scholarly journals Four-spacecraft determination of magnetopause orientation, motion and thickness: comparison with results from single-spacecraft methods

2004 ◽  
Vol 22 (4) ◽  
pp. 1347-1365 ◽  
Author(s):  
S. E. Haaland ◽  
B. U. Ö. Sonnerup ◽  
M. W. Dunlop ◽  
A. Balogh ◽  
E. Georgescu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Experiment ◽  
Residue Analysis ◽  
Minimum Variance ◽  
Normal Vector ◽  
Current Layer ◽  
Hybrid Techniques ◽  
Cluster Data ◽  
Magnetic Profile

Abstract. In this paper, we use Cluster data from one magnetopause event on 5 July 2001 to compare predictions from various methods for determination of the velocity, orientation, and thickness of the magnetopause current layer. We employ established as well as new multi-spacecraft techniques, in which time differences between the crossings by the four spacecraft, along with the duration of each crossing, are used to calculate magnetopause speed, normal vector, and width. The timing is based on data from either the Cluster Magnetic Field Experiment (FGM) or the Electric Field Experiment (EFW) instruments. The multi-spacecraft results are compared with those derived from various single-spacecraft techniques, including minimum-variance analysis of the magnetic field and deHoffmann-Teller, as well as Minimum-Faraday-Residue analysis of plasma velocities and magnetic fields measured during the crossings. In order to improve the overall consistency between multi- and single-spacecraft results, we have also explored the use of hybrid techniques, in which timing information from the four spacecraft is combined with certain limited results from single-spacecraft methods, the remaining results being left for consistency checks. The results show good agreement between magnetopause orientations derived from appropriately chosen single-spacecraft techniques and those obtained from multi-spacecraft timing. The agreement between magnetopause speeds derived from single- and multi-spacecraft methods is quantitatively somewhat less good but it is evident that the speed can change substantially from one crossing to the next within an event. The magnetopause thickness varied substantially from one crossing to the next, within an event. It ranged from 5 to 10 ion gyroradii. The density profile was sharper than the magnetic profile: most of the density change occured in the earthward half of the magnetopause. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; instruments and techniques) – Space plasma physics (discontinuities)

scholarly journals Reconstruction of two-dimensional magnetopause structures from Cluster observations: verification of method

2004 ◽  
Vol 22 (4) ◽  
pp. 1251-1266 ◽  
Author(s):  
H. Hasegawa ◽  
B. U. Ö. Sonnerup ◽  
M. W. Dunlop ◽  
A. Balogh ◽  
S. E. Haaland ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Minimum Variance ◽  
Reconstruction Technique ◽  
Current Layer ◽  
Two Dimensional ◽  
Magnetic Islands ◽  
Maximum Variance ◽  
Spacecraft Trajectory ◽  
Shafranov Equation ◽  
Mathematical Techniques

Abstract. A recently developed technique for reconstructing approximately two-dimensional (∂/∂z≈0), time-stationary magnetic field structures in space is applied to two magnetopause traversals on the dawnside flank by the four Cluster spacecraft, when the spacecraft separation was about 2000km. The method consists of solving the Grad-Shafranov equation for magnetohydrostatic structures, using plasma and magnetic field data measured along a single spacecraft trajectory as spatial initial values. We assess the usefulness of this single-spacecraft-based technique by comparing the magnetic field maps produced from one spacecraft with the field vectors that other spacecraft actually observed. For an optimally selected invariant (z)-axis, the correlation between the field components predicted from the reconstructed map and the corresponding measured components reaches more than 0.97. This result indicates that the reconstruction technique predicts conditions at the other spacecraft locations quite well. The optimal invariant axis is relatively close to the intermediate variance direction, computed from minimum variance analysis of the measured magnetic field, and is generally well determined with respect to rotations about the maximum variance direction but less well with respect to rotations about the minimum variance direction. In one of the events, field maps recovered individually for two of the spacecraft, which crossed the magnetopause with an interval of a few tens of seconds, show substantial differences in configuration. By comparing these field maps, time evolution of the magnetopause structures, such as the formation of magnetic islands, motion of the structures, and thickening of the magnetopause current layer, is discussed. Key words. Magnetospheric physics (Magnetopause, cusp, and boundary layers) – Space plasma physics (Experimental and mathematical techniques, Magnetic reconnection)

scholarly journals Magnetopause current as seen by Cluster

2005 ◽  
Vol 23 (3) ◽  
pp. 901-907 ◽  
Author(s):  
M. W. Dunlop ◽  
A. Balogh
Keyword(s):  
Magnetic Field ◽  
Electric Current ◽  
Large Scale ◽  
Field Component ◽  
Accurate Determination ◽  
Field Measurements ◽  
Magnetic Field Component ◽  
Boundary Crossing ◽  
Current Layer

Abstract. The four-spacecraft, magnetic field measurements on Cluster can be combined to produce an accurate determination of the electric current in the magnetopause boundary during stable magnetopause crossings. For events that are planar on the scale of the spacecraft configuration, the thickness of the current layer can be accurately estimated from its magnetic profile at each spacecraft and the corresponding boundary crossing times. The latter, give a determination of boundary motion relative to the Cluster array. We use the estimates of all these properties, for a range of spacecraft separation distances, to show, firstly, that the estimate of electric current density is representative even when the spatial scale of the configuration of Cluster spacecraft approaches the thickness of the current layer. Secondly, we show that the estimated current lies in the plane of the boundary and demonstrate this for crossings occurring during large-scale ripples on the magnetopause. Thirdly, we show that the magnitude of the current is accurately represented, averaged over the extent of the current layer, by comparing to the change in the boundary-parallel magnetic field component divided by the estimated current layer thickness. We demonstrate this last point using a range of crossings each having a different thickness and crossing speed, different changes in the magnetic field component and different current densities.

scholarly journals High-resolution wave number spectrum using multi-point measurements in space – the Multi-point Signal Resonator (MSR) technique

2011 ◽  
Vol 29 (2) ◽  
pp. 351-360 ◽  
Author(s):  
Y. Narita ◽  
K.-H. Glassmeier ◽  
U. Motschmann
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Synthetic Data ◽  
Minimum Variance ◽  
Wave Number ◽  
Analysis Method ◽  
Music Algorithm ◽  
Cluster Data ◽  
High Resolution Power ◽  
Proper Power

Abstract. A new analysis method is presented that provides a high-resolution power spectrum in a broad wave number domain based on multi-point measurements. The analysis technique is referred to as the Multi-point Signal Resonator (MSR) and it benefits from Capon's minimum variance method for obtaining the proper power spectral density of the signal as well as the MUSIC algorithm (Multiple Signal Classification) for considerably reducing the noise part in the spectrum. The mathematical foundation of the analysis method is presented and it is applied to synthetic data as well as Cluster observations of the interplanetary magnetic field. Using the MSR technique for Cluster data we find a wave in the solar wind propagating parallel to the mean magnetic field with relatively small amplitude, which is not identified by the Capon spectrum. The Cluster data analysis shows the potential of the MSR technique for studying waves and turbulence using multi-point measurements.

scholarly journals Cluster observes the Earth’s magnetopause: coordinated four-point magnetic field measurements

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1449-1460 ◽  
Author(s):  
M. W. Dunlop ◽  
A. Balogh ◽  
P. Cargill ◽  
R. C. Elphic ◽  
K.-H. Fornaçon ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Field Measurements ◽  
Interplanetary Shock ◽  
Minimum Variance ◽  
Magnetic Activity ◽  
High Time Resolution ◽  
Current Layer ◽  
Data Set ◽  
The Magnetic Field

Abstract. The four-spacecraft Cluster mission has provided high-time resolution measurements of the magnetic field from closely maintained separation distances (200–600 km). Four-point coverage of the Earth’s magnetopause began on the 9 and 10 November 2000 when all spacecraft first exited the dusk-side magnetosphere at about 19:00 LT, providing extensive coverage of the near flank magnetosheath and magnetopause boundary layer on re-entry to the magnetosphere. The traversals on this occasion were caused by the arrival of an intense CME at the Earth, which produced a large compression of the magnetopause and high magnetic activity. The magnetopause traversals represent an unprecedented data set, allowing detailed analysis of the local magnetic structure (gradients) and dynamics of the magnetopause boundary. By performing minimum variance analysis (MVA) on the magnetic field data from all four spacecraft, we demonstrate that the magnetopause was planar on the scale of the spacecraft separation scales and that the transverse scale size of the magnetopause boundary layer was 1000–1100 km. We also show that the motion of the boundary (defined by the magnetic shear at the current layer), is changing over the sequence of spacecraft crossings so that acceleration of the magnetopause can be very high in this region of the magnetosphere. Indeed, the magnetopause speed reaches the order of 300 km/s in response to the arrival of the interplanetary shock. Using MVA coordinates, we have identified a number of magnetospheric and magnetosheath FTE signatures, which are sampled simultaneously by all spacecraft at different distances from and on either side of the magnetopause. The signatures show a variation of scale with distance from the boundary.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers) Space plasma physics (discontinuities; magnetic reconnection)

scholarly journals A new technique for determining orientation and motion of a 2-D, non-planar magnetopause

2010 ◽  
Vol 28 (3) ◽  
pp. 753-778 ◽  
Author(s):  
A. Blagau ◽  
B. Klecker ◽  
G. Paschmann ◽  
S. Haaland ◽  
O. Marghitu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Degrees Of Freedom ◽  
Minimum Variance ◽  
Constant Thickness ◽  
Planar Geometry ◽  
Convex Shape ◽  
Cluster Data ◽  
Self Consistent ◽  
The Individual ◽  
Normal Magnetic Field

Abstract. For a four-point mission like Cluster, the differences in position and time when the satellites detect the magnetopause or any other discontinuity, can be used to infer the discontinuity local orientation, thickness and motion. This timing technique, commonly assuming a planar geometry, offers an independent check for various single-spacecraft techniques. In the present paper we propose an extension of the timing method, capable of determining in a self-consistent way the macroscopic parameters of a two-dimensional, non-planar discontinuity. Such a configuration can be produced by a local bulge or indentation in the magnetopause, or by a large amplitude wave traveling on this surface, and is recognized in Cluster data when the single spacecraft techniques provide different individual normals contained roughly in the same plane. The model we adopted for the magnetopause assumes a layer of constant thickness of either cylindrical or parabolic shape, which has one or two degrees of freedom for the motion in the plane of the individual normals. The method was further improved by incorporating in a self-consistent way the requirement of minimum magnetic field variance along the magnetopause normal. An additional assumption, required in a previously proposed non-planar technique, i.e. that the non-planarity has negligible effects on the minimum variance analysis, is thus avoided. We applied the method to a magnetopause transition for which the various planar techniques provided inconsistent results. By contrast, the solutions obtained from the different implementations of the new 2-D method were consistent and stable, indicating a convex shape for the magnetopause. These solutions perform better than the planar solutions from the normal magnetic field variance perspective. The magnetopause dynamics and the presence of a non-zero normal magnetic field component in the analyzed event are discussed.

scholarly journals Cluster observation of continuous reconnection at dayside magnetopause in the vicinity of cusp

2005 ◽  
Vol 23 (6) ◽  
pp. 2199-2215 ◽  
Author(s):  
Y. Zheng ◽  
G. Le ◽  
J. A. Slavin ◽  
M. L. Goldstein ◽  
C. Cattell ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Electric Fields ◽  
Minimum Variance ◽  
Current Layer ◽  
Normal Surface ◽  
Reconnection Process ◽  
Dayside Magnetopause ◽  
Plasma Measurements

Abstract. In this paper, we present a case study of continuous reconnection at the dayside magnetopause observed by the Cluster spacecraft. On 1 April 2003, the four Cluster spacecraft experienced multiple encounters with the Earth's dayside magnetopause under a fairly stable southwestward interplanetary magnetic field (IMF). Accelerated plasma flows, whose magnitude and direction are consistent with the predictions of the reconnection theory (the Walén relation), were observed at and around the magnetopause current layer for a prolonged interval of ~3 h at two types of magnetopause crossings, one with small magnetic shears and the other one with large magnetic shears. Reversals in the Y component of ion bulk flow between the magnetosheath and magnetopause current layer and acceleration of magnetosheath electrons were also observed. Kinetic signatures using electron and ion velocity distributions corroborate the interpretation of continuous magnetic reconnection. This event provides strong in-situ evidence that magnetic reconnection at the dayside magnetopause can be continuous for many hours. However, the reconnection process appeared to be very dynamic rather than steady, despite the steady nature of the IMF. Detailed analysis using multi-spacecraft magnetic field and plasma measurements shows that the dynamics and structure of the magnetopause current layer/boundary can be very complex. For example, highly variable magnetic and electric fields were observed in the magnetopause current layer. Minimum variance analysis shows that the magnetopause normal deviates from the model normal. Surface waves resulting from the reconnection process may be involved in the oscillation of the magnetopause. Keywords. Magnetospheric physics (Magnetopause, cusp and boundary layers; Solar wind-magnetosphere interactions) – Space plasma physics (magnetic reconnection)

The fine structure of the subsolar MPB current layer from MAVEN observations: Implications for the Lorentz force

2020 ◽  
Author(s):  
Gabriela Boscoboinik ◽  
Cesar Bertucci ◽  
Daniel Gomez ◽  
Laura Morales ◽  
Christian Mazelle ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Fine Structure ◽  
Lorentz Force ◽  
Current Density ◽  
Current System ◽  
Minimum Variance ◽  
Current Layer ◽  
The Earth ◽  
Steady Current

<p>We report on the local structure of the Martian subsolar Magnetic Pileup Boundary (MPB) from minimum variance analysis of the magnetic field measured by the MAVEN spacecraft for six orbits. In particular, we detect a well defined current layer within the MPB’s fine structure and<br>provide a local estimate of its current density and compare these results with the current density obtained by multi-fluid simulations.<br>This current is of the order of hundreds of nAm<sup>-2</sup> which results in a sunward Lorentz force of the order of 10<sup>-14</sup> Nm<sup>-3</sup>. We compare these results with multifluid numerical simulations.<br>This force is associated with the gradient of the magnetic pressure, it accounts for the deflection of the solar wind ions near the MPB and for the acceleration of solar wind electrons which carry the interplanetary magnetic field through the MPB into the MPR. We also find that the<br>thickness of the MPB current layer is of the order of both the upstream (magnetosheath) solar wind proton inertial length and convective gyroradius. The former is consistent with the demagnetization of the ions due to the Hall electric field, an effect observed recently at the Earth magnetopause, while the latter would imply kinetic processes are important at the MPB.<br>This study supports recent results that report the presence of a steady current system around Mars in a similar way to the Earth.</p>

scholarly journals More about arc-polarized structures in the solar wind

2012 ◽  
Vol 30 (5) ◽  
pp. 867-883 ◽  
Author(s):  
S. Haaland ◽  
B. Sonnerup ◽  
G. Paschmann
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Timing Analysis ◽  
Minimum Variance ◽  
Zero Magnetic Field ◽  
Normal Vector ◽  
Magnetic Islands ◽  
Open Questions ◽  
Theoretical Predictions ◽  
Eigenvalue Ratio

Abstract. We report results from a Cluster-based study of the properties of 28 arc-polarized magnetic structures (also called rotational discontinuities) in the solar wind. These Alfvénic events were selected from the database created and analyzed by Knetter (2005) by use of criteria chosen to eliminate ambiguous cases. His studies showed that standard, four-spacecraft timing analysis in most cases lacks sufficient accuracy to identify the small normal magnetic field components expected to accompany such structures, leaving unanswered the question of their existence. Our study aims to break this impasse. By careful application of minimum variance analysis of the magnetic field (MVAB) from each individual spacecraft, we show that, in most cases, a small but significantly non-zero magnetic field component was present in the direction perpendicular to the discontinuity. In the very few cases where this component was found to be large, examination revealed that MVAB had produced an unusual and unexplained orientation of the normal vector. On the whole, MVAB shows that many verifiable rotational discontinuities (Bn ≠ 0) exist in the solar wind and that their eigenvalue ratio (EVR = intermediate/minimum variance) can be extremely large (up to EVR = 400). Each of our events comprises four individual spacecraft crossings. The events include 17 ion-polarized cases and 11 electron-polarized ones. Fifteen of the ion events have widths ranging from 9 to 21 ion inertial lengths, with two outliers at 46 and 54. The electron-polarized events are generally thicker: nine cases fall in the range 20–71 ion inertial lengths, with two outliers at 9 and 13. In agreement with theoretical predictions from a one-dimensional, ideal, Hall-MHD description (Sonnerup et al., 2010), the ion-polarized events show a small depression in field magnitude, while the electron-polarized ones tend to show a small enhancement. This effect was also predicted by Wu and Lee (2000). Judging only from the sense of the plasma flow across our DDs, their propagation appears to be sunward as often as anti-sunward. However, we argue that this result can be misleading as a consequence of the possible presence of magnetic islands within the DDs. How the rotational discontinuities come into existence, how they evolve with time, and what roles they play in the solar wind remain open questions.

scholarly journals Current Strategies for Studying the Natural and Synthetic Bioactive Compounds in Food by Chromatographic Separation Techniques

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1100
Author(s):  
Wioletta Parys ◽  
Małgorzata Dołowy ◽  
Alina Pyka-Pająk
Keyword(s):  
Gas Chromatography ◽  
Bioactive Compounds ◽  
Residue Analysis ◽  
Food Products ◽  
Vital Role ◽  
Bioactive Molecules ◽  
Validation Parameters ◽  
Layer Chromatography ◽  
Natural And Synthetic

The present study summarizes the new strategies including advanced equipment and validation parameters of liquid and gas chromatography methods i.e., thin-layer chromatography (TLC), column liquid chromatography (CLC), and gas chromatography (GC) suitable for the identification and quantitative determination of different natural and synthetic bioactive compounds present in food and food products, which play an important role in human health, within the period of 2019–2021 (January). Full characteristic of some of these procedures with their validation parameters is discussed in this work. The present review confirms the vital role of HPLC methodology in combination with different detection modes i.e., HPLC-UV, HPLC-DAD, HPLC-MS, and HPLC-MS/MS for the determination of natural and synthetic bioactive molecules for different purposes i.e., to characterize the chemical composition of food as well as in the multi-residue analysis of pesticides, NSAIDs, antibiotics, steroids, and others in food and food products.

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