scholarly journals Simultaneous Double Star and Cluster FTEs observations on the dawnside flank of the magnetosphere

2005 ◽  
Vol 23 (8) ◽  
pp. 2877-2887 ◽  
Author(s):  
A. Marchaudon ◽  
C. J. Owen ◽  
J.-M. Bosqued ◽  
R. C. Fear ◽  
A. N. Fazakerley ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Southern Hemisphere ◽  
Double Star ◽  
Simultaneous Observation ◽  
Flux Transfer Events ◽  
Reconnection Site ◽  
Field Lines ◽  
Almost All ◽  
Magnetospheric Field ◽  
Imf Clock Angle

Abstract. We present Cluster and Double Star-1 (TC-1) observations from a close magnetic conjunction on 8 May 2004. The five spacecraft were on the dawnside flank of the magnetosphere, with TC-1 located near the equatorial plane and Cluster at higher geographic latitudes in the Southern Hemisphere. TC-1, at its apogee, skimmed the magnetopause for almost 8h (between 08:00-16:00 UT). Flux Transfer Events (FTEs), moving southward/tailward from the reconnection site, were observed by TC-1 throughout almost all of the period. Cluster, travelling on a mainly dawn-dusk trajectory, crossed the magnetopause at around 10:30 UT in the same Magnetic Local Time (MLT) sector as TC-1 and remained close to the magnetopause boundary layer in the Southern Hemisphere. The four Cluster spacecraft observed FTEs for a period of 6.5h between 07:30 and 14:00 UT. The very clear signatures and the finite transverse sizes of the FTEs observed by TC-1 and Cluster imply that, during this event, sporadic reconnection occurred. From the properties of these FTEs, the reconnection site was located northward of both TC-1 and Cluster on the dawn flank of the magnetosphere. Reconnection occurred between draped magnetosheath and closed magnetospheric field lines. Despite variable interplanetary magnetic field (IMF) conditions and IMF-Bz turnings, the IMF clock angle remained greater than 70° and the location site appeared to remain relatively stable in position during the whole period. This result is in agreement with previous studies which reported that the dayside reconnection remained active for an IMF clock angle greater than 70°. The simultaneous observation of FTEs at both Cluster and TC-1, separated by 2h in MLT, implies that the reconnection site on the magnetopause must have been extended over several hours in MLT.

scholarly journals Simultaneous observations of magnetopause flux transfer events and of their associated signatures at ionospheric altitudes

2004 ◽  
Vol 22 (6) ◽  
pp. 2181-2199 ◽  
Author(s):  
K. A. McWilliams ◽  
G. J. Sofko ◽  
T. K. Yeoman ◽  
S. E. Milan ◽  
D. G. Sibeck ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Southern Hemisphere ◽  
High Latitude ◽  
Field Conditions ◽  
Transfer Event ◽  
Flux Transfer Events ◽  
Subsolar Point ◽  
Reconnection Site ◽  
Flux Transfer

Abstract. An extensive variety of instruments, including Geotail, DMSP F11, SuperDARN, and IMP-8, were monitoring the dayside magnetosphere and ionosphere between 14:00 and 18:00 UT on 18 January 1999. The location of the instruments provided an excellent opportunity to study in detail the direct coupling between the solar wind, the magnetosphere, and the ionosphere. Flux transfer events were observed by Geotail near the magnetopause in the dawn side magnetosheath at about 4 magnetic local time during exclusively northward interplanetary magnetic field conditions. Excellent coverage of the entire dayside high-latitude ionosphere was achieved by the Northern Hemisphere SuperDARN radars. On the large scale, temporally and spatially, the dayside magnetosphere convection remained directly driven by the interplanetary magnetic field, despite the highly variable interplanetary magnetic field conditions, including long periods of northward field. The SuperDARN radars in the dawn sector also measured small-scale temporally varying convection velocities, which are indicative of flux transfer event activity, in the vicinity of the magnetic footprint of Geotail. DMSP F11 in the Southern Hemisphere measured typical cusp precipitation simultaneously with and magnetically conjugate to a single flux transfer event signature detected by Geotail. A study of the characteristics of the DMSP ion spectrogram revealed that the source plasma from the reconnection site originated downstream of the subsolar point. Detailed analyses of locally optimised coordinate systems for individual flux transfer events at Geotail are consistent with a series of flux tubes protruding from the magnetopause, and originating from a high-latitude reconnection site in the Southern Hemisphere. This high-latitude reconnection site agrees with plasma injected away from the subsolar point. This is the first simultaneous and independent determination from ionospheric and space-based data of the location of magnetic reconnection.

scholarly journals Coordinated Cluster/Double Star observations of dayside reconnection signatures

2005 ◽  
Vol 23 (8) ◽  
pp. 2867-2875 ◽  
Author(s):  
M. W. Dunlop ◽  
M. G. G. T. Taylor ◽  
J. A. Davies ◽  
C. J. Owen ◽  
F. Pitout ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Double Star ◽  
Low Latitude ◽  
Flux Transfer Events ◽  
Reconnection Region ◽  
Dayside Magnetopause ◽  
First Results ◽  
North And South ◽  
Imf Clock Angle

Abstract. The recent launch of the equatorial spacecraft of the Double Star mission, TC-1, has provided an unprecedented opportunity to monitor the southern hemisphere dayside magnetopause boundary layer in conjunction with northern hemisphere observations by the quartet of Cluster spacecraft. We present first results of one such situation where, on 6 April 2004, both Cluster and the Double Star TC-1 spacecraft were on outbound transits through the dawnside magnetosphere. The observations are consistent with ongoing reconnection on the dayside magnetopause, resulting in a series of flux transfer events (FTEs) seen both at Cluster and TC-1, which appear to lie north and south of the reconnection line, respectively. In fact, the observed polarity and motion of each FTE signature advocates the existence of an active reconnection region consistently located between the positions of Cluster and TC-1, with Cluster observing northward moving FTEs with +/- polarity, whereas TC-1 sees -/+ polarity FTEs. This assertion is further supported by the application of a model designed to track flux tube motion for the prevailing interplanetary conditions. The results from this model show, in addition, that the low-latitude FTE dynamics are sensitive to changes in convected upstream conditions. In particular, changing the interplanetary magnetic field (IMF) clock angle in the model suggests that TC-1 should miss the resulting FTEs more often than Cluster and this is borne out by the observations.

scholarly journals Coordinated Cluster/Double Star and ground-based observations of dayside reconnection signatures on 11 February 2004

2011 ◽  
Vol 29 (10) ◽  
pp. 1827-1847 ◽  
Author(s):  
Q.-H. Zhang ◽  
M. W. Dunlop ◽  
R.-Y. Liu ◽  
H.-G. Yang ◽  
H.-Q. Hu ◽  
...  
Keyword(s):  
Response Time ◽  
Southern Hemisphere ◽  
Ecliptic Plane ◽  
Double Star ◽  
Magnetospheric Plasma ◽  
Flux Tubes ◽  
Flux Transfer Events ◽  
Moving Plasma ◽  
Reconnection Site ◽  
Flow Components

Abstract. A number of flux transfer events (FTEs) were observed between 09:00 and 12:00 UT on 11 February 2004, during southward and dawnward IMF, while the Cluster spacecraft array moved outbound through the northern, high-altitude cusp and dayside high-latitude boundary layer, and the Double Star TC-1 spacecraft was crossing the dayside low-latitude magnetopause into the magnetosheath south of the ecliptic plane. The Cluster array grazed the equatorial cusp boundary, observing reconnection-like mixing of magnetosheath and magnetospheric plasma populations. In an adjacent interval, TC-1 sampled a series of sometimes none standard FTEs, but also with mixed magnetosheath and magnetospheric plasma populations, near the magnetopause crossing and later showed additional (possibly turbulent) activity not characteristic of FTEs when it was situated deeper in the magnetosheath. The motion of these FTEs are analyzed in some detail to compare to simultaneous, poleward-moving plasma concentration enhancements recorded by EISCAT Svalbard Radar (ESR) and "poleward-moving radar auroral forms" (PMRAFs) on the CUTLASS Finland and Kerguelen Super Dual Auroral Radar Network (SuperDARN) radar measurements. Conjugate SuperDARN observations show a predominantly two-cell convection pattern in the Northern and Southern Hemispheres. The results are consistent with the expected motion of reconnected magnetic flux tubes, arising from a predominantly sub-solar reconnection site. Here, we are able to track north and south in closely adjacent intervals as well as to map to the corresponding ionospheric footprints of the implied flux tubes and demonstrate these are temporally correlated with clear ionospheric velocity enhancements, having northward (southward) and eastward (westward) convected flow components in the Northern (Southern) Hemisphere. The durations of these enhancements might imply that the evolution time of the FTEs is about 18–22 min from their origin on magnetopause (at reconnection site) to their addition to the magnetotail lobe. However, the ionospheric response time in the Northern Hemisphere is about 2–4 min longer than the response time in the Southern Hemisphere.

Prediction and understanding of soft proton contamination in XMM-Newton: a machine learning approach

2021 ◽  
Author(s):  
Elena Kronberg ◽  
Fabio Gastaldello ◽  
Stein Haaland ◽  
Artem Smirnov ◽  
Max Berrendorf ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Machine Learning ◽  
Solar Wind ◽  
Southern Hemisphere ◽  
Solar Wind Speed ◽  
Flank Region ◽  
Learning Approach ◽  
X Ray ◽  
Machine Learning Approach ◽  
Field Lines

<p>One of the major and unfortunately unforeseen sources of background for the current generation of X-ray telescopes flying mainly in the magnetosphere are soft protons with few tens to hundreds of keV concentrated. One such telescope is the X-ray Multi-Mirror Mission (XMM-Newton) by ESA. Its observing time lost due to the contamination is  about 40%. This affects all the major broad science goals of XMM, ranging from cosmology to astrophysics of neutron stars and black holes. The soft proton background could dramatically impact future X-ray missions such Athena and SMILE missions. Magnetopsheric processes that trigger this background are still poorly understood. We use a machine learning approach to delineate related important parameters and to develop a model to predict the background contamination using 12 years of XMM observations. As predictors we use the location of XMM, solar and geomagnetic activity parameters. We revealed that the contamination is most strongly related to the distance in southern direction, ZGSE, (XMM observations were in the southern hemisphere), the solar wind velocity and the location on the magnetospheric magnetic field lines. We derived simple empirical models for the best two individual predictors and a machine learning model which utilizes an ensemble of the predictors (Extra Trees Regressor) and gives better performance. Based on our analysis, future X-Ray missions in the magnetosphere should minimize observations during  times  associated with high solar wind speed  and avoid closed magnetic field lines, especially at the dusk flank region at least in the southern hemisphere. </p>

scholarly journals North-Seeking Magnetotactic Gammaproteobacteria in the Southern Hemisphere

2016 ◽  
Vol 82 (18) ◽  
pp. 5595-5602 ◽  
Author(s):  
Pedro Leão ◽  
Lia C. R. S. Teixeira ◽  
Jefferson Cypriano ◽  
Marcos Farina ◽  
Fernanda Abreu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Geomagnetic Field ◽  
Magnetotactic Bacteria ◽  
Rrna Gene ◽  
Natural Environments ◽  
Optimal Position ◽  
Brackish Lagoon ◽  
Field Lines

ABSTRACTMagnetotactic bacteria (MTB) comprise a phylogenetically diverse group of prokaryotes capable of orienting and navigating along magnetic field lines. Under oxic conditions, MTB in natural environments in the Northern Hemisphere generally display north-seeking (NS) polarity, swimming parallel to the Earth's magnetic field lines, while those in the Southern Hemisphere generally swim antiparallel to magnetic field lines (south-seeking [SS] polarity). Here, we report a population of an uncultured, monotrichously flagellated, and vibrioid MTB collected from a brackish lagoon in Brazil in the Southern Hemisphere that consistently exhibits NS polarity. Cells of this organism were mainly located below the oxic-anoxic interface (OAI), suggesting it is capable of some type of anaerobic metabolism. Magnetosome crystalline habit and composition were consistent with elongated prismatic magnetite (Fe3O4) particles. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that this organism belongs to a distinct clade of theGammaproteobacteriaclass. The presence of NS MTB in the Southern Hemisphere and the previously reported finding of SS MTB in the Northern Hemisphere reinforce the idea that magnetotaxis is more complex than we currently understand and may be modulated by factors other than O2concentration and redox gradients in sediments and water columns.IMPORTANCEMagnetotaxis is a navigational mechanism used by magnetotactic bacteria to move along geomagnetic field lines and find an optimal position in chemically stratified sediments. For that, magnetotactic bacteria swim parallel to the geomagnetic field lines under oxic conditions in the Northern Hemisphere, whereas those in the Southern Hemisphere swim antiparallel to magnetic field lines. A population of uncultured vibrioid magnetotactic bacteria was discovered in a brackish lagoon in the Southern Hemisphere that consistently swim northward, i.e., the opposite of the overwhelming majority of other Southern Hemisphere magnetotactic bacteria. This finding supports the idea that magnetotaxis is more complex than previously thought.

scholarly journals First results from ideal 2-D MHD reconstruction: magnetopause reconnection event seen by Cluster

2008 ◽  
Vol 26 (9) ◽  
pp. 2673-2684 ◽  
Author(s):  
W.-L. Teh ◽  
B. U. Ö. Sonnerup
Keyword(s):  
Magnetic Field ◽  
Ad Hoc ◽  
Complete Characterization ◽  
Mhd Equations ◽  
New Method ◽  
Reconstruction Method ◽  
Reconnection Site ◽  
Field Lines ◽  
Actual Configuration ◽  
The Ideal

Abstract. We have applied a new reconstruction method (Sonnerup and Teh, 2008), based on the ideal single-fluid MHD equations in a steady-state, two-dimensional geometry, to a reconnection event observed by the Cluster-3 (C3) spacecraft on 5 July 2001, 06:23 UT, at the dawn-side Northern-Hemisphere magnetopause. The event has been previously studied by use of Grad-Shafranov (GS) reconstruction, performed in the deHoffmann-Teller frame, and using the assumption that the flow effects were either negligible or the flow was aligned with the magnetic field. Our new method allows the reconstruction to be performed in the frame of reference moving with the reconnection site (the X-line). In the event studied, this motion is tailward/equatorward at 140 km/s. The principal result of the study is that the new method functions well, generating a magnetic field map that is qualitatively similar to those obtained in the earlier GS-based reconstructions but now includes the reconnection site itself. In comparison with the earlier map by Hasegawa et al. (2004), our new map has a slightly improved ability (cc=0.979 versus cc=0.975) to predict the fields measured by the other three Cluster spacecraft, at distances from C3 ranging from 2132 km (C1) to 2646 km (C4). The new field map indicates the presence of a magnetic X-point, located some 5300 km tailward/equatorward of C3 at the time of its traversal of the magnetopause. In the immediate vicinity of the X-point, the ideal-MHD assumption breaks down, i.e. resistive and/or other effects should be included. We have circumvented this problem by an ad-hoc procedure in which we allow the axial part of convection electric field to be non-constant near the reconnection site. The new reconstruction method also provides a map of the velocity field, in which the inflow into the wedge of reconnected field lines and the plasma jet within it can be seen, and maps of the electric potential and of the electric current distribution. Even though the velocity map is expected to be inaccurate near the X-point, it provides high-quality predictions (cc=0.969) of the velocity components at points along the path of C1, some of which are close to the X-point; the predictions of density and pressure are less good. Except near the reconnection site, the new reconstruction provides a complete characterization, in unprecedented detail, of the entire dynamic plasma and field equilibrium, reconstructed from the C3 data. It represents our best prediction to date of what the actual configuration was like. But, since substantial time variations were present in the event, the recovered structure by necessity includes considerable time aliasing. The invariant direction used in the reconstruction, is found to agree, within 6°, with a recent theoretical prediction of the X-line orientation by Swisdak and Drake (2007).

scholarly journals The ionospheric response to flux transfer events: the first few minutes

1997 ◽  
Vol 15 (6) ◽  
pp. 685-691 ◽  
Author(s):  
A. S. Rodger ◽  
M. Pinnock
Keyword(s):  
Magnetic Field ◽  
Time Resolution ◽  
Hf Radar ◽  
High Time Resolution ◽  
Plasma Velocity ◽  
Ionospheric Response ◽  
Flux Transfer Events ◽  
Velocity Variations ◽  
Flux Transfer ◽  
Field Lines

Abstract. We utilise high-time resolution measurements from the PACE HF radar at Halley, Antarctica to explore the evolution of the ionospheric response during the first few minutes after enhanced reconnection occurs at the magnetopause. We show that the plasma velocity increases associated with flux transfer events (FTEs) occur first ~100–200 km equatorward of the region to which magnetosheath (cusp) precipitation maps to the ionosphere. We suggest that these velocity variations start near the ionospheric footprint of the boundary between open and closed magnetic field lines. We show that these velocity variations have rise times ~100 s and fall times of ~10 s. When these velocity transients reach the latitude of the cusp precipitation, sometimes the equatorward boundary of the precipitation begins to move equatorward, the expected and previously reported ionospheric signature of enhanced reconnection. A hypothesis is proposed to explain the velocity variations. It involves the rapid outflow of magnetospheric electrons into the magnetosheath along the most recently reconnected field lines. Several predictions are made arising from the proposed explanation which could be tested with ground-based and space-based observations.

Magnetic Curvature Analysis on Reconnection Related Structures at Earth’s Magnetopause

2020 ◽  
Author(s):  
Yi Qi ◽  
Christopher T. Russell ◽  
Robert J. Strangeway ◽  
Yingdong Jia ◽  
Roy B. Torbert ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Solar Wind Plasma ◽  
Radius Of Curvature ◽  
Plasma Properties ◽  
Magnetospheric Multiscale ◽  
Reconnection Site ◽  
Field Lines ◽  
The Magnetic Field

<p>Magnetic reconnection is a mechanism that allows rapid and explosive energy transfer from the magnetic field to the plasma. The magnetopause is the interface between the shocked solar wind plasma and Earth’s magnetosphere. Reconnection enables the transport of momentum from the solar wind into Earth’s magnetosphere. Because of its importance in this regard, magnetic reconnection has been extensively studied in the past and is the primary goal of the ongoing Magnetospheric Multiscale (MMS) mission. During magnetic reconnection, the originally anti-parallel fields annihilate and reconnect in a thinned current sheet. In the vicinity of a reconnection site, a prominently increased curvature of the magnetic field (and smaller radius of curvature) marks the region where the particles start to deviate from their regular gyro-motion and become available for energy conversion. Before MMS, there were no closely separated multi-spacecraft missions capable of resolving these micro-scale curvature features, nor examining particle dynamics with sufficiently fast cadence.</p><p>In this study, we use measurements from the four MMS spacecraft to determine the curvature of the field lines and the plasma properties near the reconnection site. We use this method to study FTEs (flux ropes) on the magnetopause, and the interaction between co-existing FTEs. Our study not only improves our understanding of magnetic reconnection, but also resolves the relationship between FTEs and structures on the magnetopause.</p>

scholarly journals Flux transfer events on the high-latitude magnetopause: Interball-1 observations

2005 ◽  
Vol 23 (11) ◽  
pp. 3549-3559 ◽  
Author(s):  
D. G. Sibeck ◽  
G. I. Korotova ◽  
V. Petrov ◽  
V. Styazhkin ◽  
T. J. Rosenberg
Keyword(s):  
Magnetic Field ◽  
High Latitude ◽  
Pressure Gradients ◽  
Field Orientation ◽  
Flux Transfer Events ◽  
Statistical Studies ◽  
Flux Transfer ◽  
Statistical Survey ◽  
Almost All ◽  
Marked Tendency

Abstract. We present case and statistical studies of flux transfer events (FTEs) observed by Interball-1 on the high-latitude magnetopause. The case studies provide observations of FTEs in the cusp during periods of southward interplanetary magnetic field (IMF) orientation and on the magnetopause poleward of the cusp during periods of strongly northward IMF orientation. We interpret the former in terms of reconnection on the equatorial magnetopause and subsequent antisunward motion of FTEs into the cusps. We interpret the latter in terms of bursty antiparallel merging on the high-latitude magnetopause. A statistical survey demonstrates that events observed equatorward of the cusp show a marked tendency to occur for antiparallel (northward) magnetospheric and (southward) magnetosheath magnetic field orientations, whereas events observed poleward of the cusps tend to occur for either strongly parallel or antiparallel configurations. We suggest that this discrepancy implies that events observed poleward of the cusps originate both locally and on the equatorial magnetopause. Finally, we use the sense of the bipolar signature and the prevailing magnetic field orientation to demonstrate that almost all events move antisunward, i.e. that at these latitudes pressure gradients determine the motion of FTEs and not magnetic curvature forces.

Role of interchange instability in flux transfer event origin

1994 ◽  
Vol 12 (2/3) ◽  
pp. 183-187 ◽  
Author(s):  
B. V. Rezhenov ◽  
Y. P. Maltsev
Keyword(s):  
Magnetic Field ◽  
Wave Number ◽  
Curvature Radius ◽  
Transfer Event ◽  
Flux Transfer Events ◽  
Interchange Instability ◽  
Flux Transfer ◽  
Field Lines ◽  
The Magnetic Field

Abstract. It is shown that the interaction of the interplanetary magnetic field (IMF), when it has southward component, with the geomagnetic field leads to the formation of an enhanced pressure layer (EPL) near the magnetopause. Currents flowing on the boundary between the EPL and the magnetosheath prevent the IMF from penetrating the magnetosphere. However, the outward boundary of the EPL is unstable. The interchange instability permanently destroys the EPL. Separate filaments of the EPL move away from the Earth. New colder plasma of the magnetosheath with a frozen magnetic field replaces the hotter EPL plasma, and the process of EPL formation and destruction repeats itself. The instability increment is calculated for various magnitudes of the azimuthal wave number, ky, and curvature radius of the magnetic field lines, Rc. The disturbances with R-1e≤ky≤4R-1e (where Re is the Earth's radius) and Rc≅Re are the most unstable. A possible result of the interchange instability of the EPL may be patchy reconnection, displayed as flux transfer events (FTEs) near the magnetopause.

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