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  • 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
    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
    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
    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
    Salvi P, Ceppi P, Gregory JM, 2021,

    Interpreting the dependence of cloud‐radiative adjustment on forcing agent

    , Geophysical Research Letters, Vol: 48, ISSN: 0094-8276

    Effective radiative forcing includes a contribution by rapid adjustments, that is, changes in temperature, water vapor, and clouds that modify the energy budget. Cloud adjustments in particular have been shown to depend strongly on forcing agent. We perform idealized atmospheric heating experiments to demonstrate a relationship between cloud adjustment and the vertical profile of imposed radiative heating: boundary-layer heating causes a positive cloud adjustment (a net downward radiative anomaly), while free-tropospheric heating yields a negative adjustment. This dependence is dominated by the shortwave effect of changes in low clouds. Much of the variation in cloud adjustment among common forcing agents such as CO2, CH4, solar forcing, and black carbon is explained by the “characteristic altitude” (i.e., the vertical center-of-mass) of their heating profiles, through its effect on tropospheric stability.
  • Journal article
    Tang T, Shindell D, Zhang Y, Voulgarakis A, Lamarque J-F, Myhre G, Faluvegi G, Samset BH, Andrews T, Olivie D, Takemura T, Lee Xet al., 2021,

    Distinct surface response to black carbon aerosols

    , Atmospheric Chemistry and Physics, Vol: 21, Pages: 13797-13809, ISSN: 1680-7316

    For the radiative impact of individual climate forcings, most previous studies focused on the global mean values at the top of the atmosphere (TOA), and less attention has been paid to surface processes, especially for black carbon (BC) aerosols. In this study, the surface radiative responses to five different forcing agents were analyzed by using idealized model simulations. Our analyses reveal that for greenhouse gases, solar irradiance, and scattering aerosols, the surface temperature changes are mainly dictated by the changes of surface radiative heating, but for BC, surface energy redistribution between different components plays a more crucial role. Globally, when a unit BC forcing is imposed at TOA, the net shortwave radiation at the surface decreases by −5.87±0.67 W m−2 (W m−2)−1 (averaged over global land without Antarctica), which is partially offset by increased downward longwave radiation (2.32±0.38 W m−2 (W m−2)−1 from the warmer atmosphere, causing a net decrease in the incoming downward surface radiation of −3.56±0.60 W m−2 (W m−2)−1. Despite a reduction in the downward radiation energy, the surface air temperature still increases by 0.25±0.08 K because of less efficient energy dissipation, manifested by reduced surface sensible (−2.88±0.43 W m−2 (W m−2)−1) and latent heat flux (−1.54±0.27 W m−2 (W m−2)−1), as well as a decrease in Bowen ratio (−0.20±0.07 (W m−2)−1). Such reductions of turbulent fluxes can be largely explained by enhanced air stability (0.07±0.02 K (W m−2)−1), measured as the difference of the potential temperature between 925 hPa and surface, and reduc
  • Journal article
    Hadid LZ, Genot V, Aizawa S, Milillo A, Zender J, Murakami G, Benkhoff J, Zouganelis I, Alberti T, Andre N, Bebesi Z, Califano F, Dimmock AP, Dosa M, Escoubet CP, Griton L, Ho GC, Horbury TS, Iwai K, Janvier M, Kilpua E, Lavraud B, Madar A, Miyoshi Y, Muller D, Pinto RF, Rouillard AP, Raines JM, Raouafi N, Sahraoui F, Sanchez-Cano B, Shiota D, Vainio R, Walsh Aet al., 2021,

    BepiColombo's Cruise Phase: Unique Opportunity for Synergistic Observations

    , FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, Vol: 8, ISSN: 2296-987X
    • Cite
    • Citations: 14
  • Journal article
    Shebanits O, Wahlund J-E, Waite JH, Dougherty MKet al., 2021,

    Conductivities of Titan's dusty ionosphere
  • Journal article
    Palchetti L, Brindley H, Bantges R, Buehler SA, Camy-Peyret C, Carli B, Cortesi U, Del Bianco S, Di Natale G, Dinelli BM, Feldman D, Huang XL, Labonnote LC, Libois Q, Maestri T, Mlynczak MG, Murray JE, Oetjen H, Ridolfi M, Riese M, Russell J, Saunders R, Serio Cet al., 2021,

    Completing the Picture: The FORUM Mission: Unique Satellite Data to Fully Reveal How Earth Radiates Energy to Space

    , Bulletin of the American Meteorological Society, Vol: 102, Pages: 851-855, ISSN: 0003-0007
  • Journal article
    Vuorinen L, Hietala H, Plaschke F, LaMoury ATet al., 2021,

    Magnetic field in magnetosheath jets: a statistical study of B-Z near the magnetopause

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

    Magnetosheath jets travel from the bow shock toward the magnetopause, and some of them eventually impact it. Jet impacts have recently been linked to triggering magnetopause reconnection in case studies by Hietala et al. (2018, https://doi.org/10.1002/2017gl076525) and Nykyri et al. (2019, https://doi.org/10.1029/2018ja026357). In this study, we focus on the enhancing or suppressing effect jets could have on reconnection by locally altering the magnetic shear via their own magnetic fields. Using observations from the years 2008–2011 made by the Time History of Events and Macroscale Interactions during Substorms spacecraft and solar wind OMNI data, we statistically study for the first time urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0002 within jets in the Geocentric Solar Magnetospheric coordinates. We find that urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0003 opposite to the prevailing interplanetary magnetic field (IMF) urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0004 is roughly as common in jets as in the non-jet magnetosheath near the magnetopause, but these observations are distributed differently. 60–70% of jet intervals contain bursts of opposite polarity urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0005 in comparison to around 40urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0006 of similar non-jet intervals. The median duration of such a burst in jets is 10 s and strength is urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0007nT. We also investigate the prevalence of the type of strong urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0008nT pulses that Nykyri et al. (2019, https://doi.org/10.1029/2018ja026357) linked to a substorm onset. In our data set, such pulses were observed in around 13% of jets. Our statistical results indicate that jets may have the potential to affect local magnetopause reconnection via their magnetic fields. Future studies are needed to determine whether such effects can be ob
  • Journal article
    Burne S, Bertucci C, Mazelle C, Morales LF, Meziane K, Halekas J, Fowler CM, Espley J, Mitchell D, Penou Eet al., 2021,

    The Structure of the Martian Quasi-Perpendicular Supercritical Shock as Seen by MAVEN

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
    • Cite
    • Citations: 11
  • Journal article
    Kellogg PJ, Bale SD, Goetz K, Monson SJet al., 2021,

    Toward a Physics Based Model of Hypervelocity Dust Impacts

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
  • Journal article
    LaMoury AT, Hietala H, Plaschke F, Vuorinen L, Eastwood JPet al., 2021,

    Solar wind control of magnetosheath jet formation and propagation to the magnetopause

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

    Magnetosheath jets are localized high-dynamic pressure pulses originating at Earth's bow shock and propagating earthward through the magnetosheath. Jets can influence magnetospheric dynamics upon impacting the magnetopause; however, many jets dissipate before reaching it. In this study we present a database of 13,096 jets observed by the Time History of Events and Macroscale Interactions during Substorms spacecraft from 2008 to 2018, spanning a solar cycle. Each jet is associated with upstream solar wind conditions from OMNI. We statistically examine how solar wind conditions control the likelihood of jets forming at the shock, and the conditions favorable for jets to propagate through the magnetosheath and reach the magnetopause. We see that, for each solar wind quantity, these two effects are separate, but when combined, we find that jets are over 17 times more likely to reach and potentially impact the magnetopause when the interplanetary magnetic field (IMF) orientation is at a low cone angle, and approximately 8 times more likely during high speed solar wind. Low IMF magnitude, high Alfvén Mach number, and low density approximately double the number of jets at the magnetopause, while urn:x-wiley:21699380:media:jgra56749:jgra56749-math-0001 and dynamic pressure display no net effect. Due to the strong dependence on wind speed, we infer that jet impact rates may be solar cycle dependent as well as vary during solar wind transients. This is an important step towards forecasting the magnetospheric effects of magnetosheath jets, as it allows for predictions of jet impact rates based on measurements of the upstream solar wind.
  • Journal article
    Mallet A, Squire J, Chandran BDG, Bowen T, Bale SDet al., 2021,

    Evolution of Large-amplitude Alfven Waves and Generation of Switchbacks in the Expanding Solar Wind

    , ASTROPHYSICAL JOURNAL, Vol: 918, ISSN: 0004-637X
  • Journal article
    Mozer FS, Bale SD, Bonnell JW, Drake JF, Hanson ELM, Mozer MCet al., 2021,

    On the Origin of Switchbacks Observed in the Solar Wind

    , ASTROPHYSICAL JOURNAL, Vol: 919, ISSN: 0004-637X
  • Journal article
    Shuster JR, Gershman DJ, Dorelli JC, Giles BL, Wang S, Bessho N, Chen L-J, Cassak PA, Schwartz SJ, Denton RE, Uritsky VM, Paterson WR, Schiff C, Vinas AF, Ng J, Avanov LA, da Silva DE, Torbert RBet al., 2021,

    Structures in the terms of the Vlasov equation observed at Earth's magnetopause

    , NATURE PHYSICS, Vol: 17, Pages: 1056-+, ISSN: 1745-2473
    • Cite
    • Citations: 21
  • Journal article
    Desai RT, Freeman M, Eastwood J, Eggington J, Archer M, Shprits Y, Meredith N, Staples F, Ian R, Hietala H, Mejnertsen L, Chittenden J, Horne Ret al., 2021,

    Interplanetary shock-induced magnetopause motion: Comparison between theory and global magnetohydrodynamic simulations

    , Geophysical Research Letters, Vol: 48, Pages: 1-11, ISSN: 0094-8276

    The magnetopause marks the outer edge of the Earth’s magnetosphere and a distinct boundary between solar wind and magnetospheric plasma populations. In this letter, we use global magneto-hydrodynamic simulations to examine the response of the terrestrial magnetopause to fast-forward interplanetary shocks of various strengths and compare to theoretical predictions. The theory and simulations indicate the magnetopause response can be characterised by three distinct phases; an initial acceleration as inertial forces are overcome, a rapid compressive phase comprising the majority of the distance travelled, and large-scale damped oscillations with amplitudes of the order of an Earth radius. The two approaches agree in predicting subsolar magnetopause oscillations with frequencies2–13 mHz but the simulations notably predict larger amplitudes and weaker damping rates. This phenomenon is of high relevance to space weather forecasting and provides a possible explanation for magnetopause oscillations observed following the large interplanetary shocks of August 1972 and March 1991.
  • Journal article
    Tsui EYL, Toumi R, 2021,

    Hurricanes as an enabler of Amazon fires

    , Scientific Reports, Vol: 11, Pages: 1-8, ISSN: 2045-2322

    A teleconnection between North Atlantic tropical storms and Amazon fires is investigated as a possible case of compound remote extreme events. The seasonal cycles of the storms and fires are in phase with a maximum around September and have significant inter-annual correlation. Years of high Amazon fire activity are associated with atmospheric conditions over the Atlantic which favour tropical cyclones. We propose that anomalous precipitation and latent heating in the Caribbean, partly caused by tropical storms, leads to a thermal circulation response which creates anomalous subsidence and enhances surface solar heating over the Amazon. The Caribbean storms and precipitation anomalies could thus promote favourable atmospheric conditions for Amazon fire.
  • Journal article
    Laker R, Horbury TS, Bale SD, Matteini L, Woolley T, Woodham LD, Stawarz JE, Davies EE, Eastwood JP, Owens MJ, O'Brien H, Evans V, Angelini V, Richter I, Heyner D, Owen CJ, Louarn P, Fedorov Aet al., 2021,

    Multi-spacecraft study of the solar wind at solar minimum: Dependence on latitude and transient outflows

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

    Context. The recent launches of Parker Solar Probe, Solar Orbiter (SO), and BepiColombo, along with several older spacecraft, have provided the opportunity to study the solar wind at multiple latitudes and distances from the Sun simultaneously.Aims. We take advantage of this unique spacecraft constellation, along with low solar activity across two solar rotations between May and July 2020, to investigate how the solar wind structure, including the heliospheric current sheet (HCS), varies with latitude.Methods. We visualise the sector structure of the inner heliosphere by ballistically mapping the polarity and solar wind speed from several spacecraft onto the Sun’s source surface. We then assess the HCS morphology and orientation with the in situ data and compare this with a predicted HCS shape.Results. We resolve ripples in the HCS on scales of a few degrees in longitude and latitude, finding that the local orientations of sector boundaries were broadly consistent with the shape of the HCS but were steepened with respect to a modelled HCS at the Sun. We investigate how several CIRs varied with latitude, finding evidence for the compression region affecting slow solar wind outside the latitude extent of the faster stream. We also identified several transient structures associated with HCS crossings and speculate that one such transient may have disrupted the local HCS orientation up to five days after its passage.Conclusions. We have shown that the solar wind structure varies significantly with latitude, with this constellation providing context for solar wind measurements that would not be possible with a single spacecraft. These measurements provide an accurate representation of the solar wind within ±10° latitude, which could be used as a more rigorous constraint on solar wind models and space weather predictions. In the future, this range of latitudes will increase as SO’s orbit becomes more inclined.
  • Journal article
    Sorland SL, Brogli R, Pothapakula PK, Russo E, Van de Walle J, Ahrens B, Anders I, Bucchignani E, Davin EL, Demory M-E, Dosio A, Feldmann H, Frueh B, Geyer B, Keuler K, Lee D, Li D, van Lipzig NPM, Min S-K, Panitz H-J, Rockel B, Schaer C, Steger C, Thiery Wet al., 2021,

    COSMO-CLM regional climate simulations in the Coordinated Regional Climate Downscaling Experiment (CORDEX) framework: a review

    , GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 14, Pages: 5125-5154, ISSN: 1991-959X
  • Journal article
    Kaweeyanun N, Masters A, Jia X, 2021,

    Analytical assessment of Kelvin-Helmholtz instability growth at Ganymede's upstream magnetopause

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

    Ganymede is the only Solar System moon that generates a permanent magnetic field. Dynamics within the Ganymedean magnetosphere is thought to be driven by energy-transfer interactions on its upstream magnetopause. Previously in Kaweeyanun et al. (2020), https://doi.org/10.1029/2019GL086228 we created a steady-state analytical model of Ganymede's magnetopause and predicted global-scale magnetic reconnection to occur frequently throughout the surface. This paper subsequently provides the first assessment of Kelvin-Helmholtz (K-H) instability growth on the magnetopause. Using the same analytical model, we find that linear K-H waves are expected on both Ganymedean magnetopause flanks. Once formed, the waves propagate downstream at roughly half the speed of the external Jovian plasma flow. The Ganymedean K-H instability growth is asymmetric between magnetopause flanks due to the finite Larmor radius effect arising from large gyroradii of Jovian plasma ions. A small but notable enhancement is expected on the sub-Jovian flank according to the physical understanding of bulk plasma and local ion flows alongside comparisons to the well-observed magnetopause of Mercury. Further evaluation shows that nonlinear K-H vortices should be strongly suppressed by concurring global-scale magnetic reconnection at Ganymede. Reconnection is therefore the dominant cross-magnetopause energy-transfer mechanism and driver of global-scale plasma convection within Ganymede's magnetosphere.
  • Journal article
    Reid J, Cargill PJ, Johnston CD, Hood AWet al., 2021,

    Linking computational models to follow the evolution of heated coronal plasma

    , Monthly Notices of the Royal Astronomical Society, Vol: 505, Pages: 4141-4150, ISSN: 0035-8711

    A ‘proof of principle’ is presented, whereby the Ohmic and viscous heating determined by a three-dimensional (3D) MHD model of a coronal avalanche are used as the coronal heating input for a series of field-aligned, one-dimensional (1D) hydrodynamic models. Three-dimensional coronal MHD models require large computational resources. For current numerical parameters, it is difficult to model both the magnetic field evolution and the energy transport along field lines for coronal temperatures much hotter than 1MK⁠, because of severe constraints on the time step from parallel thermal conduction. Using the 3D MHD heating derived from a simulation and evaluated on a single field line, the 1D models give coronal temperatures of 1MK and densities 1014--1015m−3 for a coronal loop length of 80Mm⁠. While the temperatures and densities vary smoothly along the field lines, the heating function leads to strong asymmetries in the plasma flows. The magnitudes of the velocities in the 1D model are comparable with those seen in 3D reconnection jets in our earlier work. Advantages and drawbacks of this approach for coronal modelling are discussed.
  • Journal article
    Hellinger P, Papini E, Verdini A, Landi S, Franci L, Matteini L, Montagud-Camps Vet al., 2021,

    Spectral Transfer and Karman-Howarth-Monin Equations for Compressible Hall Magnetohydrodynamics

    , ASTROPHYSICAL JOURNAL, Vol: 917, ISSN: 0004-637X
    • Cite
    • Citations: 11
  • Journal article
    Stansby D, Green LM, van Driel-Gesztelyi L, Horbury TSet al., 2021,

    Active Region Contributions to the Solar Wind over Multiple Solar Cycles

    , SOLAR PHYSICS, Vol: 296, ISSN: 0038-0938
  • Journal article
    Masters A, Dunn W, Stallard T, Manners H, Stawarz Jet al., 2021,

    Magnetic reconnection near the planet as a possible driver of Jupiter's mysterious polar auroras

    , Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-10, ISSN: 2169-9380

    Auroral emissions have been extensively observed at the Earth, Jupiter, and Saturn. These planets all have appreciable atmospheres and strong magnetic fields, and their auroras predominantly originate from a region encircling each magnetic pole. However, Jupiter’s auroras poleward of these “main” emissions are brighter and more dynamic, and the drivers responsible for much of these mysterious polar auroras have eluded identification to date. We propose that part of the solution may stem from Jupiter’s stronger magnetic field. We model large-scale Alfvénic perturbations propagating through the polar magnetosphere toward Jupiter, showing that the resulting <0.1° deflections of the magnetic field closest to the planet could trigger magnetic reconnection as near as ∼0.2 Jupiter radii above the cloud tops. At Earth and Saturn this physics should be negligible, but reconnection electric field strengths above Jupiter’s poles can approach ∼1 V m−1, typical of the solar corona. We suggest this near-planet reconnection could generate beams of high-energy electrons capable of explaining some of Jupiter’s polar auroras.
  • Journal article
    Rasca AP, Farrell WM, MacDowall RJ, Bale SD, Kasper JCet al., 2021,

    Near-Sun Switchback Boundaries: Dissipation with Solar Distance

    , ASTROPHYSICAL JOURNAL, Vol: 916, ISSN: 0004-637X
  • Journal article
    Brooks DH, Harra L, Bale SD, Barczynski K, Mandrini C, Polito V, Warren HPet al., 2021,

    The Formation and Lifetime of Outflows in a Solar Active Region

    , ASTROPHYSICAL JOURNAL, Vol: 917, ISSN: 0004-637X
  • Journal article
    Zank GP, Zhao L-L, Adhikari L, Telloni D, Kasper JC, Bale SDet al., 2021,

    Turbulence transport in the solar corona: Theory, modeling, and Parker Solar Probe

    , PHYSICS OF PLASMAS, Vol: 28, ISSN: 1070-664X
  • Journal article
    Liu YY, Fu HS, Cao JB, Liu CM, Wang Z, Guo ZZ, Xu Y, Bale SD, Kasper JCet al., 2021,

    Characteristics of Interplanetary Discontinuities in the Inner Heliosphere Revealed by Parker Solar Probe

    , ASTROPHYSICAL JOURNAL, Vol: 916, ISSN: 0004-637X
  • Journal article
    New AL, Smeed DA, Czaja A, Blaker AT, Mecking J, Mathews JP, Sanchez-Franks Aet al., 2021,

    Labrador Slope Water connects the subarctic with the Gulf Stream

    , ENVIRONMENTAL RESEARCH LETTERS, Vol: 16, ISSN: 1748-9326
    • Cite
    • Citations: 13

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