MAVEN Observations of Large-amplitude, Quasi-periodic Sawtooth-like Magnetic Field Oscillations Associated with Kelvin-Helmholtz Instability

2020 ◽  
Author(s):  
Gangkai Poh ◽  
Jared Espley ◽  
Norberto Romanelli ◽  
Jacob Gruesbeck ◽  
Gina DiBraccio
Keyword(s):  
Magnetic Field ◽  
Large Amplitude ◽  
Opposite Polarity ◽  
Field Vector ◽  
Flow Shear ◽  
Mars Atmosphere ◽  
Periodic Magnetic Field ◽  
Background Magnetic Field ◽  
Non Linear ◽  
Initial Survey

<p>In this study, we present a preliminary analysis of large-amplitude sawtooth-like magnetic field oscillations observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft at Mars. Initial survey of these quasi-periodic magnetic field oscillations (with periods of ~3 – 4 minutes) shows distinct sawtooth-like magnetic field signatures with steep increase in B<sub>Y</sub> of ~20 – 30 nT, followed by a gentle, but turbulent, return to background magnetic field values. The extrema in the B<sub>Y</sub> component generally coincide with an extrema of opposite polarity in the B<sub>X</sub> component. Quasi-periodic magnetic field signatures can also be observed in the z-component of the magnetic field vector. Ion and electrons measurements shows corresponding increase in ions and electrons with energies greater than 30eV and 10 eV, respectively, during observations of these sawtooth-like oscillations, indicating some mixing of plasma. We interpret these observations as Kelvin-Helmholtz (KH) waves in the non-linear stages because the plasma and fields signatures are consistent with non-linear KH waves observed at Earth and other planetary environments. KH waves are developed as a result of flow shear-driven KH instability occurring between the boundary separating two moving fluids. In the non-linear stage of the KH instability, rolled-up KH vortex can developed along the boundary, allowing the mixing of plasma between the two plasma regions. Occurrence of KH waves had been observed at Venus’ ionopause and the induced magnetopause, contributing to loss of planetary ions in the form of plasma clouds. Earlier simulations and observational studies have also explored the possibility of non-linear KH instability occurring at Mars. We will discuss the conditions required for the development of KH instability, its growth rate and implications on mass loss at Mars. Comparison with simulations will also be conducted and discussed.</p>

scholarly journals Large-amplitude electromagnetic waves in magnetized relativistic plasmas with temperature

2014 ◽  
Vol 21 (1) ◽  
pp. 217-236 ◽  
Author(s):  
V. Muñoz ◽  
F. A. Asenjo ◽  
M. Domínguez ◽  
R. A. López ◽  
J. A. Valdivia ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Thermal Effects ◽  
Large Amplitude ◽  
Plasma Frequency ◽  
Plasma Temperature ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Background Magnetic Field ◽  
Cold Case ◽  
Effective Plasma Frequency

Abstract. Propagation of large-amplitude waves in plasmas is subject to several sources of nonlinearity due to relativistic effects, either when particle quiver velocities in the wave field are large, or when thermal velocities are large due to relativistic temperatures. Wave propagation in these conditions has been studied for decades, due to its interest in several contexts such as pulsar emission models, laser-plasma interaction, and extragalactic jets. For large-amplitude circularly polarized waves propagating along a constant magnetic field, an exact solution of the fluid equations can be found for relativistic temperatures. Relativistic thermal effects produce: (a) a decrease in the effective plasma frequency (thus, waves in the electromagnetic branch can propagate for lower frequencies than in the cold case); and (b) a decrease in the upper frequency cutoff for the Alfvén branch (thus, Alfvén waves are confined to a frequency range that is narrower than in the cold case). It is also found that the Alfvén speed decreases with temperature, being zero for infinite temperature. We have also studied the same system, but based on the relativistic Vlasov equation, to include thermal effects along the direction of propagation. It turns out that kinetic and fluid results are qualitatively consistent, with several quantitative differences. Regarding the electromagnetic branch, the effective plasma frequency is always larger in the kinetic model. Thus, kinetic effects reduce the transparency of the plasma. As to the Alfvén branch, there is a critical, nonzero value of the temperature at which the Alfvén speed is zero. For temperatures above this critical value, the Alfvén branch is suppressed; however, if the background magnetic field increases, then Alfvén waves can propagate for larger temperatures. There are at least two ways in which the above results can be improved. First, nonlinear decays of the electromagnetic wave have been neglected; second, the kinetic treatment considers thermal effects only along the direction of propagation. We have approached the first subject by studying the parametric decays of the exact wave solution found in the context of fluid theory. The dispersion relation of the decays has been solved, showing several resonant and nonresonant instabilities whose dependence on the wave amplitude and plasma temperature has been studied systematically. Regarding the second subject, we are currently performing numerical 1-D particle in cell simulations, a work that is still in progress, although preliminary results are consistent with the analytical ones.

Direct Measurement of Excitation and Growth of Large Amplitude Cyclotron Waves by Reflected Ion Beams in Front of Shock

2020 ◽  
Author(s):  
Jiansen He ◽  
Chuanpeng Hou ◽  
Xingyu Zhu ◽  
Qiaowen Luo ◽  
Daniel Verscharen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Electromagnetic Field ◽  
Phase Space ◽  
Large Amplitude ◽  
Particle Interaction ◽  
Field Vector ◽  
Ion Beams ◽  
Magnetic Field Vector ◽  
Wave Particle Interaction

<p>Wave-particle interaction plays a critical role in producing the newborn waves/turbulence in the foreshock region in front of supercritical shock, which is prevalent in the heliosphere. It has been a long-lasting goal to catch and witness the excitation and growth of waves/turbulence by identifying the ongoing process of wave-particle interaction. This goal cannot be fulfilled until the arrival of the MMS’s era, during which we can simultaneously measure the electromagnetic fields and particle phase space densities with the unprecedented data quality. By surveying the data of burst mode, we are lucky to find some good examples illustrating the clear signals of wave activities in front of the shock. The active waves are diagnosed to be right-handed cyclotron waves, being highly circularly polarized and rotating right-handed about the background magnetic field vector. The waves are large amplitude with dB being greatly dominant over B0, or in other words, almost the whole magnetic field vector is involved in the circular rotation. Furthermore, we investigate the growth evolution of the large-amplitude cyclotron waves by calculating the spectrum of dJ.dE and its ratio to the electromagnetic energy spectrum. As far as we know, it is the first time to provide the spectrum of growth rate from in-situ measurements. Interestingly, we find that the contribution to the growth rate spectrum mainly comes from dJ<sub>e,perp</sub>·dE<sub>perp</sub> rather than dJ<sub>e,para</sub>·dE<sub>para</sub> or d<strong>J</strong><sub>i</sub>·d<strong>E</strong>. Although the eigen mode to couple the oscillating electromagnetic field is the electron bulk oscillation, the ultimate free energy to make the eigen mode unstable comes from the ion beams, which are reflected from the shock. The dynamics of 3D phase space densities for both ion and electron species are also studied in detail together with the fluctuating electromagnetic field, demonstrating the ongoing energy conversion during the wave-particle process.</p><p> </p>

scholarly journals Three-dimensional magnetic field structure of a flux-emerging region in the solar atmosphere

2019 ◽  
Vol 632 ◽  
pp. A112 ◽  
Author(s):  
Rahul Yadav ◽  
Jaime de la Cruz Rodríguez ◽  
Carlos José Díaz Baso ◽  
Avijeet Prasad ◽  
Tine Libbrecht ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Surface ◽  
Free Field ◽  
Opposite Polarity ◽  
Field Vector ◽  
Small Scale ◽  
Maximum Height ◽  
Horizontal Magnetic Field ◽  
Point Separation ◽  
The Magnetic Field

We analyze high-resolution spectropolarimetric observations of a flux-emerging region (FER) in order to understand its magnetic and kinematic structure. Our spectropolarimetric observations in the He I 10830 Å spectral region of a FER were recorded with GRIS at the 1.5 m aperture GREGOR telescope. A Milne–Eddington-based inversion code was employed to extract the photospheric information of the Si I spectral line, whereas the He I triplet line was analyzed with the Hazel inversion code, which takes into account the joint action of the Hanle and the Zeeman effects. The spectropolarimetric analysis of the Si I line reveals a complex magnetic structure near the vicinity of the FER, where a weak (350–600 G) and horizontal magnetic field was observed. In contrast to the photosphere, the analysis of the He I triplet presents a smooth variation of the magnetic field vector (ranging from 100 to 400 G) and velocities across the FER. Moreover, we find supersonic downflows of ∼40 km s−1 appearing near the foot points of loops connecting two pores of opposite polarity, whereas strong upflows of 22 km s−1 appear near the apex of the loops. At the location of supersonic downflows in the chromosphere, we observed downflows of 3 km s−1 in the photosphere. Furthermore, nonforce-free field extrapolations were performed separately at two layers in order to understand the magnetic field topology of the FER. We determine, using extrapolations from the photosphere and the observed chromospheric magnetic field, that the average formation height of the He I triplet line is ∼2 Mm from the solar surface. The reconstructed loops using photospheric extrapolations along an arch filament system have a maximum height of ∼10.5 Mm from the solar surface with a foot-point separation of ∼19 Mm, whereas the loops reconstructed using chromospheric extrapolations reach around ∼8.4 Mm above the solar surface with a foot-point separation of ∼16 Mm at the chromospheric height. The magnetic topology in the FER suggests the presence of small-scale loops beneath the large loops. Under suitable conditions, due to magnetic reconnection, these loops can trigger various heating events in the vicinity of the FER.

Parametric instabilities of circularly polarized large-amplitude dispersive Alfvén waves: excitation of parallel-propagating electromagnetic daughter waves

1991 ◽  
Vol 46 (1) ◽  
pp. 107-127 ◽  
Author(s):  
Adolfo F. Viñas ◽  
Melvyn L. Goldstein
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Large Amplitude ◽  
Wave Amplitude ◽  
Pump Wave ◽  
Modulational Instability ◽  
Alfven Wave ◽  
Circularly Polarized ◽  
Background Magnetic Field ◽  
Electromagnetic Instability

We investigate the parametric decay and modulational instabilities of a large-amplitude circularly polarized dispersive Alfvén wave. Our treatment is more general than that of previous derivations based on the two-fluid equations in that we allow for propagation of the unstable daughter waves at arbitrary angles to the background magnetic field, although our main concern in this paper is the exploration of new aspects of propagation parallel to the DC magnetic field. In addition to the well-known coupling of pump waves to electrostatic daughter waves, we find a new parametric channel where the pump wave couples directly to electromagnetic daughter waves. Excitation of the electromagnetic instability occurs only for modulation (k/k0 ≤ 1) and not for decay (k/k0 < 1). In contrast with the modulational instability excited by the electrostatic coupling, the electromagnetic modulational instability exists for both left-hand (K > 0) and right-hand (K < 0) polarization. For large k/k0, the electromagnetic channel dominates, while at lower values the electrostatic channel has a larger growth rate for modest values of dispersion, pump-wave amplitude and plasma β. Unlike the electrostatic modulational instability, the growth rate of the electromagnetic instability increases monotonically with increasing pump wave amplitude. This analysis confirms that, for decay, the dominant process is coupling to electrostatic daughter waves, at least for parallel propagation. For modulation, the coupling to electromagnetic daughter waves usually dominates, suggesting that the parametric modulational instability is really an electromagnetic phenomenon.

scholarly journals Discovery of long-period magnetic field oscillations and motions in isolated sunspots

2020 ◽  
Vol 635 ◽  
pp. A64
Author(s):  
A. B. Griñón-Marín ◽  
A. Pastor Yabar ◽  
H. Socas-Navarro ◽  
R. Centeno
Keyword(s):  
Magnetic Field ◽  
Temporal Evolution ◽  
Opposite Polarity ◽  
Field Vector ◽  
Interesting Property ◽  
Coronal Loops ◽  
Long Period ◽  
Use Of Data ◽  
Long Time ◽  
The Magnetic Field

We analyse the temporal evolution of the inclination component of the magnetic field vector for the penumbral area of 25 isolated sunspots. Compared to previous works, the use of data from the HMI instrument aboard the SDO observatory facilitates the study of a very long time series (≈1 week) with a good spatial and temporal resolution. We used the wavelet technique and we found some filamentary-shaped events with large wavelet power. Their distribution of periods is broad, ranging from the lower limit for this study of 48 min up to 63 h. An interesting property of these events is that they do not appear homogeneously all around the penumbra but they seem to concentrate at particular locations. The cross-comparison of these wavelet maps with AIA data shows that the regions where these events appear are visually related to the coronal loops that connect the outer penumbra to one or more neighbouring opposite polarity flux patches.

scholarly journals Anisotropic scaling features and complexity in magnetospheric-cusp: a case study

2005 ◽  
Vol 12 (6) ◽  
pp. 817-825 ◽  
Author(s):  
E. Yordanova ◽  
J. Bergman ◽  
G. Consolini ◽  
M. Kretzschmar ◽  
M. Materassi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Vector ◽  
Special Role ◽  
Anisotropic Scaling ◽  
Background Magnetic Field ◽  
Field Fluctuations ◽  
Magnetospheric Cusp ◽  
Complex Scenario ◽  
High Degree ◽  
Scaling Features

Abstract. Magnetospheric cusps are high-latitude regions characterized by a highly turbulent plasma, playing a special role in the solar wind-magnetosphere interaction. Here, using POLAR satellite magnetic field vector measurements we investigate the anisotropic scaling features of the magnetic field fluctuations in the northern cusp region. Our results seem to support the hypothesis of a 2D-MHD turbulent scenario which is consequence of a strong background magnetic field. The observed turbulent fluctuations reveal a high degree of complexity, which might be due to the interplay of many competing scales. A discussion of our findings in connection with the complex scenario proposed by Chang et al. (2004) is provided.

Non-linear dependence of the dielectric properties of chick embryo myoblast membranes exposed to a sinusoidal 50 Hz magnetic field

1991 ◽  
Vol 60 (6) ◽  
pp. 877-890 ◽  
Author(s):  
Martino Grandolfo ◽  
Maria Santini ◽  
Paolo Vecchia ◽  
Adalberto Bonincontro ◽  
Cesare Cametti ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Dielectric Properties ◽  
Chick Embryo ◽  
Linear Dependence ◽  
Non Linear

Exact nonlinear wave solutions of the incompressible magnetohydrodynamic equations in a sheared magnetic field

1990 ◽  
Vol 44 (1) ◽  
pp. 25-32 ◽  
Author(s):  
Hiromitsu Hamabata
Keyword(s):  
Magnetic Field ◽  
Incompressible Fluid ◽  
Large Amplitude ◽  
Uniform Magnetic Field ◽  
Magnetohydrodynamic Equations ◽  
Wave Solutions ◽  
Field Lines ◽  
Incompressible Magnetohydrodynamic Equations ◽  
Physical Quantities ◽  
Nonlinear Wave Solutions

Exact wave solutions of the nonlinear jnagnetohydrodynamic equations for a highly conducting incompressible fluid are obtained for the cases where the physical quantities are independent of one Cartesian co-ordina.te and for where they vary three-dimensionally but both the streamlines and magnetic field lines lie in parallel planes. It is shown that there is a class of exact wave solutions with large amplitude propagating in a straight but non-uniform magnetic field with constant or non-uniform velocity.

scholarly journals Geometry of the Rabi Problem and Duality of Loops

2020 ◽  
Vol 75 (5) ◽  
pp. 381-391 ◽  
Author(s):  
Heinz-Jürgen Schmidt
Keyword(s):  
Magnetic Field ◽  
Differential Geometry ◽  
Floquet Theory ◽  
Bloch Sphere ◽  
Classical Spin ◽  
Periodic Magnetic Field

AbstractWe investigate the motion of a classical spin processing around a periodic magnetic field using Floquet theory, as well as elementary differential geometry and considering a couple of examples. Under certain conditions, the role of spin and magnetic field can be interchanged, leading to the notion of “duality of loops” on the Bloch sphere.

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