scholarly journals Observations and modelling of the wave mode evolution of an impulse-driven 3 mHz ULF wave

2010 ◽  
Vol 28 (9) ◽  
pp. 1723-1735
Author(s):  
J. D. Borderick ◽  
T. K. Yeoman ◽  
C. L. Waters ◽  
D. M. Wright
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Low Frequency ◽  
Wave Mode ◽  
Ulf Wave ◽  
Doppler Shifts ◽  
Electric And Magnetic Fields ◽  
Spacecraft Data ◽  
Upstream Solar Wind ◽  
Oblique Magnetic Field

Abstract. A combination of an HF Doppler sounder, a network of ground magnetometers, upstream solar wind monitors and a numerical model is used to examine the temporal evolution of an Ultra Low Frequency (ULF) wave. The event occurred on 16 April 1998 and followed a solar wind density and pressure increase seen in the upstream ACE spacecraft data. The magnetometer and HF Doppler sounder data show that the event develops into a low-m (−6) field line resonance. HF signals that propagate via the ionosphere exhibit Doppler shifts due to a number of processes that give rise to a time-dependent phase path. The ULF electric and magnetic fields are calculated by a one-dimensional model which calculates the wave propagation from the magnetosphere, through the ionosphere to the ground with an oblique magnetic field. These values are then used to determine a model HF Doppler shift which is subsequently compared to HF Doppler observations. The ULF magnetic field at the ground and Doppler observations are then used to provide model inputs at various points throughout the event. We find evidence that the wave mode evolved from a mixture of fast and Alfvén modes at the beginning of the event to an almost purely shear Alfvénic mode after 6 wavecycles (33 min).

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 Ultra-low-frequency waves in the ion foreshock of Mercury: a global hybrid modelling study

2019 ◽  
Vol 491 (3) ◽  
pp. 4147-4161 ◽  
Author(s):  
R Jarvinen ◽  
M Alho ◽  
E Kallio ◽  
T I Pulkkinen
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Three Dimensional ◽  
Low Frequency ◽  
Bow Shock ◽  
Solar Wind Interaction ◽  
Ulf Wave ◽  
Upstream Condition ◽  
Upstream Solar Wind ◽  
The Imf

ABSTRACT We study the solar wind interaction with Mercury using a global three-dimensional hybrid model. In the analysed simulation run, we find a well-developed, dynamic Hermean ion foreshock ahead of the quasi-parallel bow shock under upstream solar wind and interplanetary magnetic field (IMF) conditions corresponding to the orbital perihelion of the planet. A portion of the incident solar wind ion flux is scattered back upstream near the quasi-parallel bow shock including both major solar wind ion species, protons and alphas. The scattered particles form the Hermean suprathermal foreshock ion population. A significant part of the suprathermal population is backstreaming with a velocity component towards the Sun in the near-foreshock at the planetocentric distance of few planetary radii in the plane of the IMF. The ion foreshock is associated with large-scale, oblique fast magnetosonic waves in the ultra-low-frequency (ULF) range convecting downstream with the solar wind. The ULF wave period is about 5 s in the analysed upstream condition case at Mercury, which corresponds to the 30-s foreshock waves at Earth when scaled by the IMF magnitude.

Propagation properties of foreshock cavitons and spontaneous hot flow anomalies: Statistical results from 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 ◽  
Low Frequency ◽  
Propagation Speed ◽  
Bow Shock ◽  
Linear Interaction ◽  
Frame Motion ◽  
Suprathermal Ions ◽  
Propagation Properties

<p>Foreshock cavitons are transient structures forming in Earth's foreshock as a result of non-linear interaction of ultra-low frequency waves. Cavitons are characterised by simultaneous density and magnetic field depressions with sizes of the order of 1 Earth radius. These transients are advected by the solar wind towards the bow shock, where they may accumulate shock-reflected suprathermal ions and become spontaneous hot flow anomalies (SHFAs), which are characterised by an enhanced temperature and a perturbed bulk flow inside them.<br>    Both spacecraft measurements and hybrid simulations have shown that while cavitons and SHFAs are carried towards the bow shock by the solar wind, their motion in the solar wind rest frame is directed upstream. In this work, we have made a statistical analysis of the propagation properties of cavitons and SHFAs using Vlasiator, a hybrid-Vlasov simulation model. In agreement with previous studies, we find the transients propagating upstream in the solar wind rest frame. Our results show that the solar wind rest frame motion of cavitons is aligned with the direction of the interplanetary magnetic field, while the motion of SHFAs deviates from this direction. We find that SHFAs have a faster solar wind rest frame propagation speed than cavitons, which is due to an increase in the sound speed near the bow shock, affecting the speed of the waves in the foreshock.</p>

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.

scholarly journals The low-frequency break observed in the slow solar wind magnetic spectra

2019 ◽  
Vol 627 ◽  
pp. A96 ◽  
Author(s):  
R. Bruno ◽  
D. Telloni ◽  
L. Sorriso-Valvo ◽  
R. Marino ◽  
R. De Marco ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Low Frequency ◽  
Slow Solar Wind ◽  
Velocity Spectrum ◽  
Plasma Parameters ◽  
Solar Wind Magnetic Field ◽  
Fast Wind ◽  
Slow Wind ◽  
First Time

Fluctuations of solar wind magnetic field and plasma parameters exhibit a typical turbulence power spectrum with a spectral index ranging between ∼5/3 and ∼3/2. In particular, at 1 AU, the magnetic field spectrum, observed within fast corotating streams, also shows a clear steepening for frequencies higher than the typical proton scales, of the order of ∼3 × 10−1 Hz, and a flattening towards 1/f at frequencies lower than ∼10−3 Hz. However, the current literature reports observations of the low-frequency break only for fast streams. Slow streams, as observed to date, have not shown a clear break, and this has commonly been attributed to slow wind intervals not being long enough. Actually, because of the longer transit time from the Sun, slow wind turbulence would be older and the frequency break would be shifted to lower frequencies with respect to fast wind. Based on this hypothesis, we performed a careful search for long-lasting slow wind intervals throughout 12 years of Wind satellite measurements. Our search, based on stringent requirements not only on wind speed but also on the level of magnetic compressibility and Alfvénicity of the turbulent fluctuations, yielded 48 slow wind streams lasting longer than 7 days. This result allowed us to extend our study to frequencies sufficiently low and, for the first time in the literature, we are able to show that the 1/f magnetic spectral scaling is also present in the slow solar wind, provided the interval is long enough. However, this is not the case for the slow wind velocity spectrum, which keeps the typical Kolmogorov scaling throughout the analysed frequency range. After ruling out the possible role of compressibility and Alfvénicity for the 1/f scaling, a possible explanation in terms of magnetic amplitude saturation, as recently proposed in the literature, is suggested.

scholarly journals Internally and externally induced deformations of the magnetospheric equatorial current as inferred from spacecraft data

2015 ◽  
Vol 33 (1) ◽  
pp. 1-11 ◽  
Author(s):  
N. A. Tsyganenko ◽  
V. A. Andreeva ◽  
E. I. Gordeev
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Essential Feature ◽  
Quantitative Model ◽  
Local Times ◽  
Ram Pressure ◽  
Magnetometer Data ◽  
Equatorial Current ◽  
Spacecraft Data ◽  
Dipole Tilt

Abstract. Based on a data pool of 79 yearly files of space magnetometer data by Polar, Cluster, Geotail, and THEMIS satellites between 1995 and 2013, we developed a new quantitative model of the global shape of the magnetospheric equatorial current sheet as a function of the Earth's dipole tilt angle, solar wind ram pressure, and interplanetary magnetic field (IMF). This work upgrades and generalizes an earlier model of Tsyganenko and Fairfield (2004) by extending the modeling region to all local times, including the dayside sector. In particular, an essential feature of the new model is the bowl-shaped tilt-related deformation of the equatorial surface of minimum magnetic field, similar to that observed at Saturn, whose existence in the Earth's magnetosphere has been demonstrated in our recent work (Tsyganenko and Andreeva, 2014).

scholarly journals Scale dependent anisotropy of electric field fluctuations in solar wind turbulence

2021 ◽  
Author(s):  
Deepali Deepali ◽  
Supratik Banerjee
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electric Field ◽  
Electric Power ◽  
Flow Direction ◽  
Power Spectra ◽  
Solar Wind Turbulence ◽  
Wind Turbulence ◽  
Field Fluctuations ◽  
Spacecraft Data

<p>We study the variation of average powers and spectral indices of electric field fluctuations with respect to the angle between average flow direction and the mean magnetic field in solar wind turbulence. Cluster spacecraft data from the years 2002 and 2007 are used for the present analysis. We perform a scale dependent study with respect to the local mean magnetic field using wavelet analysis technique. Prominent anisotropies are found for both the spectral index and power levels of the electric power spectra. Similar to the magnetic field fluctuations, the parallel (or antiparallel) electric fluctuation spectrum is found to be steeper than the perpendicular spectrum. However the parallel (or antiparallel) electric power is found to be greater than the perpendicular one. Below 0.1 Hz, the slope of the parallel electric power spectra deviates substantially from that of the total magnetic power spectra, supporting the existence of Alfvénic turbulence.</p>

scholarly journals Low-frequency magnetic variations at the high-<i>β</i> Earth bow shock

2019 ◽  
Vol 37 (5) ◽  
pp. 877-889
Author(s):  
Anatoli A. Petrukovich ◽  
Olga M. Chugunova ◽  
Pavel I. Shustov
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Spatial Scales ◽  
Low Frequency ◽  
Background Field ◽  
Bow Shock ◽  
Stable Phase ◽  
Main Magnetic Field ◽  
Astrophysical Plasmas ◽  
Earth’S Bow Shock

Abstract. Observations of Earth's bow shock during high-β (ratio of thermal to magnetic pressure) solar wind streams are rare. However, such shocks are ubiquitous in astrophysical plasmas. Typical solar wind parameters related to high β (here β>10) are as follows: low speed, high density, and a very low interplanetary magnetic field of 1–2 nT. These conditions are usually quite transient and need to be verified immediately upstream of the observed shock crossings. In this report, three characteristic crossings by the Cluster project (from the 22 found) are studied using multipoint analysis, allowing us to determine spatial scales. The main magnetic field and density spatial scale of about a couple of hundred of kilometers generally corresponds to the increased proton convective gyroradius. Observed magnetic variations are different from those for supercritical shocks, with β∼1. Dominant magnetic variations in the shock transition have amplitudes much larger than the background field and have a frequency of ∼ 0.3–0.5 Hz (in some events – 1–2 Hz). The wave polarization has no stable phase and is closer to linear, which complicates the determination of the wave propagation direction. Spatial scales (wavelengths) of variations are within several tens to a couple of hundred of kilometers.

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