scholarly journals Plasma Waves Near the Electron Cyclotron Frequency in the Near Sun Solar Wind: Wave Mode Identification and Driving Instabilities

2021 ◽  
Author(s):  
David Malaspina ◽  
Lynn Wilson ◽  
Robert Ergun ◽  
Stuart Bale ◽  
John Bonnell ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Cyclotron Frequency ◽  
Plasma Waves ◽  
Electron Cyclotron ◽  
Occurrence Rate ◽  
High Time Resolution ◽  
Magnetic Field Direction ◽  
Field Orientation ◽  
Electron Cyclotron Frequency

<p>Recent studies of the solar wind sunward of 0.25 AU using the Parker Solar Probe spacecraft reveal that that solar wind can be bimodal, alternating between near quiescent regions with low turbulent fluctuation amplitudes and Parker-like magnetic field direction and regions of highly turbulent plasma and magnetic field fluctuations associated with ‘switchbacks’ of the radial magnetic field.  </p><p>The quiescent solar wind regions are highly unstable to the formation of plasma waves near the electron cyclotron frequency (fce), possibly driven by strahl electrons, which carry the solar wind heat flux, and may provide one of the most direct particle diagnostics of the solar corona at the source of the solar wind.  These waves are most intense near ~0.7 fce and ~fce. The near-fce waves are found to become more intense and more frequent closer to the Sun, and statistical evidence indicates that their occurrence rate is related to the sunward drift of the core electron population.  </p><p>In this study, we examine high time resolution burst captures of these waves, demonstrating that each wave burst contains several distinct wave types, including electron Bernstein waves and extremely narrow band waves that are highly sensitive to the magnetic field orientation. Using properties of these waves we provide evidence to support the identification of their likely plasma wave modes and the instabilities responsible for generating these waves.  By understanding the driving instabilities responsible for these waves, we infer their ability to modify electron distribution functions in the quiescent near-Sun solar wind.  </p>

scholarly journals Plasma Waves near the Electron Cyclotron Frequency in the Near-Sun Solar Wind

2020 ◽  
Vol 246 (2) ◽  
pp. 21 ◽  
Author(s):  
David M. Malaspina ◽  
Jasper Halekas ◽  
Laura Berčič ◽  
Davin Larson ◽  
Phyllis Whittlesey ◽  
...  
Keyword(s):  
Solar Wind ◽  
Cyclotron Frequency ◽  
Plasma Waves ◽  
Electron Cyclotron ◽  
Electron Cyclotron Frequency

scholarly journals Magnetic clouds' structure in the magnetosheath as observed by Cluster and Geotail: four case studies

2014 ◽  
Vol 32 (10) ◽  
pp. 1247-1261 ◽  
Author(s):  
L. Turc ◽  
D. Fontaine ◽  
P. Savoini ◽  
E. K. J. Kilpua
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Fields ◽  
Bow Shock ◽  
Field Direction ◽  
Magnetic Clouds ◽  
Magnetic Field Direction ◽  
Field Orientation ◽  
The Impact ◽  
The Magnetic Field

Abstract. Magnetic clouds (MCs) are large-scale magnetic flux ropes ejected from the Sun into the interplanetary space. They play a central role in solar–terrestrial relations as they can efficiently drive magnetic activity in the near-Earth environment. Their impact on the Earth's magnetosphere is often attributed to the presence of southward magnetic fields inside the MC, as observed in the upstream solar wind. However, when they arrive in the vicinity of the Earth, MCs first encounter the bow shock, which is expected to modify their properties, including their magnetic field strength and direction. If these changes are significant, they can in turn affect the interaction of the MC with the magnetosphere. In this paper, we use data from the Cluster and Geotail spacecraft inside the magnetosheath and from the Advanced Composition Explorer (ACE) upstream of the Earth's environment to investigate the impact of the bow shock's crossing on the magnetic structure of MCs. Through four example MCs, we show that the evolution of the MC's structure from the solar wind to the magnetosheath differs largely from one event to another. The smooth rotation of the MC can either be preserved inside the magnetosheath, be modified, i.e. the magnetic field still rotates slowly but at different angles, or even disappear. The alteration of the magnetic field orientation across the bow shock can vary with time during the MC's passage and with the location inside the magnetosheath. We examine the conditions encountered at the bow shock from direct observations, when Cluster or Geotail cross it, or indirectly by applying a magnetosheath model. We obtain a good agreement between the observed and modelled magnetic field direction and shock configuration, which varies from quasi-perpendicular to quasi-parallel in our study. We find that the variations in the angle between the magnetic fields in the solar wind and in the magnetosheath are anti-correlated with the variations in the shock obliquity. When the shock is in a quasi-parallel regime, the magnetic field direction varies significantly from the solar wind to the magnetosheath. In such cases, the magnetic field reaching the magnetopause cannot be approximated by the upstream magnetic field. Therefore, it is important to take into account the conditions at the bow shock when estimating the impact of an MC with the Earth's environment because these conditions are crucial in determining the magnetosheath magnetic field, which then interacts with the magnetosphere.

Cassini observations of magnetic holes in the solar wind and Saturn magnetosheath

2020 ◽  
Author(s):  
Tomas Karlsson ◽  
Lina Hadid ◽  
Michiko Morooka ◽  
Jan-Erik Wahlund
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
High Time Resolution ◽  
Magnetic Field Direction ◽  
Scale Size ◽  
Background Magnetic Field ◽  
Cycle Dependence ◽  
The Magnetic Field

<p>We present the first Cassini observations of magnetic holes on the near-Saturn solar wind and magnetosheath, based on data from the MAG magnetometer. We conclude that magnetic holes (defined as isolated decreases of at least 50% compared to the background magnetic field strength) are common in both regions. We present statistical properties of the magnetic holes, including scale size, depth of the magnetic field reduction, orientation, change in magnetic field direction over the holes, and solar cycle dependence. For magnetosheath magnetic holes, also high-time resolution density measurements from the LP Langmuir probe are available, allowing us to study the anti-correlation of density and magnetic field strength in the magnetic holes. We compare to recent results from MESSENGER observations from Mercury orbit, and finally discuss the possible importance of magnetic holes in solar wind-magnetosphere interaction at Saturn.</p>

scholarly journals Solar Orbiter’s first Venus Flyby: MAG observations of structures and waves associated with the induced Venusian magnetosphere

2021 ◽  
Author(s):  
Martin Volwerk ◽  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Frequency ◽  
Cyclotron Frequency ◽  
Plasma Waves ◽  
Bow Shock ◽  
High Frequency Plasma ◽  
Frequency Plasma ◽  
Mirror Mode ◽  
Proton Cyclotron

<p>The induced magnetosphere of Venus is created by the interaction of the solar wind and embedded interplanetary magnetic field with the exosphere and ionosphere of Venus. Solar Orbiter entered Venus’s magnetotail far downstream, > 70 Venus radii, of the planet and exited the magnetosphere over the north pole. This offered a unique view of the system over distances that were only flown through once by three other missions before, Mariner 10, Galileo and Bepi-Colombo. The large-scale structure and activity of the induced magnetosphere is studied as well as the high-frequency plasma waves both in the magnetosphere and in a limited region upstream of the planet where interaction with Venus’s exosphere is expected.  It is shown that Venus’s magnetotail is very active during the Solar Orbiter flyby. Structures such as flux ropes, and reconnection sites are encountered as well as a strongly overdraping of the magnetic field downstream of the bow shock and planet. High-frequency plasma waves (up to 6 times the local proton cyclotron frequency) are observed in the magnetotail, which are identified as Doppler-shifted proton cyclotron waves, whereas in the upstream solar wind these waves appear just below the proton cyclotron frequency (as expected) but are very patchy. The bow shock is quasi perpendicular, however, expected mirror mode activity is not found directly behind it; instead there is strong cyclotron wave power. This is most-likely caused by the relatively low plasma-beta  behind the bow shock. Much further downstream in the magnetosheath mirror mode of magnetic hole structures are identified. This presentation will take place after the second Venus flyby by Solar Orbiter and BepiColombo and Solar Orbiter on 9 and 10 August, respectively.</p>

The magnetic moment of the proton II. The value in Bohr magnetons

1963 ◽  
Vol 272 (1348) ◽  
pp. 103-118 ◽  
Keyword(s):  
Magnetic Field ◽  
Resonance Frequency ◽  
Magnetic Moment ◽  
Cyclotron Frequency ◽  
Electron Cyclotron ◽  
Proton Spin ◽  
Radio Frequency Field ◽  
Electron Cyclotron Frequency ◽  
True Value ◽  
Spin Resonance

The magnetic moment of the proton has been measured in Bohr magnetons by comparing the proton spin-resonance frequency with the electron cyclotron frequency in the same magnetic field. The electron cyclotron signal was observed as an absorption of energy from a radio-frequency field in a cavity. Particular attention was paid to the elimination of effects which might have altered the electron cyclotron frequency from the true value. The result, related to the spin-resonance frequency of the free proton, is that the magnetic moment of the proton is (1.521043 ± 0.000006) x 10 -4 Bohr magneton.

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