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  • 1
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    Hybrid Simulation of the Interaction of Solar Wind Protons with a Concentrated Lunar Magnetic Anomaly (2015)
    Wiley
    Details
    Publication Date: 2015-05-09
    Description: Using a two-dimensional hybrid simulation, we study the physics of the interaction of the solar wind with a localized magnetic field concentration, or “magcon”, on the Moon. Our simulation treats the solar-wind protons kinetically and the electrons as a charge neutralizing fluid. This approach is necessary because the characteristic scale of the magcon is of the same order, or smaller than the proton inertial length – the characteristic scale in the hybrid simulation. Specifically we consider a case in which the incident solar wind flows exactly normal to the lunar surface and the magcon is represented by a simple dipole whose moment is parallel to the surface, with a center just below it. We find that while the magcon causes the solar wind to be deflected and decelerated, it does not completely shield the lunar surface anywhere. However, protons which impact the surface in the center of the magnetic anomaly have energies well below the solar-wind ram energy. Thus, in this region, any backscattered neutral particles resulting from the interaction of solar-wind protons with the lunar regolith would have energies lower than that of the solar wind. Moreover, very few neutrals, if any, would emanate from within the magcon with energies comparable to the solar-wind energy. This may explain recent observations of lunar energetic neutral atoms associated with a strong crustal magnetic anomaly. Our study also finds that a significant fraction of the incoming solar-wind protons are reflected back into space before reaching the surface. These particles are reflected by a strong electrostatic field which results from the difference in the proton and electron inertia. The reflected particles are seen at very high altitudes above the Moon, over 200 km, and over a much broader spatial scale than the magcon, several hundred km at least. Our simulation also revealed a second population of reflected particles which originate from the side of the magcon where the interplanetary and magcon magnetic fields are directed opposite to one another, leading to a magnetic topology much like magnetic reconnection. As previously reflected particles move through this region, they are deflected upward, away from the surface, forming a second component. Our simulation has a number of similarities to recent in situ spacecraft observations of reflected ions above and around magcons.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Initial Mapping of Mercury's Crustal Magnetic Field: Relationship to the Caloris Impact Basin (2015)
    Wiley
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    Publication Date: 2015-12-12
    Description: 78 low-altitude passes of MESSENGER magnetometer data from August and September of 2014 have been applied to produce an approximate map of the crustal magnetic field at a constant altitude of 80 km covering latitudes of 50 ∘ -80 ∘ N and longitudes of 160 ∘ -330 ∘ E. The strongest anomalies are located in the westernmost part of the mapped region just north and northeast of the Caloris impact basin. The strongest single anomaly group lies over a smooth plains unit that extends northward from Caloris. A second anomaly lies on the Odin Formation, interpreted as primary Caloris ejecta. A third broad anomaly also lies over a smooth plains unit, Suisei Planitia. Although many smooth plains on Mercury may have a volcanic origin, a subset of these plains is concentrated around Caloris and could have a dominantly impact origin. It is therefore proposed that many of the Mercurian anomaly sources consist of impact basin ejecta materials.
    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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  • 3
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    Magnetic Anomalies Concentrated Near and Within Mercury's Impact Basins: Early Mapping and Interpretation (2016)
    Wiley
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    Publication Date: 2016-05-31
    Description: Ninety-five low-altitude passes of MESSENGER magnetometer data from February, March, and April of 2015 have been applied to produce an approximate map of the crustal magnetic field at a constant altitude of 40 km covering latitudes of 35 ∘ -75 ∘ N and longitudes of 90 ∘ -270 ∘ E. Anomalies are concentrated near and within the Caloris impact basin. A smaller concentration occurs over and around Sobkou Planitia and an associated older large impact basin. The strongest anomalies are found within Caloris and are distributed in a semi-circular arc that is roughly concentric with the basin rim. They imply the existence of a core dynamo at the time when Caloris formed (∼ 3.9 Gyr ago). Anomalies over high-reflectance volcanic plains are relatively weak while anomalies over low-reflectance material that has been re-worked by impact processes are relatively strong. The latter characteristics are qualitatively consistent with the ejecta model for anomaly sources.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Solar Signals in CMIP-5 Simulations: The Ozone Response (2015)
    Wiley
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    Publication Date: 2015-03-25
    Description: A multiple linear regression statistical method is applied to model data taken from the Coupled Model Intercomparison Project, phase 5 (CMIP-5) to estimate the 11-yr solar cycle responses of stratospheric ozone, temperature, and zonal wind during the 1979-2005 period. The analysis is limited to the six CMIP-5 models that resolve the stratosphere (high-top models) and that include interactive ozone chemistry. All simulations assumed a conservative 11-yr solar spectral irradiance (SSI) variation based on the NRL model. These model responses are then compared to corresponding observational estimates derived from two independent satellite ozone profile data sets and from ERA Interim Reanalysis meteorological data. The models exhibit a range of 11-yr responses with three models (CESM1-WACCM, MIROC-ESM-CHEM, and MRI-ESM1) yielding substantial solar-induced ozone changes in the upper stratosphere that compare favorably with available observations. The remaining three models do not, apparently because of differences in the details of their radiation and photolysis rate codes. During winter in both hemispheres, the three models with stronger upper stratospheric ozone responses produce relatively strong latitudinal gradients of ozone and temperature in the upper stratosphere that are associated with accelerations of the polar night jet under solar maximum conditions. This behavior is similar to that found in the satellite ozone and ERA Interim data except that the latitudinal gradients tend to occur at somewhat higher latitudes in the models. The sharp ozone gradients are dynamical in origin and assist in radiatively enhancing the temperature gradients, leading to a stronger zonal wind response. These results suggest that simulation of a realistic solar-induced variation of upper stratospheric ozone, temperature and zonal wind in winter is possible for at least some coupled climate models even if a conservative SSI variation is adopted.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 5
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    Lunar surface magnetic fields and their interaction with the solar wind: results from lunar prospector (1998)
    American Association for the Advancement of Science (AAAS)
    Details
    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
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    The origin of chondrules at jovian resonances (1998)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1998-02-10
    Description: Isotopic dating indicates that chondrules were produced a few million years after the solar nebula formed. This timing is incompatible with dynamical lifetimes of small particles in the nebula and short time scales for the formation of planetesimals. Temporal and dynamical constraints can be reconciled if chondrules were produced by heating of debris from disrupted first-generation planetesimals. Jovian resonances can excite planetesimal eccentricities enough to cause collisional disruption and melting of dust by bow shocks in the nebular gas. The ages of chondrules may indicate the times of Jupiter's formation and dissipation of gas from the asteroidal region.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Weidenschilling -- Marzari -- Hood -- New York, N.Y. -- Science. 1998 Jan 30;279(5351):681-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉S. J. Weidenschilling, Planetary Science Institute, Tucson, AZ 85705, USA. F. Marzari, Dipartimento di Fisica, Universita di Padova, 35131 Padova, Italy. L. L. Hood, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9445468" 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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  • 7
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    A nebular origin for chondritic fine-grained phyllosilicates (2003)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2003-01-25
    Description: Hydrated minerals occur in accretionary rims around chondrules in CM chondrites. Previous models suggested that these phyllosilicates did not form by gas-solid reactions in the canonical solar nebula. We propose that chondrule-forming shock waves in icy regions of the nebula produced conditions that allowed rapid mineral hydration. The time scales for phyllosilicate formation are similar to the time it takes for a shocked system to cool from the temperature of phyllosilicate stability to that of water ice condensation. This scenario allows for simultaneous formation of chondrules and their fine-grained accretionary rims.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ciesla, Fred J -- Lauretta, Dante S -- Cohen, Barbara A -- Hood, Lon L -- New York, N.Y. -- Science. 2003 Jan 24;299(5606):549-52.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Planetary Sciences, Lunar and Planetary Laboratory, University of Arizona, 1629 East University Boulevard, Tucson, AZ 85721, USA. fciesla@lpl.arizona.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12543970" target="_blank"〉PubMed〈/a〉
    Keywords: Ice ; *Meteoroids ; Pressure ; *Silicates ; Temperature ; Thermodynamics ; *Water
    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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  • 8
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    Improved gravity field of the moon from lunar prospector (1998)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1998-09-04
    Description: An improved gravity model from Doppler tracking of the Lunar Prospector (LP) spacecraft reveals three new large mass concentrations (mascons) on the nearside of the moon beneath the impact basins Mare Humboltianum, Mendel-Ryberg, and Schiller-Zucchius, where the latter basin has no visible mare fill. Although there is no direct measurement of the lunar farside gravity, LP partially resolves four mascons in the large farside basins of Hertzsprung, Coulomb-Sarton, Freundlich-Sharonov, and Mare Moscoviense. The center of each of these basins contains a gravity maximum relative to the surrounding basin. The improved normalized polar moment of inertia (0.3932 +/- 0.0002) is consistent with an iron core with a radius of 220 to 450 kilometers.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Konopliv -- Binder -- Hood -- Kucinskas -- Sjogren -- Williams -- New York, N.Y. -- Science. 1998 Sep 4;281(5382):1476-80.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉A. S. Konopliv, A. B. Kucinskas, W. L. Sjogren, J. G. Williams, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA. A. B. Binder, Lunar Research Institute, Gilroy, CA 95020, USA. L. L. Hood, University of Arizona〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9727968" 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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  • 9
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    Lagged Response of Tropical Tropospheric Temperature to Solar Ultraviolet Variations on Intraseasonal Timescales (2016)
    Wiley
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    Publication Date: 2016-04-20
    Description: Correlative and regression analyses of daily ERA-Interim reanalysis data for three separate solar maximum periods confirm the existence of a temperature response to short-term (mainly ∼ 27-day) solar ultraviolet variations at tropical latitudes in both the lower stratosphere and troposphere. The response, which occurs at a phase lag of 6-10 days after the solar forcing peak, consists of a warming in the lower stratosphere, consistent with relative downwelling and a slowing of the mean meridional (Brewer-Dobson) circulation, and a cooling in the troposphere. The mid-tropospheric cooling response is most significant in the tropical Pacific, especially under positive ENSO conditions, and may be related to a reduction in the number of Madden-Julian oscillation events that propagate eastward into the central Pacific following peaks in short-term solar forcing.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 10
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    Mercury and the Moon (2015)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2015-09-26
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hood, Lon L -- New York, N.Y. -- Science. 2015 Sep 25;349(6255):1459. doi: 10.1126/science.349.6255.1459-a.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA. lon@lpl.arizona.edu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26404816" 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
    Published by American Association for the Advancement of Science (AAAS)
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