Effect of the solar wind density on the evolution of normal and inverse coronal mass ejections

Context. The evolution of magnetised coronal mass ejections (CMEs) and their interaction with the background solar wind leading to deflection, deformation, and erosion is still largely unclear as there is very little observational data available. Even so, this evolution is very important for the geo-effectiveness of CMEs. Aims. We investigate the evolution of both normal and inverse CMEs ejected at different initial velocities, and observe the effect of the background wind density and their magnetic polarity on their evolution up to 1 AU. Methods. We performed 2.5D (axisymmetric) simulations by solving the magnetohydrodynamic equations on a radially stretched grid, employing a block-based adaptive mesh refinement scheme based on a density threshold to achieve high resolution following the evolution of the magnetic clouds and the leading bow shocks. All the simulations discussed in the present paper were performed using the same initial grid and numerical methods. Results. The polarity of the internal magnetic field of the CME has a substantial effect on its propagation velocity and on its deformation and erosion during its evolution towards Earth. We quantified the effects of the polarity of the internal magnetic field of the CMEs and of the density of the background solar wind on the arrival times of the shock front and the magnetic cloud. We determined the positions and propagation velocities of the magnetic clouds and thus also the stand-off distance of the leading shock fronts (i.e. the thickness of the magnetic sheath region) and the deformation and erosion of the magnetic clouds during their evolution from the Sun to the Earth. Inverse CMEs were found to be faster than normal CMEs ejected in the same initial conditions, but with smaller stand-off distances. They also have a higher magnetic cloud length, opening angle, and mass. Synthetic satellite time series showed that the shock magnitude is not affected by the polarity of the CME. However, the density peak of the magnetic cloud is dependent on the polarity and, in case of inverse CMEs, also on the background wind density. The magnitude of the z-component of the magnetic field was not influenced by either the polarity or the wind density.

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Analysis of Deformation and Erosion during CME Evolution

Geosciences ◽

10.3390/geosciences11080314 ◽

2021 ◽

Vol 11 (8) ◽

pp. 314

Author(s):

Skralan Hosteaux ◽

Emmanuel Chané ◽

Stefaan Poedts

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Magnetic Flux ◽

Pressure Gradient ◽

Magnetic Cloud ◽

Plasma Pressure ◽

Closed Field ◽

Background Wind ◽

Field Lines ◽

Density Results

Magnetised coronal mass ejections (CMEs) are quite substantially deformed during their journey form the Sun to the Earth. Moreover, the interaction of their internal magnetic field with the magnetic field of the ambient solar wind can cause deflection and erosion of their mass and magnetic flux. We here analyse axisymmetric (2.5D) MHD simulations of normal and inverse CME, i.e., with the opposite or same polarity as the background solar wind, and attempt to quantify the erosion and the different forces that operate on the CMEs during their evolution. By analysing the forces, it was found that an increase of the background wind density results in a stronger plasma pressure gradient in the sheath that decelerates the magnetic cloud more. This in turn leads to an increase of the magnetic pressure gradient between the centre of the magnetic cloud and the separatrix, causing a further deceleration. Regardless of polarity, the current sheet that forms in our model between the rear of the CME and the closed field lines of the helmet streamer, results in magnetic field lines being stripped from the magnetic cloud. It is also found that slow normal CMEs experience the same amount of erosion, regardless of the background wind density. Moreover, as the initial velocity increases, so does the influence of the wind density on the erosion. We found that increasing the CME speed leads to a higher overall erosion due to stronger magnetic reconnection. For inverse CMEs, field lines are not stripped away but added to the magnetic cloud, leading to about twice as much magnetic flux at 1 AU than normal CMEs with the same initial flux.

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Magnetic field disturbances in the sheath region of a super-sonic interplanetary magnetic cloud

Annales Geophysicae ◽

10.5194/angeo-26-3153-2008 ◽

2008 ◽

Vol 26 (10) ◽

pp. 3153-3158 ◽

Cited By ~ 2

Author(s):

E. Romashets ◽

M. Vandas ◽

S. Poedts

Keyword(s):

Magnetic Field ◽

Geomagnetic Storms ◽

Magnetic Cloud ◽

The Body ◽

Magnetic Clouds ◽

Shock Surface ◽

Sheath Region ◽

Magnetic Field Magnitude ◽

The Magnetic Field ◽

Magnetic Disturbances

Abstract. It is well-known that interplanetary magnetic clouds can cause strong geomagnetic storms due to the high magnetic field magnitude in their interior, especially if there is a large negative Bz component present. In addition, the magnetic disturbances around such objects can play an important role in their "geo-effectiveness". On the other hand, the magnetic and flow fields in the CME sheath region in front of the body and in the rear of the cloud are important for understanding both the dynamics and the evolution of the interplanetary cloud. The "eventual" aim of this work is to calculate the magnetic field in this CME sheath region in order to evaluate the possible geo-efficiency of the cloud in terms of the maximum |Bz|-component in this region. In this paper we assess the potential of this approach by introducing a model with a simplified geometry. We describe the magnetic field between the CME shock surface and the cloud's boundary by means of a vector potential. We also apply our model and present the magnetic field distribution in the CME sheath region in front of the body and in the rear of the cloud formed after the event of 20 November 2003.

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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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Resistive evolution of toroidal field distributions and their relation to magnetic clouds

Journal of Plasma Physics ◽

10.1017/s0022377818001290 ◽

2019 ◽

Vol 85 (1) ◽

Author(s):

C. B. Smiet ◽

H. J. de Blank ◽

T. A. de Jong ◽

D. N. L. Kok ◽

D. Bouwmeester

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Field Strength ◽

Magnetic Field Strength ◽

Magnetic Clouds ◽

Twisted Field ◽

Field Lines ◽

Rotational Transform ◽

Universal Pattern ◽

The Magnetic Field

We study the resistive evolution of a localized self-organizing magnetohydrodynamic equilibrium. In this configuration the magnetic forces are balanced by a pressure force caused by a toroidal depression in the pressure. Equilibrium is attained when this low-pressure region prevents further expansion into the higher-pressure external plasma. We find that, for the parameters investigated, the resistive evolution of the structures follows a universal pattern when rescaled to resistive time. The finite resistivity causes both a decrease in the magnetic field strength and a finite slip of the plasma fluid against the static equilibrium. This slip is caused by a Pfirsch–Schlüter-type diffusion, similar to what is seen in tokamak equilibria. The net effect is that the configuration remains in magnetostatic equilibrium whilst it slowly grows in size. The rotational transform of the structure becomes nearly constant throughout the entire structure, and decreases according to a power law. In simulations this equilibrium is observed when highly tangled field lines relax in a high-pressure (relative to the magnetic field strength) environment, a situation that occurs when the twisted field of a coronal loop is ejected into the interplanetary solar wind. In this paper we relate this localized magnetohydrodynamic equilibrium to magnetic clouds in the solar wind.

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Solar wind interaction with the Earth's magnetosphere: the role of reconnection in the presence of a large scale sheared flow

Nonlinear Processes in Geophysics ◽

10.5194/npg-16-1-2009 ◽

2009 ◽

Vol 16 (1) ◽

pp. 1-10 ◽

Cited By ~ 10

Author(s):

F. Califano ◽

M. Faganello ◽

F. Pegoraro ◽

F. Valentini

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Magnetic Reconnection ◽

Large Scale ◽

Initial Conditions ◽

Magnetic Layer ◽

Magnetic Islands ◽

Solar Wind Interaction ◽

Earth’S Magnetosphere ◽

Earth's Magnetosphere

Abstract. The Earth's magnetosphere and solar wind environment is a laboratory of excellence for the study of the physics of collisionless magnetic reconnection. At low latitude magnetopause, magnetic reconnection develops as a secondary instability due to the stretching of magnetic field lines advected by large scale Kelvin-Helmholtz vortices. In particular, reconnection takes place in the sheared magnetic layer that forms between adjacent vortices during vortex pairing. The process generates magnetic islands with typical size of the order of the ion inertial length, much smaller than the MHD scale of the vortices and much larger than the electron inertial length. The process of reconnection and island formation sets up spontaneously, without any need for special boundary conditions or initial conditions, and independently of the initial in-plane magnetic field topology, whether homogeneous or sheared.

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On the Geoeffectiveness Structure of Solar Wind-Magnetosphere Coupling Functions during Intense Storms

ISRN Astronomy and Astrophysics ◽

10.5402/2011/961757 ◽

2011 ◽

Vol 2011 ◽

pp. 1-13 ◽

Cited By ~ 1

Author(s):

B. Olufemi Adebesin ◽

S. Oluwole Ikubanni ◽

J. Stephen Kayode

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Magnetic Cloud ◽

Recovery Phase ◽

Flow Speed ◽

Event Correlation ◽

Phase Duration ◽

Event Identification ◽

Solar Wind Flow ◽

The Magnetic Field

The geoeffectiveness of some coupling functions for the Solar Wind-Magnetosphere Interaction had been studied. 58 storms with peak Dst < −100 nT were used. The result showed that the interplanetary magnetic field Bz appeared to be more relevant with the magnetic field B (which agreed with previous results). However, both the V (solar wind flow speed) and Bz factors in the interplanetary dawn-dusk electric field (V×Bz) are effective in the generation of very intense storms (peak Dst < −250 nT) while “intense” storms (−250 nT ≤ peak Dst < −100 nT) are mostly enhanced by the Bz factor alone (in most cases). The southward Bz duration BT seems to be more relevant for Dst < −250 nT class of storms and invariably determines the recovery phase duration. Most of the storms were observed to occur at midnight hours (i.e., 2100–0400 UT), having a 41.2% incidence rate, with high frequency between 2300 UT and 0000 UT. 62% of the events were generated as a result of Magnetic Cloud (MC), while 38% were generated by complex ejecta. The B-Bz relation for the magnetic cloud attained a correlation coefficient of 0.8922, while it is 0.7608 for the latter. Conclusively, Bz appears to be the most geoeffective factor, and geoeffectiveness should be a factor that depends on methods of event identification and classification as well as the direction of event correlation.

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Outer Van Allen belt trapped and precipitating electron flux responses to two interplanetary magnetic clouds of opposite polarity

Annales Geophysicae ◽

10.5194/angeo-38-931-2020 ◽

2020 ◽

Vol 38 (4) ◽

pp. 931-951

Author(s):

Harriet George ◽

Emilia Kilpua ◽

Adnane Osmane ◽

Timo Asikainen ◽

Milla M. H. Kalliokoski ◽

...

Keyword(s):

Magnetic Field ◽

Radiation Belt ◽

Magnetic Cloud ◽

Opposite Polarity ◽

Initial Energy ◽

Magnetic Clouds ◽

Interplanetary Coronal Mass Ejections ◽

Field Orientation ◽

Outer Radiation Belt ◽

Trapped Electron

Abstract. Recently, it has been established that interplanetary coronal mass ejections (ICMEs) can dramatically affect both trapped electron fluxes in the outer radiation belt and precipitating electron fluxes lost from the belt into the atmosphere. Precipitating electron fluxes and energies can vary over a range of timescales during these events. These variations depend on the initial energy and location of the electron population and the ICME characteristics and structures. One important factor controlling electron dynamics is the magnetic field orientation within the ejecta that is an integral part of the ICME. In this study, we examine Van Allen Probes (RBSPs) and Polar Orbiting Environmental Satellites (POESs) data to explore trapped and precipitating electron fluxes during two ICMEs. The ejecta in the selected ICMEs have magnetic cloud characteristics that exhibit the opposite sense of the rotation of the north–south magnetic field component (BZ). RBSP data are used to study trapped electron fluxes in situ, while POES data are used for electron fluxes precipitating into the upper atmosphere. The trapped and precipitating electron fluxes are qualitatively analysed to understand their variation in relation to each other and to the magnetic cloud rotation during these events. Inner magnetospheric wave activity was also estimated using RBSP and Geostationary Operational Environmental Satellite (GOES) data. In each event, the largest changes in the location and magnitude of both the trapped and precipitating electron fluxes occurred during the southward portion of the magnetic cloud. Significant changes also occurred during the end of the sheath and at the sheath–ejecta boundary for the cloud with south to north magnetic field rotation, while the ICME with north to south rotation had significant changes at the end boundary of the cloud. The sense of rotation of BZ and its profile also clearly affects the coherence of the trapped and/or precipitating flux changes, timing of variations with respect to the ICME structures, and flux magnitude of different electron populations. The differing electron responses could therefore imply partly different dominant acceleration mechanisms acting on the outer radiation belt electron populations as a result of opposite magnetic cloud rotation.

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Unraveling the Internal Magnetic Field Structure of the Earth-directed Interplanetary Coronal Mass Ejections During 1995 – 2015

Solar Physics ◽

10.1007/s11207-019-1477-8 ◽

2019 ◽

Vol 294 (7) ◽

Cited By ~ 14

Author(s):

Teresa Nieves-Chinchilla ◽

Lan K. Jian ◽

Laura Balmaceda ◽

Angelos Vourlidas ◽

Luiz F. G. dos Santos ◽

...

Keyword(s):

Magnetic Field ◽

Coronal Mass Ejections ◽

Field Structure ◽

Internal Magnetic Field ◽

Interplanetary Coronal Mass Ejections ◽

Magnetic Field Structure ◽

The Earth

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Hybrid Simulation of Solar-Wind-Like Turbulence

Solar Physics ◽

10.1007/s11207-019-1548-x ◽

2019 ◽

Vol 294 (11) ◽

Cited By ~ 2

Author(s):

D. Aaron Roberts ◽

Leon Ofman

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

High Speed ◽

Radial Flow ◽

Initial Conditions ◽

Thermal Fluctuations ◽

Flow Speed ◽

Initial State ◽

Simplifying Assumptions ◽

The Magnetic Field

Abstract We present 2.5D hybrid simulations of the spectral and thermodynamic evolution of an initial state of magnetic field and plasma variables that in many ways represents solar wind fluctuations. In accordance with Helios near-Sun high-speed stream observations, we start with Alfvénic fluctuations along a mean magnetic field in which the fluctuations in the magnitude of the magnetic field are minimized. Since fluctuations in the radial flow speed are the dominant free energy in the observed fluctuations, we include a field-aligned $v_{\|}(k_{\perp })$v∥(k⊥) with an $k^{ -1}$k−1 spectrum of velocity fluctuations to drive the turbulent evolution. The flow rapidly distorts the Alfvénic fluctuations, yielding spectra (determined by spacecraft-like cuts) transverse to the field that become comparable to the $k_{\|}$k∥ fluctuations, as in spacecraft observations. The initial near constancy of the magnetic field is lost during the evolution; we show this also takes place observationally. We find some evolution in the anisotropy of the thermal fluctuations, consistent with expectations based on Helios data. We present 2D spectra of the fluctuations, showing the evolution of the power spectrum and cross-helicity. Despite simplifying assumptions, many aspects of simulations and observations agree. The greatly faster evolution in the simulations is at least in part due to the small scales being simulated, but also to the non-equilibrium initial conditions and the relatively low overall Alfvénicity of the initial fluctuations.

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SUPERSUBSTORM ON 28 MAY 2011 – GEOMAGNETIC EFFECTS IN THE GLOBAL SCALE

PHYSICS OF AURORAL PHENOMENA ◽

10.51981/2588-0039.2021.44.002 ◽

2021 ◽

Vol 44 ◽

pp. 12-15

Author(s):

I.V. Despirak ◽

◽

N.G. Kleimenova ◽

A.A. Lubchich ◽

P.V. Setsko ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Ring Current ◽

Magnetic Measurements ◽

Magnetic Cloud ◽

Dynamic Pressure ◽

Global Scale ◽

Strong Magnetic Storm ◽

Evening Sector ◽

Typical Scenario

For this analysis, we selected the supersubstorm (SSS) occurred during the strong magnetic storm on 28 May 2011 (SYM/H~100 nT). The ground-based magnetic effects of SSS have been studied basing on the data from the global SuperMAG, INTERMAGNET and IMAGE magnetometer networks, as well as on the magnetic measurements by the ionospheric satellite AMPERE system. According to the SML- index behavior, the SSS event maximum was identified at ~09:00 UT on 28 May 2011 (SML= ~-2600 nT). The SSS occurred during the passage of the magnetic cloud in the solar wind. Before the SSS, the BZ component of the Interplanetary Magnetic Field (IMF) was negative, the IMF BY component was positive, and the local jump in the solar wind dynamic pressure was registered. We found that the SSS developed in the magnetosphere in the global scale. A strong westward electrojet was observed at auroral latitudes from the evening side to the dayside. In contrast to the typical scenario of a classical substorm, a very intense eastward electrojet was detected in the afternoon-evening sector. That may be a result of the formation of an additional partial ring current during the supersubstorm.

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