Coronal mass ejections (CMEs) are magnetized plasma systems with highly complex magnetic topology and evolution. Methods developed to assess their magnetic configuration have primarily focused on reconstructing three-dimensional representations from one-dimensional time series measurements taken in situ using techniques based on the "highly twisted magnetic flux rope" approximations. However, the magnetic fields of CMEs is know to have more complicated geometries. Their structure can be quantified using measures of field line topology, which have been primarily used for solar physics research. In this work, we introduce a novel technique of directly quantifying the various form of magnetic helicity within a CME in the interplanetary space using synthetic in situ measurements. We use a relatively simple three-dimensional simulation of a CME initiated with a highly-twisted flux rope. We find that a significant portion of the magnetic helicity near 1~au is contained in writhe and mutual helicity rather than just in twist. We discuss the implications of this finding for fitting and reconstruction techniques.
{"title":"Deriving the Topological Properties of the Magnetic Field of Coronal Mass Ejections from In Situ Measurements: Techniques","authors":"Nada Al-Haddad, Mitchell Berger","doi":"arxiv-2408.04608","DOIUrl":"https://doi.org/arxiv-2408.04608","url":null,"abstract":"Coronal mass ejections (CMEs) are magnetized plasma systems with highly\u0000complex magnetic topology and evolution. Methods developed to assess their\u0000magnetic configuration have primarily focused on reconstructing\u0000three-dimensional representations from one-dimensional time series measurements\u0000taken in situ using techniques based on the \"highly twisted magnetic flux rope\"\u0000approximations. However, the magnetic fields of CMEs is know to have more\u0000complicated geometries. Their structure can be quantified using measures of\u0000field line topology, which have been primarily used for solar physics research.\u0000In this work, we introduce a novel technique of directly quantifying the\u0000various form of magnetic helicity within a CME in the interplanetary space\u0000using synthetic in situ measurements. We use a relatively simple\u0000three-dimensional simulation of a CME initiated with a highly-twisted flux\u0000rope. We find that a significant portion of the magnetic helicity near 1~au is\u0000contained in writhe and mutual helicity rather than just in twist. We discuss\u0000the implications of this finding for fitting and reconstruction techniques.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"276 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shreeyesh Biswal, Marianna B. Korsós, Manolis K. Georgoulis, Alexander Nindos, Spiros Patsourakos, Robertus Erdélyi
The R-value is a measure of the strength of photospheric magnetic Polarity Inversion Lines (PILs) in Active Regions (ARs). This work investigates the possibility of a relation between R-value variations and the occurrence of X-class flares in ARs, not in the solar photosphere, as usual, but above it in regions, closer to where flares occur. The modus operandi is to extrapolate the Solar Dynamic Observatory's (SDO) Helioseismic and Magnetic Imager (HMI) magnetogram data up to a height of 3.24 Mm above the photosphere and then compute the R-value based on the extrapolated magnetic field. Recent studies have shown that certain flare-predictive parameters such as the horizontal gradient of the vertical magnetic field and magnetic helicity may improve flare prediction lead times significantly if studied at a specific height range above the photosphere, called the Optimal Height Range (OHR). Here we define the OHR as a collection of heights where a sudden but sustained increase in R-value is found. For the eight case studies discussed in this paper, our results indicate that it is possible for OHRs to exist in the low solar atmosphere (between 0.36 - 3.24 Mm), where R-value spikes occur 48-68 hrs before the first X-class flare of an emerging AR. The temporal evolution of R-value before the first X-class flare for an emerging AR is also found to be distinct from that of non-flaring ARs. For X-class flares associated with non-emerging ARs, an OHR could not be found.
R 值是对活动区（ARs）光球磁极反转线（PILs）强度的测量。这项工作研究的是R值变化与ARs中X级耀斑发生之间的关系的可能性，而不是像通常那样在太阳光层中，而是在太阳光层之上的区域中，更接近耀斑发生的地方。工作方式是将太阳动力学观测站（SDO）的日震和磁成像仪（HMI）磁图数据推断到光球以上 3.24 毫米的高度，然后根据推断的磁场计算 R 值。最近的研究表明，如果在光球上方的特定高度范围（称为 "最佳高度范围"）进行研究，某些耀斑预测参数（如垂直磁场的水平梯度和磁螺旋度）可能会显著改善耀斑预测的提前时间。在这里，我们将 OHR 定义为发现 R 值突然但持续增加的高度集合。对于本文讨论的八个案例研究，我们的结果表明，在低太阳大气层（0.36-3.24 毫米之间）可能存在最佳高度范围，在那里，R 值峰值出现在新出现的 AR 的第一个 X 级耀斑之前 48-68 小时。研究还发现，新出现的AR在第一次X级耀斑之前R值的时间演变也与非耀斑AR不同。对于与非正在出现的AR有关的X级耀斑，则无法找到OHR。
{"title":"Case studies on pre-eruptive X-class flares using R-value in the lower solar atmosphere","authors":"Shreeyesh Biswal, Marianna B. Korsós, Manolis K. Georgoulis, Alexander Nindos, Spiros Patsourakos, Robertus Erdélyi","doi":"arxiv-2408.04018","DOIUrl":"https://doi.org/arxiv-2408.04018","url":null,"abstract":"The R-value is a measure of the strength of photospheric magnetic Polarity\u0000Inversion Lines (PILs) in Active Regions (ARs). This work investigates the\u0000possibility of a relation between R-value variations and the occurrence of\u0000X-class flares in ARs, not in the solar photosphere, as usual, but above it in\u0000regions, closer to where flares occur. The modus operandi is to extrapolate the\u0000Solar Dynamic Observatory's (SDO) Helioseismic and Magnetic Imager (HMI)\u0000magnetogram data up to a height of 3.24 Mm above the photosphere and then\u0000compute the R-value based on the extrapolated magnetic field. Recent studies\u0000have shown that certain flare-predictive parameters such as the horizontal\u0000gradient of the vertical magnetic field and magnetic helicity may improve flare\u0000prediction lead times significantly if studied at a specific height range above\u0000the photosphere, called the Optimal Height Range (OHR). Here we define the OHR\u0000as a collection of heights where a sudden but sustained increase in R-value is\u0000found. For the eight case studies discussed in this paper, our results indicate\u0000that it is possible for OHRs to exist in the low solar atmosphere (between 0.36\u0000- 3.24 Mm), where R-value spikes occur 48-68 hrs before the first X-class flare\u0000of an emerging AR. The temporal evolution of R-value before the first X-class\u0000flare for an emerging AR is also found to be distinct from that of non-flaring\u0000ARs. For X-class flares associated with non-emerging ARs, an OHR could not be\u0000found.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946759","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
It is shown, using results of fully kinetic 3D numerical simulations and observations in solar wind and Earth's magnetosphere that the transition from deterministic chaos to turbulence at kinetic (sub-ion) scales in space plasmas is generally dominated by magnetic helicity (an adiabatic invariant in a weakly dissipative plasma) directly or through the Kolmogorov-Iroshnikov phenomenology (the magneto-inertial range of scales as a precursor of hard turbulence). Despite the considerable differences in the scales and physical parameters, the results of numerical simulations are in quantitative agreement with the space observations in the frames of this approach.
{"title":"Kinetic scales dominated by magnetic helicity in space plasmas","authors":"A. Bershadskii","doi":"arxiv-2408.03267","DOIUrl":"https://doi.org/arxiv-2408.03267","url":null,"abstract":"It is shown, using results of fully kinetic 3D numerical simulations and\u0000observations in solar wind and Earth's magnetosphere that the transition from\u0000deterministic chaos to turbulence at kinetic (sub-ion) scales in space plasmas\u0000is generally dominated by magnetic helicity (an adiabatic invariant in a weakly\u0000dissipative plasma) directly or through the Kolmogorov-Iroshnikov phenomenology\u0000(the magneto-inertial range of scales as a precursor of hard turbulence).\u0000Despite the considerable differences in the scales and physical parameters, the\u0000results of numerical simulations are in quantitative agreement with the space\u0000observations in the frames of this approach.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"59 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jiawei Gao, Shibang Li, Anna Mittelholz, Zhaojin Rong, Moa Persson, Zhen Shi, Haoyu Lu, Chi Zhang, Xiaodong Wang, Chuanfei Dong, Lucy Klinger, Jun Cui, Yong Wei, Yongxin Pan
When the solar wind interacts with the ionosphere of an unmagnetized planet, it induces currents that form an induced magnetosphere. These currents and their associated magnetic fields play a pivotal role in controlling the movement of charged particles, which is essential for understanding the escape of planetary ions. Unlike the well-documented magnetospheric current systems, the ionospheric current systems on unmagnetized planets remain less understood, which constrains the quantification of electrodynamic energy transfer from stars to these planets. Here, utilizing eight years of data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the global distribution of ionospheric currents on Mars. We have identified two distinct current systems in the ionosphere: one aligns with the solar wind electric field yet exhibits hemispheric asymmetry perpendicular to the electric field direction; the other corresponds to the flow pattern of annually-averaged neutral winds. We propose that these two current systems are driven by the solar wind and atmospheric neutral winds, respectively. Our findings reveal that Martian ionospheric dynamics are influenced by the neutral winds from below and the solar wind from above, highlighting the complex and intriguing nature of current systems on unmagnetized planets.
{"title":"Characterizing the current systems in the Martian ionosphere","authors":"Jiawei Gao, Shibang Li, Anna Mittelholz, Zhaojin Rong, Moa Persson, Zhen Shi, Haoyu Lu, Chi Zhang, Xiaodong Wang, Chuanfei Dong, Lucy Klinger, Jun Cui, Yong Wei, Yongxin Pan","doi":"arxiv-2408.03075","DOIUrl":"https://doi.org/arxiv-2408.03075","url":null,"abstract":"When the solar wind interacts with the ionosphere of an unmagnetized planet,\u0000it induces currents that form an induced magnetosphere. These currents and\u0000their associated magnetic fields play a pivotal role in controlling the\u0000movement of charged particles, which is essential for understanding the escape\u0000of planetary ions. Unlike the well-documented magnetospheric current systems,\u0000the ionospheric current systems on unmagnetized planets remain less understood,\u0000which constrains the quantification of electrodynamic energy transfer from\u0000stars to these planets. Here, utilizing eight years of data from the Mars\u0000Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the global\u0000distribution of ionospheric currents on Mars. We have identified two distinct\u0000current systems in the ionosphere: one aligns with the solar wind electric\u0000field yet exhibits hemispheric asymmetry perpendicular to the electric field\u0000direction; the other corresponds to the flow pattern of annually-averaged\u0000neutral winds. We propose that these two current systems are driven by the\u0000solar wind and atmospheric neutral winds, respectively. Our findings reveal\u0000that Martian ionospheric dynamics are influenced by the neutral winds from\u0000below and the solar wind from above, highlighting the complex and intriguing\u0000nature of current systems on unmagnetized planets.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Rosetta spacecraft accompanied the comet 67P/C-G for nearly 2 years, collecting valuable data on the neutral and ion composition of the coma. The Rosetta Plasma Consortium (RPC) provided continuous measurements of the in situ plasma density while ROSINA-COPS monitored the neutral composition. In this work, we aim to estimate the composition of the cometary ionosphere at different heliocentric distances of the comet. Lauter et al. (2020) derived the temporal evolution of the volatile sublimation rates for 50 separated time intervals on the orbit of 67P/C-G using the COPS and DFMS data. We use these sublimation rates as inputs in a multifluid chemical-hydrodynamical model for 36 of the time intervals for heliocentric distances < 3 au. We compare the total ion densities obtained from our models with the local plasma density measured by the RPC instruments. We find that at the location of the spacecraft, our modeled ion densities match with the in situ measured plasma density within factors of 1 - 3 for many of the time intervals. We obtain the cometocentric distance variation of the ions H2O+ and H3O+ and the ion groups created respectively by the ionization and protonation of neutral species. We see that H3O+ is dominant at the spacecraft location for nearly all the time intervals while ions created due to protonation are dominant at low cometocentric distances for the intervals near perihelion. We also discuss our ion densities in the context of their detection by DFMS.
{"title":"Modeling the Plasma Composition of 67P/C-G at different Heliocentric Distances","authors":"Sana Ahmed, Vikas Soni","doi":"arxiv-2408.02338","DOIUrl":"https://doi.org/arxiv-2408.02338","url":null,"abstract":"The Rosetta spacecraft accompanied the comet 67P/C-G for nearly 2 years,\u0000collecting valuable data on the neutral and ion composition of the coma. The\u0000Rosetta Plasma Consortium (RPC) provided continuous measurements of the in situ\u0000plasma density while ROSINA-COPS monitored the neutral composition. In this\u0000work, we aim to estimate the composition of the cometary ionosphere at\u0000different heliocentric distances of the comet. Lauter et al. (2020) derived the\u0000temporal evolution of the volatile sublimation rates for 50 separated time\u0000intervals on the orbit of 67P/C-G using the COPS and DFMS data. We use these\u0000sublimation rates as inputs in a multifluid chemical-hydrodynamical model for\u000036 of the time intervals for heliocentric distances < 3 au. We compare the\u0000total ion densities obtained from our models with the local plasma density\u0000measured by the RPC instruments. We find that at the location of the\u0000spacecraft, our modeled ion densities match with the in situ measured plasma\u0000density within factors of 1 - 3 for many of the time intervals. We obtain the\u0000cometocentric distance variation of the ions H2O+ and H3O+ and the ion groups\u0000created respectively by the ionization and protonation of neutral species. We\u0000see that H3O+ is dominant at the spacecraft location for nearly all the time\u0000intervals while ions created due to protonation are dominant at low\u0000cometocentric distances for the intervals near perihelion. We also discuss our\u0000ion densities in the context of their detection by DFMS.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"59 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The properties of energy transfer in the kinetic range of plasma turbulence have fundamental implications on the turbulent heating of space and astrophysical plasmas. It was recently suggested that magnetic reconnection may be responsible for driving the sub-ion scale cascade, and that this process would be characterized by a direct energy transfer towards even smaller scales (until dissipation), and a simultaneous inverse transfer of energy towards larger scales, until the ion break. Here we employ the space-filter technique on high-resolution 2D3V hybrid-Vlasov simulations of continuously driven turbulence providing for the first time quantitative evidence that magnetic reconnection is indeed able to trigger a dual energy transfer originating at sub-ion scales.
{"title":"Evidence of dual energy transfer driven by magnetic reconnection at sub-ion scales","authors":"Raffaello Foldes, Silvio Sergio Cerri, Raffaele Marino, Enrico Camporeale","doi":"arxiv-2408.02505","DOIUrl":"https://doi.org/arxiv-2408.02505","url":null,"abstract":"The properties of energy transfer in the kinetic range of plasma turbulence\u0000have fundamental implications on the turbulent heating of space and\u0000astrophysical plasmas. It was recently suggested that magnetic reconnection may\u0000be responsible for driving the sub-ion scale cascade, and that this process\u0000would be characterized by a direct energy transfer towards even smaller scales\u0000(until dissipation), and a simultaneous inverse transfer of energy towards\u0000larger scales, until the ion break. Here we employ the space-filter technique\u0000on high-resolution 2D3V hybrid-Vlasov simulations of continuously driven\u0000turbulence providing for the first time quantitative evidence that magnetic\u0000reconnection is indeed able to trigger a dual energy transfer originating at\u0000sub-ion scales.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"180 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Robert F. Wimmer-Schweingruber, Javier Rodriguez-Pacheco, George C. Ho, Christina M. Cohen, Glenn M. Mason, the Solar Orbiter EPD, Parker Solar Probe ISIS teams
The Sun drives a supersonic wind which inflates a giant plasma bubble in our very local interstellar neighborhood, the heliosphere. It is bathed in an extremely variable background of energetic ions and electrons which originate from a number of sources. Solar energetic particles (SEPs) are accelerated in the vicinity of the Sun, whereas shocks driven by solar disturbances are observed to accelerate energetic storm particles (ESPs). Moreover, a dilute population with a distinct composition forms the anomalous cosmic rays (ACRs) which are of a mixed interstellar-heliospheric origin. Particles are also accelerated at planetary bow shocks. We will present recent observations of energetic particles by Solar Orbiter and Parker Solar Probe, as well as other spacecraft that allow us to study the acceleration and transport of energetic particles at multiple locations in the inner heliosphere.
{"title":"SEP environment in the inner heliosphere from Solar Orbiter and Parker Solar Probe","authors":"Robert F. Wimmer-Schweingruber, Javier Rodriguez-Pacheco, George C. Ho, Christina M. Cohen, Glenn M. Mason, the Solar Orbiter EPD, Parker Solar Probe ISIS teams","doi":"arxiv-2408.02330","DOIUrl":"https://doi.org/arxiv-2408.02330","url":null,"abstract":"The Sun drives a supersonic wind which inflates a giant plasma bubble in our\u0000very local interstellar neighborhood, the heliosphere. It is bathed in an\u0000extremely variable background of energetic ions and electrons which originate\u0000from a number of sources. Solar energetic particles (SEPs) are accelerated in\u0000the vicinity of the Sun, whereas shocks driven by solar disturbances are\u0000observed to accelerate energetic storm particles (ESPs). Moreover, a dilute\u0000population with a distinct composition forms the anomalous cosmic rays (ACRs)\u0000which are of a mixed interstellar-heliospheric origin. Particles are also\u0000accelerated at planetary bow shocks. We will present recent observations of\u0000energetic particles by Solar Orbiter and Parker Solar Probe, as well as other\u0000spacecraft that allow us to study the acceleration and transport of energetic\u0000particles at multiple locations in the inner heliosphere.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"88 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vladimir Zeković, Anatoly Spitkovsky, Zachary Hemler
Short Large Amplitude Magnetic Structures (SLAMS) are frequently detected during spacecraft crossings over the Earth bow shock. We investigate the existence of such structures at astrophysical shocks, where they could result from the steepening of cosmic-ray (CR) driven waves. Using kinetic particle-in-cell simulations, we study the growth of SLAMS and the appearance of associated transient shocks in the upstream region of quasi-parallel, non-relativistic, high-Mach number collisionless shocks. We find that high-energy CRs significantly enhance the transverse magnetic field within SLAMS, producing highly inclined field lines. As SLAMS are advected towards the shock, these fields lines form an intermittent superluminal configuration which traps magnetized electrons at fast shocks. Due to their oscillatory nature, SLAMS are periodically separated by subluminal gaps with lower transverse magnetic field strength. In these regions, electrons diffuse and accelerate by bouncing between the shock and the approaching SLAMS region through a mechanism that we call quasi-periodic shock acceleration (QSA). We analytically derive the distribution of electrons accelerated via QSA, $f(p)sim p^{[-4.7,-5.7]}$, which agrees well with the simulation spectra. We find that the electron power law remains steep until the end of our longest runs, providing a possible explanation for the steep electron spectra observed at least up to GeV energies in young and fast supernova remnants.
{"title":"SLAMS-Propelled Electron Acceleration at High-Mach Number Astrophysical Shocks","authors":"Vladimir Zeković, Anatoly Spitkovsky, Zachary Hemler","doi":"arxiv-2408.02084","DOIUrl":"https://doi.org/arxiv-2408.02084","url":null,"abstract":"Short Large Amplitude Magnetic Structures (SLAMS) are frequently detected\u0000during spacecraft crossings over the Earth bow shock. We investigate the\u0000existence of such structures at astrophysical shocks, where they could result\u0000from the steepening of cosmic-ray (CR) driven waves. Using kinetic\u0000particle-in-cell simulations, we study the growth of SLAMS and the appearance\u0000of associated transient shocks in the upstream region of quasi-parallel,\u0000non-relativistic, high-Mach number collisionless shocks. We find that\u0000high-energy CRs significantly enhance the transverse magnetic field within\u0000SLAMS, producing highly inclined field lines. As SLAMS are advected towards the\u0000shock, these fields lines form an intermittent superluminal configuration which\u0000traps magnetized electrons at fast shocks. Due to their oscillatory nature,\u0000SLAMS are periodically separated by subluminal gaps with lower transverse\u0000magnetic field strength. In these regions, electrons diffuse and accelerate by\u0000bouncing between the shock and the approaching SLAMS region through a mechanism\u0000that we call quasi-periodic shock acceleration (QSA). We analytically derive\u0000the distribution of electrons accelerated via QSA, $f(p)sim p^{[-4.7,-5.7]}$,\u0000which agrees well with the simulation spectra. We find that the electron power\u0000law remains steep until the end of our longest runs, providing a possible\u0000explanation for the steep electron spectra observed at least up to GeV energies\u0000in young and fast supernova remnants.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Artem Bohdan, Aaron Tran, Lorenzo Sironi, Lynn B. Wilson III
Collisionless low Mach number shocks are abundant in astrophysical and space plasma environments, exhibiting complex wave activity and wave-particle interactions. In this paper, we present 2D Particle-in-Cell (PIC) simulations of quasi-perpendicular nonrelativistic ($vsh approx (5500-22000)$ km/s) low Mach number shocks, with a specific focus on studying electrostatic waves in the shock ramp and the precursor regions. In these shocks, an ion-scale oblique whistler wave creates a configuration with two hot counter-streaming electron beams, which drive unstable electron acoustic waves (EAWs) that can turn into electrostatic solitary waves (ESWs) at the late stage of their evolution. By conducting simulations with periodic boundaries, we show that EAW properties agree with linear dispersion analysis. The characteristics of ESWs in shock simulations, including their wavelength and amplitude, depend on the shock velocity. When extrapolated to shocks with realistic velocities ($vsh approx 300$ km/s), the ESW wavelength is reduced to one tenth of the electron skin depth and the ESW amplitude is anticipated to surpass that of the quasi-static electric field by more than a factor of 100. These theoretical predictions may explain a discrepancy, between PIC and satellite measurements, in the relative amplitude of high- and low-frequency electric field fluctuations.
{"title":"Electrostatic Waves and Electron Holes in Simulations of Low-Mach Quasi-Perpendicular Shocks","authors":"Artem Bohdan, Aaron Tran, Lorenzo Sironi, Lynn B. Wilson III","doi":"arxiv-2408.01699","DOIUrl":"https://doi.org/arxiv-2408.01699","url":null,"abstract":"Collisionless low Mach number shocks are abundant in astrophysical and space\u0000plasma environments, exhibiting complex wave activity and wave-particle\u0000interactions. In this paper, we present 2D Particle-in-Cell (PIC) simulations\u0000of quasi-perpendicular nonrelativistic ($vsh approx (5500-22000)$ km/s) low\u0000Mach number shocks, with a specific focus on studying electrostatic waves in\u0000the shock ramp and the precursor regions. In these shocks, an ion-scale oblique\u0000whistler wave creates a configuration with two hot counter-streaming electron\u0000beams, which drive unstable electron acoustic waves (EAWs) that can turn into\u0000electrostatic solitary waves (ESWs) at the late stage of their evolution. By\u0000conducting simulations with periodic boundaries, we show that EAW properties\u0000agree with linear dispersion analysis. The characteristics of ESWs in shock\u0000simulations, including their wavelength and amplitude, depend on the shock\u0000velocity. When extrapolated to shocks with realistic velocities ($vsh approx\u0000300$ km/s), the ESW wavelength is reduced to one tenth of the electron skin\u0000depth and the ESW amplitude is anticipated to surpass that of the quasi-static\u0000electric field by more than a factor of 100. These theoretical predictions may\u0000explain a discrepancy, between PIC and satellite measurements, in the relative\u0000amplitude of high- and low-frequency electric field fluctuations.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The basic equations, concepts, and modes of linear, ideal, MHD waves -- slow, Alfv'en and fast -- are set out and generalised to gravitationally-stratified atmospheres. Particular attention is devoted to mode conversion, wherein the local behavior of a global wave changes from one mode to another in passing through particular atmospheric layers. Exact solutions are explored where available. Eikonal methods -- WKBJ and ray theory -- are described. Although our emphasis is on the theoretical underpinning of the subject, the solar atmospheric heating implications of fast/slow and fast/Alfv'en conversions are discussed in detail.
{"title":"MHD waves in homogeneous and continuously stratified atmospheres","authors":"Paul S. Cally, Thomas J. Bogdan","doi":"arxiv-2408.01591","DOIUrl":"https://doi.org/arxiv-2408.01591","url":null,"abstract":"The basic equations, concepts, and modes of linear, ideal, MHD waves -- slow,\u0000Alfv'en and fast -- are set out and generalised to gravitationally-stratified\u0000atmospheres. Particular attention is devoted to mode conversion, wherein the\u0000local behavior of a global wave changes from one mode to another in passing\u0000through particular atmospheric layers. Exact solutions are explored where\u0000available. Eikonal methods -- WKBJ and ray theory -- are described. Although\u0000our emphasis is on the theoretical underpinning of the subject, the solar\u0000atmospheric heating implications of fast/slow and fast/Alfv'en conversions are\u0000discussed in detail.","PeriodicalId":501423,"journal":{"name":"arXiv - PHYS - Space Physics","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141947133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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