Statistical Study of Small-scale Magnetic Holes in the Upstream Regime of the Martian Bow Shock

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.

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Foreshock cavitons and spontaneous hot flow anomalies: a statistical study with a global hybrid-Vlasov simulation

Annales Geophysicae ◽

10.5194/angeo-39-911-2021 ◽

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.

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Energetic particle parallel diffusion in a cascading wave turbulence in the foreshock region

Nonlinear Processes in Geophysics ◽

10.5194/npg-14-587-2007 ◽

2007 ◽

Vol 14 (5) ◽

pp. 587-601 ◽

Cited By ~ 5

Author(s):

F. Otsuka ◽

Y. Omura ◽

O. Verkhoglyadova

Keyword(s):

Solar Wind ◽

Pitch Angle ◽

Homogeneous Model ◽

Bow Shock ◽

Isotropic Scattering ◽

Wave Turbulence ◽

Small Scale ◽

Dimensional System ◽

Inverse Cascade ◽

Background Magnetic Field

Abstract. We study parallel (field-aligned) diffusion of energetic particles in the upstream of the bow shock with test particle simulations. We assume parallel shock geometry of the bow shock, and that MHD wave turbulence convected by the solar wind toward the shock is purely transverse in one-dimensional system with a constant background magnetic field. We use three turbulence models: a homogeneous turbulence, a regular cascade from a large scale to smaller scales, and an inverse cascade from a small scale to larger scales. For the homogeneous model the particle motions along the average field are Brownian motions due to random and isotropic scattering across 90 degree pitch angle. On the other hand, for the two cascade models particle motion is non-Brownian due to coherent and anisotropic pitch angle scattering for finite time scale. The mean free path λ|| calculated by the ensemble average of these particle motions exhibits dependence on the distance from the shock. It also depends on the parameters such as the thermal velocity of the particles, solar wind flow velocity, and a wave turbulence model. For the inverse cascade model, the dependence of λ|| at the shock on the thermal energy is consistent with the hybrid simulation done by Giacalone (2004), but the spatial dependence of λ|| is inconsistent with it.

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A statistical study of the upstream wave boundary outside the Earth's bow shock

Journal of Geophysical Research Atmospheres ◽

10.1029/ja081i001p00199 ◽

1976 ◽

Vol 81 (1) ◽

pp. 199-204 ◽

Cited By ~ 36

Author(s):

L. Diodato ◽

E. W. Greenstadt ◽

G. Moreno ◽

V. Formisano

Keyword(s):

Statistical Study ◽

Bow Shock ◽

Earth’S Bow Shock ◽

Wave Boundary

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Small-scale deformation of the bow shock

Advances in Space Research ◽

10.1016/j.asr.2007.04.050 ◽

2008 ◽

Vol 41 (10) ◽

pp. 1519-1527 ◽

Cited By ~ 2

Author(s):

K. Jelínek ◽

Z. Němeček ◽

J. Šafránková

Keyword(s):

Bow Shock ◽

Small Scale

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Large- and small-scale periodicities in the mesosphere as obtained from variations in O<sub>2</sub> and OH nightglow emissions

Annales Geophysicae ◽

10.5194/angeo-35-227-2017 ◽

2017 ◽

Vol 35 (2) ◽

pp. 227-237 ◽

Cited By ~ 3

Author(s):

Ravindra P. Singh ◽

Duggirala Pallamraju

Keyword(s):

Gravity Wave ◽

Statistical Study ◽

Small Scale ◽

Radio Flux ◽

Low Latitude ◽

Atmospheric Processes ◽

Solar Influence ◽

Seasonal Dependence

Abstract. Using 3 years (2013–2015) of O2(0–1) and OH(6–2) band nightglow emission intensities and corresponding rotational temperatures as tracers of mesospheric dynamics, we have investigated large- and small-timescale variations in the mesosphere over a low-latitude location, Gurushikhar, Mount Abu (24.6° N, 72.8° E), in India. Both O2 and OH intensities show variations similar to those of the number of sunspots and F10.7 cm radio flux with coherent periodicities of 150 ± 2.1, 195 ± 3.6, 270 ± 6.4, and 420 ± 14.8 days, indicating a strong solar influence on mesospheric dynamics. In addition, both mesospheric airglow intensities also showed periodicities of 84 ± 0.6, 95 ± 0.9, and 122 ± 1.3 days which are of atmospheric origin. With regard to the variability of the order of a few days, O2 and OH intensities were found to be correlated, in general, except when altitude-dependent atmospheric processes were operative. To understand mesospheric gravity wave behavior over the long term, we have carried out a statistical study using the periodicities derived from the nocturnal variations in all four parameters (O2 and OH intensities and their respective temperatures). It was found that the major wave periodicity of around 2 h duration is present in all the four parameters. Our analyses also reveal that the range of periods in O2 and OH intensities and temperatures is 11 to 24 and 20 to 60 min, respectively. Periods less than 15 min were not present in the temperatures but were prevalent in both emission intensities. No seasonal dependence was found in either the wave periodicities or the number of their occurrence.

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EDR signatures observed by MMS : a statistical study of dayside events found with machine learning

10.5194/egusphere-egu21-2381 ◽

2021 ◽

Author(s):

Quentin Lenouvel ◽

Vincent Génot ◽

Philippe Garnier ◽

Benoit Lavraud ◽

Sergio Toledo

Keyword(s):

Machine Learning ◽

Statistical Study ◽

Learning Algorithm ◽

Small Scale ◽

Diffusion Region ◽

Machine Learning Algorithm ◽

Physical Processes ◽

The Core ◽

Machine Learning Methods ◽

Guide Field

<p>The understanding of magnetic reconnection's physical processes has considerably been improved thanks to the data of the Magnetopsheric Multiscale mission (MMS). However, a lot of work still has to be done to better characterize the core of the reconnection process : the electron diffusion region (EDR). We previously developed a machine learning algorithm to automatically detect EDR candidates, in order to increase the available list of events identified in the literature. However, identifying the parameters that are the most relevant to describe EDRs is complex, all the more that some of the small scale plasma/fields parameters show limitations in some configurations such as for low particle densities or large guide fields cases. In this study, we perform a statistical study of previously reported dayside EDRs as well as newly reported EDR candidates found using machine learning methods. We also show different single and multi-spacecraft parameters that can be used to better identify dayside EDRs in time series from MMS data recorded at the magnetopause. And finally we show an analysis of the link between the guide field and the strength of the energy conversion around each EDR.</p>

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Statistical study of foreshock cavitons

Annales Geophysicae ◽

10.5194/angeo-31-2163-2013 ◽

2013 ◽

Vol 31 (12) ◽

pp. 2163-2178 ◽

Cited By ~ 14

Author(s):

P. Kajdič ◽

X. Blanco-Cano ◽

N. Omidi ◽

K. Meziane ◽

C. T. Russell ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Statistical Study ◽

Low Frequency ◽

Bow Shock ◽

Occurrence Rate ◽

Time Intervals ◽

Distinct Structure ◽

Wide Range ◽

The Magnetic Field

Abstract. In this work we perform a statistical analysis of 92 foreshock cavitons observed with the Cluster spacecraft 1 during the period 2001–2006. We analyze time intervals during which the spacecraft was located in the Earth's foreshock with durations longer than 10 min. Together these amount to ~ 50 days. The cavitons are transient structures in the Earth's foreshock. Their main signatures in the data include simultaneous depletions of the magnetic field intensity and plasma density, which are surrounded by a rim of enhanced values of these two quantities. Cavitons form due to nonlinear interaction of transverse and compressive ultra-low frequency (ULF) waves and are therefore always surrounded by intense compressive ULF fluctuations. They are carried by the solar wind towards the bow shock. This work represents the first systematic study of a large sample of foreshock cavitons. We find that cavitons appear for a wide range of solar wind and interplanetary magnetic field conditions and are therefore a common feature upstream of Earth's quasi-parallel bow shock with an average occurrence rate of ~ 2 events per day. We also discuss their observational properties in the context of other known upstream phenomena and show that the cavitons are a distinct structure in the foreshock.

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