outward. Those flux tubes are carried outward to the magnetotail where they deposit their mass and return to the mass loading region. It may take days for the magnetic flux to be carried outward to the tail, but the return of the nearly empty flux tubes can last only several hours, with speeds of inward motion around 200 km/s. Using time sequences of Cassini particle count rate, the difference in curvature drift and gradient drift is accounted for to determine the return speed, age, and starting dipole L-shell of return flux tubes. Determination of this flux-return process improves our understanding of the magnetic flux circulation at Saturn and provides insight into how other giant planets remove the mass added by their moons.
  • Journal article
    Kajdic P, Pfau-Kempf Y, Turc L, Dimmock AP, Palmroth M, Takahashi K, Kilpua E, Soucek J, Takahashi N, Preisser L, Blanco-Cano X, Trotta D, Burgess Det al., 2021,

    ULF Wave Transmission Across Collisionless Shocks: 2.5D Local Hybrid Simulations

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
  • Journal article
    Gurnett DA, Kurth WS, Burlaga LF, Berdichevsky DB, Pogorelov N, Pulupa M, Bale SDet al., 2021,

    Origin of the Weak Plasma Emission Line Detected by Voyager 1 in the Interstellar Medium: Evidence for Suprathermal Electrons

    , ASTROPHYSICAL JOURNAL, Vol: 921, ISSN: 0004-637X
  • Journal article
    Teixeira JC, Folberth GA, O'Connor FM, Unger N, Voulgarakis Aet al., 2021,

    Coupling interactive fire with atmospheric composition and climate in the UK Earth System Model

    , Geoscientific Model Development, Vol: 14, Pages: 6515-6539, ISSN: 1991-959X

    Fire constitutes a key process in the Earth system (ES), being driven by climate as well as affecting the climate by changing atmospheric composition and impacting the terrestrial carbon cycle. However, studies on the effects of fires on atmospheric composition, radiative forcing and climate have been limited to date, as the current generation of ES models (ESMs) does not include fully atmosphere–composition–vegetation coupled fires feedbacks. The aim of this work is to develop and evaluate a fully coupled fire–composition–climate ES model. For this, the INteractive Fires and Emissions algoRithm for Natural envirOnments (INFERNO) fire model is coupled to the atmosphere-only configuration of the UK's Earth System Model (UKESM1). This fire–atmosphere interaction through atmospheric chemistry and aerosols allows for fire emissions to influence radiation, clouds and generally weather, which can consequently influence the meteorological drivers of fire. Additionally, INFERNO is updated based on recent developments in the literature to improve the representation of human and/or economic factors in the anthropogenic ignition and suppression of fire. This work presents an assessment of the effects of interactive fire coupling on atmospheric composition and climate compared to the standard UKESM1 configuration that uses prescribed fire emissions. Results show a similar performance when using the fire–atmosphere coupling (the “online” version of the model) when compared to the offline UKESM1 that uses prescribed fire. The model can reproduce observed present-day global fire emissions of carbon monoxide (CO) and aerosols, despite underestimating the global average burnt area. However, at a regional scale, there is an overestimation of fire emissions over Africa due to the misrepresentation of the underlying vegetation types and an underestimation over equatorial Asia due to a lack of representation of peat fires. Despite this, co
  • 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
    Nakamura R, Baumjohann W, Nakamura TKM, Panov E, Schmid D, Varsani A, Apatenkov S, Sergeev VA, Birn J, Nagai T, Gabrielse C, Andre M, Burch JL, Carr C, Dandouras IS, Escoubet CP, Fazakerley AN, Giles BL, Le Contel O, Russell CT, Torbert RBet al., 2021,

    Thin current sheet behind the dipolarization front

    , JGR: Space Physics, Vol: 126, Pages: 1-19, ISSN: 2169-9402

    We report a unique conjugate observation of fast flows and associated current sheet disturbances in the near-Earth magnetotail by MMS (Magnetospheric Multiscale) and Cluster preceding a positive bay onset of a small substorm at ∼14:10 UT, September 8, 2018. MMS and Cluster were located both at X ∼ −14 RE. A dipolarization front (DF) of a localized fast flow was detected by Cluster and MMS, separated in the dawn-dusk direction by ∼4 RE, almost simultaneously. Adiabatic electron acceleration signatures revealed from the comparison of the energy spectra confirm that both spacecraft encounter the same DF. We analyzed the change in the current sheet structure based on multi-scale multi-point data analysis. The current sheet thickened during the passage of DF, yet, temporally thinned subsequently associated with another flow enhancement centered more on the dawnward side of the initial flow. MMS and Cluster observed intense perpendicular and parallel current in the off-equatorial region mainly during this interval of the current sheet thinning. Maximum field-aligned currents both at MMS and Cluster are directed tailward. Detailed analysis of MMS data showed that the intense field-aligned currents consisted of multiple small-scale intense current layers accompanied by enhanced Hall-currents in the dawn-dusk flow-shear region. We suggest that the current sheet thinning is related to the flow bouncing process and/or to the expansion/activation of reconnection. Based on these mesoscale and small-scale multipoint observations, 3D evolution of the flow and current-sheet disturbances was inferred preceding the development of a substorm current wedge.
  • Journal article
    Archer M, Hartinger M, Plaschke F, Southwood D, Rastaetter Let al., 2021,

    Magnetopause ripples going against the flow form azimuthally stationary surface waves

    , Nature Communications, Vol: 12, Pages: 1-14, ISSN: 2041-1723

    Surface waves process the turbulent disturbances which drive dynamics in many space, astrophysical and laboratory plasma systems, with the outer boundary of Earth’s magnetosphere, the magnetopause, providing an accessible environment to study them. Like waves on water, magnetopause surface waves are thought to travel in the direction of the driving solar wind, hence a paradigm in global magnetospheric dynamics of tailward propagation has been well-established. Here we show through multi-spacecraft observations, global simulations, and analytic theory that the lowest-frequency impulsively-excited magnetopause surface waves, with standing structure along the terrestrial magnetic field, propagate against the flow outside the boundary. Across a wide local time range (09–15h) the waves’ Poynting flux exactly balances the flow’s advective effect, leading to no net energy flux and thus stationary structure across the field also. Further down the equatorial flanks, however, advection dominates hence the waves travel downtail, seeding fluctuations at the resonant frequency which subsequently grow in amplitude via the Kelvin-Helmholtz instability and couple to magnetospheric body waves. This global response, contrary to the accepted paradigm, has implications on radiation belt, ionospheric, and auroral dynamics and potential applications to other dynamical systems.
  • 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
    Misios S, Kasoar M, Kasoar E, Gray L, Haigh J, Stathopoulos S, Kourtidis K, Myhre G, Olivie D, Shindell D, Tang Tet al., 2021,

    Similar patterns of tropical precipitation and circulation changes under solar and greenhouse gas forcing

    , Environmental Research Letters, Vol: 16, Pages: 1-10, ISSN: 1748-9326

    Theory and model evidence indicate a higher global hydrological sensitivity for the same amount of surface warming to solar as to greenhouse gas (GHG) forcing, but regional patterns are highly uncertain due to their dependence on circulation and dynamics. We analyse a multi-model ensemble of idealized experiments and a set of simulations of the last millennium and we demonstrate similar global signatures and patterns of forced response in the tropical Pacific, of higher sensitivity for the solar forcing. In the idealized simulations, both solar and GHG forcing warm the equatorial Pacific, enhance precipitation in the central Pacific, and weaken and shift the Walker circulation eastward. Centennial variations in the solar forcing over the last millennium cause similar patterns of enhanced equatorial precipitation and slowdown of the Walker circulation in response to periods with stronger solar forcing. Similar forced patterns albeit of considerably weaker magnitude are identified for variations in GHG concentrations over the 20th century, with the lower sensitivity explained by fast atmospheric adjustments. These findings differ from previous studies that have typically suggested divergent responses in tropical precipitation and circulation between the solar and GHG forcings. We conclude that tropical Walker circulation and precipitation might be more susceptible to solar variability rather than GHG variations during the last-millennium, assuming comparable global mean surface temperature changes.
  • Journal article
    Goldman M, Newman DL, Eastwood JP, Lapenta G, Burch JL, Giles Bet al., 2021,

    Multi-beam energy moments of measured compound ion velocity distributions

    , Physics of Plasmas, Vol: 28, ISSN: 1070-664X

    Compound ion distributions, fi(v), have been measured with high-time resolution by NASA's Magnetospheric Multi-Scale Mission (MMS) and have been found in reconnection simulations. A compound distribution, fi(v), consisting, for example, of essentially disjoint pieces will be called a multi-beam distribution and modeled as a sum of “beams,” fi(v) = f1(v) + ⋯ + fN(v). Velocity moments of fi(v) are taken beam by beam and summed. Such multi-beam moments of fi(v) have advantages over the customary standard velocity moments of fi(v), for which there is only one mean flow velocity. For example, the standard thermal energy moment of a pair of equal and opposite cold particle beams is non-zero even though each beam has zero thermal energy. We therefore call this thermal energy pseudothermal. By contrast, a multi-beam moment of two or more beams has no pseudothermal energy. We develop three different ways of approximating a compound ion velocity distribution, fi(v), as a sum of beams and finding multi-beam moments for both a compound fi(v) measured by MMS in the dayside magnetosphere during reconnection and a compound fi(v) found in a particle-in-cell simulation of magnetotail reconnection. The three methods are (i) a visual method in which the velocity centroid of each beam is estimated and the beam densities are determined self-consistently, (ii) a k-means method in which particles in a particle representation of fi(v) are sorted into a minimum energy configuration of N (= k) clusters, and (iii) a nonlinear least squares method based on a fit to a sum of N kappa functions. Multi-beam energy moments are calculated and compared with standard moments for the thermal energy density, pressure tensor, thermal energy flux (heat plus enthalpy fluxes), bulk kinetic energy density, ram pressure, and bulk kinetic energy flux. Applying this new formalism to real data demonstrates in detail how multi-beam techniques provide new insig
  • Journal article
    Gingell I, Schwartz SJ, Kucharek H, Farrugia CJ, Trattner KJet al., 2021,

    Observing the prevalence of thin current sheets downstream of Earth's bow shock

    , PHYSICS OF PLASMAS, Vol: 28, ISSN: 1070-664X
  • Journal article
    Lario D, Richardson IG, Palmerio E, Lugaz N, Bale SD, Stevens ML, Cohen CMS, Giacalone J, Mitchell DG, Szabo A, Nieves-Chinchilla T, Wilson LB, Christian ER, Hill ME, McComas DJ, McNutt RL, Schwadron NA, Wiedenbeck MEet al., 2021,

    Comparative Analysis of the 2020 November 29 Solar Energetic Particle Event Observed by Parker Solar Probe

    , ASTROPHYSICAL JOURNAL, Vol: 920, ISSN: 0004-637X
  • Journal article
    Desai R, Eastwood J, Horne R, Allison H, Allanson O, Watt C, Eggington J, Glauert S, Meredith N, Archer M, Staples F, Mejnertsen L, Tong J, Chittenden Jet al., 2021,

    Drift orbit bifurcations and cross-field transport in the outer radiation belt: global MHD and integrated test-particle simulations

    , Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-14, ISSN: 2169-9380

    Energetic particle fluxes in the outer magnetosphere present a significant challenge to modellingefforts as they can vary by orders of magnitude in response to solar wind driving conditions. In thisarticle, we demonstrate the ability to propagate test particles through global MHD simulations to ahigh level of precision and use this to map the cross-field radial transport associated with relativisticelectrons undergoing drift orbit bifurcations (DOBs). The simulations predict DOBs primarily occurwithin an Earth radius of the magnetopause loss cone and appears significantly different for southwardand northward interplanetary magnetic field orientations. The changes to the second invariant areshown to manifest as a dropout in particle fluxes with pitch angles close to 90◦and indicate DOBsare a cause of butterfly pitch angle distributions within the night-time sector. The convective electricfield, not included in previous DOB studies, is found to have a significant effect on the resultant longterm transport, and losses to the magnetopause and atmosphere are identified as a potential methodfor incorporating DOBs within Fokker-Planck transport models.
  • Journal article
    Zomerdijk-Russell S, Masters A, Heyner D, 2021,

    Variability of the interplanetary magnetic field as a driver of electromagnetic induction in Mercury’s interior

    , Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-15, ISSN: 2169-9380

    Mercury’s magnetosphere is a unique and dynamic system, primarily due to the proximity of the planet to the Sun and its small size. Interactions between solar wind and embedded Interplanetary Magnetic Field (IMF) and the dayside Hermean magnetosphere drive an electric current on the system’s magnetopause boundary. So far, electromagnetic induction due to magnetopause motion in response to changing external pressure has been used to constrain Mercury’s iron core size. Here we assess the impact a changing IMF direction has on the Hermean magnetopause currents, and the resulting inducing magnetic field. Observations made by MESSENGER during dayside magnetopause boundary crossings in the first ‘hot season’, are used to demonstrate the importance of the IMF direction to Mercury’s magnetopause currents. Our 16 boundary crossings show that introduction of external IMFs change the magnetopause current direction by 10° to 100°, compared to the case where only the internal planetary field is considered. Analytical modelling was used to fill in the bigger picture and suggests for an east-west reversal of the IMF, typical of the heliospheric current 3 sheet sweeping over Mercury’s magnetosphere, the inducing field at Mercury’s surface caused by the resulting magnetopause current dynamics is on the order of 30% of the global planetary field. These results suggest that IMF variability alone has an appreciable effect on Mercury’s magnetopause current and generates a significant inducing magnetic field around the planet. The arrival of the BepiColombo mission will allow this response to be further explored as a method of probing Mercury’s interior.
  • Journal article
    Moore KMM, Bolton B, Cao H, Dougherty MK, Bloxham Jet al., 2021,

    No Evidence for Time Variation in Saturn's Internal Magnetic Field

    , PLANETARY SCIENCE JOURNAL, Vol: 2
  • Journal article
    Szalay JR, Pokorny P, Malaspina DM, Pusack A, Bale SD, Battams K, Gasque LC, Goetz K, Kruger H, McComas DJ, Schwadron NA, Strub Pet al., 2021,

    Collisional Evolution of the Inner Zodiacal Cloud

    , PLANETARY SCIENCE JOURNAL, Vol: 2
  • Journal article
    Pusack A, Malaspina DM, Szalay JR, Bale SD, Goetz K, MacDowall RJ, Pulupa Met al., 2021,

    Dust Directionality and an Anomalous Interplanetary Dust Population Detected by the Parker Solar Probe

    , PLANETARY SCIENCE JOURNAL, Vol: 2
  • Journal article
    Fargette N, Lavraud B, Rouillard AP, Reville V, De Wit TD, Froment C, Halekas JS, Phan TD, Malaspina DM, Bale SD, Kasper JC, Louarn P, Case AW, Korreck KE, Larson DE, Pulupa M, Stevens ML, Whittlesey PL, Berthomier Met al., 2021,

    Characteristic Scales of Magnetic Switchback Patches Near the Sun and Their Possible Association With Solar Supergranulation and Granulation

    , ASTROPHYSICAL JOURNAL, Vol: 919, ISSN: 0004-637X
  • Journal article
    Verscharen D, Bale SD, Velli M, 2021,

    Flux conservation, radial scalings, Mach numbers, and critical distances in the solar wind: magnetohydrodynamics and <i>Ulysses</i> observations

    , MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 506, Pages: 4993-5004, ISSN: 0035-8711
  • Journal article
    Telloni D, Andretta V, Antonucci E, Bemporad A, Capuano GE, Fineschi S, Giordano S, Habbal S, Perrone D, Pinto RF, Sorriso-Valvo L, Spadaro D, Susino R, Woodham LD, Zank GP, Romoli M, Bale SD, Kasper JC, Auchère F, Bruno R, Capobianco G, Case AW, Casini C, Casti M, Chioetto P, Corso AJ, Da Deppo V, De Leo Y, Dudok de Wit T, Frassati F, Frassetto F, Goetz K, Guglielmino SL, Harvey PR, Heinzel P, Jerse G, Korreck KE, Landini F, Larson D, Liberatore A, Livi R, MacDowall RJ, Magli E, Malaspina DM, Massone G, Messerotti M, Moses JD, Naletto G, Nicolini G, Nisticò G, Panasenco O, Pancrazzi M, Pelizzo MG, Pulupa M, Reale F, Romano P, Sasso C, Schühle U, Stangalini M, Stevens ML, Strachan L, Straus T, Teriaca L, Uslenghi M, Velli M, Verscharen D, Volpicelli CA, Whittlesey P, Zangrilli L, Zimbardo G, Zuppella Pet al., 2021,

    Exploring the solar wind from its source on the corona into the inner heliosphere during the first solar orbiter-parker solar probe quadrature

    , The Astrophysical Journal Letters, Vol: 920, Pages: L14-L14

    This Letter addresses the first Solar Orbiter (SO)–Parker Solar Probe (PSP) quadrature, occurring on 2021 January 18 to investigate the evolution of solar wind from the extended corona to the inner heliosphere. Assuming ballistic propagation, the same plasma volume observed remotely in the corona at altitudes between 3.5 and 6.3 solar radii above the solar limb with the Metis coronagraph on SO can be tracked to PSP, orbiting at 0.1 au, thus allowing the local properties of the solar wind to be linked to the coronal source region from where it originated. Thanks to the close approach of PSP to the Sun and the simultaneous Metis observation of the solar corona, the flow-aligned magnetic field and the bulk kinetic energy flux density can be empirically inferred along the coronal current sheet with an unprecedented accuracy, allowing in particular estimation of the Alfvén radius at 8.7 solar radii during the time of this event. This is thus the very first study of the same solar wind plasma as it expands from the sub-Alfvénic solar corona to just above the Alfvén surface.
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    Energetic Electron Observations by Parker Solar Probe/IS⊙IS during the First Widespread SEP Event of Solar Cycle 25 on 2020 November 29

    , ASTROPHYSICAL JOURNAL, Vol: 919, ISSN: 0004-637X

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