Low-frequency magnetic field fluctuations in Venus' solar wind interaction region: Venus Express observations

Abstract. We investigate wave properties of low-frequency magnetic field fluctuations in Venus' solar wind interaction region based on the measurements made on board the Venus Express spacecraft. The orbit geometry is very suitable to investigate the fluctuations in Venus' low-altitude magnetosheath and mid-magnetotail and provides an opportunity for a comparative study of low-frequency waves at Venus and Mars. The spatial distributions of the wave properties, in particular in the dayside and nightside magnetosheath as well as in the tail and mantle region, are similar to observations at Mars. As both planets do not have a global magnetic field, the interaction process of the solar wind with both planets is similar and leads to similar instabilities and wave structures. We focus on the spatial distribution of the wave intensity of the fluctuating magnetic field and detect an enhancement of the intensity in the dayside magnetosheath and a strong decrease towards the terminator. For a detailed investigation of the intensity distribution we adopt an analytical streamline model to describe the plasma flow around Venus. This allows displaying the evolution of the intensity along different streamlines. It is assumed that the waves are generated in the vicinity of the bow shock and are convected downstream with the turbulent magnetosheath flow. However, neither the different Mach numbers upstream and downstream of the bow shock, nor the variation of the cross sectional area and the flow velocity along the streamlines play probably an important role in order to explain the observed concentration of wave intensity in the dayside magnetosheath and the decay towards the nightside magnetosheath. But, the concept of freely evolving or decaying turbulence is in good qualitative agreement with the observations, as we observe a power law decay of the intensity along the streamlines. The observations support the assumption of wave convection through the magnetosheath, but reveal at the same time that wave sources may not only exist at the bow shock, but also in the magnetosheath.

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Ultra-low frequency foreshock waves at Venus and Mercury in a global hybrid simulation

10.5194/epsc2020-202 ◽

2020 ◽

Author(s):

Riku Jarvinen ◽

Esa Kallio ◽

Tuija I. Pulkkinen

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Large Scale ◽

Low Frequency ◽

Hybrid Simulation ◽

Bow Shock ◽

Upstream Region ◽

Ulf Waves ◽

Solar Wind Interaction ◽

Low Frequency Waves

We study the solar wind interaction with Venus and Mercury in a 3-dimensional global hybrid simulation where ions are treated as particles and electrons are a charge-neutralizing fluid. We concentrate on the formation of large-scale ultra-low frequency (ULF) waves in ion foreshocks and their dependence on the solar wind and interplanetary magnetic field conditions. The ion foreshock forms in the upstream region ahead of the quasi-parallel bow shock, where the angle between the shock normal and the magnetic field is smaller than about 45 degrees. The magnetic connection with the bow shock allows backstreaming of the solar wind ions leading to the formation of the ion foreshock. This kind of beam-plasma configuration is a source of free energy for the excitation of plasma waves. The foreshock ULF waves convect downstream with the solar wind flow and encounter the bow shock. We compare the waves between Venus and Mercury, and analyze the coupling of the ULF waves with the planetary ion acceleration at Venus. References: Jarvinen R., Alho M., Kallio E., Pulkkinen T.I., 2020, Oxygen Ion Escape From Venus Is Modulated by Ultra-Low Frequency Waves, Geophys. Res. Lett., 47, 11, doi:10.1029/2020GL087462 Jarvinen R., Alho M., Kallio E., Pulkkinen T.I., 2020, Ultra-low frequency waves in the ion foreshock of Mercury: A global hybrid modeling study, Mon. Notices Royal Astron. Soc., 491, 3, 4147-4161, doi:10.1093/mnras/stz3257

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Low-frequency magnetic field fluctuations in Earth's plasma environment observed by THEMIS

Annales Geophysicae ◽

10.5194/angeo-30-1271-2012 ◽

2012 ◽

Vol 30 (8) ◽

pp. 1271-1283 ◽

Cited By ~ 3

Author(s):

L. Guicking ◽

K.-H. Glassmeier ◽

H.-U. Auster ◽

Y. Narita ◽

G. Kleindienst

Keyword(s):

Magnetic Field ◽

Low Frequency ◽

Wave Generation ◽

Wave Activity ◽

Wave Intensity ◽

Magnetic Wave ◽

Plasma Environment ◽

Frequency Magnetic Field ◽

Field Fluctuations ◽

Generation Mechanisms

Abstract. Low-frequency magnetic wave activity in Earth's plasma environment was determined based on a statistical analysis of THEMIS magnetic field data. We observe that the spatial distribution of low-frequency magnetic field fluctuations reveals highest values in the magnetosheath, but the observations differ qualitatively from observations at Venus presented in a previous study since significant wave activity at Earth is also observed in the nightside magnetosheath. Outside the magnetosheath the low-frequency wave activity level is generally very low. By means of an analytical streamline model for the magnetosheath plasma flow, we are able to investigate the spatial and temporal evolution of wave intensity along particular streamlines in order to characterise possible wave generation mechanisms. We observe a decay of wave intensity along the streamlines, but contrary to the situation at Venus, we obtain good qualitative agreement with the theoretical concept of freely evolving/decaying turbulence. Differences between the dawn region and the dusk region can be observed only further away from the magnetopause. We conclude that wave generation mechanisms may be primarily attributed to processes at or in the vicinity of the bow shock. The difference with the observations of the Venusian magnetosheath we interpret to be the result of the different types of solar wind interaction processes since the Earth possesses a global magnetic field while Venus does not, and therefore the observed magnetic wave activities may be caused by diverse magnetic field controlled characteristics of wave generation processes.

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Statistical properties of low-frequency magnetic field fluctuations in the solar wind from 0.29 to 1.0 AU during solar minimum conditions: HELIOS 1 and HELIOS 2

Journal of Geophysical Research Atmospheres ◽

10.1029/ja087ia04p02215 ◽

1982 ◽

Vol 87 (A4) ◽

pp. 2215 ◽

Cited By ~ 103

Author(s):

K. U. Denskat ◽

F. M. Neubauer

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Minimum ◽

Low Frequency ◽

Statistical Properties ◽

Frequency Magnetic Field ◽

Field Fluctuations

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Propagation properties of foreshock cavitons and spontaneous hot flow anomalies: Statistical results from a global hybrid-Vlasov simulation

10.5194/egusphere-egu21-5635 ◽

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

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. &#160; &#160; 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.

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Solar wind interaction with the Earth's magnetic field: 3. On the Earth's bow shock structure

Journal of Geophysical Research Atmospheres ◽

10.1029/ja078i019p03745 ◽

1973 ◽

Vol 78 (19) ◽

pp. 3745-3760 ◽

Cited By ~ 36

Author(s):

V. Formisano ◽

P. C. Hedgecock

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Shock Structure ◽

Bow Shock ◽

Earth’S Magnetic Field ◽

Solar Wind Interaction ◽

Earth’S Bow Shock ◽

Earth's Magnetic Field

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Modulation of the solar wind driven ion escape from unmagnetized planets by ultra-low-frequency foreshock waves in a global hybrid simulation

10.5194/egusphere-egu2020-6891 ◽

2020 ◽

Author(s):

Riku Jarvinen ◽

Esa Kallio ◽

Tuija Pulkkinen

Keyword(s):

Solar Wind ◽

Large Scale ◽

Low Frequency ◽

Hybrid Simulation ◽

Bow Shock ◽

Upstream Region ◽

Ulf Waves ◽

Solar Wind Interaction ◽

Ion Escape ◽

A Charge

We study the solar wind interaction with Venus in a 3-dimensional global hybrid model where ions are treated as particles and electrons are a charge-neutralizing fluid. We concentrate on large-scale ultra-low frequency (ULF) waves in the ion foreshock and how they affect the energization and escape of planetary ions. The ion foreshock forms in the upstream region ahead of the quasi-parallel bow shock, where the angle between the shock normal and the magnetic field is smaller than about 45 degrees. The magnetic connection with the bow shock allows backstreaming of the solar wind ions leading to the formation of the ion foreshock. This kind of beam-plasma configuration is a source of free energy for the excitation of plasma waves. The foreshock ULF waves convect downstream with the solar wind flow and encounter the bow shock and transmit in the downstream region. We analyze the coupling of the ULF waves with the planetary ion acceleration and compare Venus and Mars in a global hybrid simulation.

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Low-frequency magnetic variations at the high-β Earth bow shock

Annales Geophysicae ◽

10.5194/angeo-37-877-2019 ◽

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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