Tangential discontinuities and the optical analogy for stationary fields. VII. Effects of resistivity     

E. N. Parker 《地球物理与天体物理流体动力学》2013,107(3-4):161-182

Abstract

The relatively large resistivity in the solar photosphere and chromosphere softens the ideal tangential discontinuities of magnetostatic equilibrium into continuous transitions in field direction over scales of 0.1–10 km. This softening is communicated upward at the Alfvén speed into the active solar corona. The degree of softening is a vital part of the theory of magnetic heat input to the active X-ray corona, because the very low resistivity of the coronal gas provides effective dissipation only if the current sheets are reduced to a thickness of 10^?2km.

A close examination of the problem shows that the Alfvén transit time up into the corona is large compared to the characteristic time of 1 sec in which the coronal tangential discontinutities are formed. It also shows that the principal effect of the resistivity is to create a thin surface layer of fluid on adjacent flux bundles, which causes a general drift of the flux but does not directly broaden the current sheets higher up in the field. In fact the motions of the surface layers do not extend upwards beyond the first winding pattern at each end of a coronal loop.

It appears that the photospheric and chromospheric resistivity is without striking consequences for magnetic heating in the corona.  相似文献   

Modelled and measured concentrations of peroxy radicals and nitrate radical in the U.S. Gulf Coast region during TexAQS 2006     

Roberto Sommariva  Tim S. Bates  Daniel Bon  Daniel M. Brookes  Joost A. de Gouw  Jessica B. Gilman  Scott C. Herndon  William C. Kuster  Brian M. Lerner  Paul S. Monks  Hans D. Osthoff  Alex E. Parker  James M. Roberts  Sara C. Tucker  Carsten Warneke  Eric J. Williams  Mark S. Zahniser  Steven S. Brown 《Journal of Atmospheric Chemistry》2011,68(4):331-362

Measurements of total peroxy radicals (HO₂?+?RO₂) and nitrate radical (NO₃) were made on the NOAA research vessel R/V?Brown along the U.S. Gulf Coast during the TexAQS 2006 field campaign. The measurements were modelled using a constrained box-model based upon the Master Chemical Mechanism (MCM). The agreement between modelled and measured HO₂?+?RO₂ was typically within ??40% and, in the unpolluted regions, within 30%. The analysis of the model results suggests that the MCM might underestimate the concentrations of some acyl peroxy radicals and other small peroxy radicals. The model underestimated the measurements of NO₃ by 60?C70%, possibly because of rapid heterogeneous uptake of N₂O₅. The MCM model results were used to estimate the composition of the peroxy radical pool and to quantify the role of DMS, isoprene and alkenes in the formation of RO₂ in the different regions. The measurements of HO₂?+?RO₂ and NO₃ were also used to calculate the gas-phase budget of NO₃ and quantify the importance of organic peroxy radicals as NO₃ sinks. RO₂ accounted, on average, for 12?C28% of the total gas-phase NO₃ losses in the unpolluted regions and for 1?C2% of the total gas-phase NO₃ losses in the polluted regions.  相似文献   

Mixed deposits of complex magmatic and phreatomagmatic volcanism: an example from Crater Hill,Auckland, New Zealand     

B. F. Houghton  C. J. N. Wilson  M. D. Rosenberg  I. E. M. Smith  R. J. Parker 《Bulletin of Volcanology》1996,58(1):59-66

 A series of alternating phreatomagmatic ("wet") and magmatic ("dry") basaltic pyroclastic deposits forming the Crater Hill tuff ring in New Zealand contains one unit (M1) which can only be interpreted as the products of mixing of ejecta from simultaneous wet and dry explosions at different portions of a multiple vent system. The principal characteristics of M1 are (a) rapid lateral changes in the thicknesses of, and proportions in juvenile components in individual beds, and (b) wide ranges of juvenile clast densities in every sample. M1 appears to have been associated with an elongate source of highly variable and fluctuating magma : water ratios and magma discharge rates. This contrasts with the only other documented mixed (wet and dry) basaltic pyroclastic deposits where mixing from two point sources of quite different but stable character has been inferred. Received: July 11, 1995 / Accepted: February 13, 1996  相似文献   

Groundwater quality in the recharged London Basin,England I: Phase associations of iron,manganese, and sulfur in Tertiary Sands     

J. E. Rae  A. Parker 《Environmental Geology》1992,19(2):127-135

Mineralogical and geochemical factors influencing the quality of the recharge water in the London Basin aquifer system (Tertiary Sands and Cretaceous Chalk) are identified, and phase associations for Fe (pyrite, glauconite, and smectite), Mn (carbonates, gypsum, and clays) and S (gypsum, pyrite, and organic matter) established. Concentrations of these elements vary considerably on a local scale, making basinwide predictions difficult. The oxidation of pyrite is a process of major significance, controlled to a certain extent by stratigraphic factors, particularly the thickness of clay cover to the aquifer sediments that controls access of air and surface water.  相似文献   

Geomagnetic field models incorporating frozen-flux constraints     

Catherine G. Constable  Robert L. Parker  Philip B. Stark 《Geophysical Journal International》1993,113(2):419-433

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Oscillations of sea level rise along the Atlantic coast of North America north of Cape Hatteras     

Albert Parker 《Natural Hazards》2013,65(1):991-997

It is shown in the short comment that the sea levels are oscillating about a longer-term trend and that the sea level rise (SLR) computed with time windows of 20, 30 or 60?years also oscillates, with the amplitude of these latter oscillations reducing as the time window increases. The use of only two values of the SLR distribution is misleading to infer conclusions about the accelerating behaviour. In particular, the comparison of the 30-year SLR 1950?C1979 with the 30-year SLR 1980?C2009 for the tide gauges along the Atlantic coast of North America north of Cape Hatteras to infer an accelerating behaviour is particularly wrong because the 30-year time window is a too short interval to appreciate the longer-term sea level trend cleared of the multi-decadal oscillations, and the two values from the SLR distribution are computed, respectively, at the times of a valley and a peak for the 60-year Atlantic Ocean multi-decadal oscillation. By using a 60-year time window or all the data since opening when more than 60?years of recording are available and by analysing the SLR time history, the only conclusion that can be inferred from the analysis of the tide gauges along the North American Atlantic coast is that the sea levels are oscillating without too much of a positive acceleration along their longer-term trend.  相似文献   

Reconstruction of the early Proterozoic stratigraphy of the Gawler Craton,South Australia     

A. J. Parker  N. M. Lemon 《Australian Journal of Earth Sciences》2013,60(1-2):221-238

Detailed structural mapping on NE Eyre Peninsula, South Australia, has led to a revised stratigraphy and model of sedimentation for Early Proterozoic metasediments of the Gawler Craton. Four stages of deformation have been recognised; three stages are associated with the Kimban Orogeny (c. 1820–1580 Ma) and a fourth stage is known as the Wartakan Event (c. 1500–1450 Ma). The recognition of major D₂ folds has shown the previously used stratigraphy to be incorrect and has necessitated its revision. At the base of the sequence, unconformably overlying a 2300 Ma or older basement, is the Warrow Quartzite. A transgressive cycle of schist, dolomite (Katunga Dolomite) and iron formation (Lower Middleback Jaspilite) overlies the quartzite, and this is overlain in turn by a regressive semipelitic unit containing local amphibolites (Cook Gap Schist), and another transgressive iron‐formation bearing cycle (Upper Middleback Jaspilite). At the top of the sequence is the Yadnarie Schist. All units overlying the older basement to the top of the Yadnarie Schist are defined collectively as the Hutchison Group. The Middle‐back ‘Group’ consisting of units from the top of the Warrow Quartzite to the base of the Yadnarie Schist is redefined as the Middleback Subgroup. Sediments of the Hutchison Group were probably derived from 2300+ Ma rocks on western Eyre Peninsula and deposited on a shallow platform now oriented approximately N‐S.  相似文献   

Multi-object spectroscopy field configuration by simulated annealing     

Brent Miszalski  K. Shortridge  W. Saunders  Q. A. Parker  S. M. Croom 《Monthly notices of the Royal Astronomical Society》2006,371(4):1537-1549

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Scientific rationale for the D-CIXS X-ray spectrometer on board ESA's SMART-1 mission to the Moon     

S.K Dunkin  M GrandeI Casanova  V FernandesD.J Heather  B KellettK Muinonen  S.S RussellR Browning  N WalthamD Parker  B KentC.H Perry  B SwinyardA Perry  J FeradayC Howe  K PhillipsG McBride  J HuovelinP Muhli  P.J HakalaO Vilhu  N ThomasD Hughes  H AlleyneM Grady  R LundinS Barabash  D BakerP.E Clark  C.D MurrayJ Guest  L.C d'UstonS Maurice  B FoingA Christou  C OwenP Charles  J LaukkanenH Koskinen  M KatoK Sipila  S NenonenM Holmstrom  N BhandariR Elphic  D Lawrence 《Planetary and Space Science》2003,51(6):435-442

The D-CIXS X-ray spectrometer on ESA's SMART-1 mission will provide the first global coverage of the lunar surface in X-rays, providing absolute measurements of elemental abundances. The instrument will be able to detect elemental Fe, Mg, Al and Si under normal solar conditions and several other elements during solar flare events. These data will allow for advances in several areas of lunar science, including an improved estimate of the bulk composition of the Moon, detailed observations of the lateral and vertical nature of the crust, chemical observations of the maria, investigations into the lunar regolith, and mapping of potential lunar resources. In combination with information to be obtained by the other instruments on SMART-1 and the data already provided by the Clementine and Lunar Prospector missions, this information will allow for a more detailed look at some of the fundamental questions that remain regarding the origin and evolution of the Moon.  相似文献   

More on the evolution of bed material waves in alluvial rivers     

Yantao Cui  Gary Parker  Thomas E. Lisle  James E. Pizzuto  Annjanette M. Dodd 《地球表面变化过程与地形》2005,30(1):107-114

Sediment waves or pulses can form in rivers following variations in input from landslides, debris flows, and other sources. The question as to how rivers cope with such sediment inputs is of considerable practical interest. Experimental, numerical and field evidence assembled by the authors suggests that in mountain gravel‐bed streams, such pulses show relatively little translation, instead mostly dispersing in place. This research has recently been the subject of discussion. In particular it has been suggested that (a) the equations of flow and sediment mass balance used in the analyses, and in most other morphodynamic analyses, require correction; (b) the dominance of dispersion appears only because the hyperbolic nature of the governing equations has not been adequately considered; and (c) the sediment transport equation used in the analyses does not lead to generalizable results. Here we suggest that (a) the relations for mass balance do not require the indicated correction; (b) the hyperbolic nature of the governing equations does not preclude the result of dispersion dominating translation in mountain streams; and (c) the general behaviour of an appropriate hyperbolic model of sediment waves (pulses) includes the relative roles of dispersion and translation, and is not affected by the precise choice of a sediment transport relation (as long as the choice is reasonable for the case in question). Copyright © 2005 John Wiley & Sons, Ltd.  相似文献