Effects of upstream conditions on ULF waves and SLAMS formation at Saturn

2021 ◽  
Author(s):  
Zsofia Bebesi ◽  
Antal Juhasz
Keyword(s):  
Magnetic Field ◽  
Simple Model ◽  
Shock Front ◽  
Large Amplitude ◽  
Plasma Pressure ◽  
Bow Shock ◽  
Wave Formation ◽  
Ulf Waves ◽  
Magnetic Structures ◽  
Ulf Wave

<p>In this study we present occurences of SLAMS (short large-amplitude magnetic structures) upstream of the quasi-parallel bow shock of Saturn. Five events are analyzed in more detail using the data of the CAPS and MAG instruments of Cassini. Directional and speed analysis of the backstreaming particles related to ULF wave formation (and subsequent SLAMS evolution) in the foreshock region is presented. We also correlate the measured the ULF wave frequencies with the variations of the upstream magnetic field.<br>With a simple model we estimate the distance of the observed SLAMS from the bow shock front based on the measured plasma pressure. We also <br>discuss the spatial characteristics of SLAMS observed near Saturn.</p>

Analysis of short large amplitude magnetic structures at the Kronian bow shock

2020 ◽  
Author(s):  
Zsofia Bebesi ◽  
Geza Erdos ◽  
Melinda Dosa ◽  
Karoly Szego
Keyword(s):  
Large Amplitude ◽  
Ion Beam ◽  
Plasma Heating ◽  
Bow Shock ◽  
Ulf Waves ◽  
Fast Mode ◽  
Magnetic Structures ◽  
Earth Observations ◽  
Plasma Spectrometer ◽  
Beam Reflection

<p>            We present a comprehensive statistical analysis of Short Large Amplitude Magnetic Structures (SLAMS) upstream of the quasi-parallel bow shock of Saturn. During its mission Cassini extensive surveyed the quasi-parallel regime. For this study we used the measurements of the Cassini Plasma Spectrometer (CAPS) and the Magnetometer (MAG).</p><p>            The SLAM structures locally act as fast mode shock waves, and we observed possible ion beam reflection, multiple ion beams, deceleration and plasma heating of the solar wind protons. These features are in agreement with the near Earth observations. We also detected whistler precursor waves multiple times, which was also documented in studies of the Earth's foreshock region. Since the frequency of the upstream ULF waves detected at Saturn is lower than it is at Earth, it also has an effect on the spatial extension of the SLAM structures, which arise from these waves. With only one spacecraft's measurements it is not possible to study the SLAMS with the same efficiency as with the four-point measurements of the CLUSTER probes, but the basic observational features and the description of their evolutional characteristics are summarized.</p>

Magnetic structures and reformation at quasi-parallel shocks

2021 ◽  
Author(s):  
Andreas Johlander ◽  
Markus Battarbee ◽  
Lucile Turc ◽  
Yann Pfau-Kempf ◽  
Urs Ganse ◽  
...  
Keyword(s):  
Shock Waves ◽  
Shock Front ◽  
Large Amplitude ◽  
Bow Shock ◽  
Particle Accelerators ◽  
Magnetic Structures ◽  
Collisionless Plasmas ◽  
Simulation Results ◽  
High Cadence

<p>Shock waves in collisionless plasmas are common in heliospheric and astrophysical settings and are some of the most efficient particle accelerators in space. Shocks can undergo self-reformation where a new shock front appears in front of the previous shock front. Shock reformation has been observed previously in both spacecraft observations and simulations, but the process is not yet fully understood. We here study self-reformation of Earth's quasi-parallel bow shock with observations from the four MMS spacecraft and simulation results from the hybrid-Vlasov simulation Vlasiator. We find, in both observations and simulation, that short large amplitude magnetic structures (SLAMS) can constitute shock reformation. The SLAMS form upstream of the shock and grow in amplitude while being convected towards the shock and eventually forming the new shock front. Using MMS's and Vlasiator's high-cadence field and ion measurements, we study how the shock reformation process influences the dynamics and acceleration of ions at the quasi-parallel shock.</p>

scholarly journals Foreshock cavitons and spontaneous hot flow anomalies: A statistical study with a global hybrid-Vlasov simulation

2021 ◽  
Author(s):  
Vertti Tarvus ◽  
Lucile Turc ◽  
Markus Battarbee ◽  
Jonas Suni ◽  
Xóchitl Blanco-Cano ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Rest Frame ◽  
Statistical Study ◽  
Plasma Temperature ◽  
Propagation Speed ◽  
Bow Shock ◽  
Ulf Waves ◽  
Subsequent Formation ◽  
Comparable Amount

Abstract. The foreshock located upstream of Earth's bow shock hosts a wide variety of phenomena related to the reflection of solar wind particles from the bow shock and the subsequent formation of ultra-low frequency (ULF) waves. In this work, we investigate foreshock cavitons, which are transient structures resulting from the non-linear evolution of ULF waves, and spontaneous hot flow anomalies (SHFAs), which evolve from cavitons as they accumulate suprathermal ions while being carried to the bow shock by the solar wind. Using the global hybrid-Vlasov simulation model Vlasiator, we have conducted a statistical study in which we track the motion of individual cavitons and SHFAs in order to examine their properties and evolution. In our simulation run where the interplanetary magnetic field (IMF) is directed at a sunward-southward angle of 45 degrees, continuous formation of cavitons is found up to ~ 11 Earth radii (RE) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within ~ 2 RE from the shock. A third of the cavitons in our run evolve into SHFAs, and we find a comparable amount of SHFAs forming independently near the bow shock. We compare the properties of cavitons and SHFAs to prior spacecraft observations and simulations, finding good agreement. We also investigate the variation of the properties as a function of position in the foreshock, showing that the transients close to the bow shock are associated with larger depletions in the plasma density and magnetic field magnitude, along with larger increases in the plasma temperature and the level of bulk flow deflection. Our measurements of the propagation velocities of cavitons and SHFAs agree with earlier studies, showing that the transients propagate sunward in the solar wind rest frame. We show that SHFAs have a greater solar wind rest frame propagation speed than cavitons, which is related to an increase in the magnetosonic speed near the bow shock.

scholarly journals Foreshock cavitons and spontaneous hot flow anomalies: a statistical study with a global hybrid-Vlasov simulation

2021 ◽  
Vol 39 (5) ◽  
pp. 911-928
Author(s):  
Vertti Tarvus ◽  
Lucile Turc ◽  
Markus Battarbee ◽  
Jonas Suni ◽  
Xóchitl Blanco-Cano ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Rest Frame ◽  
Statistical Study ◽  
Plasma Temperature ◽  
Propagation Speed ◽  
Bow Shock ◽  
Ulf Waves ◽  
Subsequent Formation ◽  
Comparable Amount

Abstract. The foreshock located upstream of Earth's bow shock hosts a wide variety of phenomena related to the reflection of solar wind particles from the bow shock and the subsequent formation of ultra-low-frequency (ULF) waves. In this work, we investigate foreshock cavitons, which are transient structures resulting from the non-linear evolution of ULF waves, and spontaneous hot flow anomalies (SHFAs), which are thought to evolve from cavitons as they accumulate suprathermal ions while being carried to the bow shock by the solar wind. Using the global hybrid-Vlasov simulation model Vlasiator, we have conducted a statistical study in which we track the motion of individual cavitons and SHFAs in order to examine their properties and evolution. In our simulation run where the interplanetary magnetic field (IMF) is directed at a sunward–southward angle of 45∘, continuous formation of cavitons is found up to ∼11 Earth radii (RE) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within ∼2 RE from the shock. A third of the cavitons in our run evolve into SHFAs, and we find a comparable amount of SHFAs forming independently near the bow shock. We compare the properties of cavitons and SHFAs to prior spacecraft observations and simulations, finding good agreement. We also investigate the variation of the properties as a function of position in the foreshock, showing that transients close to the bow shock are associated with larger depletions in the plasma density and magnetic field magnitude, along with larger increases in the plasma temperature and the level of bulk flow deflection. Our measurements of the propagation velocities of cavitons and SHFAs agree with earlier studies, showing that the transients propagate sunward in the solar wind rest frame. We show that SHFAs have a greater solar wind rest frame propagation speed than cavitons, which is related to an increase in the magnetosonic speed near the bow shock.

Observations of simultaneously occurring ULF and Ion Cyclotron Waves by the GOES-16 satellite magnetometer and particle detectors at geostationary orbit

2020 ◽  
Author(s):  
Paul Loto'aniu
Keyword(s):  
Magnetic Field ◽  
Ring Current ◽  
Resonance Condition ◽  
Sampling Rate ◽  
Ion Fluxes ◽  
Ulf Waves ◽  
Ulf Wave ◽  
Ion Cyclotron ◽  
Generation Mechanisms ◽  
Emic Waves

<p>The GOES-16 spacecraft, launched in November 2016, is the first of the GOES-R series next generation NOAA weather satellites. The spacecraft has a similar suite of space weather instruments to previous GOES satellites but with improved magnetometer sampling rate and wider energy range of particle flux observations. Presented are observations of simultaneously occurring Pc 4/5 ULF waves and electromagnetic ion cyclotron (EMIC) waves with a discussion on the relationship between the two wave modes including possible generation mechanisms. The waves were also observed in the particle data and we discuss both adiabatic and non-adiabatic wave-particle effects. Relativistic electron fluxes showed strong adiabatic motion with the magnetic field ULF waves. Estimates of Pc 4/5 ULF wave m-numbers suggest they were high, while ring current energy ion fluxes showed ULF variations with non-zero phasing relative to magnetic field ULF wave. This suggests ULF wave drift resonance with ring current ions. In one event we observed EMIC variations in the ion fluxes around energies that can drift resonate with simultaneously observed Pc 5 waves, suggesting that one particle population may be responsible for generating and/or modifying both observed Pc 5 and EMIC waves. ULF variations were also observed in electron/ion fluxes at lower energies down to 30 eV. We looked into ULF bounce resonance with 30 eV electrons, but the resonance condition did not match the observations. We will also discuss future plans to expand this study of ULF waves and wave-particle interactions using the two newest GOES satellites.</p>

A Deep Learning Technique for Automated Detection of ULF Waves in Swarm Time Series

2020 ◽  
Author(s):  
Alexandra Antonopoulou ◽  
Constantinos Papadimitriou ◽  
Georgios Balasis ◽  
Adamantia Zoe Boutsi ◽  
Konstantinos Koutroumbas ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Deep Learning ◽  
Building Blocks ◽  
Data Availability ◽  
Topside Ionosphere ◽  
Ulf Waves ◽  
Dense Layer ◽  
Ulf Wave ◽  
The Earth ◽  
Swarm Satellites

<p>Ultra-low frequency (ULF) magnetospheric plasma waves play a key role in the dynamics of the Earth’s magnetosphere and, therefore, their importance in Space Weather studies is indisputable. Magnetic field measurements from recent multi-satellite missions (e.g. Cluster, THEMIS, Van Allen Probes and Swarm) are currently advancing our knowledge on the physics of ULF waves. In particular, Swarm satellites, one of the most successful mission for the study of the near-Earth electromagnetic environment, have contributed to the expansion of data availability in the topside ionosphere, stimulating much recent progress in this area. Coupled with the new successful developments in artificial intelligence (AI), we are now able to use more robust approaches devoted to automated ULF wave event identification and classification. The goal of this effort is to use a deep learning method in order to classify ULF wave events using magnetic field data from Swarm. We construct a Convolutional Neural Network (CNN) that takes as input the wavelet spectra of the Earth’s magnetic field variations per track, as measured by each one of the three Swarm satellites, and whose building blocks consist of two convolution layers, two pooling layers and a fully connected (dense) layer, aiming to classify ULF wave events in four different categories: 1) Pc3 wave events (i.e., frequency range 20-100 MHz), 2) non-events, 3) false positives, and 4) plasma instabilities. Our primary experiments show promising results, yielding successful identification of more than 95% accuracy. We are currently working on producing larger training/test datasets, by analyzing Swarm data from the mid-2014 onwards, when the final constellation was formed, aiming to construct a dataset comprising of more than 50000 wavelet image inputs for our network.</p>

scholarly journals The Pulsating Magnetosphere at Jupiter

2020 ◽  
Author(s):  
Harry Manners ◽  
Adam Masters
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Dynamic Pressure ◽  
Wave Spectrum ◽  
Low Frequency ◽  
Global Scale ◽  
Wave Activity ◽  
Ulf Waves ◽  
Ulf Wave ◽  
Wide Range

<p>The magnetosphere of Jupiter is the largest planetary magnetosphere in the solar system, and plays host to internal dynamics that remain, in many ways, mysterious. Prominent among these mysteries are the ultra-low-frequency (<strong>ULF</strong>) pulses ubiquitous in this system. Pulsations in the electromagnetic emissions, magnetic field and flux of energetic particles have been observed for decades, with little to indicate the source mechanism. While ULF waves have been observed in the magnetospheres of all the magnetized planets, the magnetospheric environment at Jupiter seems particularly conducive to the emergence of ULF waves over a wide range of periods (1-100+ minutes). This is mainly due to the high variability of the system on a global scale: internal plasma sources and a powerful intrinsic magnetic field produce a highly-compressible magnetospheric cavity, which can be reduced to a size significantly smaller than its nominal expanded state by variations in the dynamic pressure of the solar wind. Compressive fronts in the solar wind, turbulent surface interactions on the magnetopause and internal plasma processes can also all lead to ULF wave activity inside the magnetosphere.</p><p>To gain the first comprehensive view of ULF waves in the Jovian system, we have performed a heritage survey of magnetic field data measured by six spacecraft that visited the magnetosphere (Galileo, Ulysses, Voyager 1 & 2 and Pioneer 10 & 11). We found several-hundred wave events consisting of wave packets parallel or transverse to the mean magnetic field, interpreted as fast-mode or Alfvénic MHD wave activity, respectively. Parallel and transverse events were often coincident in space and time, which may be evidence of global Alfvénic resonances of the magnetic field known as field-line-resonances. We found that 15-, 30- and 40-minute periods dominate the Jovian ULF wave spectrum, in agreement with the dominant “magic frequencies” often reported in existing literature.</p><p>We will discuss potential driving mechanisms as informed by the results of the heritage survey, how this in turn affects our understanding of energy transfer in the magnetosphere, and potential investigations to be made using data from the JUNO spacecraft. We will also discuss the potential for multiple resonant cavities, and how the resonance modes of the Jovian magnetosphere may differ from those of the other magnetized planets.</p>

scholarly journals Evidence of the Nonstationarity of the Terrestrial Bow Shock from Multi-Spacecraft Observations: Methodology, Results and Quantitative Comparison with PIC Simulations

2020 ◽  
Author(s):  
Christian Mazelle ◽  
Bertrand Lembege
Keyword(s):  
Magnetic Field ◽  
Lower Bound ◽  
Data Processing ◽  
Shock Front ◽  
Upper Bound ◽  
Spatial Scales ◽  
Large Fraction ◽  
Field Measurements ◽  
Bow Shock ◽  
Time Variability

Abstract. The nonstationarity of the terrestrial bow shock is analyzed in detail from in situ magnetic field measurements issued from the FGM experiment on board of Cluster mission. Attention is focused on statistical analysis of quasiperpendicular supercritical shock crossings. The present analysis stresses for the first time the importance of a careful and accurate methodology in the data processing which can be a source of confusion/misunderstanding if not treated properly. The analysis performed using 96 shock front crossings shows evidence of a strong variability of the microstructures of the shock front (foot and ramp) which are analyzed in deep details. Main results are: (i) most statistics clearly evidence that the ramp thickness is very narrow and can be as low as a few c/ωpe (electron inertia length), (ii) the width is narrower when the angle θBn (between the shock normal and the upstream magnetic field) approaches 90°, (iii) the foot thickness strongly varies but its variation has an upper limit provided by theoretical estimates given in previous studies (e.g., Schwartz et al., 1983; Gosling and Thomsen, 1985; Gosling and Robson, 1985); (iv) the presence of foot and overshoot, as shown in all front profiles confirms the importance of dissipative effects. Present results indicate that these features can be signatures of the shock front self-reformation among a few mechanisms of nonstationarity identified from numerical simulation/theoretical works. A comparison 2D PIC simulation for a perpendicular supercritical shock (used as reference), has been performed and it shows that: (a) the ramp thickness varies only slightly in time over a large fraction of the reformation cycle and reaches a lower bound value of the order of a few electron inertial length, (ii) in contrast, the foot width strongly varies during a self-reformation cycle but always stays lower than an upper bound value in agreement with the value given by Woods (1971), and (iii) as a consequence, the time variability of the whole shock front is depending on both ramp and foot variations. Moreover, a detailed comparative analysis shows that much elements of analysis were missing in previous reported works concerning both (i) the important criteria used in the data selection and (ii) the different and careful steps of the methodology used in the data processing itself. This absence of these precise elements of analysis makes the comparison with present work difficult, worse, it makes some final results and conclusive statements quite questionable at present time. A least, looking for a precise estimate of the shock transition thickness presents nowadays a restricted interest, since recent results show that the terrestrial shock is rather nonstationary and one unique typical spatial scaling of the microstructures of the front (ramp, foot) must be replaced by some variation ranges (with lower bound/upper bound values) within which the spatial scales of the fine structures can extend.

scholarly journals Foreshock-like density cavity in the outflow region of magnetotail reconnection

2009 ◽  
Vol 27 (8) ◽  
pp. 3043-3053 ◽  
Author(s):  
C. L. Cai ◽  
I. Dandouras ◽  
H. Rème ◽  
J. B. Cao ◽  
G. C. Zhou ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Shock Front ◽  
Time Sequence ◽  
Field Observations ◽  
Loss Cone ◽  
Ulf Wave ◽  
Field Fluctuations ◽  
Outflow Region ◽  
Magnetotail Reconnection ◽  
Wave Boundary

Abstract. During Cluster spacecraft crossing of the magnetotail, a novel density depleted cavity in association with magnetic compressions in the outflow region of reconnection was observed. It contains intense reflected field-aligned particles, which are produced by a generation mechanism similar to that of the terrestrial foreshock, and hence manifests a foreshock-like morphology. In this cavity, reflected field-aligned proton beams were observed and simultaneously the feature of magnetic-mirror loss-cone proton distributions were found. Magnetic field fluctuations, especially quasi-monochromatic oscillations, were recorded. Both the leading egde and the ULF wave boundary of the ion foreshock are identified from the time sequence of proton and magnetic field observations. Just upstream of the leading egde of the ion foreshock, reflected field-aligned electrons were detected, whose distribution has a narrow bump-on-tail pattern. However, close to the shock front, reflected electrons with a broad bump-on-tail pattern was measured. These two different manifestations of reflected electrons reveal the differences in their microscopic physics of the reflecting process. Moreover, a part of incident ions was further accelerated in the cavity due to trans-time magnetic pumping which provides another possible mechanism in the multi-step acceleration processes in reconnection.

Observations of Short Large Amplitude Magnetic Structures at the Kronian bow shock

2020 ◽  
Author(s):  
Zsofia Bebesi ◽  
Geza Erdos ◽  
Melinda Dosa ◽  
Antal Juhasz ◽  
Karoly Szego
Keyword(s):  
Large Amplitude ◽  
Ion Beam ◽  
Plasma Heating ◽  
Bow Shock ◽  
Time Interval ◽  
Magnetic Structures ◽  
Earth Observations ◽  
Multiple Beams ◽  
Plasma Spectrometer ◽  
Beam Reflection

<p>We observed Short Large Amplitude Magnetic Structures (SLAMS) at Saturn upstream of the quasi-parallel bow shock. Cassini surveyed the quasi-parallel regime mainly during 2004 and 2005, and we present a few detailed case studies from this time interval. For our analysis we used the measurements of the Cassini Plasma Spectrometer and the Magnetometer.<br />Locally the SLAMS act as fast mode shock waves, and we observed ion beam reflection, multiple beams, deceleration and plasma heating of the solar wind protons. These features are in agreement with the near Earth observations of SLAMS. We also detected whistler precursor waves multiple times, which was also documented in studies of the Earth's foreshock region. Since the frequency of the upstream ULF waves observed at Saturn is lower than it is at Earth, it also has an effect on the spatial extension of the SLAM structures, which arise from these waves. With only one spacecraft's measurements it is not possible to study the SLAMS with the same efficiency as with the four-point measurements of the CLUSTER probes, but the basic observational features and the description of their evolutional characteristics are summarized. </p>

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