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  • Journal article
    Ma B, Chen L, Wu D, Pulupa M, Bale SDet al., 2022,

    Discrepancy between the Low-frequency Cutoffs of Type III Radio Bursts Based on Simultaneous Observations by WIND and PSP

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 932, ISSN: 2041-8205
  • Journal article
    Hunt GJ, Provan G, Bradley TJ, Cowley SWH, Dougherty MK, Roussos Eet al., 2022,

    The response of Saturn's dawn field-aligned currents to magnetospheric and ring current conditions during Cassini's proximal orbits: evidence for a Region 2 response at Saturn

    , Journal of Geophysical Research: Space Physics, Vol: 127, Pages: 1-15, ISSN: 2169-9380

    Cassini's 2017 proximal orbits provided the opportunity to examine the auroral field-aligned currents in the northern hemisphere dawn sector in relation to wider magnetospheric conditions. We combine three recent studies to examine the response of the dawn region auroral field-aligned currents and the azimuthal ring currents to compressions and expansions of the Saturnian magnetosphere. For compressions of Saturn's magnetosphere resulting in tail reconnection, the currents within the downward current sheet, located equatorward of the main auroral oval, increases in strength with increasing total ring current and location of the peak downwards current moves inwards toward Saturn. While the inverse relation occurs during intervals of quiet or expanded magnetospheric conditions. During compression events there is an increase in the energetic particle intensities, in particular in the protons (35–506 keV), within the downward current region. This current system is akin to an Earth-like “region 2” field aligned current within Saturn's magnetosphere, with tail reconnection occurring when the magnetosphere is compressed resulting in a partial nightside ring current closed by a downward current near to dawn. Within the upward current sheet, mapping to Saturn's main auroral oval, both non-rotating subcorotating current and the rotating Planetary Period Oscillations (PPOs) currents flow. The upward current is strongly modulated by the PPOs but also increases in strength, with enhanced high-energy protons, during intervals of magnetospheric compressions and tail reconnection. We conclude that the enhanced plasma injected into the midnight-dawn sector during tail reconnection events results in an enhanced subcorotation current system.
  • Journal article
    Bourouaine S, Perez JC, Raouafi NE, Chandran BDG, Bale SD, Velli Met al., 2022,

    Features of Magnetic Field Switchbacks in Relation to the Local-field Geometry of Large-amplitude Alfvenic Oscillations: Wind and PSP Observations

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 932, ISSN: 2041-8205
  • Journal article
    Badman ST, Brooks DH, Poirier N, Warren HP, Petrie G, Rouillard AP, Arge CN, Bale SD, Aguero DDP, Harra L, Jones S, Kouloumvakos A, Riley P, Panasenco O, Velli M, Wallace Set al., 2022,

    Constraining Global Coronal Models with Multiple Independent Observables

    , ASTROPHYSICAL JOURNAL, Vol: 932, ISSN: 0004-637X
  • Journal article
    Agiwal O, Masters A, Hunt G, Dougherty Met al., 2022,

    The contribution of planetary period oscillations towards circulation and mass loss in Saturn’s magnetosphere

    , Journal of Geophysical Research: Space Physics, Vol: 127, Pages: 1-17, ISSN: 2169-9380

    Magnetic reconnection is a process during which magnetic energy is released as kinetic energy. It is considered a crucial driver of energy transport and mass loss within Saturn's magnetosphere. On long-term timescales, is thought to be predominantly driven by the rapid rotation of equatorially mass-loaded flux tubes (i.e., the Vasyliunas cycle), but there is some non-negligible driving from the solar wind as well (i.e., the Dungey cycle). In this study, we investigate an atmospheric driven phenomenon that modulates Saturn's magnetosphere every ∼10.6–10.8 hr, known as planetary period oscillations (PPOs), as an additional driver of magnetic reconnection at Saturn. Using an empirical model of PPO dynamics and Cassini magnetic field and plasma measurements, we find that PPO-driven magnetic reconnection is likely to occur in Saturn's magnetosphere, however, the occurrence of the phenomenon depends on temporally variable characteristics of the PPO systems and spatial asymmetries within Saturn's equatorial magnetosphere. Thus, it is not expected to be an on-going process. On year-long timescales, we find that PPOs are expected to be on par with the Dungey Cycle in driving circulation within Saturn's magnetosphere. However, on ∼1–2 weeks-long timescales, under specific conditions where PPO-driven reconnection is expected to be active, this phenomenon can become more significant than the Vasyliunas cycle, and thus dominate circulation within Saturn's magnetosphere. On year-long timescales, this process is estimated to remove upwards of ∼20% of the mass loaded into the magnetosphere by Enceladus.
  • Journal article
    Pal S, Lynch BJ, Good SW, Palmerio E, Asvestari E, Pomoell J, Stevens ML, Kilpua EKJet al., 2022,

    Eruption and Interplanetary Evolution of a Stealthy Streamer-Blowout CME Observed by PSP at ∼0.5 AU

    , FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, Vol: 9, ISSN: 2296-987X
  • Journal article
    Dumont V, Bowen TA, Roglans R, Dobler G, Sharma MS, Karpf A, Bale SD, Wickenbrock A, Zhivun E, Kornack T, Wurtele JS, Budker Det al., 2022,

    Do cities have a unique magnetic pulse?

    , JOURNAL OF APPLIED PHYSICS, Vol: 131, ISSN: 0021-8979
  • Journal article
    Gangopadhyay A, Sparks NJ, Toumi R, Seshadri AKet al., 2022,

    Risk assessment of wind droughts over India

    , Current Science, Vol: 122, Pages: 1145-1153, ISSN: 0011-3891

    Wind power growth makes it essential to simulateweather variability and its impacts on the electricitygrid. Low-probability, high-impact weather events suchas a wind drought are important but difficult to identify based on limited historical datasets. A stochasticweather generator, Imperial College Weather Generator (IMAGE), is employed to identify extreme eventsthrough long-period simulations. IMAGE capturesmean, spatial correlation and seasonality in wind speedand estimates return periods of extreme wind eventsover India. Simulations show that when Rajasthan experiences wind drought, southern India continues tohave wind, and vice versa. Regional grid-scale winddroughts could be avoided if grids are strongly interconnected across the country.
  • Journal article
    Phan TD, Verniero JL, Larson D, Lavraud B, Drake JF, Øieroset M, Eastwood JP, Bale SD, Livi R, Halekas JS, Whittlesey PL, Rahmati A, Stansby D, Pulupa M, MacDowall RJ, Szabo PA, Koval A, Desai M, Fuselier SA, Velli M, Hesse M, Pyakurel PS, Maheshwari K, Kasper JC, Stevens JM, Case AW, Raouafi NEet al., 2022,

    Parker solar probe observations of solar wind energetic proton beams produced by magnetic reconnection in the near‐sun heliospheric current sheet

    , Geophysical Research Letters, Vol: 49, ISSN: 0094-8276

    We report observations of reconnection exhausts in the Heliospheric Current Sheet (HCS) during Parker Solar Probe Encounters 08 and 07, at 16 Rs and 20 Rs, respectively. Heliospheric current sheet (HCS) reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ∼3, due to the Alfvén speed being comparable to the solar wind flow speed at these near-Sun distances. Furthermore, protons were energized to super-thermal energies. During E08, energized protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field-aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was not the local HCS reconnection exhaust.
  • Journal article
    Schwartz SJ, Goodrich KA, Wilson III LB, Turner DL, Trattner K, Kucharek H, Gingell I, Fuselier SA, Cohen IJ, Madanian H, Ergun RE, Gershman DJ, Strangeway RJet al., 2022,

    Energy partition at collisionless supercritical quasiperpendicular shocks
  • Conference paper
    Deca J, Stephenson P, Divin A, Henri P, Galand Met al., 2022,

    A Fully Kinetic Perspective on Weakly Active Comets: Symmetric versus Asymmetric Outgassing

    , Publisher: Copernicus GmbH

    <jats:p>&amp;lt;p&amp;gt;For more than two years, ESA&amp;amp;#8217;s Rosetta mission measured the complex and ever-evolving plasma environment surrounding comet 67P/Churyumov-Gerasimenko. In this work, we explore the structure and dynamics of the near-comet plasma environment at steady state, comparing directly the results of a spherically symmetric Haser model and an asymmetric outgassing profile based on the measurements from the ROSINA instrument onboard Rosetta during 67P&amp;amp;#8217;s weakly outgassing stages. Using a fully kinetic semi-implicit particle-in-cell code, we are able to characterise (1) the various ion and electron populations and their interactions, and (2) the implications to the mass-loading process caused by taking into account asymmetric outgassing. Our model complements observations by providing a full 3D picture that is directly relevant to help interpret the measurements made by the Rosetta Plasma Consortium instruments. In addition, understanding such details better is key to help disentangle the physical drivers active in the plasma environment of comets visited by future exploration missions.&amp;lt;/p&amp;gt;</jats:p>
  • Journal article
    Murray-Watson RJ, Gryspeerdt E, 2022,

    Stability-dependent increases in liquid water with droplet number in the Arctic

    , Atmospheric Chemistry and Physics, Vol: 22, Pages: 5743-5756, ISSN: 1680-7316

    The effects of aerosols on cloud microphysical properties are a large source of uncertainty when assessing anthropogenic climate change. The aerosol–cloud relationship is particularly unclear in high-latitude polar regions due to a limited number of observations. Cloud liquid water path (LWP) is an important control on cloud radiative properties, particularly in the Arctic, where clouds play a central role in the surface energy budget. Therefore, understanding how aerosols may alter cloud LWP is important, especially as aerosol sources such as industry and shipping move further north in a warming Arctic.Using satellite data, this work investigates the effects of aerosols on liquid Arctic clouds over open ocean by considering the relationship between cloud droplet number concentration (Nd) and LWP, an important component of the aerosol–LWP relationship. The LWP response to Nd varies significantly across the region, with increases in LWP with Nd observed at very high latitudes in multiple satellite datasets, with this positive signal observed most strongly during the summer months. This result is in contrast to the negative response typically seen in global satellite studies and previous work on Arctic clouds showing little LWP response to aerosols.The lower tropospheric stability (LTS) was found to be an important control on the spatial variations in LWP response, strongly influencing the sign and magnitude of the Nd–LWP relationship, with increases in LWP in high-stability environments. The influence of humidity varied depending on the stability, with little impact at low LTS but a strong influence at high LTS. The mean Nd state does not dominate the LWP response, despite the non-linearities in the relationship. As the Nd–LWP sensitivity changed from positive to negative when moving from high- to low-LTS environments, this work shows evidence of a temperature-dependent aerosol indirect effect. Additionally, the LWP–LTS relationship chan
  • Journal article
    Sishtla CP, Pomoell J, Kilpua E, Good S, Daei F, Palmroth Met al., 2022,

    Flux-tube-dependent propagation of Alfven waves in the solar corona

    , ASTRONOMY & ASTROPHYSICS, Vol: 661, ISSN: 0004-6361
  • Journal article
    Nieves-Chinchilla T, Alzate N, Cremades H, Rodriguez-Garcia L, Dos Santos LFG, Narock A, Xie H, Szabo A, Palmerio E, Krupar V, Pulupa M, Lario D, Stevens ML, Wilson LB, Kwon R-Y, Mays ML, St Cyr OC, Hess P, Reeves KK, Seaton DB, Niembro T, Bale SD, Kasper JCet al., 2022,

    Direct First Parker Solar Probe Observation of the Interaction of Two Successive Interplanetary Coronal Mass Ejections in 2020 November

    , ASTROPHYSICAL JOURNAL, Vol: 930, ISSN: 0004-637X
  • Journal article
    Hellinger P, Montagud-Camps V, Franci L, Matteini L, Papini E, Verdini A, Landi Set al., 2022,

    Ion-scale Transition of Plasma Turbulence: Pressure-Strain Effect

    , ASTROPHYSICAL JOURNAL, Vol: 930, ISSN: 0004-637X
  • Journal article
    Sishtla CP, Pomoell J, Kilpua E, Good S, Daei F, Palmroth Met al., 2022,

    Flux-tube-dependent propagation of Alfvén waves in the solar corona

    , Astronomy &amp; Astrophysics, Vol: 661, Pages: A58-A58, ISSN: 0004-6361

    <jats:p><jats:italic>Context.</jats:italic> Alfvén-wave turbulence has emerged as an important heating mechanism to accelerate the solar wind. The generation of this turbulent heating is dependent on the presence and subsequent interaction of counter-propagating Alfvén waves. This requires us to understand the propagation and evolution of Alfvén waves in the solar wind in order to develop an understanding of the relationship between turbulent heating and solar-wind parameters.</jats:p><jats:p><jats:italic>Aims.</jats:italic> We aim to study the response of the solar wind upon injecting monochromatic single-frequency Alfvén waves at the base of the corona for various magnetic flux-tube geometries.</jats:p><jats:p><jats:italic>Methods.</jats:italic> We used an ideal magnetohydrodynamic model using 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.</jats:p><jats:p><jats:italic>Results.</jats:italic> Alfvén waves were found to be reflected due to the development of the parametric decay instability (PDI). Further investigation revealed that the PDI was suppressed both by efficient reflections at low frequencies as well as magnetic flux-tube geometries.</jats:p>
  • Journal article
    Palmerio E, Lee CO, Mays ML, Luhmann JG, Lario D, Sanchez-Cano B, Richardson IG, Vainio R, Stevens ML, Cohen CMS, Steinvall K, Mostl C, Weiss AJ, Nieves-Chinchilla T, Li Y, Larson DE, Heyner D, Bale SD, Galvin AB, Holmstrom M, Khotyaintsev Y, Maksimovic M, Mitrofanov IGet al., 2022,

    CMEs and SEPs During November-December 2020: A Challenge for Real-Time Space Weather Forecasting

    , SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS, Vol: 20
  • Journal article
    Akbari H, Newman D, Fowler C, Pfaff R, Andersson L, Malaspina D, Schwartz S, Ergun R, McFadden J, Mitchell D, Halekas J, Rowland Det al., 2022,

    Micro-Scale Plasma Instabilities in the Interaction Region of the Solar Wind and the Martian Upper Atmosphere

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 127, ISSN: 2169-9380
  • Journal article
    Archer M, Waters C, Dewan S, Foster S, Portas Aet al., 2022,

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

    , Geoscience Communication, Vol: 5, Pages: 119-123, ISSN: 2569-7110

    Educational research highlights that improved careers education is needed to increase participation in science, technology, engineering, and mathematics (STEM). Current UK careers resources concerning the space sector, however, are found to perhaps not best reflect the diversity of roles present and may in fact perpetuate misconceptions about the usefulness of science. We, therefore, compile a more diverse set of space-related jobs, which will be used in the development of a new space careers resource.
  • Journal article
    Bale SD, 2022,

    Eugene N. Parker (1927-2022)

    , SCIENCE, Vol: 376, Pages: 461-461, ISSN: 0036-8075
  • Journal article
    Brown ZL, Medvedev AS, Starichenko ED, Koskinen TT, Mueller-Wodarg ICFet al., 2022,

    Evidence for Gravity Waves in the Thermosphere of Saturn and Implications for Global Circulation

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 49, ISSN: 0094-8276
  • Journal article
    Salvi P, Ceppi P, Gregory JM, 2022,

    Interpreting differences in radiative feedbacks from aerosols versus greenhouse gases

    , Geophysical Research Letters, Vol: 49, Pages: 1-9, ISSN: 0094-8276

    Experiments with seven Coupled Model Intercomparison Project phase 6 models were used to assess the climate feedback parameter for net historical, historical greenhouse gas (GHG) and anthropogenic aerosol forcings. The net radiative feedback is found to be more amplifying (higher effective climate sensitivity) for aerosol than GHG forcing, and hence also less amplifying for net historical (GHG + aerosol) than GHG only. We demonstrate that this difference is consistent with their different latitudinal distributions. Historical aerosol forcing is most pronounced in northern extratropics, where the boundary layer is decoupled from the free troposphere, so the consequent temperature change is confined to low altitude and causes low-level cloud changes. This is caused by change in stability, which also affects upper-tropospheric clear-sky emission, affecting both shortwave and longwave radiative feedbacks. This response is a feature of extratropical forcing generally, regardless of its sign or hemisphere.
  • Journal article
    Hall RJ, Mitchell DM, Seviour WJM, Wright CJet al., 2022,

    How Well Are Sudden Stratospheric Warming Surface Impacts Captured in CMIP6 Climate Models?

    , JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 127, ISSN: 2169-897X
  • Journal article
    Warwick L, Brindley H, Di Roma A, Fox S, Havemann S, Murray J, Oetjen H, Price H, Schüttemeyer D, Sgheri L, Tiddeman Det al., 2022,

    Retrieval of tropospheric water vapour from airborne far-infrared measurements: a case study

    , Journal of Geophysical Research: Atmospheres, Vol: 127, ISSN: 2169-897X

    We describe studies undertaken in support of the Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission, ESA’s ninth Earth Explorer, designed to investigate whether airborne observations of far-infrared radiances can provide beneficial information on mid and upper tropospheric water vapour concentrations.Initially we perform a joint temperature and water vapour retrieval and show that the water vapour retrieval exploiting far-infrared measurements from the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) shows improvement over the a-priori Unified Model global forecast when compared to in situ dropsonde measurements. For this case the improvement is particularly noticeable in the mid-upper troposphere. Equivalent retrievals using mid-infrared radiances measured by the Airborne Research Interferometer Evaluation System (ARIES) show much reduced performance, with the degrees of freedom for signal (DFS), reduced by a factor of almost 2. Further sensitivity studies show that this advantage is decreased, but still present when the spectral resolution of the TAFTS measurements is reduced to match that of ARIES.The beneficial role of the far infrared for this case is further confirmed by performing water vapour only retrievals using ARIES and TAFTS individually, and then in combination. We find that the combined retrieval has a DFS value of 6.7 for water vapour, marginally larger than that obtained for the TAFTS retrieval and almost twice as large as that obtained for ARIES.These results provide observational support of theoretical studies highlighting the potential improvement that far-infrared observations could bring for the retrieval of tropospheric water vapour.
  • Journal article
    Dimmock AP, Khotyaintsev YV, Lalti A, Yordanova E, Edberg NJT, Steinvall K, Graham DB, Hadid LZ, Allen RC, Vaivads A, Maksimovic M, Bale SD, Chust T, Krasnoselskikh V, Kretzschmar M, Lorfevre E, Plettemeier D, Soucek J, Steller M, Stverak S, Travnicek P, Vecchio A, Horbury TS, O'Brien H, Evans V, Angelini Vet al., 2022,

    Analysis of multiscale structures at the quasi-perpendicular Venus bow shock Results from Solar Orbiter's first Venus flyby

    , ASTRONOMY & ASTROPHYSICS, Vol: 660, ISSN: 0004-6361
  • Journal article
    Bessho N, Chen L-J, Stawarz J, Wang S, Hesse M, Wilson III L, Ng Jet al., 2022,

    Strong reconnection electric fields in shock-driven turbulence

    , Physics of Plasmas, Vol: 29, Pages: 1-23, ISSN: 1070-664X

    Turbulent magnetic reconnection in a quasi-parallel shock under parameters relevant to the Earth's bow shock is investigated by means of a two-dimensional particle-in-cell simulation. The addressed aspects include the reconnection electric field, the reconnection rate, and the electron and the ion outflow speeds. In the shock transition region, many current sheets are generated in shock-driven turbulence, and electron-only reconnection and reconnection where both ions and electrons are involved can occur in those current sheets. The electron outflow speed in electron-only reconnection shows a positive correlation with the theoretical speed, which is close to the local electron Alfvén speed, and a strong convection electric field is generated by the large electron outflow. As a result, the reconnection electric field becomes much larger than those in the standard magnetopause or magnetotail reconnection. In shock-driven reconnection that involves ion dynamics, both electron outflows and ion outflows can reach of the order of 10 times the Alfvén speed in the X-line rest frame, leading to a reconnection electric field the same order as that in electron-only reconnection. An electron-only reconnection event observed by the magnetospheric multiscale mission downstream of a quasi-parallel shock is qualitatively similar to those in the simulation and shows that the outflow speed reaches approximately half the local electron Alfvén speed, supporting the simulation prediction.
  • Journal article
    Grillakis M, Voulgarakis A, Rovithakis A, Seiradakis KD, Koutroulis A, Field RD, Kasoar M, Papadopoulos A, Lazaridis Met al., 2022,

    Climate drivers of global wildfire burned area

    , Environmental Research Letters, Vol: 17, Pages: 1-10, ISSN: 1748-9326

    Wildfire is an integral part of the Earth system, but at the same time it can pose serious threats to human society and to certain types of terrestrial ecosystems. Meteorological conditions are a key driver of wildfire activity and extent, which led to the emergence of the use of fire danger indices that depend solely on weather conditions. The Canadian Fire Weather Index (FWI) is a widely used fire danger index of this kind. Here, we evaluate how well the FWI, its components, and the climate variables from which it is derived, correlate with observation-based burned area (BA) for a variety of world regions. We use a novel technique, according to which monthly BA are grouped by size for each Global Fire Emissions Database (GFED) pyrographic region. We find strong correlations of BA anomalies with the FWI anomalies, as well as with the underlying deviations from their climatologies for the four climate variables from which FWI is estimated, namely, temperature, relative humidity, precipitation, and wind. We quantify the relative sensitivity of the observed BA to each of the four climate variables, finding that this relationship strongly depends on the pyrographic region and land type. Our results indicate that the BA anomalies strongly correlate with FWI anomalies at a GFED region scale, compared to the strength of the correlation with individual climate variables. Additionally, among the individual climate variables that comprise the FWI, relative humidity and temperature are the most influential factors that affect the observed BA. Our results support the use of the composite fire danger index FWI, as well as its sub-indices, the Build-Up Index (BUI) and the Initial Spread Index (ISI), comparing to single climate variables, since they are found to correlate better with the observed forest or non-forest BA, for the most regions across the globe.
  • Journal article
    Stephenson P, Galand M, Deca J, Henri P, Carnielli Get al., 2022,

    A collisional test particle model of electrons at a comet

    , Monthly Notices of the Royal Astronomical Society, Vol: 511, Pages: 4090-4108, ISSN: 0035-8711

    We have developed the first 3D collisional model of electrons at a comet, which we use to examine the impact of electron-neutral collisions in the weakly outgassing regime. The test-particle Monte Carlo model uses electric and magnetic fields from a fully kinetic Particle-in-Cell (PiC) model as an input. In our model, electrons originate from the solar wind or from ionization of the neutral coma, either by electron impact or absorption of an extreme ultraviolet photon. All relevant electron-neutral collision processes are included in the model including elastic scattering, excitation, and ionization. Trajectories of electrons are validated against analytically known drifts and the stochastic energy degradation used in the model is compared to the continuous slowing down approximation. Macroscopic properties of the solar wind and cometary electron populations, such as density and temperature, are validated with simple known cases and via comparison with the collisionless PiC model. We demonstrate that electrons are trapped close to the nucleus by the ambipolar electric field, causing an increase in the efficiency of electron-neutral collisions. Even at a low-outgassing rate (Q = 1026 s−1), electron-neutral collisions are shown to cause significant cooling in the coma. The model also provides a multistep numerical framework that is used to assess the influence of the electron-to-ion mass ratio, enabling access to electron dynamics with a physical electron mass.
  • Journal article
    Zhao L-L, Zank GP, Telloni D, Stevens M, Kasper JC, Bale SDet al., 2022,

    The Turbulent Properties of the Sub-Alfvenic Solar Wind Measured by the Parker Solar Probe

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 928, ISSN: 2041-8205
  • Journal article
    Eggington J, Desai R, Mejnertsen L, Chittenden J, Eastwood Jet al., 2022,

    Time-varying magnetopause reconnection during sudden commencement: global MHD simulations

    , Journal of Geophysical Research: Space Physics, Vol: 127, ISSN: 2169-9380

    In response to a solar wind dynamic pressure enhancement, the compression of the magnetosphere generates strong ionospheric signatures and a sharp variation in the ground magnetic field, termed sudden commencement (SC). Whilst such compressions have also been associated with a contraction of the ionospheric polar cap due to the triggering of reconnection in the magnetotail, the effect of any changes in dayside reconnection is less clear and is a key component in fully understanding the system response. In this study we explore the time-dependent nature of dayside coupling during SC by performing global simulations using the Gorgon MHD code, and impact the magnetosphere with a series of interplanetary shocks with different parameters. We identify the location and evolu tion of the reconnection region in each case as the shock propagates through the magnetosphere, finding strong enhancement in the dayside reconnection rate and prompt expansion of the dayside polar cap prior to the eventual triggering of tail reconnection. This effect pervades for a variety of IMF orientations, and the reconnection rate is most enhanced for events with higher dynamic pressure. We explain this by repeating the simulations with a large explicit resistivity, showing that compression of the magnetosheath plasma near the propagating shock front allows for reconnection of much greater intensity and at different locations on the dayside magnetopause than during typical solar wind conditions. The results indicate that the dynamic behaviour of dayside coupling may render steady models of reconnection inaccurate during the onset of a severe space weather event.

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