scholarly journals Statistical study of ULF waves in the magnetotail by THEMIS observations

2018 ◽  
Author(s):  
Shuai Zhang ◽  
Anmin Tian ◽  
Quanqi Shi ◽  
Hanlin Li ◽  
Alexander W. Degeling ◽  
...  
Keyword(s):  
Statistical Study ◽  
Low Frequency ◽  
Radial Distance ◽  
Ulf Waves

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 

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.

ULF waves in the foreshock formed by the radial IMF: their effect on solar wind sheath-like deflection

2020 ◽  
Author(s):  
Olga Gutynska ◽  
Jaroslav Urbář ◽  
Jana Šafránková ◽  
Zdeněk Němeček
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Statistical Study ◽  
Low Frequency ◽  
Bow Shock ◽  
Ulf Waves ◽  
Wind Flow ◽  
Solar Wind Flow ◽  
The Mean

&lt;p&gt;Particle reflection at the bow shock provides a source of free energy to drive local instabilities and turbulence within the foreshock. A variety of low-frequency fluctuations (up to 16 mHz) results from the interactions of back-streaming ions with the incoming solar wind flow. We report observations of low-frequency magnetosonic waves observed during intervals of a radial interplanetary magnetic field in the foreshock. A case study of simultaneous dual THEMIS spacecraft observations of asymmetrical fluctuations in V&lt;sub&gt;y&lt;/sub&gt; is complemented by a statistical study of similar solar wind deflections in the foreshock.&amp;#160; Our moment calculations do not include the reflected particles as well as heavier ions, revealed the modulation of a solar wind core and deflection of the solar wind in the foreshock. This effect decreases with the distance from the bow shock. We conclude that large asymmetrical Vy velocity component fluctuations are typical for the foreshock formed by the radial IMF. The asymmetry of fluctuations changes the mean direction of the incoming solar wind flow within the foreshock leading to preconditioning prior to its encounter with the bow shock.&lt;/p&gt;

Foreshock ULF fluctuations near the Moon: THEMIS observations

2021 ◽  
Author(s):  
Anna Salohub ◽  
Jana Šafránková ◽  
Zdeněk Němeček
Keyword(s):  
Solar Wind ◽  
Rest Frame ◽  
Low Frequency ◽  
Solar Wind Plasma ◽  
Turbulent Plasma ◽  
Bow Shock ◽  
Ulf Waves ◽  
The Moon ◽  
Shock Surface ◽  
The Earth

&lt;p&gt;The foreshock is a region filled with a turbulent plasma located upstream the Earth&amp;#8217;s bow shock where interplanetary magnetic field (IMF) lines are connected to the bow shock surface. In this region, ultra-low frequency (ULF) waves are generated due to the interaction of the solar wind plasma with particles reflected from the bow shock back into the solar wind. It is assumed that excited waves grow and they are convected through the solar wind/foreshock, thus the inner spacecraft (close to the bow shock) would observe larger wave amplitudes than the outer (far from the bow shock) spacecraft. The paper presents a statistical analysis of excited ULF fluctuations observed simultaneously by two closely separated THEMIS spacecraft orbiting the Moon under a nearly radial IMF. We found that ULF fluctuations (in the plasma rest frame) can be characterized as a mixture of transverse and compressional modes with different properties at both locations. We discuss the growth and/or damping of ULF waves during their propagation.&lt;/p&gt;

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.

scholarly journals Geomagnetic activity and local time dependence of the distribution of ultra low-frequency wave power in azimuthal wavenumbers, <i>m</i>

2017 ◽  
Vol 35 (3) ◽  
pp. 629-638 ◽  
Author(s):  
Theodore E. Sarris ◽  
Xinlin Li
Keyword(s):  
Phase Difference ◽  
Low Frequency ◽  
Field Measurements ◽  
Resonant Interaction ◽  
Total Power ◽  
Ulf Waves ◽  
Quiet Time ◽  
Frequency Wave ◽  
Drift Frequency ◽  
Diffusion Rates

Abstract. The azimuthal wavenumber m of ultra low-frequency (ULF) waves in the magnetosphere is a required parameter in the calculations of the diffusion rates of energetic electrons and protons in the magnetosphere, as electrons and protons of drift frequency ωd have been shown to radially diffuse due to resonant interaction with ULF waves of frequency ω = mωd. However, there are difficulties in estimating m, due to lack of multipoint measurements. In this paper we use magnetic field measurements at geosynchronous orbit to calculate the cross-spectrogram power and phase differences between time series from magnetometer pairs. Subsequently, assuming that ULF waves of a certain frequency and m would be observed with a certain phase difference between two azimuthally aligned magnetometers, the fraction of the total power in each phase difference range is calculated. As part of the analysis, both quiet-time and storm-time distributions of power per m number are calculated, and it is shown that during active times, a smaller fraction of total power is confined to lower m than during quiet times. It is also shown that in the dayside region, power is distributed mostly to the lowest azimuthal wavenumbers m = 1 and 2, whereas on the nightside it is more equally distributed to all m that can be resolved by the azimuthal separation between two spacecraft.

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 A Statistical Study of Low-Frequency Solar Radio Type III Bursts

Solar Physics ◽  
2020 ◽  
Vol 295 (11) ◽  
Author(s):  
Aroori Mahender ◽  
K. Sasikumar Raja ◽  
R. Ramesh ◽  
Vemareddy Panditi ◽  
Christian Monstein ◽  
...  
Keyword(s):  
Solar Radio ◽  
Statistical Study ◽  
Low Frequency ◽  
Type Iii

ULF waves and their influence on radiation belt dynamics in Earth's magnetosphere

2020 ◽  
Author(s):  
Robert Rankin ◽  
Alexander Degeling
Keyword(s):  
Radiation Belt ◽  
Geomagnetic Storms ◽  
Low Frequency ◽  
Recovery Phase ◽  
Ulf Waves ◽  
Wave Source ◽  
Initial Plasma ◽  
Plasma State ◽  
Van Allen Probes ◽  
Geomagnetic Fields

&lt;p&gt;Recent observations from the Van Allen Probes mission have established that Pc3-5 ultra-low-frequency (ULF) waves can energize ions and electrons via drift-resonance and drift-bounce resonance. The extent to which these waves contribute to the space weather of the belts is relatively poorly understood and requires sophisticated modelling and characterization of the dominant wave modes that arise in the development and recovery phase of geomagnetic storms. Despite more than four decades of observations and theoretical analysis of ULF waves, there is no framework for accurately assessing the global distribution of ULF waves and their influence on the ring current.&amp;#160;&lt;br&gt;In this presentation, we describe a new global model of ULF waves that incorporates non-dipolar geomagnetic fields. The model is constrained using the GCPM of cold plasma density model and a specification of the ionosphere using the IRI and MSIS models. An algorithm is applied to adjust the initial plasma state to a quasi-static equilibrium that is then driven by a global convection electric field and ULF wave source. For specific observations by the Van Allen Probes and ARASE mission, the effect of these ULF waves on radiation belt ions and electrons is evaluated utilizing test-particle methodology and Liouville's theorem, which enables the phase space density to be followed and compared one-for-one with the satellite observations. &amp;#160;&lt;/p&gt;

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