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Journal articleEglinton TI, Graven HD, Raymond PA, et al., 2023,
A special issue preface: radiocarbon in the Anthropocene
, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 381, ISSN: 1364-503XThe Anthropocene is defined by marked acceleration in human-induced perturbations to the Earth system. Anthropogenic emissions of CO2 and other greenhouse gases to the atmosphere and attendant changes to the global carbon cycle are among the most profound and pervasive of these perturbations. Determining the magnitude, nature and pace of these carbon cycle changes is crucial for understanding the future climate that ecosystems and humanity will experience and need to respond to. This special issue illustrates the value of radiocarbon as a tool to shed important light on the nature, magnitude and pace of carbon cycle change. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.
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Book chapterCargill P, 2023,
Sydney Chapman
, Oxford's Sedleian Professors of Natural Philosophy, Editors: Hollings, McCartney, Publisher: OUP, ISBN: 9780192843210Sydney Chapman FRS was the Sedleian professor between 1946 and 1953. He was also one of the outstanding geophysicists of the 20th century. This chapter reviews his career with particular reference to his work on solar terrestrial relations.
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Journal articleMozer FS, Agapitov O, Bale SD, et al., 2023,
Density Enhancement Streams in The Solar Wind
, Astrophysical Journal Letters, Vol: 957, ISSN: 2041-8205This Letter describes a new phenomenon on the Parker Solar Probe of recurring plasma density enhancements that have Δn/n ∼ 10% and that occur at a repetition rate of ∼5 Hz. They were observed sporadically for about 5 hr between 14 and 15 solar radii on Parker Solar Probe orbit 12 and they were also seen in the same radial range on both the inbound and outbound orbits 11. Their apparently steady-state existence suggests that their pressure gradient was balanced by the electric field. The X-component of the electric field component produced from this requirement is in good agreement with that measured. This provides strong evidence for the measurement accuracy of the density fluctuations and the X- and Y-components of the electric field (the Z-component was not measured). The electrostatic density waves were accompanied by an electromagnetic low-frequency wave, which occurred with the electrostatic harmonics. The amplitudes of these electrostatic and electromagnetic waves at ≥1 Hz were greater than the amplitude of the Alfvénic turbulence in their vicinity so they can be important for the heating, scattering, and acceleration of the plasma. The existence of this pair of waves is consistent with the observed plasma distributions and is explained as an oscilliton due to the nonlinear coupling between the kinetic Alfvén wave and the ion cyclotron mode, which belongs with the minor population of alpha particles.
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Journal articleBizien N, Dudok de Wit T, Froment C, et al., 2023,
Are Switchback Boundaries Observed by Parker Solar Probe Closed?
, Astrophysical Journal, Vol: 958, ISSN: 0004-637XSwitchbacks are sudden and large deflections in the magnetic field that Parker Solar Probe frequently observes in the inner heliosphere. Their ubiquitous occurrence has prompted numerous studies to determine their nature and origin. Our goal is to describe the boundary of these switchbacks using a series of events detected during the spacecraft’s first encounter with the Sun. Using FIELDS and SWEAP data, we investigate different methods for determining the boundary normal. The observed boundaries are arc-polarized structures with a rotation that is always contained in a plane. Classical minimum variance analysis gives misleading results and overestimates the number of rotational discontinuities. We propose a robust geometric method to identify the nature of these discontinuities, which involves determining whether or not the plane that contains them also includes the origin ( B = 0). Most boundaries appear to have the same characteristics as tangential discontinuities in the context of switchbacks, with little evidence for having rotational discontinuities. We find no effect of the size of the Parker spiral deviation. Furthermore, the thickness of the boundary is within MHD scales. We conclude that most of the switchback boundaries observed by Parker Solar Probe are likely to be closed, in contrast to previous studies. Our results suggest that their erosion may be much slower than expected.
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Journal articleAfanasiev A, Vainio R, Trotta D, et al., 2023,
Self-consistent modeling of the energetic storm particle event of November 10, 2012
, Astronomy and Astrophysics, Vol: 679, ISSN: 0004-6361Context. It is thought that solar energetic ions associated with coronal and interplanetary shock waves are accelerated to high energies by the diffusive shock acceleration mechanism. For this mechanism to be efficient, intense magnetic turbulence is needed in the vicinity of the shock. The enhanced turbulence upstream of the shock can be produced self-consistently by the accelerated particles themselves via streaming instability. Comparisons of quasi-linear-theory-based particle acceleration models that include this process with observations have not been fully successful so far, which has motivated the development of acceleration models of a different nature. Aims. Our aim is to test how well our self-consistent quasi-linear SOLar Particle Acceleration in Coronal Shocks (SOLPACS) simulation code, developed earlier to simulate proton acceleration in coronal shocks, models the particle foreshock region. Methods. We applied SOLPACS to model the energetic storm particle (ESP) event observed by the STEREO A spacecraft on November 10, 2012. Results. All but one main input parameter of SOLPACS are fixed by the in situ plasma measurements from the spacecraft. By comparing a simulated proton energy spectrum at the shock with the observed one, we were able to fix the last simulation input parameter related to the efficiency of particle injection to the acceleration process. A subsequent comparison of simulated proton time-intensity profiles in a number of energy channels with the observed ones shows a very good correspondence throughout the upstream region. Conclusions. Our results strongly support the quasi-linear description of the foreshock region.
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Journal articleDunn C, Bowen TA, Mallet A, et al., 2023,
Effect of Spherical Polarization on the Magnetic Spectrum of the Solar Wind
, Astrophysical Journal, Vol: 958, ISSN: 0004-637XMagnetic fluctuations in the solar wind are often observed to maintain constant magnitude of the magnetic field in a manner consistent with spherically polarized large-amplitude Alfvén waves. We investigate the effect of spherical polarization on the magnetic spectral index through a statistical survey of magnetic fluctuations observed by Parker Solar Probe between 20 R ⊙ and 200 R ⊙. We find that deviations from spherical polarization, i.e., changes in ∣ B ∣ (compressive fluctuations) and one-dimensional discontinuities, have a dramatic effect on the scaling behavior of the turbulent fluctuations. We show that shallow k −3/2 spectra are only observed for three-dimensional structures of constant magnetic field strength, which we identify as large-amplitude Alfvén waves. The presence of compressive fluctuations coincides with a steepening of the spectrum up to k −5/3. Steeper power-law scalings approaching k −2 are observed when the fluctuations are dominated by discontinuities. Near-Sun fluctuations are found to be the most spherically polarized, suggesting that this spherical state is fundamental to the generation of the solar wind. With increasing distance from the Sun, fluctuations are found to become less three-dimensional and more compressive, which may indicate the breakdown of the Alfvénic equilibrium state.
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Journal articleKruparova O, Krupar V, Szabo A, et al., 2023,
Quasi-thermal Noise Spectroscopy Analysis of Parker Solar Probe Data: Improved Electron Density Model for Solar Wind
, Astrophysical Journal, Vol: 957, ISSN: 0004-637XWe present a comprehensive analysis of electron density measurements in the solar wind using quasi-thermal noise (QTN) spectroscopy applied to data from the first 15 encounters of the Parker Solar Probe mission (2018 November-2023 March). Our methodology involves the identification of the plasma line frequency and the calculation of plasma density based on in situ measurements. By analyzing over 2.1 million data points, we derive a power-law model for electron density as a function of radial distance from the Sun in the range of 13 to 50 R ☉: n e(r) = (343,466 ± 19921) × r (−1.87±0.11). This model provides improved estimates for localizing interplanetary solar radio bursts. Moreover, obtained electron densities can be used for calibrating particle instruments on board the Parker Solar Probe. We discuss its limitations and potential for further refinement with additional Parker Solar Probe encounters.
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Journal articleStephenson P, Beth A, Deca J, et al., 2023,
The source of electrons at comet 67P
, Monthly Notices of the Royal Astronomical Society, Vol: 525, Pages: 5041-5065, ISSN: 0035-8711We examine the origin of electrons in a weakly outgassing comet, using Rosetta mission data and a 3D collisional model of electrons at a comet. We have calculated a new data set of electron-impact ionization (EII) frequency throughout the Rosetta escort phase, with measurements of the Rosetta Plasma Consortium’s Ion and Electron Sensor (RPC/IES). The EII frequency is evaluated in 15-min intervals and compared to other Rosetta data sets. EII is the dominant source of electrons at 67P away from perihelion and is highly variable (by up to three orders of magnitude). Around perihelion, EII is much less variable and less efficient than photoionization at Rosetta. Several drivers of the EII frequency are identified, including magnetic field strength and the outgassing rate. Energetic electrons are correlated to the Rosetta-upstream solar wind potential difference, confirming that the ionizing electrons are solar wind electrons accelerated by an ambipolar field. The collisional test particle model incorporates a spherically symmetric, pure water coma and all the relevant electron-neutral collision processes. Electric and magnetic fields are stationary model inputs, and are computed using a fully kinetic, collision-less Particle-in-Cell simulation. Collisional electrons are modelled at outgassing rates of Q = 1026 s−1 and Q = 1.5 × 1027 s−1. Secondary electrons are the dominant population within a weakly outgassing comet. These are produced by collisions of solar wind electrons with the neutral coma. The implications of large ion flow speed estimates at Rosetta, away from perihelion, are discussed in relation to multi-instrument studies and the new results of the EII frequency obtained in this study.
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Journal articleZomerdijk-Russell S, Masters A, Sun WJ, et al., 2023,
Does reconnection only occur at points of maximum shear on Mercury’s dayside magnetopause?
, JGR: Space Physics, Vol: 128, ISSN: 2169-9402MESSENGER observations of large numbers of flux transfer events (FTEs) during dayside crossings of Mercury's magnetopause have shown that the highly dynamic Hermean magnetosphere is strongly driven by frequent and intense magnetic reconnection. Since FTEs are products of reconnection, study of them can reveal information about whether reconnection sites favor points of maximum shear on the magnetopause. Here, we analyze 201 FTEs formed under relatively stable upstream solar wind conditions as observed by MESSENGER during inbound magnetopause crossings. By modeling paths of these FTEs along the magnetopause, we determine the conditions and locations of the reconnection sites at which these FTEs were likely formed. The majority of these FTE formation paths were found to intersect with high-magnetic shear regions, defined as shear angles above 135°. Seven FTEs were found where the maximum shear angle possible between the reconnecting magnetic field lines was less than 80° and three of these had shear angles less than 70°, supporting the idea that very low-shear reconnection could be occurring on Mercury's dayside magnetopause under this global-scale picture of magnetic reconnection. Additionally, for the FTEs formed under these low-shear reconnection conditions, tracing a dominant X-line connecting points of maximum shear along the magnetopause that passes through a region of very low-shear may be difficult to justify, implying reconnection could be occurring anywhere along Mercury's magnetopause and may not be confined to points of maximum shear.
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Journal articleGuilbert-Lepoutre A, Benseguane S, Martinien L, et al., 2023,
Pits on Jupiter-family Comets and the Age of Cometary Surfaces
, Planetary Science Journal, Vol: 4Large and deep depressions, also known as pits, are observed at the surface of all Jupiter-family comets (JFCs) imaged by spacecraft missions. They offer the opportunity to glimpse the subsurface characteristics of comet nuclei and study the complex interplay between surface structures and cometary activity. This work investigates the evolution of pits at the surface of 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2, in continuation of the work by Benseguane et al. on 67P/Churyumov-Gerasimenko. Pits are selected across the surface of each nucleus, and high-resolution shape models are used to compute the energy they receive. A thermal evolution model is applied to constrain how cometary activity sustained under current illumination conditions could modify them. Similar to what was found for 67P, we show that erosion resulting from water-driven activity is primarily controlled by seasonal patterns that are unique to each comet as a consequence of their shape and rotational properties. However, progressive erosion sustained after multiple perihelion passages is not able to carve any of the observed pits. Instead, cometary activity tends to erase sharp morphological features; they become wider and shallower over time. Our results reinforce the evolutionary sequence evidenced from independent measurables to transform “young” cometary surfaces, with sharp surface topography prone to outbursts, into “old” cometary surfaces. Finally, we suggest that the mechanism at the origin of the pits on JFCs should be able to carve these structures in a region of the solar system where water ice does not sublimate; the Centaur phase thus appears critical to understand JFC surface properties.
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Journal articlePalmerio E, Maharana A, Lynch BJ, et al., 2023,
Modeling a Coronal Mass Ejection from an Extended Filament Channel. II. Interplanetary Propagation to 1 au
, Astrophysical Journal, Vol: 958, ISSN: 0004-637XWe present observations and modeling results of the propagation and impact at Earth of a high-latitude, extended filament channel eruption that commenced on 2015 July 9. The coronal mass ejection (CME) that resulted from the filament eruption was associated with a moderate disturbance at Earth. This event could be classified as a so-called “problem storm” because it lacked the usual solar signatures that are characteristic of large, energetic, Earth-directed CMEs that often result in significant geoeffective impacts. We use solar observations to constrain the initial parameters and therefore to model the propagation of the 2015 July 9 eruption from the solar corona up to Earth using 3D magnetohydrodynamic heliospheric simulations with three different configurations of the modeled CME. We find the best match between observed and modeled arrival at Earth for the simulation run that features a toroidal flux rope structure of the CME ejecta, but caution that different approaches may be more or less useful depending on the CME-observer geometry when evaluating the space weather impact of eruptions that are extreme in terms of their large size and high degree of asymmetry. We discuss our results in the context of both advancing our understanding of the physics of CME evolution and future improvements to space weather forecasting.
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Journal articleSishtla CP, Pomoell J, Vainio R, et al., 2023,
Modelling the interaction of Alfvénic fluctuations with coronal mass ejections in the low solar corona
, Astronomy and Astrophysics, Vol: 679, ISSN: 0004-6361Context. Alfvénic fluctuations of various scales are ubiquitous in the corona; their non-linear interactions and eventual turbulent cascade result in an important heating mechanism that accelerates the solar wind. These fluctuations may be processed by large-scale, transient, and coherent heliospheric structures such as coronal mass ejections (CMEs). In this study we investigate the interactions between Alfvénic solar wind fluctuations and CMEs using magnetohydrodynamic (MHD) simulations. Aims. We study the transmission of upstream solar wind fluctuations into the CME leading to the formation of CME sheath fluctuations. Additionally, we investigate the influence of the fluctuation frequencies on the extent of the CME sheath. Methods. We used an ideal MHD model with an adiabatic equation of state. An Alfvén pump wave is injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components, and a CME is injected by inserting a flux-rope modelled as a magnetic island into the quasi-steady solar wind. Results. The upstream Alfvén waves experience a decrease in wavelength and change in the wave vector direction due to the non-radial topology of the CME shock front. The CME sheath inhibits the transmission of long-wavelength fluctuations due to the presence of non-radial flows in this region. The frequency of the solar wind fluctuations also affects the steepening of MHD fast waves causing the CME shock propagation speed to vary with the solar wind fluctuation frequencies.
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Journal articleTrotta D, Horbury TS, Lario D, et al., 2023,
Irregular Proton Injection to High Energies at Interplanetary Shocks
, Astrophysical Journal Letters, Vol: 957, ISSN: 2041-8205How thermal particles are accelerated to suprathermal energies is an unsolved issue, crucial for many astrophysical systems. We report novel observations of irregular, dispersive enhancements of the suprathermal particle population upstream of a high-Mach-number interplanetary shock. We interpret the observed behavior as irregular “injections” of suprathermal particles resulting from shock front irregularities. Our findings, directly compared to self-consistent simulation results, provide important insights for the study of remote astrophysical systems where shock structuring is often neglected.
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Journal articleHorner G, Gryspeerdt E, 2023,
The evolution of deep convective systems and their associated cirrus outflows
, Atmospheric Chemistry and Physics, Vol: 23, Pages: 14239-14253, ISSN: 1680-7316Tropical deep convective clouds, particularly their large cirrus outflows, play an important role in modulating the energy balance of the Earth’s atmosphere. Whilst the cores of these deep convective clouds have a significant shortwave (SW) cooling effect, they dissipate quickly. Conversely, the thin cirrus that flow from these cores can persist for days after the core has dissipated, reaching hundreds of kilometers in extent. These thin cirrus have a potential for large warming in the tropics. Understanding the evolution of these clouds and how they change in response to anthropogenic emissions is therefore important to understand past and future climate change.This work uses a novel approach to investigate the evolution of tropical convective clouds by introducing the concept of ‘Time Since Convection’ (TSC). This is used to build a composite picture of the lifecycle of deep convection, from anvil cirrus to thin detrained cirrus. Cloud properties are a strong function of time since convection, showing decreases in the optical thickness, cloud top height, and cloud fraction over time. After an initial dissipation of the convective core, changes in thin cirrus cloud amount were seen beyond 200 hours from convection.Finally, in the initial stages of convection there was a large net negative cloud radiative effect (CRE). However, once the convective core had dissipated after 6–12 hours, the sign of the CRE flipped, and there was a sustained net warming CRE beyond 120 hours from the convective event. Changes are present in the cloud properties long after the main convective activities have dissipated, signalling the need to continue further analysis at longer time scales than previously studied.
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Journal articleSalvi P, Gregory JM, Ceppi P, 2023,
Time‐evolving radiative feedbacks in the historical period
, Journal of Geophysical Research: Atmospheres, Vol: 128, ISSN: 2169-8996We investigate the time-dependence of radiative feedback in the historical period (since the late 19th century), by analyzing experiments using coupled atmosphere–ocean climate models with historical greenhouse gas, anthropogenic aerosol, and natural forcings, each separately. We find that radiative feedback depends on forcing agent, primarily through the effect of cloud on shortwave radiation, because the various forcings cause different changes in global-mean tropospheric stability per degree of global-mean temperature change. The large time-variation of historical feedback driven by observed sea surface temperature change alone, with no forcing agents, is also consistent with tropospheric stability change, and differs from the similarly large and significant historical time-variation of feedback that is simulated in response to all forcing agents together. We show that the latter results from the varying relative sizes of individual forcings. We highlight that volcanic forcing is especially important for understanding the time-variation, because it stimulates particularly strong feedbacks that tend to reduce effective climate sensitivity. We relate this to stability changes due to enhanced surface temperature response in the Indo-Pacific warm pool.
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Journal articleRosu I-A, Grillakis M, Papadopoulos A, et al., 2024,
Fractal and Spectral Analysis of Recent Wildfire Scars in Greece
, FIRE TECHNOLOGY, ISSN: 0015-2684 -
Journal articleBlasl KA, Nakamura TKM, Nakamura R, et al., 2023,
Electron-Scale Reconnecting Current Sheet Formed Within the Lower-Hybrid Wave-Active Region of Kelvin-Helmholtz Waves
, GEOPHYSICAL RESEARCH LETTERS, Vol: 50, ISSN: 0094-8276 -
Journal articleGeorge H, Malaspina DM, Goodrich K, et al., 2023,
Non-Lightning-Generated Whistler Waves in Near-Venus Space
, GEOPHYSICAL RESEARCH LETTERS, Vol: 50, ISSN: 0094-8276 -
Journal articleShi P, Scime EE, Barbhuiya MH, et al., 2023,
Using Direct Laboratory Measurements of Electron Temperature Anisotropy to Identify the Heating Mechanism in Electron-Only Guide Field Magnetic Reconnection.
, Phys Rev Lett, Vol: 131Anisotropic electron heating during electron-only magnetic reconnection with a large guide magnetic field is directly measured in a laboratory plasma through in situ measurements of electron velocity distribution functions. Electron heating preferentially parallel to the magnetic field is localized to one separatrix, and anisotropies of 1.5 are measured. The mechanism for electron energization is identified as the parallel reconnection electric field because of the anisotropic nature of the heating and spatial localization. These characteristics are reproduced in a 2D particle-in-cell simulation and are also consistent with numerous magnetosheath observations. A measured increase in the perpendicular temperature along both separatrices is not reproduced by our 2D simulations. This work has implications for energy partition studies in magnetosheath and laboratory reconnection.
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Conference paperZhang Z, Desai R, Shebanits O, et al., 2023,
Cassini's floating potential in Titan's ionosphere: 3-D particle-in-cell simulations
, URSI GASS 2023, Publisher: IEEE, Pages: 1-4Accurate determination of Cassini’s spacecraft potential in Titan’s ionosphere is important for interpreting measurements by its low energy plasma instruments. Estimates of the floating potential varied significantly, however, between the various different plasma instruments. In this study we utilize 3-D particle-in-cell simulations to understand the key features of Cassini’s plasma interaction in Titan’s ionosphere. The spacecraft is observed to charge to negative potentials for all scenarios considered, and close agreement is found between the current onto the simulated Langmuir Probe and that observed in Titan’s ionosphere. These simulations are therefore shown to provide a viable technique for modeling spacecraft interacting with Titan’s dusty ionosphere.
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Journal articleAla-Lahti M, Pulkkinen TI, Ruohotie J, et al., 2023,
Multipoint Observations of the Dynamics at an ICME Sheath-Ejecta Boundary
, ASTROPHYSICAL JOURNAL, Vol: 956, ISSN: 0004-637X -
Journal articleGood SW, Rantala OK, Jylhä AM, et al., 2023,
Turbulence Properties of Interplanetary Coronal Mass Ejections in the Inner Heliosphere: Dependence on Proton Beta and Flux Rope Structure
, Astrophysical Journal Letters, Vol: 956, ISSN: 2041-8205Interplanetary coronal mass ejections (ICMEs) have low proton beta across a broad range of heliocentric distances and a magnetic flux rope structure at large scales, making them a unique environment for studying solar wind fluctuations. Power spectra of magnetic field fluctuations in 28 ICMEs observed between 0.25 and 0.95 au by Solar Orbiter and Parker Solar Probe have been examined. At large scales, the spectra were dominated by power contained in the flux ropes. Subtraction of the background flux rope fields increased the mean spectral index from −5/3 to −3/2 at kd i ≤ 10−3. Rope subtraction also revealed shorter correlation lengths in the magnetic field. The spectral index was typically near −5/3 in the inertial range at all radial distances regardless of rope subtraction and steepened to values consistently below −3 with transition to kinetic scales. The high-frequency break point terminating the inertial range evolved approximately linearly with radial distance and was closer in scale to the proton inertial length than the proton gyroscale, as expected for plasma at low proton beta. Magnetic compressibility at inertial scales did not show any significant correlation with radial distance, in contrast to the solar wind generally. In ICMEs, the distinctive spectral properties at injection scales appear mostly determined by the global flux rope structure while transition-kinetic properties are more influenced by the low proton beta; the intervening inertial range appears independent of both ICME features, indicative of a system-independent scaling of the turbulence.
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Journal articleTrotta D, Pezzi O, Burgess D, et al., 2023,
Three-dimensional modelling of the shock-turbulence interaction
, Monthly Notices of the Royal Astronomical Society, Vol: 525, Pages: 1856-1866, ISSN: 0035-8711The complex interaction between shocks and plasma turbulence is extremely important to address crucial features of energy conversion in a broad range of astrophysical systems. We study the interaction between a supercritical, perpendicular shock and pre-existing, fully developed plasma turbulence, employing a novel combination of magnetohydrodynamic and small-scale, hybrid-kinetic simulations where a shock is propagating through a turbulent medium. The variability of the shock front in the unperturbed case and for two levels of upstream fluctuations is addressed. We find that the behaviour of shock ripples, i.e. shock surface fluctuations with short (a few ion skin depths, di) wavelengths, is modified by the presence of pre-existing turbulence, which also induces strong corrugations of the shock front at larger scales. We link this complex behaviour of the shock front and the shock downstream structuring with the proton temperature anisotropies produced in the shock-turbulence system. Finally, we put our modelling effort in the context of spacecraft observations, elucidating the role of novel cross-scale, multispacecraft measurements in resolving shock front irregularities at different scales. These results are relevant for a broad range of astrophysical systems characterized by the presence of shock waves interacting with plasma turbulence.
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Journal articlePaouris E, Vourlidas A, Kouloumvakos A, et al., 2023,
The Space Weather Context of the First Extreme Event of Solar Cycle 25, on 2022 September 5
, Astrophysical Journal, Vol: 956, ISSN: 0004-637XThe coronal mass ejection (CME) on 2022 September 5 was the fastest CME yet observed and measured in situ by a spacecraft inside the corona (0.06 au for the Parker Solar Probe). Here we assess the significance of this event for space weather studies by analyzing the source region characteristics and its temporal evolution via a magnetic complexity index. We also examine the kinematics and energetics of the CME. We find that it was a very fast and massive event, with a speed greater than 2200 km s−1 and a mass of 2 × 1016 g. Consequently, this is within the top 1% of all CMEs observed by SOHO/LASCO since 1996. It is therefore natural to ask, “What if this CME was an Earth-directed one?” To answer this question, we put the CME and the associated flare properties in the context of similar previous extreme events (namely, the 2012 July 23 and 2012 March 7 eruptions), discussing the possibility that these trigger a solar energetic particle (SEP) event. We find that 2022 September 5 could have resulted in a high-energy SEP event. We also estimate the transit time and speed of the CME and calculate the likely Dst variations if this was an Earth-directed event.
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Journal articleBandyopadhyay R, Meyer CM, Matthaeus WH, et al., 2023,
Estimates of Proton and Electron Heating Rates Extended to the Near-Sun Environment
, Astrophysical Journal Letters, Vol: 955, ISSN: 2041-8205A central problem of space plasma physics is how protons and electrons are heated in a turbulent, magnetized plasma. The differential heating of charged species due to dissipation of turbulent fluctuations plays a key role in solar wind evolution. Measurements from previous heliophysics missions have provided estimates of proton and electron heating rates beyond 0.27 au. Using Parker Solar Probe (PSP) data accumulated during the first 10 encounters, we extend the evaluation of the individual rates of heat deposition for protons and electrons to a distance of 0.063 au (13.5 Re) in the newly formed solar wind. The PSP data in the near-Sun environment show different behavior of the electron heat conduction flux from what was predicted from previous fits to Helios and Ulysses data. Consequently, the empirically derived proton and electron heating rates exhibit significantly different behavior than previous reports, with the proton heating becoming increasingly dominant over electron heating at decreasing heliocentric distances. We find that the protons receive about 80% of the total plasma heating at ≈13 Re, slightly higher than the near-Earth values. This empirically derived heating partition between protons and electrons will help to constrain theoretical models of solar wind heating.
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Journal articleColomban L, Agapitov OV, Krasnoselskikh V, et al., 2023,
Reconstruction of Polarization Properties of Whistler Waves From Two Magnetic and Two Electric Field Components: Application to Parker Solar Probe Measurements
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380 -
Journal articleZhou Y-J, He F, Zhang X-X, et al., 2023,
A radial standing Pc5-6 wave and its energy coupling with field line resonance within the dusk-sector magnetosphere
, JGR: Space Physics, Vol: 128, ISSN: 2169-9402Global ultra-low frequency (ULF) oscillations are believed to play a significant role in the mass, energy, and momentum transport within the Earth's magnetosphere. In this letter, we observe a ∼1.2 mHz radial standing wave in the dusk-sector magnetosphere accompanied by the field line resonance (FLR) on 16 July 2017. The frequency estimation from the simple box model also confirms the radial standing wave. The essential characteristics of FLR are concurrently identified at the dusk-sector magnetosphere and the conjugated ground location. Further, the radial standing wave dissipates energy into upper atmosphere to enhance the local aurora by coupling itself to the FLR. The magnetospheric dominant 1.2/1.1 mHz ULF waves plausibly correspond well with the discrete ∼1 mHz magnetosheath ion dynamic pressure/velocity oscillation, suggesting this radial standing wave and FLR in the flank magnetosphere may be triggered by the solar-wind and/or magnetosheath dynamic pressure/velocity fluctuations.
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Journal articleVuorinen L, Hietala H, Lamoury AT, et al., 2023,
Solar Wind Parameters Influencing Magnetosheath Jet Formation: Low and High IMF Cone Angle Regimes
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380 -
Journal articlePookkandy B, Graven H, Martin A, 2023,
Contemporary oceanic radiocarbon response to ocean circulation changes
, Climate Dynamics, Vol: 61, Pages: 3223-3235, ISSN: 0930-7575Radiocarbon (14C) is a valuable tracer of ocean circulation, owing to its natural decay over thousands of years and to its perturbation by nuclear weapons testing in the 1950s and 1960s. Previous studies have used 14C to evaluate models or to investigate past climate change. However, the relationship between ocean 14C and ocean circulation changes over the past few decades has not been explored. Here we use an Ocean-Sea-ice model (NEMO) forced with transient or fixed atmospheric reanalysis (JRA-55-do) and atmospheric 14C and CO2 boundary conditions to investigate the effect of ocean circulation trends and variability on 14C. We find that 14C/C (∆14C) variability is generally anti-correlated with potential density variability. The areas where the largest variability occurs varies by depth: in upwelling regions at the surface, at the edges of the subtropical gyres at 300 m depth, and in Antarctic Intermediate Water and North Atlantic Deep Water at 1000 m depth. We find that trends in the Atlantic Meridional Overturning Circulation may influence trends in ∆14C in the North Atlantic. In the high-variability regions the simulated variations are larger than typical ocean ∆14C measurement uncertainty of 2–5‰ suggesting that ∆14C data could provide a useful tracer of circulation changes.
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Journal articleFletcher LN, Cavalié T, Grassi D, et al., 2023,
Jupiter science Enabled by ESA's Jupiter Icy Moons Explorer
, Space Science Reviews, Vol: 219, ISSN: 0038-6308ESA's Jupiter Icy Moons Explorer (JUICE) will provide a detailed investigation of the Jovian system in the 2030s, combining a suite of state-of-the-art instruments with an orbital tour tailored to maximise observing opportunities. We review the Jupiter science enabled by the JUICE mission, building on the legacy of discoveries from the Galileo, Cassini, and Juno missions, alongside ground- and space-based observatories. We focus on remote sensing of the climate, meteorology, and chemistry of the atmosphere and auroras from the cloud-forming weather layer, through the upper troposphere, into the stratosphere and ionosphere. The Jupiter orbital tour provides a wealth of opportunities for atmospheric and auroral science: global perspectives with its near-equatorial and inclined phases, sampling all phase angles from dayside to nightside, and investigating phenomena evolving on timescales from minutes to months. The remote sensing payload spans far-UV spectroscopy (50-210 nm), visible imaging (340-1080 nm), visible/near-infrared spectroscopy (0.49-5.56 μm), and sub-millimetre sounding (near 530-625 GHz and 1067-1275 GHz). This is coupled to radio, stellar, and solar occultation opportunities to explore the atmosphere at high vertical resolution; and radio and plasma wave measurements of electric discharges in the Jovian atmosphere and auroras. Cross-disciplinary scientific investigations enable JUICE to explore coupling processes in giant planet atmospheres, to show how the atmosphere is connected to (i) the deep circulation and composition of the hydrogen-dominated interior; and (ii) to the currents and charged particle environments of the external magnetosphere. JUICE will provide a comprehensive characterisation of the atmosphere and auroras of this archetypal giant planet.
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