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

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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Cluster observations of sudden impulses in the magnetotail caused by interplanetary shocks and pressure increases

Annales Geophysicae ◽

10.5194/angeo-23-609-2005 ◽

2005 ◽

Vol 23 (2) ◽

pp. 609-624 ◽

Cited By ~ 26

Author(s):

K. E. J. Huttunen ◽

J. Slavin ◽

M. Collier ◽

H. E. J. Koskinen ◽

A. Szabo ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Dynamic Pressure ◽

Solar Wind Speed ◽

Interplanetary Shock ◽

Wind Pressure ◽

Shock Propagation ◽

Interplanetary Shocks ◽

Maximum Variance ◽

The Magnetic Field

Abstract. Sudden impulses (SI) in the tail lobe magnetic field associated with solar wind pressure enhancements are investigated using measurements from Cluster. The magnetic field components during the SIs change in a manner consistent with the assumption that an antisunward moving lateral pressure enhancement compresses the magnetotail axisymmetrically. We found that the maximum variance SI unit vectors were nearly aligned with the associated interplanetary shock normals. For two of the tail lobe SI events during which Cluster was located close to the tail boundary, Cluster observed the inward moving magnetopause. During both events, the spacecraft location changed from the lobe to the magnetospheric boundary layer. During the event on 6 November 2001 the magnetopause was compressed past Cluster. We applied the 2-D Cartesian model developed by collier98 in which a vacuum uniform tail lobe magnetic field is compressed by a step-like pressure increase. The model underestimates the compression of the magnetic field, but it fits the magnetic field maximum variance component well. For events for which we could determine the shock normal orientation, the differences between the observed and calculated shock propagation times from the location of WIND/Geotail to the location of Cluster were small. The propagation speeds of the SIs between the Cluster spacecraft were comparable to the solar wind speed. Our results suggest that the observed tail lobe SIs are due to lateral increases in solar wind dynamic pressure outside the magnetotail boundary.

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Experimental and numerical investigation of plasma parameters in the magnetosheath

MATEC Web of Conferences ◽

10.1051/matecconf/201814503003 ◽

2018 ◽

Vol 145 ◽

pp. 03003

Author(s):

Polya Dobreva ◽

Monio Kartalev ◽

Olga Nitcheva ◽

Natalia Borodkova ◽

Georgy Zastenker

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Numerical Investigation ◽

Euler Equations ◽

Ideal Gas ◽

Bow Shock ◽

Plasma Parameters ◽

Wind Spacecraft ◽

The Magnetic Field ◽

Good Agreement

We investigate the behaviour of the plasma parameters in the magnetosheath in a case when Interball-1 satellite stayed in the magnetosheath, crossing the tail magnetopause. In our analysis we apply the numerical magnetosheath-magnetosphere model as a theoretical tool. The bow shock and the magnetopause are self-consistently determined in the process of the solution. The flow in the magnetosheath is governed by the Euler equations of compressible ideal gas. The magnetic field in the magnetosphere is calculated by a variant of the Tsyganenko model, modified to account for an asymmetric magnetopause. Also, the magnetopause currents in Tsyganenko model are replaced by numericaly calulated ones. Measurements from WIND spacecraft are used as a solar wind monitor. The results demonstrate a good agreement between the model-calculated and measured values of the parameters under investigation.

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Scattering of field-aligned beam ions upstream of Earth's bow shock

Annales Geophysicae ◽

10.5194/angeo-25-785-2007 ◽

2007 ◽

Vol 25 (3) ◽

pp. 785-799 ◽

Cited By ~ 24

Author(s):

A. Kis ◽

M. Scholer ◽

B. Klecker ◽

H. Kucharek ◽

E. A. Lucek ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Field Measurements ◽

Bow Shock ◽

Ion Distribution ◽

Parallel Side ◽

Earth’S Bow Shock ◽

High Mach ◽

The Magnetic Field

Abstract. Field-aligned beams are known to originate from the quasi-perpendicular side of the Earth's bow shock, while the diffuse ion population consists of accelerated ions at the quasi-parallel side of the bow shock. The two distinct ion populations show typical characteristics in their velocity space distributions. By using particle and magnetic field measurements from one Cluster spacecraft we present a case study when the two ion populations are observed simultaneously in the foreshock region during a high Mach number, high solar wind velocity event. We present the spatial-temporal evolution of the field-aligned beam ion distribution in front of the Earth's bow shock, focusing on the processes in the deep foreshock region, i.e. on the quasi-parallel side. Our analysis demonstrates that the scattering of field-aligned beam (FAB) ions combined with convection by the solar wind results in the presence of lower-energy, toroidal gyrating ions at positions deeper in the foreshock region which are magnetically connected to the quasi-parallel bow shock. The gyrating ions are superposed onto a higher energy diffuse ion population. It is suggested that the toroidal gyrating ion population observed deep in the foreshock region has its origins in the FAB and that its characteristics are correlated with its distance from the FAB, but is independent on distance to the bow shock along the magnetic field.

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

Annales Geophysicae ◽

10.5194/angeo-32-1247-2014 ◽

2014 ◽

Vol 32 (10) ◽

pp. 1247-1261 ◽

Cited By ~ 7

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.

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Magnetosheath dynamic pressure enhancements: occurrence and typical properties

Annales Geophysicae ◽

10.5194/angeo-31-319-2013 ◽

2013 ◽

Vol 31 (2) ◽

pp. 319-331 ◽

Cited By ~ 45

Author(s):

M. O. Archer ◽

T. S. Horbury

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Wavelet Transforms ◽

Large Amplitude ◽

Statistical Study ◽

Average Duration ◽

Dynamic Pressure ◽

Random Events ◽

Fractional Increase ◽

The Magnetic Field

Abstract. The first comprehensive statistical study of large-amplitude (> 100%) transient enhancements of the magnetosheath dynamic pressure reveals events of up to ~ 15 times the ambient dynamic pressure with durations up to 3 min and an average duration of around 30 s, predominantly downstream of the quasi-parallel shock. The dynamic pressure transients are most often dominated by velocity increases along with a small fractional increase in the density, though the velocity is generally only deflected by a few degrees. Superposed wavelet transforms of the magnetic field show that, whilst most enhancements exhibit changes in the magnetosheath magnetic field, the majority are not associated with changes in the Interplanetary Magnetic Field (IMF). However, there is a minority of enhancements that do appear to be associated with solar wind discontinuities which cannot be explained simply by random events. In general, it is found that during periods of magnetosheath dynamic pressure enhancements the IMF is steadier than usual. This suggests that a stable foreshock and hence foreshock structures or processes may be important in the generation of the majority of magnetosheath dynamic pressure enhancements.

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Comparison of the magnetic field before the subsolar magnetopause with the magnetic field in the solar wind before the bow shock

Advances in Space Research ◽

10.1016/j.asr.2014.04.023 ◽

2014 ◽

Vol 54 (4) ◽

pp. 604-616 ◽

Cited By ~ 10

Author(s):

Maria S. Pulinets ◽

Elizaveta E. Antonova ◽

Maria O. Riazantseva ◽

Svetlana S. Znatkova ◽

Igor P. Kirpichev

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Bow Shock ◽

The Magnetic Field

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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

Annales Geophysicae ◽

10.5194/angeo-29-1549-2011 ◽

2011 ◽

Vol 29 (9) ◽

pp. 1549-1569 ◽

Cited By ~ 6

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.

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Asymmetries in the Earth's dayside magnetosheath: results from global hybrid-Vlasov simulations

10.5194/angeo-2020-13 ◽

2020 ◽

Author(s):

Lucile Turc ◽

Vertti Tarvus ◽

Andrew Dimmock ◽

Markus Battarbee ◽

Urs Ganse ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Mach Number ◽

Bow Shock ◽

Strong Impact ◽

Parker Spiral ◽

Wide Range ◽

The Magnetic Field ◽

Single Set ◽

Shock Configuration

Abstract. Bounded by the bow shock and the magnetopause, the magnetosheath forms the interface between solar wind and magnetospheric plasmas and regulates solar wind-magnetosphere coupling. Previous works have revealed pronounced dawn-dusk asymmetries in the magnetosheath properties. The dependence of these asymmetries on the upstream parameters remains however largely unknown. One of the main sources of these asymmetries is the bow shock configuration, which is typically quasi-parallel on the dawn side and quasi-perpendicular on the dusk side of the terrestrial magnetosheath because of the Parker spiral orientation of the interplanetary magnetic field (IMF) at Earth. Most of these previous studies rely on collections of spacecraft measurements associated with a wide range of upstream conditions which are processed in order to obtain average values of the magnetosheath parameters. In this work, we use a different approach and quantify the magnetosheath asymmetries in global hybrid-Vlasov simulations performed with the Vlasiator model. We concentrate on three parameters: the magnetic field strength, the plasma density and the flow velocity. We find that the Vlasiator model reproduces accurately the polarity of the asymmetries, but that their level tends to be higher than in spacecraft measurements, probably because the magnetosheath parameters are obtained from a single set of upstream conditions in the simulation, making the asymmetries more prominent. We investigate how the asymmetries change when the angle between the IMF and the Sun-Earth line is reduced and when the Alfven Mach number decreases. We find that a more radial IMF results in a stronger magnetic field asymmetry and a larger variability of the magnetosheath density. In contrast, a lower Alfven Mach number leads to a reduced magnetic field asymmetry and a decrease in the variability of the magnetosheath density and velocity, the latter likely due to weaker foreshock processes. Our results highlight the strong impact of the foreshock on global magnetosheath properties, in particular on the magnetosheath density, which is extremely sensitive to transient foreshock processes.

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Venus's induced magnetosphere during active solar wind conditions at BepiColombo's Venus 1 flyby

10.5194/angeo-2021-24 ◽

2021 ◽

Author(s):

Martin Volwerk ◽

Beatriz Sánchez-Cano ◽

Daniel Heyner ◽

Sae Aizawa ◽

Nicolas André ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Coronal Mass Ejection ◽

Interplanetary Magnetic Field ◽

Bow Shock ◽

Gravity Assist ◽

Highly Active ◽

Field Lines ◽

Mass Ejection ◽

The Magnetic Field

Abstract. Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the YVSO-direction. In this paper, the BepiColombo Mercury Planetary Orbiter Magnetometer (MPO-MAG) data are discussed, with support from three other plasma instruments: the Planetary Ion Camera (PICAM), the Mercury Electron Analyser (MEA) and the radiation monitor (BERM). Behind the bow shock crossing, the magnetic field showed a draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with, e.g., strong flapping motions at a period of ~7 min. This activity was driven by solar wind conditions. Just before this flyby, Venus's induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii.

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

10.5194/egusphere-egu2020-11030 ◽

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&#8211;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>

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