scholarly journals On the edge of the foreshock: model-data comparisons

2008 ◽  
Vol 26 (6) ◽  
pp. 1539-1544 ◽  
Author(s):  
D. G. Sibeck ◽  
N. Omidi ◽  
I. Dandouras ◽  
E. Lucek
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Large Amplitude ◽  
Bow Shock ◽  
Model Data ◽  
Solar Wind Interaction ◽  
Hybrid Code ◽  
Amplitude Density

Abstract. We present the results of a global hybrid code simulation for the solar wind-interaction with the Earth's magnetosphere during an interval of steady radial IMF. The model predicts a foreshock marked by innumerable localized, correlated, and large amplitude, density and magnetic field strength variations, depressed velocities, and enhanced temperatures. The foreshock is bounded by a broad (~0.8 RE) region of enhanced densities, temperatures, and magnetic field strengths that extends far (~8.6 RE) upstream from the bow shock. Flow perturbations within the boundary are directed perpendicular to the boundary, towards the unperturbed solar wind and away from the foreshock. Cluster observations of the ion foreshock and pristine solar wind confirm the predictions of the model. The observations suggest that foreshock cavities, crater-like density and magnetic field strength structures whose cores are filled with suprathermal particles, can be interpreted in terms of transient encounters with the foreshock boundary.

scholarly journals Radial dependence of foreshock cavities: a case study

2004 ◽  
Vol 22 (12) ◽  
pp. 4143-4151 ◽  
Author(s):  
D. G. Sibeck ◽  
K. Kudela ◽  
T. Mukai ◽  
Z. Nemecek ◽  
J. Safrankova
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Bow Shock ◽  
Radial Dependence ◽  
Energetic Ions ◽  
Interplanetary Physics ◽  
Bow Shocks

Abstract. We present a case study of Geotail, Interball-1, IMP-8, and Wind observations of density and magnetic field strength cavities excavated by the enhanced pressures associated with bursts of energetic ions in the foreshock. Consistent with theoretical predictions, the pressure of the energetic ions diminishes rapidly with upstream distance due to a decrease in the flux of energetic ions and a transition from near-isotropic to streaming pitch angle distributions. Consequently, the cavities can only be observed immediately upstream from the bow shock. A comparison of conditions upstream from the pre- and post-noon bow shock demonstrates that foreshock cavities introduce perturbations into the oncoming solar wind flow with dimensions smaller than those of the magnetosphere. Dayside geosynchronous magnetic field strength variations observed by GOES-8 do not track the density variations seen by any of the spacecraft upstream from the bow shock in a one-to-one manner, indicating that none of these spacecraft observed the precise sequence of density variations that actually struck the subsolar magnetopause. Key words. Interplanetary physics (energetic particles; planetary bow shocks) – Magnetospheric physics (solar wind-magnetosphere interactions)

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

2020 ◽  
Author(s):  
Lucile Turc ◽  
Vertti Tarvus ◽  
Andrew Dimmock ◽  
Markus Battarbee ◽  
Urs Ganse ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Mach Number ◽  
Field Strength ◽  
Flow Velocity ◽  
Magnetic Field Strength ◽  
Bow Shock ◽  
Wide Range ◽  
The Magnetic Field ◽  
The Imf

<p>The magnetosheath is the region bounded by the bow shock and the magnetopause which is home to shocked solar wind plasma. At the interface between the solar wind and the magnetosphere, the magnetosheath plays a key role in the coupling between these two media. Previous works have revealed pronounced dawn-dusk asymmetries in the magnetosheath properties, with for example the magnetic field strength and flow velocity being larger on the dusk side, while the plasma is denser, hotter and more turbulent on the dawn side. 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 that have been processed to obtain the 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 due to the different processing methods. We investigate how the asymmetries change when the IMF becomes more radial and when the Alfvén Mach number decreases. When the IMF makes a 30° angle with the Sun-Earth line instead of 45°, we find a stronger magnetic field asymmetry and a larger variability of the magnetosheath density. In contrast, a lower Alfvén Mach number leads to a decrease of the magnetic field asymmetry level and of the variability of the magnetosheath density and velocity, likely due to weaker foreshock processes.</p>

Asymmetric reconnection at the bow shock

2020 ◽  
Author(s):  
Herbert Gunell ◽  
Maria Hamrin ◽  
Oleksandr Goncharov ◽  
Alexandre De Spiegeleer ◽  
Stephen Fuselier ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Plasma Flow ◽  
Bow Shock ◽  
The Other ◽  
Magnetospheric Multiscale ◽  
The Magnetic Field

<p>Can reconnection be triggered as a directional discontinuity (DD) crosses the bow shock? Here we present some unique observations of asymmetric reconnection at a quasi-perpendicular bow shock as an interplanetary DD is crossing it simultaneously with the Magnetospheric Multiscale (MMS) mission. The data show indications of ongoing reconnection at the bow shock southward of the spacecraft. The DD is also observed by several upstream spacecraft (ACE, WIND, Geotail, and THEMIS B) and one downstream in the magnetosheath (Cluster 4), but none of them resolve signatures of ongoing reconnection. We therefore suggest that reconnection was temporarily triggered as the DD was compressed by the shock. Bow shock reconnection is inevitably asymmetric with both the density and the magnetic field strength being higher on one side of the X-line (the magneosheath side) than on the other side where the plasma flow also is supersonic (the solar wind side). Asymmetric reconnection of the bow shock type has never been studied before, and the data discussed here are hence unique.</p>

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

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.

Cassini observations of magnetic holes in the solar wind and Saturn magnetosheath

2020 ◽  
Author(s):  
Tomas Karlsson ◽  
Lina Hadid ◽  
Michiko Morooka ◽  
Jan-Erik Wahlund
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
High Time Resolution ◽  
Magnetic Field Direction ◽  
Scale Size ◽  
Background Magnetic Field ◽  
Cycle Dependence ◽  
The Magnetic Field

<p>We present the first Cassini observations of magnetic holes on the near-Saturn solar wind and magnetosheath, based on data from the MAG magnetometer. We conclude that magnetic holes (defined as isolated decreases of at least 50% compared to the background magnetic field strength) are common in both regions. We present statistical properties of the magnetic holes, including scale size, depth of the magnetic field reduction, orientation, change in magnetic field direction over the holes, and solar cycle dependence. For magnetosheath magnetic holes, also high-time resolution density measurements from the LP Langmuir probe are available, allowing us to study the anti-correlation of density and magnetic field strength in the magnetic holes. We compare to recent results from MESSENGER observations from Mercury orbit, and finally discuss the possible importance of magnetic holes in solar wind-magnetosphere interaction at Saturn.</p>

scholarly journals Simultaneous longitudinal and transverse oscillations in filament threads after a failed eruption

2019 ◽  
Vol 633 ◽  
pp. A12 ◽  
Author(s):  
Rakesh Mazumder ◽  
Vaibhav Pant ◽  
Manuel Luna ◽  
Dipankar Banerjee
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Large Amplitude ◽  
Large Scale ◽  
Radius Of Curvature ◽  
Solar Dynamics Observatory ◽  
Solar Prominences ◽  
Solar Dynamics ◽  
Transverse Oscillations

Context. Longitudinal and transverse oscillations are frequently observed in the solar prominences and/or filaments. These oscillations are excited by a large-scale shock wave, impulsive flares at one leg of the filament threads, or due to any low coronal eruptions. We report simultaneous longitudinal and transverse oscillations in the filament threads of a quiescent region filament. We observe a large filament in the northwest of the solar disk on July 6, 2017. On July 7, 2017, it starts rising around 13:00 UT. We then observe a failed eruption and subsequently the filament threads start to oscillate around 16:00 UT. Aims. We analyse oscillations in the threads of a filament and utilize seismology techniques to estimate magnetic field strength and length of filament threads. Methods. We placed horizontal and vertical artificial slits on the filament threads to capture the longitudinal and transverse oscillations of the threads. Data from Atmospheric Imaging Assembly onboard Solar Dynamics Observatory were used to detect the oscillations. Results. We find signatures of large-amplitude longitudinal oscillations (LALOs). We also detect damping in LALOs. In one thread of the filament, we observe large-amplitude transverse oscillations (LATOs). Using the pendulum model, we estimate the lower limit of magnetic field strength and radius of curvature from the observed parameter of LALOs. Conclusions. We show the co-existence of two different wave modes in the same filament threads. We estimate magnetic field from LALOs and suggest a possible range of the length of the filament threads using LATOs.

Predicting geo-effectiveness of CMEs using a novel 3D CME model FRi3D integrated into EUHFORIA 

2021 ◽  
Author(s):  
Stefaan Poedts ◽  
Anwesha Maharana ◽  
Camilla Scolini ◽  
Alexey Isavnin
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Three Dimensional ◽  
Flux Rope ◽  
Future Perspective ◽  
The European Union ◽  
Horizon 2020 ◽  
The Magnetic Field

<p>Previous studies of Coronal Mass Ejections (CMEs) have shown the importance of understanding their geometrical structure and internal magnetic field configuration for improving forecasting at Earth. The precise prediction of the CME shock and the magnetic cloud arrival time, their magnetic field strength and the orientation upon impact at Earth is still challenging and relies on solar wind and CME evolution models and precise input parameters. In order to understand the propagation of CMEs in the interplanetary medium, we need to understand their interaction with the complex features in the magnetized background solar wind which deforms, deflects and erodes the CMEs and determines their geo-effectiveness. Hence, it is important to model the internal magnetic flux-rope structure in the CMEs as they interact with CIRs/SIRs, other CMEs and solar transients in the heliosphere. The spheromak model (Verbeke et al. 2019) in the heliospheric wind and CME evolution simulation EUHFORIA (Pomoell and Poedts, 2018), fits well with the data near the CME nose close to its axis but fails to predict the magnetic field in CME legs when these impact Earth (Scolini et al. 2019). Therefore, we implemented the FRi3D stretched flux-rope CME model (Isavnin, 2016) in EUHFORIA to model a more realistic CME geometry. Fri3D captures the three-dimensional magnetic field structure with parameters like skewing, pancaking and flattening that quantify deformations experienced by an interplanetary CME. We perform test runs of real CME events and validate the ability of FRi3D coupled with EUHFORIA in predicting the CME geo-effectiveness. We have modeled two real events with FRi3D. First, a CME event on 12 July 2012 which was a head-on encounter at Earth. Second, the flank CME encounter of 14 June 2012 which did not leave any magnetic field signature at Earth when modeled with Spheromak. We compare our results with the results from non-magnetized cone simulations and magnetized simulations employing the spheromak flux-rope model. We further discuss how constraining observational parameters using the stretched flux rope CME geometry in FRi3D affects the prediction of the magnetic field strength in our simulations, highlighting improvements and discussing future perspective.</p><p><em>This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405 (EUHFORIA 2.0)</em></p>

Solar wind interaction with the Earth's magnetic field: 2. Magnetohydrodynamic bow shock

1973 ◽  
Vol 78 (19) ◽  
pp. 3731-3744 ◽  
Author(s):  
V. Formisano ◽  
P. C. Hedgecock ◽  
G. Moreno ◽  
F. Palmiotto ◽  
J. K. Chao
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Bow Shock ◽  
Earth’S Magnetic Field ◽  
Solar Wind Interaction ◽  
Earth's Magnetic Field

scholarly journals First observations of magnetic holes deep within the coma of a comet

2018 ◽  
Vol 618 ◽  
pp. A114 ◽  
Author(s):  
F. Plaschke ◽  
T. Karlsson ◽  
C. Götz ◽  
C. Möstl ◽  
I. Richter ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
European Space Agency ◽  
Time Frame ◽  
Fluxgate Magnetometer ◽  
Space Agency ◽  
First Time ◽  
Comet 67P

The Rosetta spacecraft of the European Space Agency made ground-breaking observations of comet 67P/Churyumov-Gerasimenko and of its cometary environment. We search for magnetic holes in that environment, i.e., significant depressions in the magnetic field strength, measured by the Rosetta fluxgate Magnetometer (MAG) in April and May 2015. In that time frame of two months, we identified 23 magnetic holes. The cometary activity was intermediate and increasing because Rosetta was on the inbound leg toward the Sun. While in April solar wind protons were still observed by Rosetta near the comet, in May these protons were already mostly replaced by heavy cometary ions. Magnetic holes have frequently been observed in the solar wind. We find, for the first time, that magnetic holes exist in the cometary environment even when solar wind protons are almost absent. Some of the properties of the magnetic holes are comparable to those of solar wind holes; they are associated with density enhancements, sometimes associated with co-located current sheets and fast solar wind streams, and are of similar scales. However, particularly in May, the magnetic holes near the comet appear to be more processed, featuring shifted density enhancements and, sometimes, bipolar signatures in magnetic field strength rather than simple depressions. The magnetic holes are of global size with respect to the coma. However, at the comet, they are compressed owing to magnetic field pile-up and draping so that they change in shape. There, the magnetic holes become of comparable size to heavy cometary ion gyroradii, potentially enabling kinetic interactions.

Sign in / Sign up

Export Citation Format

Share Document