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  • Journal article
    Allen RC, Ho GC, Jian LK, Vines SK, Bale SD, Case AW, Hill ME, Joyce CJ, Kasper JC, Korreck KE, Malaspina DM, McComas DJ, McNutt R, Mostl C, Odstrcil D, Raouafi N, Schwadron NA, Stevens MLet al., 2021,

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
    • Cite
    • Citations: 28
  • Journal article
    Drake JF, Agapitov O, Swisdak M, Badman ST, Bale SD, Horbury TS, Kasper JC, MacDowall RJ, Mozer FS, Phan TD, Pulupa M, Szabo A, Velli Met al., 2021,

    , Astronomy and Astrophysics: a European journal, Vol: 650, Pages: 1-8, ISSN: 0004-6361

    The structure of magnetic flux ropes injected into the solar wind duringreconnection in the coronal atmosphere is explored with particle-in-cellsimulations and compared with {\it in situ} measurements of magnetic"switchbacks" from the Parker Solar Probe. We suggest that multi-x-linereconnection between open and closed flux in the corona will inject flux ropesinto the solar wind and that these flux ropes can convect outward over longdistances before disintegrating. Simulations that explore the magneticstructure of flux ropes in the solar wind reproduce key features of the"switchback" observations: a rapid rotation of the radial magnetic field intothe transverse direction (a consequence of reconnection with a strong guidefield); and the potential to reverse the radial field component. The potentialimplication of the injection of large numbers of flux ropes in the coronalatmosphere for understanding the generation of the solar wind is discussed.
  • Journal article
    Woodham L, Horbury T, Matteini L, Woolley T, Laker R, Bale S, Nicolaou G, Stawarz J, Stansby D, Hietala H, Larson D, Livi R, Verniero J, McManus M, Kasper J, Korreck K, Raouafi N, Moncuquet M, Pulupa Met al., 2021,

    , Astronomy and Astrophysics: a European journal, Vol: 650, Pages: 1-7, ISSN: 0004-6361

    Context. Switchbacks are discrete angular deflections in the solar wind magnetic field that have been observed throughout the helio-sphere. Recent observations by Parker Solar Probe(PSP) have revealed the presence of patches of switchbacks on the scale of hours to days, separated by ‘quieter’ radial fields. Aims. We aim to further diagnose the origin of these patches using measurements of proton temperature anisotropy that can illuminate possible links to formation processes in the solar corona. Methods. We fit 3D bi-Maxwellian functions to the core of proton velocity distributions measured by the SPAN-Ai instrument onboard PSP to obtain the proton parallel, Tp,鈥, and perpendicular, Tp,⊥, temperature. Results. We show that the presence of patches is highlighted by a transverse deflection in the flow and magnetic field away from the radial direction. These deflections are correlated with enhancements in Tp,鈥, while Tp,⊥remains relatively constant. Patches sometimes exhibit small proton and electron density enhancements. Conclusions. We interpret that patches are not simply a group of switchbacks, but rather switchbacks are embedded within a larger-scale structure identified by enhanced Tp,鈥杢hat is distinct from the surrounding solar wind. We suggest that these observations are consistent with formation by reconnection-associated mechanisms in the corona.
  • Journal article
    Laker R, Horbury TS, Bale SD, Matteini L, Woolley T, Woodham LD, Badman ST, Pulupa M, Kasper JC, Stevens M, Case AW, Korreck KEet al., 2021,

    , Astronomy & Astrophysics, Vol: 650, Pages: 1-7, ISSN: 0004-6361

    One of the main discoveries from the first two orbits of Parker Solar Probe(PSP) was the presence of magnetic switchbacks, whose deflections dominated themagnetic field measurements. Determining their shape and size could provideevidence of their origin, which is still unclear. Previous work with a singlesolar wind stream has indicated that these are long, thin structures althoughthe direction of their major axis could not be determined. We investigate ifthis long, thin nature extends to other solar wind streams, while determiningthe direction along which the switchbacks within a stream were aligned. We tryto understand how the size and orientation of the switchbacks, along with theflow velocity and spacecraft trajectory, combine to produce the observedstructure durations for past and future orbits. We searched for the alignmentdirection that produced a combination of a spacecraft cutting direction andswitchback duration that was most consistent with long, thin structures. Theexpected form of a long, thin structure was fitted to the results of the bestalignment direction, which determined the width and aspect ratio of theswitchbacks for that stream. The switchbacks had a mean width of $50,000 \,\rm{km}$, with an aspect ratio of the order of $10$. We find that switchbacksare not aligned along the background flow direction, but instead aligned alongthe local Parker spiral, perhaps suggesting that they propagate along themagnetic field. Since the observed switchback duration depends on how thespacecraft cuts through the structure, the duration alone cannot be used todetermine the size or influence of an individual event. For future PSP orbits,a larger spacecraft transverse component combined with more radially alignedswitchbacks will lead to long duration switchbacks becoming less common.
  • Journal article
    Vech D, Martinovic MM, Klein KG, Malaspina DM, Bowen TA, Verniero JL, Paulson K, de Wit TD, Kasper JC, Huang J, Stevens ML, Case AW, Korreck K, Mozer FS, Goodrich KA, Bale SD, Whittlesey PL, Livi R, Larson DE, Pulupa M, Bonnell J, Harvey P, Goetz K, MacDowall Ret al., 2021,

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
    • Cite
    • Citations: 19
  • Journal article
    Quaas J, Gryspeerdt E, Vautard R, Boucher Oet al., 2021,

    , Environmental Research Letters, Vol: 16, Pages: 1-6, ISSN: 1748-9326

    Aircraft produce condensation trails, which are thought to increase high-level cloudiness under certain conditions. Howeverthe magnitude of such an effect and whether this contributes substantially to the radiative forcing due to the aviation sectorremain uncertain. The very substantial, near-global reduction in air traffic in response to the COVID-19 outbreak offers anunprecedented opportunity to identify the anthropogenic contribution to the observed cirrus coverage and thickness. Here weshow, using an analysis of satellite observations for the period March-May 2020, that in the 20% of the Northern Hemispheremid-latitudes with the largest air traffic reduction, cirrus fraction was reduced by ~9 ± 1.5% on average, and cirrus emissivitywas reduced by ~2 ±5% relative to what they should have been with normal air traffic. The changes are corroborated by aconsistent estimate based on linear trends over the period 2011 – 2019. The change in cirrus translates to a global radiativeforcing of 61 ±39 mWm-2. This estimate is somewhat smaller than previous assessments.
  • Journal article
    Cattell C, Glesener L, Leiran B, Dombeck J, Goetz K, Oliveros JCM, Badman ST, Pulupa M, Bale SDet al., 2021,

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Stansby D, Bercic L, Matteini L, Owen CJ, French RJ, Baker D, Badman STet al., 2021,

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Zhang Z, Desai R, Miyake Y, Usui H, Shebanits Oet al., 2021,

    , Monthly Notices of the Royal Astronomical Society, Vol: 504, Pages: 964-973, ISSN: 0035-8711

    A surprising and unexpected phenomenon observed during Cassini’s Grand Finale was the spacecraft charging to positive potentials in Saturn’s ionosphere. Here, the ionospheric plasma was depleted of free electrons with negatively charged ions and dust accumulating up to over 95 per cent of the negative charge density. To further understand the spacecraft–plasma interaction, we perform a three-dimensional Particle-In-Cell study of a model Cassini spacecraft immersed in plasma representative of Saturn’s ionosphere. The simulations reveal complex interaction features such as electron wings and a highly structured wake containing spacecraft-scale vortices. The results show how a large negative ion concentration combined with a large negative to positive ion mass ratio is able to drive the spacecraft to the observed positive potentials. Despite the high electron depletions, the electron properties are found as a significant controlling factor for the spacecraft potential together with the magnetic field orientation which induces a potential gradient directed across Cassini’s asymmetric body. This study reveals the global spacecraft interaction experienced by Cassini during the Grand Finale and how this is influenced by the unexpected negative ion and dust populations.
  • Journal article
    Desai RT, Zhang Z, Wu X, Lue Cet al., 2021,

    , The Planetary Science Journal, Vol: 2, Pages: 99-99

    <jats:title>Abstract</jats:title> <jats:p>Negative ions have been detected in abundance in recent years by spacecraft across the solar system. These detections were, however, made by instruments not designed for this purpose and, as such, significant uncertainties remain regarding the prevalence of these unexpected plasma components. In this article, the phenomenon of photodetachment is examined, and experimentally and theoretically derived cross-sections are used to calculate photodetachment rates for a range of atomic and molecular negative ions subjected to the solar photon spectrum. These rates are applied to negative ions outflowing from Europa, Enceladus, Titan, Dione, and Rhea and their trajectories are traced to constrain source production rates and the extent to which negative ions are able to pervade the surrounding space environments. Predictions are also made for further negative ion populations in the outer solar system with Triton used as an illustrative example. This study demonstrates how, at increased heliocentric distances, negative ions can form stable ambient plasma populations and can be exploited by future missions to the outer solar system.</jats:p>
  • Journal article
    Starkey MJ, Fuselier SA, Desai MI, Schwartz SJ, Russell CT, Wei H, Madanian H, Mukherjee J, Wilson LBet al., 2021,

    , ASTROPHYSICAL JOURNAL, Vol: 913, ISSN: 0004-637X
  • Journal article
    Weiss Z, Concepcion-Mairey F, Pickering JC, Smid Pet al., 2021,

    , SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY, Vol: 180, ISSN: 0584-8547
  • Journal article
    Johlander A, Battarbee M, Vaivads A, Turc L, Pfau-Kempf Y, Ganse U, Grandin M, Dubart M, Khotyaintsev YV, Caprioli D, Haggerty C, Schwartz SJ, Giles BL, Palmroth Met al., 2021,

    , ASTROPHYSICAL JOURNAL, Vol: 914, ISSN: 0004-637X
  • Journal article
    Gonzalez CA, Tenerani A, Matteini L, Hellinger P, Velli Met al., 2021,

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 914, ISSN: 2041-8205
  • Journal article
    Schwartz SJ, Ergun RE, Harald K, Wilson LB, Chen L-J, Goodrich KA, Turner DL, Gingell I, Madanian H, Gershman DJ, Strangeway RJet al., 2021,

  • Journal article
    Kuhn-R茅gnier A, Voulgarakis A, Nowack P, Forkel M, Prentice IC, Harrison SPet al., 2020,

    , Biogeosciences, ISSN: 1726-4170
  • Journal article
    Telloni D, Sorriso-Valvo L, Woodham LD, Panasenco O, Velli M, Carbone F, Zank GP, Bruno R, Perrone D, Nakanotani M, Shi C, D'Amicis R, De Marco R, Jagarlamudi VK, Steinvall K, Marino R, Adhikari L, Zhao L, Liang H, Tenerani A, Laker R, Horbury TS, Bale SD, Pulupa M, Malaspina DM, MacDowall RJ, Goetz K, de Wit TD, Harvey PR, Kasper JC, Korreck KE, Larson D, Case AW, Stevens ML, Whittlesey P, Livi R, Owen CJ, Livi S, Louarn P, Antonucci E, Romoli M, O'Brien H, Evans V, Angelini Vet al., 2021,

    , Letters of the Astrophysical Journal, Vol: 912, Pages: 1-8, ISSN: 2041-8205

    The first radial alignment between Parker Solar Probe and Solar Orbiter spacecraft is used to investigate the evolution of solar wind turbulence in the inner heliosphere. Assuming ballistic propagation, two 1.5 hr intervals are tentatively identified as providing measurements of the same plasma parcels traveling from 0.1 to 1 au. Using magnetic field measurements from both spacecraft, the properties of turbulence in the two intervals are assessed. Magnetic spectral density, flatness, and high-order moment scaling laws are calculated. The Hilbert–Huang transform is additionally used to mitigate short sample and poor stationarity effects. Results show that the plasma evolves from a highly Alfvénic, less-developed turbulence state near the Sun, to fully developed and intermittent turbulence at 1 au. These observations provide strong evidence for the radial evolution of solar wind turbulence.
  • Journal article
    Galand M, Feldman PD, Bockelee-Morvan D, Biver N, Cheng Y-C, Rinaldi G, Rubin M, Altwegg K, Deca J, Beth A, Stephenson P, Heritier KL, Henri P, Parker JW, Carr C, Eriksson AI, Burch Jet al., 2021,

    , NATURE ASTRONOMY, ISSN: 2397-3366
  • Journal article
    Cheng IK, Achilleos N, Masters A, Lewis GR, Kane M, Guio Pet al., 2021,

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

    Magnetic reconnection at the magnetopause (MP) energizes ambient plasma via the release of magnetic energy and produces an “open” magnetosphere allowing solar wind particles to directly enter the system. At Saturn, the nature of MP reconnection remains unclear. The current study examines electron bulk heating at MP crossings, in order to probe the relationship between observed and predicted reconnection heating proposed by Phan et al. (2013, https://doi.org/10.1002/grl.50917) under open and closed MP, and how this may pertain to the position of the crossings in the Δβ鈥恗agnetic shear parameter space. The electron heating for 70 MP crossings made by the Cassini spacecraft from April 2005 to July 2007 was found using 1d and 3d moment methods. Minimum variance analysis was used on the magnetic field data to help indicate whether the MP is open or closed. We found better agreement between observed and predicted heating for events suggestive of locally “open” MP. For events suggestive of locally “closed” MP, we observed a cluster of points consistent with no electron heating, but also numerous cases with significant heating. Examining the events in the Δβ鈥恗agnetic shear parameter space, we find 83% of events without evidence of energization were situated in the “reconnection suppressed” regime, whilst between 43% to 68% of events with energization lie in the “reconnection possible” regime depending on the threshold used. The discrepancies could be explained by a combination of spatial and temporal variability which makes it possible to observe heated electrons with different conditions from the putative reconnection site.
  • Journal article
    Gibbins G, Haigh JD, 2021,

    , Journal of Climate, Vol: 34, Pages: 3721-3728, ISSN: 0894-8755

    A recent paper by Kato and Rose reports a negative correlation between the annual mean entropy production rate of the climate and the absorption of solar radiation in the CERES SYN1deg dataset, using the simplifying assumption that the system is steady in time. It is shown here, however, that when the nonsteady interannual storage of entropy is accounted for, the dataset instead implies a positive correlation; that is, global entropy production rates increase with solar absorption. Furthermore, this increase is consistent with the response demonstrated by an energy balance model and a radiative–convective model. To motivate this updated analysis, a detailed discussion of the conceptual relationship between entropy production, entropy storage, and entropy flows is provided. The storage-corrected estimate for the mean global rate of entropy production in the CERES dataset from all irreversible transfer processes is 81.9 mW m−2 K−1 and from only nonradiative processes is 55.2 mW m−2 K−1 (observations from March 2000 to February 2018).
  • Journal article
    Lai T-K, Hendricks EA, Yau MK, Menelaou Ket al., 2021,

    , JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 78, Pages: 1411-1428, ISSN: 0022-4928
  • Journal article
    Hoilijoki S, Pucci F, Ergun RE, Schwartz SJ, Wilder FD, Eriksson S, Chasapis A, Ahmadi N, Webster JM, Burch JL, Torbert RB, Strangeway RJ, Giles BLet al., 2021,

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
  • Journal article
    Martinovic MM, Klein KG, Huang J, Chandran BDG, Kasper JC, Lichko E, Bowen T, Chen CHK, Matteini L, Stevens M, Case AW, Bale SDet al., 2021,

    , ASTROPHYSICAL JOURNAL, Vol: 912, ISSN: 0004-637X
    • Cite
    • Citations: 30
  • Journal article
    Ma B, Chen L, Wu D, Bale SDet al., 2021,

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 913, ISSN: 2041-8205
  • Journal article
    Diaz-Aguado MF, Bonnell JW, Bale SD, Wang J, Gruntman Met al., 2021,

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
  • Journal article
    Diaz-Aguado MF, Bonnell JW, Bale SD, Wang J, Gruntman Met al., 2021,

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
  • Journal article
    Song S, Choi Y-S, Jeon H, Kang H, Sung C, Paik H-Y, Lee Het al., 2021,

    , Journal of Climate Change Research, Vol: 12, Pages: 121-135, ISSN: 2093-5919
  • Journal article
    Nair V, Heus T, van Reeuwijk M, 2021,

    , Journal of the Atmospheric Sciences, Vol: 78, Pages: 2397-2412, ISSN: 0022-4928

    Interfaces at the edge of an idealised, non-precipitating, warm cloud are studied using Direct Numerical Simulation (DNS) complemented with a Lagrangian particle tracking routine. Once a shell has formed, four zones can be distinguished: the cloud core, visible shell, invisible shell and the environment. The union of the visible and invisible regions is the shell commonly referred to in literature. The boundary between the invisible shell and the environment is the Turbulent-NonTurbulent Interface (TNTI) which is typically not considered in cloud studies. Three million particles were seeded homogeneously across the domain and properties were recorded along individual trajectories. The results demonstrate that the traditional cloud boundary (separating cloudy and non-cloudy regions using thresholds applied on liquid condensate or updraft velocity) are some distance away from the TNTI. Furthermore, there is no dynamic difference between the traditional liquid-condensate boundary and the region extending to the TNTI. However, particles crossing the TNTI exhibit a sharp jump in enstrophy and a smooth increase in buoyancy. The traditional cloud boundary coincides with the location of minimum buoyancy in the shell. The shell pre-mixes the entraining and detraining air and analysis reveals a highly skewed picture of entrainment and detrainment at the traditional cloud boundary. A preferential entrainment of particles with velocity and specific humidity higher than the mean values in the shell is observed. Large-eddy simulation of a more realistic setup detects an interface with similar properties using the same thresholds as in the DNS, indicating that the DNS results extrapolate beyond their idealised conditions.
  • Journal article
    Pulupa M, Bale SD, Curry SM, Farrell WM, Goodrich KA, Goetz K, Harvey PR, Malaspina DM, Raouafi NEet al., 2021,

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 48, ISSN: 0094-8276
  • Journal article
    Gryspeerdt E, Goren T, Smith T, 2021,

    , Atmospheric Chemistry and Physics, Vol: 21, Pages: 6093-6109, ISSN: 1680-7316

    The response of cloud processes to an aerosol perturbation is one of the largest uncertainties in the anthropogenic forcing of the climate. It occurs at a variety of timescales, from the near-instantaneous Twomey effect to the longer timescales required for cloud adjustments. Understanding the temporal evolution of cloud properties following an aerosol perturbation is necessary to interpret the results of so-called “natural experiments” from a known aerosol source such as a ship or industrial site. This work uses reanalysis wind fields and ship emission information matched to observations of ship tracks to measure the timescales of cloud responses to aerosol in instantaneous (or“snapshot”) images taken by polar-orbiting satellites.As in previous studies, the local meteorological environment is shown to have a strong impact on the occurrence and properties of ship tracks, but there is a strong time dependence in their properties. The largest droplet number concentration (Nd) responses are found within 3 h of emission, while cloud adjustments continue to evolve over periods of 10 h or more. Cloud fraction is increased within the early life of ship tracks, with the formation of ship tracks in otherwise clear skies indicating that around 5 %–10 % of clear-sky cases in this region may be aerosol-limited.The liquid water path (LWP) enhancement and the Nd–LWP sensitivity are also time dependent and strong functions of the background cloud and meteorological state. The near-instant response of the LWP within ship tracks may be evidence of a bias in estimates of the LWP response to aerosol derived from natural experiments. These results highlight the importance of temporal development and the background cloud field for quantifying the aerosol impact on clouds, even in situations where the aerosol perturbation is clear.

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