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  • 1
    Publication Date: 2011-12-24
    Description: The observed weakness of Mercury's magnetic field poses a long-standing puzzle to dynamo theory. Using numerical dynamo simulations, we show that it could be explained by a negative feedback between the magnetospheric and the internal magnetic fields. Without feedback, a small internal field was amplified by the dynamo process up to Earth-like values. With feedback, the field strength saturated at a much lower level, compatible with the observations at Mercury. The classical saturation mechanism via the Lorentz force was replaced by the external field impact. The resulting surface field was dominated by uneven harmonic components. This will allow the feedback model to be distinguished from other models once a more accurate field model is constructed from MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and BepiColombo data.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Heyner, Daniel -- Wicht, Johannes -- Gomez-Perez, Natalia -- Schmitt, Dieter -- Auster, Hans-Ulrich -- Glassmeier, Karl-Heinz -- New York, N.Y. -- Science. 2011 Dec 23;334(6063):1690-3. doi: 10.1126/science.1207290.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut fur Geophysik und extraterrestrische Physik, Technische Universitat, Braunschweig, Germany. d.heyner@tu-braunschweig.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22194574" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2012-04-12
    Description: Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behavior in the near-Venus wake that is symptomatic of magnetic reconnection, a process that occurs in Earth's magnetotail but is not expected in the magnetotail of a nonmagnetized planet such as Venus. On 15 May 2006, the plasma flow in this region was toward the planet, and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail, where energy is stored and later released from the magnetic field to the plasma.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhang, T L -- Lu, Q M -- Baumjohann, W -- Russell, C T -- Fedorov, A -- Barabash, S -- Coates, A J -- Du, A M -- Cao, J B -- Nakamura, R -- Teh, W L -- Wang, R S -- Dou, X K -- Wang, S -- Glassmeier, K H -- Auster, H U -- Balikhin, M -- New York, N.Y. -- Science. 2012 May 4;336(6081):567-70. doi: 10.1126/science.1217013. Epub 2012 Apr 5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Chinese Academy of Sciences Key Laboratory of Geospace Environment, University of Science and Technology of China, Hefei 230026, China. tielong.zhang@oeaw.ac.at〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22491094" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2015-04-16
    Description: Knowledge of the magnetization of planetary bodies constrains their origin and evolution, as well as the conditions in the solar nebular at that time. On the basis of magnetic field measurements during the descent and subsequent multiple touchdown of the Rosetta lander Philae on the comet 67P/Churyumov-Gerasimenko (67P), we show that no global magnetic field was detected within the limitations of analysis. The Rosetta Magnetometer and Plasma Monitor (ROMAP) suite of sensors measured an upper magnetic field magnitude of less than 2 nanotesla at the cometary surface at multiple locations, with the upper specific magnetic moment being 〈3.1 x 10(-5) ampere-square meters per kilogram for meter-size homogeneous magnetized boulders. The maximum dipole moment of 67P is 1.6 x 10(8) ampere-square meters. We conclude that on the meter scale, magnetic alignment in the preplanetary nebula is of minor importance.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Auster, Hans-Ulrich -- Apathy, Istvan -- Berghofer, Gerhard -- Fornacon, Karl-Heinz -- Remizov, Anatoli -- Carr, Chris -- Guttler, Carsten -- Haerendel, Gerhard -- Heinisch, Philip -- Hercik, David -- Hilchenbach, Martin -- Kuhrt, Ekkehard -- Magnes, Werner -- Motschmann, Uwe -- Richter, Ingo -- Russell, Christopher T -- Przyklenk, Anita -- Schwingenschuh, Konrad -- Sierks, Holger -- Glassmeier, Karl-Heinz -- New York, N.Y. -- Science. 2015 Jul 31;349(6247):aaa5102. doi: 10.1126/science.aaa5102. Epub 2015 Apr 14.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut fur Geophysik und extraterrestrische Physik, Technische Universitat Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany. uli.auster@tu-bs.de. ; Centre for Energy Research, Hungarian Academy of Sciences, H-1121 Konkoly Thege Street 29-33, Budapest, Hungary. ; Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria. ; Institut fur Geophysik und extraterrestrische Physik, Technische Universitat Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany. ; Institut fur Geophysik und extraterrestrische Physik, Technische Universitat Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany. Space Research Institute, Russian Academy of Sciences, Moscow, Profsoyuznaja Street 84/32, 117810 Moscow, Russia. ; Imperial College London, Exhibition Road, London SW7 2AZ, UK. ; Max-Planck-Institut fur Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Gottingen. ; Max-Planck-Institute fur Extraterrestrische Physik, Giessenbachstrasse, D-85741 Garching bei Munchen. ; German Aerospace Center (DLR), Institute of Planetary Research, D-12489 Berlin, Rutherfordstrasse 2, Germany. ; German Aerospace Center (DLR), Institute of Planetary Research, D-12489 Berlin, Rutherfordstrasse 2, Germany. Institut fur Theoretische Physik, Technische Universitat Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany. ; Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA. ; Institut fur Geophysik und extraterrestrische Physik, Technische Universitat Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany. Max-Planck-Institute fur Extraterrestrische Physik, Giessenbachstrasse, D-85741 Garching bei Munchen.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25873744" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Cluster mission provides a new opportunity to study plasma processes and structures in the near-Earth plasma environment. Four-point measurements of the magnetic field will enable the analysis of the three dimensional structure and dynamics of a range of phenomena which shape the macroscopic properties of the magnetosphere. Difference measurements of the magnetic field data will be combined to derive a range of parameters, such as the current density vector, wave vectors, and discontinuity normals and curvatures, using classical time series analysis techniques iteratively with physical models and simulation of the phenomena encountered along the Cluster orbit. The control and understanding of error sources which affect the four-point measurements are integral parts of the analysis techniques to be used. The flight instrumentation consists of two, tri-axial fluxgate magnetometers and an on-board data-processing unit on each spacecraft, built using a highly fault-tolerant architecture. High vector sample rates (up to 67 vectors s-1) at high resolution (up to 8 pT) are combined with on-board event detection software and a burst memory to capture the signature of a range of dynamic phenomena. Data-processing plans are designed to ensure rapid dissemination of magnetic-field data to underpin the collaborative analysis of magnetospheric phenomena encountered by Cluster.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0992-7689
    Keywords: Magnetospheric physics (MHD waves and instabilities; plasma waves and instabilities)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A filter method is presented which allows a qualitative and quantitative identification of wave modes observed with plasma experiments on satellites. Hitherto existing mode filters are based on the MHD theory and thus they are restricted to low frequencies well below the ion cyclotron frequency. The present method is generalized to cover wave modes up to the characteristic ion frequencies. The spectral density matrix determined by the observations is decomposed using the eigenvectors of the linearized Hall-MHD equations. As the wave modes are dispersive in this formalism, a precise determination of the κ-vectors requires the use of multi-point measurements. Therefore the method is particularly relevant to multi-satellite missions. The method is tested using simulated plasma data. The Hall-MHD filter is able to identify the modes excited in the model plasma and to assign the correct energetic contributions. By comparison with the former method it is shown that the simple MHD filter leads to large errors if the frequency is not well below the ion cyclotron frequency. Further the range of validity of the linear theory is examined rising the simulated wave amplitudes.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 18 (2000), S. 167-169 
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0992-7689
    Keywords: Ionosphere ; (Ionosphere–magnetosphere interactions) ; Magnetospheric physics ; Magnetosphere – ionosphere interactions ; MHD waves and instabilities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The ionosphere influences magnetohydrodynamic waves in the magnetosphere by damping because of Joule heating and by varying the wave structure itself. There are different eigenvalues and eigensolutions of the three dimensional toroidal wave equation if the height integrated Pedersen conductivity exceeds a critical value, namely the wave conductance of the magnetosphere. As a result a jump in frequency can be observed in ULF pulsation records. This effect mainly occurs in regions with gradients in the Pedersen conductances, as in the auroral oval or the dawn and dusk areas. A pulsation event recorded by the geostationary GOES-6 satellite is presented. We explain the observed change in frequency as a change in the wave structure while crossing the terminator. Furthermore, selected results of numerical simulations in a dipole magnetosphere with realistic ionospheric conditions are discussed. These are in good agreement with the observational data.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0992-7689
    Keywords: Magnetospheric physics (energetic particles, trapped; MHD waves and instabilities) ; Space plasma physics (wave-particle interactions)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Giant pulsations are nearly monochromatic ULF-pulsations of the Earth’s magnetic field with periods of about 100 s and amplitudes of up to 40 nT. For one such event ground-magnetic observations as well as simultaneous GEOS-2 magnetic and electric field data and proton flux measurements made in the geostationary orbit have been analysed. The observations of the electromagnetic field indicate the excitation of an odd-mode type fundamental field line oscillation. A clear correlation between variations of the proton flux in the energy range 30–90 keV with the giant pulsation event observed at the ground is found. Furthermore, the proton phase space density exhibits a bump-on-the-tail signature at about 60 keV. Assuming a drift-bounce resonance instability as a possible generation mechanism, the azimuthal wave number of the pulsation wave field may be determined using a generalized resonance condition. The value determined in this way, m = −21±4, is in accord with the value m = −27±6 determined from ground-magnetic measurements. A more detailed examination of the observed ring current plasma distribution function f shows that odd-mode type eigenoscillations are expected for the case ∂f/∂W ≥ 0, much as observed. This result is different from previous theoretical studies as we not only consider local gradients of the distribution function in real space, but also in velocity space. It is therefore concluded that the observed giant pulsation is the result of a drift-bounce resonance instability of the ring current plasma coupling to an odd-mode fundamental standing wave. The generation of the bump-on-the-tail distribution causing ≥f/≥W ≥ 0 can be explained due to velocity dispersion of protons injected into the ring current. Both this velocity dispersion and the necessary substorm activity causing the injection of protons into the nightside magnetosphere are observed.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0992-7689
    Keywords: Magnetospheric physics (instruments and techniques) ; Space plasma physics (instruments and techniques)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The special feature of the ringcore fluxgate magnetometer on Equator-S is the high time and field resolution. The scientific aim of the experiment is the investigation of waves in the 10–100 picotesla range with a time resolution up to 64 Hz. The instrument characteristics and the influence of the spacecraft on the magnetic field measurement will be discussed. The work shows that the applied pre- and inflight calibration techniques are sufficient to suppress spacecraft interferences. The offset in spin axis direction was determined for the first time with an independent field measurement by the Equator-S Electron Drift Instrument. The data presented gives an impression of the accuracy of the measurement.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0992-7689
    Keywords: Magnetospheric physics (MHD waves and instabilities)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A 16 mHz Pc4 pulsation was recorded on March 17, 1998, in the prenoon sector of the Earth’s magnetosphere by the Equator-S satellite. The event is strongly localized in radial direction at approximately L = 5 and exhibits properties of a field line resonance such as an ellipticity change as seen by applying the method of the analytical signal to the magnetic field data. The azimuthal wave number was estimated as m ≈ 150. We discuss whether this event can be explained by the FLR mechanism and find out that the change in ellipticity is more a general feature of a localized Alfvén wave than indicative of a resonant process.
    Type of Medium: Electronic Resource
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