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  • 11
    Publication Date: 2011-07-29
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 12
    Publication Date: 2019
    Description: Abstract Current sheets (CSs) play a crucial role in the storage and conversion of magnetic energy in planetary magnetotails. Using high‐resolution magnetic field data from MAVEN spacecraft, we report the existence of super thin current sheets (STCSs) in the Martian magnetotail. The typical half‐thickness of the STCSs is ~5 km, and it is much less than the gyroradius of thermal protons (ρp). The STCSs are embedded into a thicker sheet with L ≥ ρp forming a multiscale current configuration. The formation of STCS does not depend on ion composition, but it is controlled by the small value of the normal component of the magnetic field at the neutral plane (BN). A number of the observed multiscale CSs are located in the parametric map close to the tearing‐unstable domain, and thus, the inner STCS can provide an additional free energy to excite ion tearing mode in the Martian magnetotail.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 13
    Publication Date: 2011-09-14
    Description: Ice fall velocity has a strong impact on climate feedback, influencing cirrus cloud coverage and radiative forcing as well as upper troposphere relative humidity. This study aims to provide the atmospheric modeling community with better parameterizations of the ice fall speed in cirrus clouds on the basis of aircraft measurements from recent field campaigns, especially the Tropical Composition, Cloud and Climate Coupling (TC4) campaign in 2007 and the Indirect and Semi-Direct Aerosol Campaign (ISDAC) in 2008. These campaigns provide improved measurements of the ice particle size distribution (PSD) where the concentrations of artifact small ice particles (due to shattering of ice particles on the probe inlet tube) are greatly reduced. In addition to the PSD, the mass-weighted fall velocity (Vm) depends on the ice particle projected area and mass. The calculation of Vm was based on improved direct measurements of the PSD number and area concentration and improved estimates of ice particle mass. The effective diameter (De) was calculated in a similar way. The TC4 analysis has provided a diagnostic relationship that relates Vm to both cloud temperature (T) and ice water content (IWC) with an r2 of 0.78. A similar relationship for De was also obtained with an r2 of 0.82. The Vm relationship and associated Vm-IWC-T measurements were found to agree well with a Vm scheme based on T and cloud radar retrievals of Vm and IWC in tropical cirrus clouds. However, a critical climate-influencing parameter like the ice fall speed needs to be coupled with the cloud microphysics and radiation in climate models. This is made possible through strong correlations between De and Vm regarding TC4 and ISDAC cirrus. Finally, TC4 satellite retrievals of De and Vm are found to be consistent with corresponding observations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 14
    Publication Date: 2019
    Description: Abstract Prior to the Mars Atmosphere and Volatile Evolution (MAVEN) mission, the only information on the composition of the Martian ionosphere came from the Viking Retarding Potential Analyzer data, revealing the presence of substantial ion outflow on the dayside of Mars. Extensive measurements made by the MAVEN Neutral Gas and Ion Mass Spectrometer allow us to examine the morphology of the Martian ionosphere not only in unprecedented detail but also on both the dayside and the nightside of the planet. Above 300 km, various ionospheric species present a roughly constant density scale height around 100 km on the dayside and 180 km on the nightside. An evaluation of the ion force balance, appropriate for regions with near horizontal magnetic field lines, suggests the presence of supersonic ion outflow predominantly driven by the ambient magnetic pressure, with characteristic dayside and nightside flow velocities of 4 km s−1 and 20 km s−1, respectively, both referred to an altitude of 500 km. The corresponding total ion outflow rates are estimated to be 5 × 1025 s−1 on the dayside and 1 × 1025 s−1 on the nightside. The data also indicate a prominent variation with magnetic field orientation in that the ion distribution over regions with near vertical field lines tends to be more extended on the dayside but more concentrated on the nightside, as compared to regions with near horizontal field lines. These observations should have important implications on the pattern of ion dynamics in the vicinity of Mars.
    Print ISSN: 2169-9097
    Electronic ISSN: 2169-9100
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 15
    Publication Date: 1999-04-30
    Description: The Mars Global Surveyor spacecraft, in a highly elliptical polar orbit, obtained vector magnetic field measurements above the surface of Mars (altitudes 〉100 kilometers). Crustal magnetization, mainly confined to the most ancient, heavily cratered martian highlands, is frequently organized in east-west-trending linear features, the longest extending over 2000 kilometers. Crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude. Groups of quasi-parallel linear features of alternating magnetic polarity were found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale. They may be a relic of an era of plate tectonics on Mars.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Connerney -- Acuna -- Wasilewski -- Ness -- Reme -- Mazelle -- Vignes -- Lin -- Mitchell -- Cloutier -- New York, N.Y. -- Science. 1999 Apr 30;284(5415):794-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. Bartol Research Institute, University of Delaware, Newark, DE 19716, USA. Centre d'Etude Spatiale des Rayonnements, 31028 Toulouse Cedex 4, France. Space Sciences Laboratory, University.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10221909" 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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  • 16
    Publication Date: 1998-09-04
    Description: The magnetometer and electron reflectometer experiment on the Lunar Prospector spacecraft has obtained maps of lunar crustal magnetic fields and observed the interaction between the solar wind and regions of strong crustal magnetic fields at high selenographic latitude (30 degreesS to 80 degreesS) and low ( approximately 100 kilometers) altitude. Electron reflection maps of the regions antipodal to the Imbrium and Serenitatis impact basins, extending to 80 degreesS latitude, show that crustal magnetic fields fill most of the antipodal zones of those basins. This finding provides further evidence for the hypothesis that basin-forming impacts result in magnetization of the lunar crust at their antipodes. The crustal magnetic fields of the Imbrium antipode region are strong enough to deflect the solar wind and form a miniature (100 to several hundred kilometers across) magnetosphere, magnetosheath, and bow shock system.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lin -- Mitchell -- Curtis -- Anderson -- Carlson -- McFadden -- Acuna -- Hood -- Binder -- New York, N.Y. -- Science. 1998 Sep 4;281(5382):1480-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉R. P. Lin, Space Sciences Laboratory and Physics Department, University of California, Berkeley, CA 94720, USA. D. L. Mitchell, D. W. Curtis, K. A. Anderson, C. W. Carlson, J. McFadden, Space Sciences Laboratory, University of California〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9727969" 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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  • 17
    Publication Date: 1997-12-24
    Description: Radar observations of comet Hyakutake (C/1996 B2) made at the Goldstone Deep Space Communications Complex in California have detected echoes from the nucleus and from large grains in the inner coma. The nucleus of this bright comet was estimated to be only 2 to 3 kilometers in diameter. Models of the coma echo indicate backscatter from porous, centimeter-size grains ejected anisotropically at velocities of tens of meters per second. The radar observations suggest that a comet's activity may be a poor indicator of its size and provide evidence that large grains constitute an important component of the mass loss from a typical active comet.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Harmon -- Ostro -- Benner -- Rosema -- Jurgens -- Winkler -- Yeomans -- Choate -- Cormier -- Giorgini -- Mitchell -- Chodas -- Rose -- Kelley -- Slade -- Thomas -- New York, N.Y. -- Science. 1997 Dec 12;278(5345):1921-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉J. K. Harmon, National Astronomy and Ionosphere Center, Arecibo Observatory, Post Office Box 995, Arecibo, PR 00614, USA. S. J. Ostro, L. A. M. Benner, K. D. Rosema, R. F. Jurgens, R. Winkler, D. K. Yeomans, D. Choate, R. Cormier, J. D. Giorg.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9395389" 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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  • 18
    Publication Date: 2016-02-12
    Description: We present initial MAVEN observations and preliminary interpretation of bulk plasma loss from Mars. MAVEN particle and field measurements show that planetary heavy ions derived from the Martian atmosphere can escape in the form of discrete coherent structures or “clouds”. The ions in these clouds are unmagnetized or weakly magnetized, have velocities well above the escape speed, and lie directly downstream from magnetic field amplifications, suggesting a “snowplow” effect. This postulated escape process, similar to that successfully used to explain the dynamics of active gas releases in the solar wind and terrestrial magnetosheath, relies on momentum transfer from the shocked solar wind protons to the planetary heavy ions, with the electrons and magnetic field acting as intermediaries. Fluxes of planetary ions on the order of 10 7 cm -2 s -1 can escape by this process, and if it operates regularly it could contribute 10-20% of the current ion escape from Mars.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 19
    Publication Date: 1995-06-09
    Description: Microwave and mid-infrared observations reveal that Mercury's surface contains less FeO + TiO2 and at least as much feldspar as the lunar highlands. The results are compatible with the high albedo (brightness) of Mercury's surface at visible wavelengths in suggesting a rock and soil composition that is devoid of basalt, the primary differentiate of terrestrial mantles. The occurrence of a basalt-free, highly differentiated crust is in accord with recent models of the planet's thermal evolution and suggests that Mercury has retained a hot interior as a result of a combination of inefficient mantle convection and minimal volcanic heat loss.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jeanloz, R -- Mitchell, D L -- Sprague, A L -- de Pater, I -- New York, N.Y. -- Science. 1995 Jun 9;268(5216):1455-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geology and Geophysics, University of California, Berkeley 94720, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7770770" target="_blank"〉PubMed〈/a〉
    Keywords: Ferrous Compounds/*analysis ; Hot Temperature ; *Mercury (Planet) ; Minerals/*analysis ; Silicates/*analysis ; Titanium/*analysis
    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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  • 20
    Publication Date: 2015-11-07
    Description: Planetary auroras reveal the complex interplay between an atmosphere and the surrounding plasma environment. We report the discovery of low-altitude, diffuse auroras spanning much of Mars' northern hemisphere, coincident with a solar energetic particle outburst. The Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, detected auroral emission in virtually all nightside observations for ~5 days, spanning nearly all geographic longitudes. Emission extended down to ~60 kilometer (km) altitude (1 microbar), deeper than confirmed at any other planet. Solar energetic particles were observed up to 200 kilo--electron volts; these particles are capable of penetrating down to the 60 km altitude. Given minimal magnetic fields over most of the planet, Mars is likely to exhibit auroras more globally than Earth.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schneider, N M -- Deighan, J I -- Jain, S K -- Stiepen, A -- Stewart, A I F -- Larson, D -- Mitchell, D L -- Mazelle, C -- Lee, C O -- Lillis, R J -- Evans, J S -- Brain, D -- Stevens, M H -- McClintock, W E -- Chaffin, M S -- Crismani, M -- Holsclaw, G M -- Lefevre, F -- Lo, D Y -- Clarke, J T -- Montmessin, F -- Jakosky, B M -- New York, N.Y. -- Science. 2015 Nov 6;350(6261):aad0313. doi: 10.1126/science.aad0313.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Boulder, CO 80303, USA. nick.schneider@lasp.colorado.edu. ; Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Boulder, CO 80303, USA. ; Space Sciences Lab, University of California, Berkeley, Berkeley, CA 94720, USA. ; Institut de Recherche en Astrophysique et Planetologie (IRAP), CNRS, Toulouse, France. University Paul Sabatier, IRAP, CNRS, Toulouse, France. ; Computational Physics, Inc, Springfield, VA 22151, USA. ; Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA. ; Laboratoire Atmospheres, Milieux, Observations Spatiales, Institut Pierre Simon Laplace, Guyancourt, France. ; Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA. ; Center for Space Physics, Boston University, Boston, MA 02215, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26542577" 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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