Long-term evolution of a high-latitude active region     

William H. Marquette  Sara F. Martin 《Solar physics》1988,117(2):227-241

We describe the decay phase of one of the largest active regions of solar cycle 22 that developed by the end of June 1987. The center of both polarities of the magnetic fields of the region systematically shifted north and poleward throughout the decay phase. In addition, a substantial fraction of the trailing magnetic fields migrated equatorward and south of the leading, negative fields. The result of this migration was the apparent rotation of the magnetic axis of the region such that a majority of the leading polarity advanced poleward at a faster rate than the trailing polarity. As a consequence, this region could not contribute to the anticipated reversal of the polar field.The relative motions of the sunspots in this active region were also noteworthy. The largest, leading, negative polarity sunspot at N24 exhibited a slightly slower-than-average solar rotation rate equivalent to the mean differential rotation rate at N25. In contrast, the westernmost, leading, negative polarity sunspot at N21 consistently advanced further westward at a mean rate of 0.13 km s^–1 with respect to the mean differential rotation rate at its latitude. These sunspot motions and the pattern of evolution of the magnetic fields of the whole region constitute evidence of the existence of a large-scale velocity field within the active region.Solar Cycle Workshop Paper.  相似文献   

Characterization of the bivalve ultrafiltration barrier: What pollutants pass through?     

M.Patricia Morse  Edgar Meyhofer  William E. Robinson 《Marine environmental research》1988,24(1-4)

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Simplify or perish     

André Deprit  Bruce Miller 《Celestial Mechanics and Dynamical Astronomy》1988,45(1-3):189-200

Three suggestions are made for breaking the gridlock which paralyses progress in automating massive symbolic calculations in celestial mechanics: (i) simplifications by canonical transformations, (ii) object oriented programming to endow the algebra of Poisson series with various structures, (iii) massively parallel processing.  相似文献   

Synchronization of perturbed non-linear Hamiltonians     

Bruce R. Miller  Vincent T. Coppola 《Celestial Mechanics and Dynamical Astronomy》1993,55(4):331-350

We propose a new method based on Lie transformations for simplifying perturbed Hamiltonians in one degree of freedom. The method is most useful when the unperturbed part has solutions in non-elementary functions. A non-canonical Lie transformation is used to eliminate terms from the perturbation that are not of the same form as those in the main part. The system is thus transformed into a modified version of the principal part. In conjunction with a time transformation, the procedure synchronizes the motions of the perturbed system onto those of the unperturbed part.A specific algorithm is given for systems whose principal part consists of a kinetic energy plus an arbitrary potential which is polynomial in the coordinate; the perturbation applied to the principal part is a polynomial in the coordinate and possibly the momentum.We demonstrate the strategy by applying it in detail to a perturbed Duffing system. Our procedure allow us to avoid treating the system as a perturbed harmonic oscillator. In contrast to a canonical simplification, our method involves only polynomial manipulations in two variables. Only after the change of time do we start manipulating elliptic functions in an exhaustive discussion of the flows.  相似文献   

Stability considerations for one-dimensional inverse problems     

Samuel H. Gray  William W. Symes 《Geophysical Journal International》1985,80(1):149-163

Summary. We investigate the issues of stability and conditioning for the one-dimensional seismic inverse problem. We show that these issues are distinct; i.e. that numerically stable implementations of solutions to the inverse problem will not give accurate results if the problem is ill-conditioned. In addition, we identify the factors which determine the condition of the inverse problem. These are the total variation of the acoustic impedance profile being sought and the accuracy of the low-frequency content of the reflection data. We illustrate these results on implementations of two numerically stable algorithms for the inverse problem, one of which has a reputation for being unstable. A comparison shows nearly identical results for the two methods on noise-contaminated and frequency band limited reflection data. In fact, we conjecture that all of the well-known 'layer-stripping' inverse scattering methods share the same mathematical stability characteristics. On the other hand, we also show that ill-conditioning can lead to failure of such algorithms, through amplification of error due either to inaccurate data or to discretization or roundoff. Finally, we observe that appropriate smoothing of the seismic data for an ill-conditioned inverse problem (high-variation impedance profile) can cause the problem to become well-conditioned (lower-variation profile). As is typical with regularizations, the price paid for the newly-acquired ability to solve the problem is a loss of accuracy in the solution.  相似文献   

Discussion of a possible magnetic transient in UVSP observations     

William Henze Jr. 《Solar physics》1986,104(2):359-362

As part of a search for possible magnetic transients in the transition region, polarization observations were made in the C iv line at 1548 Å during a flare on 1980, July 13. In contradiction to earlier informal reports, it is not possible to state that magnetic transients of several thousand gauss have really been detected. This conclusion is based primarily on the lack of correlation in the circular polarization signals observed in the two halves of the spectral line and also on the possible effects of rapid fluctuations of intensity, velocity, and line width and shape.  相似文献   

The meteorite collection sites of Antarctica     

William Cassidy  Ralph Harvey  John Schutt  Georg Delisle  Keizo Yanai 《Meteoritics & planetary science》1992,27(5):490-525

Abstract— Antarctic meteorites have been and are being well studied but the potential for glaciological and climatological information in the sites where they are found is only beginning to be realized. To date, meteorite stranding surfaces have been identified only in East Antarctica: (1) The MacKay Glacier/David Glacier region contains the Allan Hills and the Reckling Moraine/Elephant Moraine stranding surfaces. Because the Allan Hills Main Icefield has a large proportion of meteorites with long terrestrial ages, these concentrations of meteorites must have had catchment areas extending well inland, in contrast to the present. Where known, bedrock topography is mesa-like in form and influences ice flow directions. Ice levels at the Allan Hills may have been higher by 50–100 m in the past. Reckling Moraine and Elephant Moraine are located on a long patch of ice running westward from Reckling Peak; the ice appears to be pouring over a bedrock escarpment. (2) In North Victoria Land, ice diverges around Frontier Mountain and flows into a site behind the barrier where ablation occurs extensively. It is proposed that meteorites and rocks were dumped by ice flow at the mouth of a valley in the lee of the mountain at the site where a meltwater pond existed, in a depression produced by ablation. Later, the pond migrated headward along the valley to a point where it is today, leaving a morainal deposit with the meteorites at a higher level. (3) Between the Beardmore and Law Glaciers, ice flows sluggishly into the southwestern margin of the Walcott Névé. Northeastern sections of the Walcott are virtually barren of meteorites. The entering Plateau ice is diverted northward to flow along the base of Lewis Cliff. This flow apparently terminates in an ice tongue protruding into a vast moraine, where a very large concentration of meteorites was found on the ice. This final segment of flowing ice is called the Lewis Cliff Ice Tongue. Meteorite Moraine, a subsidiary occurrence 2 km to the northeast, is also found against morainal deposits. The origin of the moraines and the history of meteorite concentration at this site is the subject of some debate. (4) The Transantarctic Mountains are submerged along one segment many hundreds of km in length by ice flowing off the Polar Plateau. The Thiel Mountains, Pecora Escarpment and Patuxent Range are the only surface indications of the underlying mountains along this interval, and meteorite stranding surfaces are found at each of these sites. Little is yet known about ice dynamics at these sites. (5) The immense Yamato Mountains meteorite stranding surface covers an area of about 4000 km². So far, most meteorites have been recovered in the upper reaches of this blue ice field, where ice flow is slowed by outlying subice barriers of the Yamato Mountains. Individual massifs in this range extend northward over 50 km, and the Yamato Meteorite Icefield loses 1100 m in elevation over this distance. (6) The Sør Rondane Mountains form a barrier to ice flow off the Polar Plateau. The major meteorite stranding surface associated with this barrier is the Nansenisen Icefield, a large ablation area about 50 km upstream of the mountains. The existence of a meteorite stranding surface at this site has not been explained so far. Most meteorite stranding surfaces have been functioning for a long time. They are sites where net ablation of the surface is occurring; the ice at these sites is stagnant or flowing only slowly, and the numbers of meteorites with great terrestrial ages decrease exponentially. Concentration mechanisms operating at these sites involve ablation, direct infall, time, low temperatures, moderate weathering and wind ablation. Detrimental to concentration are ice flow out of the area and extreme weathering. In spite of the fact that the Antarctic Ice Sheet is thought to be over 10 Ma old, we do not find stranding surfaces with meteorites having greater terrestrial ages than 1 Ma. This suggests that stranding surfaces are transient features, affected on a continental scale by possible extreme warming during late Pliocene and on a smaller scale by regional changes that produce differential effects between icefields. The latter effect is suggested by differences in the average terrestrial age of meteorites at different stranding surfaces. In either case, these sites seem to appear as a result of thinning near the edges of the ice sheet, and stratigraphic sequences may be exposed in the ice at stranding surfaces. We review five models for the production of meteorite stranding surfaces: (1) simple deflation of the ice sheet, in which ablation removes great thicknesses of overlying ice, exposing the contained meteorites while allowing direct falls to accumulate, (2) simple accumulation of direct falls on a bare ice surface that is not deflating, (3) ablation of ice trapped against a barrier, in which meteorites accumulate by direct infall while inflowing ice contributes meteorites by ablation discovery, (4) deceleration of ice by a subice barrier, which allows ablation discovery of meteorites in incoming ice and accumulation of other meteorites on the surface by direct infall and (5) stagnation of ice by encounter with an ice mass able to produce an opposing flow vector, in which ablation discovery and direct infall accumulation processes operate to build the meteorite concentration.  相似文献   

Excursion to Upnor: Saturday,May 8th, 1880     

William Whitaker 《Proceedings of the Geologists' Association. Geologists' Association》1880,6(7):336-337

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COUNTER-URBANIZATION IN SOCIETAL CONTEXT: LONG-DISTANCE MIGRATION TO THE HIGHLANDS AND ISLANDS OF SCOTLAND*     

Huw Jones  Nicholas Ford  James Caird  William Berry 《The Professional geographer》1984,36(4):437-444

Recent growth in long-distance migration by non-Scots to remote parts of the Scottish Highlands is evaluated in relation to key explanatory themes in counter-urbanization literature: rural-urban convergence, expansion of the affluent middle class, and changing residential preferences. A survey of in-migrants' motivations and livelihood adjustments reveals the primacy of quality of life considerations and a ‘satisficing’ approach to work, lifestyle and residential location. It is concluded that peripheral area counter-urbanization could be maintained without the context of societal affluence that spawned the movement in the 1960s.  相似文献   

Estimating macropore and matrix flow using the hydrograph separation procedure in an experimental forest plot     

Jos Nvar  Donald J. Turton  Edwin L. Miller 《水文研究》1995,9(7):743-753

This study was conducted to estimate macropore space, macropore flow and matrix flow in an experimental forest plot in the Ouachita Mountains of Arkansas. Lateral soil water fluxes and soil capillary potentials were observed in the isolated plot during applied rainfall experiments. Rainfalls were applied 17 times during the period 17 July to 10 October 1991. The subsurface hydrograph separation technique was used to estimate macropore space, macropore flux and matrix flux. The boundary between macropore and matrix flow was statistically determined by covariance analysis. The maximum estimated lateral macropore space was approximately 0.006 (cm³ cm^?3). The maximum estimated lateral macropore and matrix flow were 0.042 and 0.00066 cm s^?1, respectively. This report also emphasizes the need for further research on the hydrograph separation procedure for estimating macropores and macropore flow.  相似文献