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211.
In this paper we seek the origin of the axial component of the magnetic field in filaments by adapting theory to observations.
A previous paper (Mackay, Gaizauskas, and van Ballegooijen, 2000) showed that surface flows acting on potential magnetic fields
for 27 days – the maximum time between the emergence of magnetic flux and the formation of large filaments between the resulting
activity complexes – cannot explain the chirality or inverse polarity nature of the observed filaments. We show that the inclusion
of initial helicity, for which there is observational evidence, in the flux transport model results in sufficiently strong
dextral fields of inverse polarity to account for the existence and length of an observed filament within the allotted time.
The simulations even produce a large length of dextral chirality when just small amounts of helicity are included in the initial
configuration. The modeling suggests that the axial field component in filaments can result from a combination of surface
(flux transport) and sub-surface (helicity) effects acting together. Here surface effects convert the large-scale helicity
emerging in active regions into a smaller-scale magnetic-field component parallel to the polarity inversion line so as to
form a magnetic configuration suitable for a filament. 相似文献
212.
213.
214.
Jonathan D. Radley 《Geology Today》2009,25(4):140-144
The Hornton Stone is an unusually pure ooidal ironstone of the Lower Jurassic Marlstone Rock Formation, cropping out on the Edge Hill escarpment and adjacent ironstone plateau in central England. The stone has been quarried for building and ornamental purposes since Medieval times, and more recently as a source of iron ore. Local quarries and buildings provide excellent opportunities to appreciate its fossil content, sedimentary structures and origin. 相似文献
215.
Abstract— In this study, we have performed pulse‐heating experiments at different temperatures for three organic molecules (a polycyclic aromatic hydrocarbon [PAH], a ketone, and an amino acid) absorbed into microporous aluminum oxide (Al2O3) in order to imitate the heating of the organic molecules in interplanetary dust particles (IDPs) and micrometeorites (MMs) during atmospheric entry and to investigate their survival. We have shown that modest amounts (a few percent) of these organic molecules survive pulse‐heating at temperatures in the 700 to 900 °C range. This suggests that the porosity in IDPs and MMs, combined with a sublimable phase (organic material, water), produces an ablative cooling effect, which permits the survival of organic molecules that would otherwise be lost either by thermal degradation or evaporation during atmospheric entry. 相似文献
216.
217.
The seasonal variation of the surface temperature is calculated for various idealized paleogeographic conditions with a 1.5-dimensional (1.5-D) coupled climate-sea ice model. The sensitivity of the annual and summer polar temperatures to the meridional oceanic heat transport and to the parameterizations adopted for the snow and sea ice albedos is examined in connection with the location and size of a polar global super-continent. It is shown that the high latitude summer temperatures remain below the freezing point in all numerical simulations with a polar super-continent, thus suggesting the potential role played by a large polar continental mass in the initiation of glaciations. These results are in agreement with a previous 1.5-D energy balance model (EBM) study but in conflict with two-dimensional (2-D) EBMs suggesting above-freezing high latitude summer temperatures in the case of a polar-centered super-continent. It is also found that the amount of seasonality is strongly dependent on the details of the surface albedo feedback parameterizations and could explain the various model diverging results.If a simplified temperature dependence of the silicate weathering rate controlling the long-term carbon cycle is included, the atmospheric CO2 level is significantly increased in the case of a polar-centered continent but summer temperatures still remain below freezing. 相似文献
218.
219.
R. A. JAMIESON N. G. CULSHAW N. WODICKA D. CORRIGAN J. W. F. KETCHUM 《Journal of Metamorphic Geology》1992,10(3):321-332
Systematic mapping of a transect along the well-exposed shores of Georgian Bay, Ontario, combined with the preliminary results of structural analysis, geochronology and metamorphic petrology, places some constraints on the geological setting of high-grade metamorphism in this part of the Central Gneiss Belt. Correlations within and between map units (gneiss associations) have allowed us to recognize five tectonic units that differ in various aspects of their lithology, metamorphic and plutonic history, and structural style. The lowest unit, which forms the footwall to a regional decollement, locally preserves relic pre-Grenvillian granulite facies assemblages reworked under amphibolite facies conditions during the Grenvillian orogeny. Tectonic units above the decollement apparently lack the early granulite facies metamorphism; out-of-sequence thrusting in the south produced a duplex-like structure. Two distinct stages of Grenvillian metamorphism are apparent. The earlier stage (c. 1160–1120 Ma) produced granulite facies assemblages in the Parry Sound domain and upper amphibolite facies assemblages in the Parry Island thrust sheet. The later stage (c. 1040–1020 Ma) involved widespread, dominantly upper amphibolite facies metamorphism within and beneath the duplex. Deformation and metamorphism recently reported from south and east of the Parry Sound domain at c. 1100–1040 Ma have not yet been documented along the Georgian Bay transect. The data suggest that early convergence was followed by a period of crustal thickening in the orogenic core south-east of the transect area, with further advance to the north-west during and after the waning stages of this deformation. 相似文献
220.
J. Rajchl J. Bočcek D. Očenáš J. Škvarka P. Zimnikoval H. Murayama K. Ohtsuka 《Earth, Moon, and Planets》1995,68(1-3):479-486
Some results following from two contemporary photographical programs (Slovakia and Japan) for persistent meteor train spectra are compared. It shows that even though both programs are not too different according to their lenses and films used, the spectral interval detected is very different. In this respect prism as a dispersion element is more favourable than the grating with blaze wavelength near 610 nm. However, some results previously assumed as typicai for presented persistent trains-e.g. the forbidden Herzberg O2 emission, the NO2 continuum and OH red emissions-seem to be substanciated especially due to higher and linear dispersion of those grating spectra. 相似文献