103 results found
Trotta D, Horbury TS, Lario D, et al., 2023, Irregular Proton Injection to High Energies at Interplanetary Shocks, Astrophysical Journal Letters, Vol: 957, ISSN: 2041-8205
How 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.
Afanasiev A, Vainio R, Trotta D, et al., 2023, Self-consistent modeling of the energetic storm particle event of November 10, 2012, Astronomy & Astrophysics, Vol: 679, Pages: A111-A111, ISSN: 0004-6361
<jats:p><jats:italic>Context.</jats:italic> 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.</jats:p><jats:p><jats:italic>Aims.</jats:italic> 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.</jats:p><jats:p><jats:italic>Methods.</jats:italic> We applied SOLPACS to model the energetic storm particle (ESP) event observed by the STEREO A spacecraft on November 10, 2012.</jats:p><jats:p><jats:italic>Results.</jats:italic> 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.</jats:p><jats:p><jats:italic>Conclusions.</jats:italic> Our results strongly support the quasi-linear description of the foreshock region.</jat
Trotta 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: 0035-8711
The 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.
Vuorinen 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
Magnetosheath jets are localized flows of enhanced dynamic pressure that are frequently observed downstream of the Earth's bow shock. They are significantly more likely to occur downstream of the quasi-parallel shock than the quasi-perpendicular shock. However, as the quasi-perpendicular geometry is a more common configuration at the Earth's subsolar bow shock, quasi-perpendicular jets comprise a significant fraction of the observed jets. We study the influence of solar wind conditions on jet formation by looking separately at jets during low and high interplanetary magnetic field (IMF) cone angles. According to our results, jet formation commences when Alfvén Mach number MA ≳ 5. We find that during low IMF cone angles (downstream of the quasi-parallel shock) other solar wind parameters do not influence jet occurrence. However, during high IMF cone angles (downstream of the quasi-perpendicular shock) jet occurrence is higher during low IMF magnitude, low density, high plasma beta (β), and high MA conditions. The distribution of quasi-parallel (quasi-perpendicular) jet sizes parallel to flow peaks at ∼0.3 RE (∼0.1 RE). Some quasi-perpendicular jets formed during high β and MA are particularly small. We show two examples of high β and MA quasi-perpendicular shock crossings. Jets were observed in the transition region, but not deeper in the magnetosheath. A more detailed look into one jet revealed signatures of gyrating ions, indicating that gyrobunched ions near the shock may produce jet-like enhancements. Our results suggest that jets form as part of the quasi-perpendicular shock dynamics amplified by high solar wind MA and β.
Collinson GA, Hietala H, Plaschke F, et al., 2023, Shocklets and short large amplitude magnetic structures (SLAMS) in the high mach foreshock of Venus, Geophysical Research Letters, Vol: 50, ISSN: 0094-8276
Shocklets and short large-amplitude magnetic structures (SLAMS) are steepened magnetic fluctuations commonly found in Earth's upstream foreshock. Here we present Venus Express observations from the 26th of February 2009 establishing their existence in the steady-state foreshock of Venus, building on a past study which found SLAMS during a substantial disturbance of the induced magnetosphere. The Venusian structures were comparable to those reported near Earth. The 2 Shocklets had magnetic compression ratios of 1.23 and 1.34 with linear polarization in the spacecraft frame. The 3 SLAMS had ratios between 3.22 and 4.03, two of which with elliptical polarization in the spacecraft frame. Statistical analysis suggests SLAMS coincide with unusually high solar wind Alfvén mach-number at Venus (12.5, this event). Thus, while we establish Shocklets and SLAMS can form in the stable Venusian foreshock, they may be rarer than at Earth. We estimate a lower limit of their occurrence rate of ≳14%.
Earth’s orbit and rotation produces systematic variations in geomagnetic activity, most notably via the changing orientation of the dayside magnetospheric magnetic field with respect to the heliospheric magnetic field (HMF). Aside from these geometric effects, it is generally assumed that the solar wind in near-Earth is uniformly sampled. But systematic changes in the intrinsic solar wind conditions in near-Earth space could arise due to the annual variations in Earth heliocentric distance and heliographic latitude. In this study, we use 24 years of Advanced Composition Explorer data to investigate the annual variations in the scalar properties of the solar wind, namely the solar wind proton density, the radial solar wind speed and the HMF intensity. All parameters do show some degree of systematic annual variation, with amplitudes of around 10 to 20%. For HMF intensity, the variation is in phase with the Earth’s heliocentric distance variation, and scaling observations for distance largely explains the observed variation. For proton density and solar wind speed, however, the phase of the annual variation is inconsistent with Earth’s heliocentric distance. Instead, we attribute the variations in speed and density to Earth’s heliographic latitude variation and systematic sampling of higher speed solar wind at higher latitudes. Indeed, these annual variations are most strongly ordered at solar minimum. Conversely, combining scalar solar wind parameters to produce estimates of dynamic pressure and potential power input to the magnetosphere results in solar maximum exhibiting a greater annual variation, with an amplitude of around 40%. This suggests Earth’s position in the heliosphere makes a significant contribution to annual variations in space weather, in addition to the already well-studied geometric effects.
Vuorinen L, LaMoury AT, Hietala H, et al., 2023, Magnetosheath Jets Over Solar Cycle 24: An Empirical Model, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380
Battarbee M, Archer M, Hietala H, et al., 2023, Morphology and evolution of foreshock structures in a high-Mach number hybrid-Vlasov simulation of Earth's magnetosphere
<jats:p>Counter-streaming particles reflected from the Earth's bow shock towards the Sun build up the ion foreshock, exciting right-handed ultra-low frequency (ULF) waves, which convect with the solar wind back to the bow shock. As these waves move Earthward, they steepen and interact with each other, forming a complex wave field consisting of various foreshock structures. Observations of foreshock structures have classified them as, for example, ULF waves, shocklets, short large-amplitude magnetic structures (SLAMS), cavitons, and spontaneous hot flow anomalies (SHFAs). We present results from a high Mach number 2D-3V hybrid-Vlasov Vlasiator simulation of the Earth's bow shock and foreshock&#160;during quasi-radial IMF and place them in the context of spacecraft observations. We combine spatial analysis of bulk characteristics within the foreshock with virtual spacecraft observations to evaluate the morphology of foreshock structures as they form, and how they subsequently evolve as they approach the Earth's bow shock.</jats:p>
<jats:p>Interplanetary (IP) shocks can be driven in the solar wind by fast coronal mass ejections and by the interaction of fast solar wind with slow streams of plasma. These shocks can be preceded by extended waves and suprathermal ion foreshocks. Shocks characteristics as well as the level of wave activity near them change as they propagate through the heliosphere and this can impact particle acceleration, and modify the ambient solar wind. In this work we study IP shock evolution and the wave modes upstream of them using a multispacecraft approach with data of Solar Orbiter, STEREO, Parker Solar Probe and Wind. We find that upstream regions can be permeated by whistler waves (f ~ 1 Hz) and/or ultra low frequency (ULF) right-handed waves (f~10-2&#8211;10-1 Hz). While whistlers appear to be generated at the shock, the origin of ULF waves is most probably associated with local kinetic ion instabilities. In contrast with planetary bow shocks, most IP shocks have a small Mach number (<4) and most of the upstream waves studied here are mainly transverse and steepening rarely occurs.&#160;</jats:p>
Trotta D, Horbury T, Hietala H, et al., 2023, Observations of energetic particles at interplanetary shocks with Solar Orbiter
<jats:p>Interplanetary (IP) shocks are important sites of particle acceleration in the Heliosphere and can be observed in-situ utilizing spacecraft measurements. Such observations are crucial to address important aspects of energy conversion for a variety of astrophysical systems.Under this point of view, Solar Orbiter provides observations of interplanetary shocks at different locations in the inner heliosphere with unprecedented time and energy resolution in the suprathermal (usually above 50 keV) energy range. We present a comprehensive identification of such shocks, highlighting their typical parameters.We then study a strong shock showing novel dispersive signals in the suprathermal particle fluxes observed by the Solar Orbiter SupraThermal Electron and Proton sensor. These are probably due to irregular injection of particles to suprathermal energies along the shock front, as inferred using the Solar Orbiter in-situ observations and self-consistent, kinetic modelling of the shock transition.</jats:p>
Vuorinen L, Hietala H, LaMoury AT, 2023, Solar wind parameters influencing magnetosheath jet formation: low and high IMF cone angle regimes
<jats:p>Magnetosheath jets are dynamic pressure enhancements that are frequently observed downstream of the Earth's bow shock. Earthward propagating jets are significantly more likely to occur downstream of the quasi-parallel shock than the quasi-perpendicular shock. However, as the quasi-perpendicular geometry is the more common configuration at the Earth's bow shock, quasi-perpendicular jets can constitute a significant fraction of jets observed at Earth. Moreover, at other more quasi-perpendicular shock environments, such as at interplanetary shocks or the bow shocks of outer planets, they would be expected to form an even more significant portion of jets. We study the solar wind influence on jet formation in the quasi-parallel and quasi-perpendicular regimes by investigating jets in the Earth&#8217;s subsolar magnetosheath separately during low and high IMF cone angles. We find that during low IMF cone angles (downstream of the quasi-parallel shock) jet occurrence near the bow shock is not sensitive to other solar wind parameters. However, during high IMF cone angles (downstream of the quasi-perpendicular shock) jet occurrence is higher during low B, low n, high beta, and high MA conditions. This suggests that quasi-perpendicular jet formation is related to shock dynamics amplified by higher beta and MA. These observations from a wide range of solar wind parameters&#160;also allow us to make predictions of jet occurrence at other planetary systems.</jats:p>
<jats:p>Magnetic holes are significant depressions of the interplanetary magnetic field (IMF) that can be found embedded in the solar wind everywhere within the heliosphere. They resemble mirror mode magnetic structures that form as a response to excess perpendicular temperatures. Magnetic holes situated at IMF discontinuities (current sheets) may also be the result of reconnection. Magnetic holes occur more often under fast solar wind conditions, and their scale sizes are known to be on the order of thousands to tens of thousands of km, determined essentially from temporal width and plasma velocity observations. So far, the scale sizes have only been estimated for the directions parallel to the respective solar wind plasma flows. In this study, we attempt to calculate the first distributions of the scale sizes for the orthogonal, flow-perpendicular directions. Therefore, we use multi-point observations of magnetic holes by the ARTEMIS spacecraft in lunar orbit. The method we use has been previously applied to plasma jets present in the magnetosheath of Earth. The knowledge of the flow-perpendicular scale sizes is important to assess the holes&#8217; impact on planetary magnetospheres and cometary environments.</jats:p>
Trotta D, Pecora F, Settino A, et al., 2023, Transmission of turbulent structures and energetic particles dynamics in the interaction between collisionless shocks and plasma turbulence.
<jats:p>The interaction between shock and turbulence is an important pathway to energy conversion and particle acceleration in a large variety of astrophysical systems. Novel insights of such an interaction will be presented.Using a combination of in-situ observations (using the Wind spacecraft and Magnetospheric Multiscale mission, MMS) and self-consistent kinetic simulations, the transmission of turbulent structures across the Earth&#8217;s bow shock will be discussed first. Then, the role of turbulence strength for efficient particle diffusion in phase space will be discussed using novel kinetic simulations and will be put in the context of observations of very-long lasting field aligned beams in interplanetary space. Finally, novel three-dimensional simulations of the shock turbulence interplay will be presented, with a focus on the shock front behaviour and irregular proton heating in presence of pre-existing fluctuations. In this scenario, the importance of novel multi-spacecraft missions will be discussed.</jats:p>
Hietala H, 2023, Jets downstream of the Earth’s bow shock
<jats:p>The downstream region of a collisionless quasi-parallel shock is structured containing localized bulk flows with high kinetic energy density and dynamic pressure. In 2009, we presented Cluster multi-spacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock within the sheath. These observations allowed us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasi-parallel shocks can create fast, slightly deflected jets accompanied by density variations in the downstream region. If the speed of the jet is super(magneto)sonic in the reference frame of the surrounding flow and/or the magnetopause, a second shock front forms in the sheath.During the following years, magnetosheath jets have been a continually active research topic. Studies using increasingly large databases of spacecraft observations have gathered the statistics of jet formation conditions and properties. Simulations and case studies have shed light on jet formation mechanisms. Within the magnetosheath, the jet-driven secondary bow waves/shocks have been shown to contribute to particle energization. Investigations of jet impacts on the magnetosphere have revealed a plethora of effects, ranging from surface waves and magnetopause reconnection to diffuse auroral brightenings.In this talk, we will summarize the progress to date and highlight some still open questions.</jats:p>
Hietala H, Trotta D, Wilson III L, et al., 2023, Candidates for downstream jets at interplanetary shocks
<jats:p>Localized dynamic pressure enhancements - jets - are regularly observed downstream of the Earth&#8217;s bow shock. They drive enhanced particle acceleration, larger amplitude magnetic field variations and reconnecting current sheets. Various shock simulations have also exhibited jets, suggesting that they are not unique to Earth.In this study, we search for similar dynamic pressure pulses downstream of interplanetary shocks observed by the Wind spacecraft. We discuss how the jet selection criteria are adapted for such conditions. The interplanetary shocks where we have found jet candidates feature foreshock activity, a favourable condition for jet formation according to bow shock studies. We examine the properties of the candidate jets and compare them to those reported for magnetosheath jets. Widening the range of environments where downstream jets are observed can shed light on their dynamics and formation mechanisms.</jats:p>
Trotta D, Hietala H, Horbury T, et al., 2023, Multi-spacecraft observations of shocklets at an interplanetary shock, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 520, Pages: 437-445, ISSN: 0035-8711
Wang B, Nishimura Y, Hietala H, et al., 2022, Investigating the Role of Magnetosheath High-Speed Jets in Triggering Dayside Ground Magnetic Ultra-Low Frequency Waves, GEOPHYSICAL RESEARCH LETTERS, Vol: 49, ISSN: 0094-8276
Trotta D, Vuorinen L, Hietala H, et al., 2022, Single-spacecraft techniques for shock parameters estimation: a systematic approach, Frontiers in Astronomy and Space Sciences, Vol: 9, Pages: 1-16, ISSN: 2296-987X
Spacecraft missions provide the unique opportunity to study the properties of collisionless shocks utilising in situ measurements. In the past years, several diagnostics have been developed to address key shock parameters using time series of magnetic field (and plasma) data collected by a single spacecraft crossing a shock front. A critical aspect of such diagnostics is the averaging process involved in the evaluation of upstream/downstream quantities. In this work, we discuss several of these techniques, with a particular focus on the shock obliquity (defined as the angle between the upstream magnetic field and the shock normal vector) estimation. We introduce a systematic variation of the upstream/downstream averaging windows, yielding to an ensemble of shock parameters, which is a useful tool to address the robustness of their estimation. This approach is first tested with a synthetic shock dataset compliant with the Rankine-Hugoniot jump conditions for a shock, including the presence of noise and disturbances. We then employ self-consistent, hybrid kinetic shock simulations to apply the diagnostics to virtual spacecraft crossing the shock front at various stages of its evolution, highlighting the role of shock-induced fluctuations in the parameters’ estimation. This approach has the strong advantage of retaining some important properties of collisionless shock (such as, for example, the shock front microstructure) while being able to set a known, nominal set of shock parameters. Finally, two recent observations of interplanetary shocks from the Solar Orbiter spacecraft are presented, to demonstrate the use of this systematic approach to real events of shock crossings. The approach is also tested on an interplanetary shock measured by the four spacecraft of the Magnetospheric Multiscale (MMS) mission. All the Python software developed and used for the diagnostics (SerPyShock) is made available for the public, including an example of parameter estimation fo
Vuorinen L, Vainio R, Hietala H, et al., 2022, Monte Carlo simulations of electron acceleration at bow waves driven by fast jets in the Earth’s magnetosheath, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 934, Pages: 1-7, ISSN: 0004-637X
The shocked solar wind flows around the Earth’s magnetosphere in the magnetosheath downstreamof the Earth’s bow shock. Within this region, faster flows of plasma, called magnetosheath jets, arefrequently observed. These jets have been shown to sometimes exhibit supermagnetosonic speedsrelative to the magnetosheath flow and to develop bow waves or shocks of their own. Such jet-drivenbow waves have been observed to accelerate ions and electrons. We model electron acceleration bymagnetosheath jet-driven bow waves using test-particle Monte Carlo simulations. Our simulationssuggest that the energy increase of electrons with energies of a few hundred eV to 10 keV can beexplained by a collapsing magnetic trap forming between the bow wave and the magnetopause withshock drift acceleration at the moving bow wave. Our simulations allow us to estimate the efficiencyof acceleration as a function of different jet and magnetosheath parameters. Electron acceleration byjet-driven bow waves can increase the total acceleration in the parent shock environment, most likelyalso at shocks other than the Earth’s bow shock.
Trotta D, Pecora F, Settino A, et al., 2022, On the Transmission of Turbulent Structures across the Earth's Bow Shock, ASTROPHYSICAL JOURNAL, Vol: 933, ISSN: 0004-637X
Koller F, Temmer M, Preisser L, et al., 2022, Magnetosheath jet occurrence rate in relation to CMEs and SIRs
Koller F, Temmer M, Preisser L, et al., 2022, Magnetosheath jet occurrence rate in relation to CMEs and SIRs, Journal of Geophysical Research: Space Physics, Vol: 127, ISSN: 2169-9380
Magnetosheath jets constitute a significant coupling effect between the solar wind (SW) and the magnetosphere of the Earth. In order to investigate the effects and forecasting of these jets, we present the first-ever statistical study of the jet production during large-scale SW structures like coronal mass ejections (CMEs), stream interaction regions (SIRs) and high speed streams (HSSs). Magnetosheath data from Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft between January 2008 and December 2020 serve as measurement source for jet detection. Two different jet definitions were used to rule out statistical biases induced by our jet detection method. For the CME and SIR + HSS lists, we used lists provided by literature and expanded on incomplete lists using OMNI data to cover the time range of May 1996 to December 2020. We find that the number and total time of observed jets decrease when CME-sheaths hit the Earth. The number of jets is lower throughout the passing of the CME-magnetic ejecta (ME) and recovers quickly afterward. On the other hand, the number of jets increases during SIR and HSS phases. We discuss a few possibilities to explain these statistical results.
LaMoury A, Hietala H, Eastwood J, et al., 2022, Magnetosheath jets at the magnetopause: reconnection onset conditions
<jats:p>&lt;p&gt;Magnetosheath jets are localised pulses of high dynamic pressure plasma observed in Earth&amp;#8217;s magnetosheath. They are believed to form from the interaction between the solar wind and ripples in Earth&amp;#8217;s collisionless bow shock, before propagating into the turbulent magnetosheath. Upon impacting the magnetopause, jets can influence magnetospheric dynamics. In particular, previous studies have suggested that, by virtue of their internal magnetic field orientations, jet impacts may be able to trigger local magnetic reconnection at the magnetopause. This is most notable during traditionally unfavourable solar wind conditions, such as intervals of northward interplanetary magnetic field. This idea has been supported by a small number of case studies and simulations. We present a large statistical study into the properties of jets near the magnetopause. We examine the components of the magnetic reconnection onset condition &amp;#8211; the competing effects of magnetic shear angle and plasma beta &amp;#8211; to determine how jets may affect magnetopause reconnection in a statistical sense. We find that, due to their increased beta, jet plasma is typically not favourable to reconnection, often more so than the non-jet magnetosheath. Most jets do contain some reconnection-favourable plasma, however, suggesting that jets may be able to both trigger and suppress magnetopause reconnection. We complement this with new case studies of jets interacting with the magnetopause.&lt;/p&gt;</jats:p>
Plaschke F, Koller F, Preisser Renteria LF, et al., 2022, Magnetosheath jet occurrence in solar wind parameter space
<jats:p>&lt;p&gt;Plasma jets in the magnetosheath are identified as strong local enhancements in dynamic pressure. Being created at the bow shock, they are able to traverse the entire magnetosheath and impact the magnetopause. There, they can severely indent the boundary, set up waves on it, and trigger magnetic reconnection. They are a key yet heavily underexplored element in the solar wind &amp;#8211; magnetosphere coupling. Jets are mostly (but not exclusively) observed downstream of the quasi-parallel shock. Consequently, they have been observed significantly more often under low interplanetary magnetic field cone angle conditions.&lt;/p&gt;&lt;p&gt;In this study, we revisit the occurrence of jets, this time taking into account the whole space of parameters of solar wind input conditions. We answer the question where in this space jet occurrences cluster and how the emerging patterns change when the solar wind input becomes significantly different in nature, e.g., under the influence of coronal mass ejections or stream interaction regions.&lt;/p&gt;</jats:p>
Telloni D, Scolini C, Moestl C, et al., 2021, Study of two interacting interplanetary coronal mass ejections encountered by Solar Orbiter during its first perihelion passage Observations and modeling, Astronomy and Astrophysics: a European journal, Vol: 656, ISSN: 0004-6361
Context. Solar Orbiter, the new-generation mission dedicated to solar and heliospheric exploration, was successfully launched on February 10, 2020, 04:03 UTC from Cape Canaveral. During its first perihelion passage in June 2020, two successive interplanetary coronal mass ejections (ICMEs), propagating along the heliospheric current sheet (HCS), impacted the spacecraft.Aims. This paper addresses the investigation of the ICMEs encountered by Solar Orbiter on June 7−8, 2020, from both an observational and a modeling perspective. The aim is to provide a full description of those events, their mutual interaction, and their coupling with the ambient solar wind and the HCS.Methods. Data acquired by the MAG magnetometer, the Energetic Particle Detector suite, and the Radio and Plasma Waves instrument are used to provide information on the ICMEs’ magnetic topology configuration, their magnetic connectivity to the Sun, and insights into the heliospheric plasma environment where they travel, respectively. On the modeling side, the Heliospheric Upwind eXtrapolation model, the 3D COronal Rope Ejection technique, and the EUropean Heliospheric FORecasting Information Asset (EUHFORIA) tool are used to complement Solar Orbiter observations of the ambient solar wind and ICMEs, and to simulate the evolution and interaction of the ejecta in the inner heliosphere, respectively.Results. Both data analysis and numerical simulations indicate that the passage of two distinct, dynamically and magnetically interacting (via magnetic reconnection processes) ICMEs at Solar Orbiter is a possible scenario, supported by the numerous similarities between EUHFORIA time series at Solar Orbiter and Solar Orbiter data.Conclusions. The combination of in situ measurements and numerical simulations (together with remote sensing observations of the corona and inner heliosphere) will significantly lead to a deeper understanding of the physical processes occurring during the CME-CME interaction.
Koller F, Temmer M, Preisser L, et al., 2021, Magnetosheath jet occurrence rate in relation to CMEs and SIRs
Vuorinen L, Hietala H, Plaschke F, et 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
LaMoury AT, Hietala H, Plaschke F, et 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.
Desai RT, Freeman M, Eastwood J, et 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.
Runov A, Grandin M, Palmroth M, et al., 2021, Ion distribution functions in magnetotail reconnection: global hybrid-Vlasov simulation results, ANNALES GEOPHYSICAE, Vol: 39, Pages: 599-612, ISSN: 0992-7689
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