Particle acceleration by transient structures around Earth’s bow shock

2020 ◽  
Author(s):  
Terry Zixu Liu ◽  
Vassilis Angelopoulos ◽  
Heli Hietala ◽  
San Lu ◽  
Drew Turner
Keyword(s):  
Solar Wind ◽  
Particle Acceleration ◽  
Dynamic Pressure ◽  
Bow Shock ◽  
Fermi Acceleration ◽  
Bow Wave ◽  
Nonlinear Transient ◽  
High Dynamic ◽  
Shock Environment ◽  
Transient Structures

<p>Upstream of Earth’s bow shock, the foreshock is filled with particles that have been reflected at the bow shock and are streaming away from it. Interaction of these particles with solar wind particles and discontinuities within this region can cause foreshock transients to form. Downstream of Earth’s bow shock, localized magnetosheath jets with high dynamic pressure are frequently observed. When such a fast magnetosheath jet compresses the ambient magnetosheath plasma, an earthward compressional bow wave/shock can form. Here we present that foreshock transients and magnetosheath jets can accelerate particles through shock drift acceleration, Fermi acceleration, and the betatron acceleration. Foreshock transients and magnetosheath jets therefore can increase the particle acceleration efficiency of the parent shock by providing additional acceleration. The shock environment relevant for particle acceleration is not just the shock itself, but also the nonlinear transient structures both upstream and downstream of it.</p>

scholarly journals Supermagnetosonic subsolar magnetosheath jets and their effects: from the solar wind to the ionospheric convection

2012 ◽  
Vol 30 (1) ◽  
pp. 33-48 ◽  
Author(s):  
H. Hietala ◽  
N. Partamies ◽  
T. V. Laitinen ◽  
L. B. N. Clausen ◽  
G. Facskó ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
High Speed ◽  
Dynamic Pressure ◽  
Bow Shock ◽  
Ionospheric Convection ◽  
Scale Size ◽  
High Dynamic ◽  
High Speed Flows

Abstract. It has recently been proposed that ripples inherent to the bow shock during radial interplanetary magnetic field (IMF) may produce local high speed flows in the magnetosheath. These jets can have a dynamic pressure much larger than the dynamic pressure of the solar wind. On 17 March 2007, several jets of this type were observed by the Cluster spacecraft. We study in detail these jets and their effects on the magnetopause, the magnetosphere, and the ionospheric convection. We find that (1) the jets could have a scale size of up to a few RE but less than ~6 RE transverse to the XGSE axis; (2) the jets caused significant local magnetopause perturbations due to their high dynamic pressure; (3) during the period when the jets were observed, irregular pulsations at the geostationary orbit and localised flow enhancements in the ionosphere were detected. We suggest that these inner magnetospheric phenomena were caused by the magnetosheath jets.

scholarly journals Interplanetary magnetic field rotations followed from L1 to the ground: the response of the Earth's magnetosphere as seen by multi-spacecraft and ground-based observations

2011 ◽  
Vol 29 (9) ◽  
pp. 1549-1569 ◽  
Author(s):  
M. Volwerk ◽  
J. Berchem ◽  
Y. V. Bogdanova ◽  
O. D. Constantinescu ◽  
M. W. Dunlop ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Dynamic Pressure ◽  
Earth’S Magnetosphere ◽  
Solar Wind Magnetic Field ◽  
Earth's Magnetosphere ◽  
High Dynamic ◽  
First Time ◽  
Current Systems ◽  
The Magnetic Field

Abstract. A study of the interaction of solar wind magnetic field rotations with the Earth's magnetosphere is performed. For this event there is, for the first time, a full coverage over the dayside magnetosphere with multiple (multi)spacecraft missions from dawn to dusk, combined with ground magnetometers, radar and an auroral camera, this gives a unique coverage of the response of the Earth's magnetosphere. After a long period of southward IMF Bz and high dynamic pressure of the solar wind, the Earth's magnetosphere is eroded and compressed and reacts quickly to the turning of the magnetic field. We use data from the solar wind monitors ACE and Wind and from magnetospheric missions Cluster, THEMIS, DoubleStar and Geotail to investigate the behaviour of the magnetic rotations as they move through the bow shock and magnetosheath. The response of the magnetosphere is investigated through ground magnetometers and auroral keograms. It is found that the solar wind magnetic field drapes over the magnetopause, while still co-moving with the plasma flow at the flanks. The magnetopause reacts quickly to IMF Bz changes, setting up field aligned currents, poleward moving aurorae and strong ionospheric convection. Timing of the structures between the solar wind, magnetosheath and the ground shows that the advection time of the structures, using the solar wind velocity, correlates well with the timing differences between the spacecraft. The reaction time of the magnetopause and the ionospheric current systems to changes in the magnetosheath Bz seem to be almost immediate, allowing for the advection of the structure measured by the spacecraft closest to the magnetopause.

scholarly journals Magnetosheath jet properties and evolution as determined by a global hybrid-Vlasov simulation

2018 ◽  
Author(s):  
Minna Palmroth ◽  
Heli Hietala ◽  
Ferdinand Plaschke ◽  
Martin Archer ◽  
Tomas Karlsson ◽  
...  
Keyword(s):  
Observational Studies ◽  
High Speed ◽  
Dynamic Pressure ◽  
Cone Angle ◽  
Low Frequency ◽  
Bow Shock ◽  
High Dynamic ◽  
Temporal Dimensions ◽  
First Time ◽  
Geomagnetic Dipole

Abstract. We use a global hybrid-Vlasov simulation for the magnetosphere, Vlasiator, to investigate magnetosheath high-speed jets. Unlike many other hybrid-kinetic simulations, Vlasiator includes an unscaled geomagnetic dipole, indicating that the simulation spatial and temporal dimensions can be given without scaling. Thus, for the first time, this allows investigating the magnetosheath jet properties and comparing them directly with the observed jets within the Earth's magnetosheath. In the run shown in this paper, the interplanetary magnetic field (IMF) cone angle is 30°, and a foreshock develops upstream of the quasi-parallel magnetosheath. We visually detect a structure with high dynamic pressure propagating from the bow shock towards the magnetopause. The structure is confirmed as a jet using three different criteria, which have been adopted in previous observational studies. We compare these criteria against the simulation results. We find that the magnetosheath jet is an elongated structure extending Earthward of the bow shock by ~ 2.3 RE, while its size perpendicular to the direction of propagation is ~ 0.5 RE. We also investigate the jet evolution, and find that the jet originates due to the interaction of the foreshock Ultra Low Frequency (ULF) waves with the bow shock surface. The simulation shows that magnetosheath jets can develop also under steady IMF, as inferred by observational studies.

A kinetic formation model of foreshock transients

2021 ◽  
Author(s):  
Terry Zixu Liu ◽  
Xin An ◽  
Hui Zhang ◽  
Drew Turner
Keyword(s):  
Magnetic Field ◽  
Positive Feedback ◽  
Formation Process ◽  
Hall Current ◽  
Dynamic Pressure ◽  
Bow Shock ◽  
Fermi Acceleration ◽  
Formation Model ◽  
Particle In Cell ◽  
Pressure Perturbations

<p>Foreshock transients are ion kinetic structures in the ion foreshock. Due to their dynamic pressure perturbations, they can disturb the bow shock, magnetosheath, magnetopause, and magnetosphere-ionosphere system. Recent studies found that they can also accelerate particles through shock drift acceleration, Fermi acceleration, betatron acceleration, and magnetic reconnection. Although foreshock transients are important, how they form is still not fully understood. Using particle-in-cell simulations and MMS observations, we propose a physical formation process that the positive feedback of demagnetized foreshock ions on the varying magnetic field caused by the foreshock ion Hall current enables an “instability” and the growth of the structure.      </p>

The Teardrop Magnetosphere

1996 ◽  
Author(s):  
Charles F. Kennel
Keyword(s):  
Solar Wind ◽  
Dynamic Pressure ◽  
Confining Pressure ◽  
Weak Field ◽  
Bow Shock ◽  
Dayside Magnetopause ◽  
Blunt Bodies ◽  
Model Section ◽  
Plasma Depletion ◽  
Average Position

In this chapter, we try to infer from magnetohydrodynamic reasoning and observation how the magnetosphere might look and behave if the magnetopause were inactive. Since there probably never has been an occasion when both viscosity and reconnection were absent, all we can do is array observations of phenomena that do not depend on either mechanism for their existence. As a result, we end up focusing on how the magnetosphere arrives at a balance of pressure with the solar wind. How it responds to changes in its confining pressure will be the topic of the next chapter. All discussions of the magnetosphere start with the magnetopause, and, indeed, the first models of the magnetosphere were calculations of the shape of the magnetopause. Without reconnection and without viscosity, the magnetopause would be given by the Chapman-Ferraro model on the dayside and close due to the reexpansion of the finite-temperature solar wind on the nightside (Section 2.2). This magnetosphere has a teardrop shape. After the dependence upon the interplanetary field via the reconnection process is taken into account, the average position and shape of the dayside magnetopause is in general accord with the Chapman-Ferraro model (Section 2.3). Because the magnetopause is always in motion, the early estimates of its thickness were uncertain until the first twospacecraft observations were made (Section 2.4). The magnetopause current layer proved to be several ion Larmor radii thick, significantly thicker than the electron inertial length. Once the average position of the magnetopause is specified, the position of the bow shock can be calculated using methods first employed for hypersonic flow around blunt bodies, which are easily extended to a weak-field MHD regime. The measured average positions of the bow shock and magnetopause agree once variations in solar wind dynamic pressure are taken into account (Section 2.5). While weak-field MHD does a good job with the bow shock, it fails in the subsolar magnetosheath, where a plasma depletion layer forms just upstream of the magnetopause (Section 2.6). Full MHD theory suggests that as many as three shocks could be standing in the flow enclosing the magnetosphere, a fast bow shock, an intermediate shock, and a slow shock.

Magnetic field within magnetosheath jets during northward and southward interplanetary magnetic field conditions

2020 ◽  
Author(s):  
Laura Vuorinen ◽  
Heli Hietala ◽  
Ferdinand Plaschke
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Dynamic Pressure ◽  
Time History ◽  
Magnetic Shear ◽  
History Of ◽  
High Dynamic ◽  
The Magnetic Field ◽  
Magnetopause Reconnection

<p>Downstream of the Earth's quasi-parallel shock, transients with higher earthward velocities than the surrounding magnetosheath plasma are often observed. These transients have been named magnetosheath jets. Due to their high dynamic pressure, jets can cause multiple types of effects when colliding into the magnetopause. Recently, jets have been linked to triggering magnetopause reconnection in case studies by Hietala et al. (2018) and Nykyri et al. (2019). Jets have been proposed to affect magnetopause reconnection in multiple ways. Jets can compress the magnetopause and make it thin enough for reconnection to occur. Jets could also affect the magnetic shear either by indenting the magnetopause or via the magnetic field of the jets themselves. Here we want to study whether the magnetic field of jets can statistically affect magnetopause reconnection. In particular, we are interested in whether jets could enhance reconnection during more quiet northward IMF conditions.</p><p>We statistically study the magnetic field within jets in the subsolar magnetosheath using measurements from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and OMNI solar wind data from 2008–2011. We investigate jets next to the magnetopause and find that the magnetic field within jets is statistically different compared to the non-jet magnetosheath. Our results suggest that during southward IMF, the non-jet magnetosheath magnetic field itself has more variation than the jets. This suggests that jets should have no statistical, neither enhancing nor suppressing, effect on reconnection during southward IMF. However, during northward IMF, the magnetic field within jets is statistically favorable for enhancing magnetic reconnection at the subsolar magnetopause as around 70 % of these jets exhibit southward fields close to the magnetopause.</p>

scholarly journals The responses of the earth’s magnetopause and bow shock to the IMF Bz and the solar wind dynamic pressure: a parametric study using the AMR-CESE-MHD model

2018 ◽  
Vol 8 ◽  
pp. A41 ◽  
Author(s):  
Juan Wang ◽  
Zhifang Guo ◽  
Yasong S. Ge ◽  
Aimin Du ◽  
Can Huang ◽  
...  
Keyword(s):  
Solar Wind ◽  
Mach Number ◽  
Dynamic Pressure ◽  
Bow Shock ◽  
Solar Wind Dynamic Pressure ◽  
The Earth ◽  
Shock Location ◽  
Mhd Model ◽  
Upstream Solar Wind ◽  
The Imf

We have used the AMR-CESE-MHD model to investigate the influences of the IMF Bz and the upstream solar wind dynamic pressure (Dp) on Earth’s magnetopause and bow shock. Our results present that the earthward displacement of the magnetopause increases with the intensity of the IMF Bz. The increase of the northward IMF Bz also brings the magnetopause closer to the Earth even though with a small distance. Our simulation results show that the subsolar bow shock during the southward IMF is much closer to the Earth than during the northward IMF. As the intensity of IMF Bz increases (also the total field strength), the subsolar bow shock moves sunward as the solar wind magnetosonic Mach number decreases. The sunward movement of the subsolar bow shock during southward IMF are much smaller than that during northward IMF, which indicates that the decrease of solar wind magnetosonic Mach number hardly changes the subsolar bow shock location during southward IMF. Our simulations also show that the effects of upstream solar wind dynamic pressure (Dp) changes on both the subsolar magnetopause and bow shock locations are much more significant than those due to the IMF changes, which is consistent with previous studies. However, in our simulations the earthward displacement of the subsolar magnetopause during high solar wind Dp is greater than that predicted by the empirical models.

Magnetosheath high speed jets observed simultaneously by Cluster and MMS

2020 ◽  
Author(s):  
C.-Philippe Escoubet ◽  
Keyword(s):  
Solar Wind ◽  
Mach Number ◽  
High Speed ◽  
Smooth Surface ◽  
Dynamic Pressure ◽  
Dust Cloud ◽  
Bow Shock ◽  
Solar Wind Dynamic Pressure ◽  
Typical Size ◽  
Dust Clouds

<p>The supersonic solar wind is decelerated and thermalized when it encounters the Earth's magnetosphere and cross the bow shock. Sometimes, however, due to discontinuities in the solar wind, bow shock ripples or ionised dust clouds carried by the solar wind, high speed jets (HSJs) are observed in the magnetosheath. These HSJs have typically a Vx component larger than 200 km s-1 and their dynamic pressure can be a few times the solar wind dynamic pressure. They are typically observed downstream from the quasi-parallel bow shock and have a typical size around one Earth radius (RE) in XGSE. We use a conjunction of Cluster and MMS, crossing simultaneously the magnetopause, to study the characteristics of these HSJs and their impact on the magnetopause. Over one hour-fifteen minutes interval in the magnetosheath, Cluster observed 21 HSJs. During the same period, MMS observed 12 HSJs and entered the magnetosphere several times. A jet was observed simultaneously by both MMS and Cluster and it is very likely that they were two distinct HSJs. This shows that HSJs are not localised into small regions but could span a region larger than 10 RE, especially when the quasi-parallel shock is covering the entire dayside magnetosphere under radial IMF. During this period, two and six magnetopause crossings were observed respectively on Cluster and MMS with a significant angle between the observation and the expected normal deduced from models. The angles observed range between from 11° up to 114°. One inbound magnetopause crossing observed by Cluster (magnetopause moving out at 142 km s-1) was observed simultaneous to an outbound magnetopause crossing observed by MMS (magnetopause moving in at -83 km s-1), showing that the magnetopause can have multiple local indentation places, most likely independent from each other. Under the continuous impacts of HSJs, the magnetopause is deformed significantly and can even move in opposite directions at different places. It can therefore not be considered as a smooth surface anymore but more as surface full of local indents. Four dust impacts were observed on MMS, although not at the time when HSJs are observed, showing that dust clouds would have been present during the observations. No dust cloud in the form of Interplanetary Field Enhancements was however observed in the solar wind which may exclude large clouds of dust as a cause of HSJs. Radial IMF and Alfvén Mach number above 10 would fulfill the criteria for the creation of bow shock ripples and the subsequent crossing of HSJs in the magnetosheath.</p>

scholarly journals Interchange instability of a curved current layerconvecting in the magnetosheath from the bow shock towards themagnetopause

2004 ◽  
Vol 22 (3) ◽  
pp. 993-999 ◽  
Author(s):  
I. L. Arshukova ◽  
N. V. Erkaev ◽  
H. K. Biernat
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Solar Wind ◽  
Layer Structure ◽  
Dynamic Pressure ◽  
Bow Shock ◽  
Curvature Radius ◽  
Current Layer ◽  
Interchange Instability ◽  
The Magnetic Field

Abstract. This paper deals with nonsteady perturbations of the magnetosheath parameters which are related to variations of the interplanetary magnetic field from north to south under a constant solar wind dynamic pressure. The magnetic field changes its direction within a thin layer which is convected with the plasma from the bow shock to the ionopause. In the course of time, this current layer is amplified during its motion towards the magnetopause. The intensity of the current is increasing, the layer thickness is decreasing, and the gradients of parameters are becoming much sharper while the layer is approaching the magnetopause. The curvature radius of this layer is decreasing while it is draping around the magnetopause. This curved layer structure with reversed magnetic field in the magnetosheath is found to be unstable with respect to the interchange instability. The growth rate of the instability is obtained for different positions of the layer. Key words. Magnetospheric physics (magnetosheath)

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