scholarly journals ULF wave transmission across collisionless shocks: 2.5D local hybrid simulations

2021 ◽  
Author(s):  
Primož Kajdič ◽  
Yann Pfau-Kempf ◽  
Lucile Turc ◽  
Andrew Dimmock ◽  
Minna Palmroth
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Simulation Models ◽  
Ulf Waves ◽  
Collisionless Shocks ◽  
Ulf Wave ◽  
Field Fluctuations ◽  
Fourier Spectra ◽  
The Waves ◽  
Upstream Waves

<p>We study the interaction of upstream ultra-low frequency (ULF) waves with collisionless shocks by analyzing the outputs of eleven 2.5D local hybrid simulation models. Our simulated shocks have Alfvénic Mach numbers between 4.29-7.42 and their θ<sub>BN</sub> angles are 15º, 30º, 45º and 50º. Thus all are quasi-parallel or marginally quasi-perpendicular shocks. Upstream of all of the shocks the ULF wave foreshock develops. It is populated by transverse and compressive ULF magnetic field fluctuations that propagate upstream in the rest frame of upstream plasma. We show that the properties of the upstream waves reflect on the properties of the shock ripples. We also show that due to these ripples, as different portions of upstream waves reach the shocks, they encounter shock sections with different properties, such as the downstream magnetic field and the orientation of the local shock normals. This means that the waves are not simply transmitted into the downstream region but are heavily processed by the shocks. The identity of upstream fluctuations is largely lost, since the downstream fluctuations do not resemble the upstream waves in their shape, waveform extension, orientation nor in their wavelength. However some features are conserved. For example, the Fourier spectra of upstream waves present a bump or flattening at wavelengths corresponding to those of the upstream ULF waves. Most of the corresponding compressive downstream spectra also exhibit these features, while transverse downstream spectra are largely featureless.</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 Alfvén waves in the near-PSBL lobe: Cluster observations

2006 ◽  
Vol 24 (3) ◽  
pp. 1001-1013 ◽  
Author(s):  
T. Takada ◽  
R. Nakamura ◽  
W. Baumjohann ◽  
K. Seki ◽  
Z. Vörös ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Ion Beam ◽  
Low Frequency ◽  
Poynting Flux ◽  
Field Fluctuations ◽  
The Rich ◽  
Field Lines ◽  
The Waves ◽  
The Magnetic Field ◽  
Low Frequency Waves

Abstract. Electromagnetic low-frequency waves in the magnetotail lobe close to the PSBL (Plasma Sheet Boundary Layer) are studied using the Cluster spacecraft. The lobe waves show Alfvénic properties and transport their wave energy (Poynting flux) on average toward the Earth along magnetic field lines. Most of the wave events are rich with oxygen (O+) ion plasma. The rich O+ plasma can serve to enhance the magnetic field fluctuations, resulting in a greater likelihood of observation, but it does not appear to be necessary for the generation of the waves. Taking into account the fact that all events are associated with auroral electrojet enhancements, the source of the lobe waves might be a substorm-associated instability, i.e. some instability near the reconnection site, or an ion beam-related instability in the PSBL.

Wave activities during different phase of solar cycle : Cassini observations on Saturn

2020 ◽  
Author(s):  
Dongxiao Pan ◽  
Zhonghua Yao
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Cycle ◽  
Low Frequency ◽  
Giant Planets ◽  
Mhd Waves ◽  
Ulf Waves ◽  
Helmholtz Instability ◽  
Ultralow Frequency ◽  
Field Fluctuations

<p>Low frequency quasiperiodic (QP) magnetic field fluctuations are commonly observed in terrestrial and planetary magnetosphere.  At Earth,  these magnetohydrodynamic (MHD) waves are often observed in ultralow frequency (ULF) band (~1 mHz to 1 Hz), which could be generated by solar wind buffeting, Kelvin-Helmholtz instability and/or wave-particle interactions inside the Earth's magnetosphere. At giant planets (Saturn or Jupiter), their enormous magnetospheres often produce QP fluctuations with frequencies lower than the terrestrial ULF waves. In this study, we use Cassini spacecraft observations to analysis waves at period of 10 min to 60 min in Saturnian magnetosphere. We compare wave activities during different solar activities.</p>

scholarly journals Investigation of  ∼ 20–40 mHz ULF waves and their driving mechanisms in Mercury's dayside magnetosphere

2017 ◽  
Vol 35 (4) ◽  
pp. 879-884 ◽  
Author(s):  
Elisabet Liljeblad ◽  
Tomas Karlsson
Keyword(s):  
Low Frequency ◽  
Space Environment ◽  
Ulf Waves ◽  
Magnetic Field Data ◽  
Mercury Surface ◽  
Ulf Wave ◽  
Driving Mechanisms ◽  
Detection Tool ◽  
The Waves ◽  
Dawn Sector

Abstract. Ultra-low-frequency (ULF) waves in the  ∼  20–40 mHz range are frequently observed in the Mercury magnetosphere using Mercury Surface Space Environment Geochemistry, and Ranging (MESSENGER) magnetic field data. The majority of these waves have very similar characteristics to the waves likely driven by Kelvin–Helmholtz (KH) ULF waves (which are retained as a subset of the wave events studied in this paper) identified in a previous study. Significant ULF wave activity is observed in the dawn sector of the magnetosphere. This indicates that Mercury KH waves may be more common between 6 and 12 magnetic local time than previously predicted and that magnetospheric ULF waves in the frequency band  ∼ 20–40 mHz can be used as a detection tool for Hermean KH waves.

scholarly journals Quasiperiodic ULF-pulsations in Saturn's magnetosphere

2009 ◽  
Vol 27 (2) ◽  
pp. 885-894 ◽  
Author(s):  
G. Kleindienst ◽  
K.-H. Glassmeier ◽  
S. Simon ◽  
M. K. Dougherty ◽  
N. Krupp
Keyword(s):  
Magnetic Field ◽  
Local Time ◽  
Large Scale ◽  
Rotation Period ◽  
Low Frequency ◽  
Radial Distance ◽  
Main Magnetic Field ◽  
Ulf Wave ◽  
Field Investigations ◽  
Magnetosphere Of Saturn

Abstract. Recent magnetic field investigations made onboard the Cassini spacecraft in the magnetosphere of Saturn show the existence of a variety of ultra low frequency plasma waves. Their frequencies suggest that they are presumably not eigenoscillations of the entire magnetospheric system, but excitations confined to selected regions of the magnetosphere. While the main magnetic field of Saturn shows a distinct large scale modulation of approximately 2 nT with a periodicity close to Saturn's rotation period, these ULF pulsations are less obvious superimposed oscillations with an amplitude generally not larger than 3 nT and show a package-like structure. We have analyzed these wave packages and found that they are correlated to a certain extent with the large scale modulation of the main magnetic field. The spatial localization of the ULF wave activity is represented with respect to local time and Kronographic coordinates. For this purpose we introduce a method to correct the Kronographic longitude with respect to a rotation period different from its IAU definition. The observed wave packages occur in all magnetospheric regions independent of local time, elevation, or radial distance. Independent of the longitude correction applied the wave packages do not occur in an accentuated Kronographic longitude range, which implies that the waves are not excited or confined in the same selected longitude ranges at all times or that their lifetime leads to a variable phase with respect to the longitudes where they have been exited.

Helicity waves propagating in a plasma

1991 ◽  
Vol 45 (3) ◽  
pp. 481-488 ◽  
Author(s):  
Z. Yoshida
Keyword(s):  
Magnetic Field ◽  
Faraday Effect ◽  
Low Frequency ◽  
Plasma Waves ◽  
Frequency Limit ◽  
High Frequencies ◽  
Transverse Modes ◽  
Longitudinal Part ◽  
The Waves ◽  
Perturbed Magnetic Field

There exist plasma waves that transport helicity although they do not propagate electromagnetic energy. The dispersion relations of such helicity waves are studied. The electric field of the waves is parallel to the perturbed magnetic field, and both are perpendicular to the perturbed current. In cross-field propagation, a helicity wave is decomposed into two transverse modes with different polarizations and a longitudinal part. The helicity waves are principally Alfvénic in the low-frequency limit. At high frequencies, the Faraday effect comes into the polarization.

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 Statistical study of ULF waves in the magnetotail by THEMIS observations

2018 ◽  
Vol 36 (5) ◽  
pp. 1335-1346 ◽  
Author(s):  
Shuai Zhang ◽  
Anmin Tian ◽  
Quanqi Shi ◽  
Hanlin Li ◽  
Alexander W. Degeling ◽  
...  
Keyword(s):  
Standing Waves ◽  
Low Frequency ◽  
Radial Distance ◽  
Time History ◽  
Flank Region ◽  
Wave Frequency ◽  
Ulf Waves ◽  
Tail Region ◽  
Ulf Wave ◽  
Field Lines

Abstract. Ultra-low-frequency (ULF) waves are ubiquitous in the magnetosphere. Previous studies mostly focused on ULF waves in the dayside or near-Earth region (with radial distance R<12 RE). In this study, using the data of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission during the period from 2008 to 2015, the Pc5–6 ULF waves in the tail region with XGSM∗<0, 8 RE<R<32 RE (mostly on the stretched magnetic field lines) are studied statistically. A total of 1089 azimuthal oscillating events and 566 radial oscillating events were found. The statistical results show that both the azimuthal and radial oscillating events in the magnetotail region (12 RE<R<32 RE) are more frequently observed in the post-midnight region. The frequency decreases with increasing radial distance from Earth for both azimuthal oscillating events (8 RE<R<16 RE) and radial oscillating events (8 RE<R<14 RE), which is consistent with the field line resonances theory. About 52 % of events (including the azimuthal and radial oscillating events) are standing waves in the region of 8–16 RE, while only 2 % are standing waves in the region of 16–32 RE. There is no obvious dawn–dusk asymmetry of ULF wave frequency for events in 8 RE<R<32 RE, which contrasts with the obvious dawn–dusk asymmetry found by previous studies in the inner magnetosphere (4 RE<R<9 RE). An examination for possible statistical relationships between the ULF wave parameters and substorm occurrences is carried out. We find that the wave frequency is higher after the substorm onset than before it, and the frequency differences are more obvious in the midnight region than in the flank region.

scholarly journals <i>Letter to the Editor</i> Low-frequency electric field fluctuations and field-aligned electron beams around the edge of an auroral acceleration region

2001 ◽  
Vol 19 (3) ◽  
pp. 389-393 ◽  
Author(s):  
W. Miyake ◽  
R. Yoshioka ◽  
A. Matsuoka ◽  
T. Mukai ◽  
T. Nagatsuma
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Electron Beams ◽  
Low Frequency ◽  
Static Field ◽  
Acceleration Region ◽  
Auroral Acceleration Region ◽  
Field Fluctuations ◽  
Current Region ◽  
Frequency Electric Field

Abstract. Electron beams narrowly collimated to the magnetic field line were observed continuously from a down-ward current region to an auroral acceleration region (i.e., upward current region). They were well correlated with low-frequency electric field fluctuations in the auroral acceleration region as well as in the adjacent downward current region. Magnetic field fluctuations were found only in the downward current region. The analysis suggests that static field-aligned electric fields are not fully responsible for the filed-aligned electron acceleration; the ac electric field, presumably associated with Alfvenic fluctuations, should also be involved in the acceleration of ionospheric electrons.Key words. Ionosphere (particle acceleration) – Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions)

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