Helium-uranium dating of corals from Middle Pleistocene Barbados reef tracts     

Michael L. Bender  F.T. Taylor  R.K. Matthews 《Quaternary Research》1973,3(1):142-146

By He-U dating of corals from elevated Pleistocene reef tracts on Barbados, we have extended back to the Middle Pleistocene the high sea stand chronology previously deduced by Th²³⁰-U dating. Six samples from the first major reef tract complex older than the 200,000-yr complex gave ages of 350,000 ± 25,000 yr B.P. Two corals from the crest of Second High Cliff, an unusually large escarpment occurring approximately midway in the terrace sequence, gave concordant ages of 480,000 and 500,000 yr. Unrecrystallized corals from older reefs gave ages ranging back to 650,000 yr.The results date episodes of high sea stands at 350,000 and 500,000 yr B.P.  相似文献   

Actinometric measurements and the radiation climate of South-West Africa     

A. J. Drummond  J. D. Wentzel 《Theoretical and Applied Climatology》1955,6(3):236-273

Summary In the paper two records of solar radiation obtained on the high plateau of South-West Africa are analysed. One of them contains about 6000 observations (until recently unpublished) of the intensity of direct radiation made, at Brukkaros, over the five-year period from 1927 to 1931, by the solar-constant observing-team of the Smithsonian Institution. The other is a double record of total and of diffuse hemispherical radiation at Windhoek. This latter station has been operating since August 1951 and is one of a number maintained by the Weather Bureau of South Africa. An account is included of the techniques which have been adopted for the operation of such radiation stations in the Union's network.For Brukkaros not only are various aspects of the basic intensity record discussed but an attempt has been made to build up a set of representative data for the total radiation which would be received on a horizontal plane at all times of the year from a cloudless sky. Sections of the paper are devoted to a preliminary investigation of the turbidity and the absorptive and reflective properties of the atmosphere over this semi-desert sub-tropical highland. The Windhoek material, especially, has been subjected to statistical analysis and a number of summaries are presented of the salient features of the record. A comparison is drawn between the two assemblages of values and generalizations are made regarding the solar radiation climate of the territory.As this would appear to be the first comprehensive study to be undertaken of the distribution of solar radiation in an arid zone of Africa, detail which has been considered of importance, particularly from the viewpoint of the future utilization of solar energy, has been included. The perfect integration of the two distinctly different records places a very high degree of confidence upon their interpretation.

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Zusammenfassung In der vorliegenden Arbeit werden zwei Registrierreihen der Sonnenstrahlung untersucht, die auf dem Hochplateau von Südwestafrika gewonnen wurden. Die eine davon umfaßt etwa 6000 erst kürzlich veröffentlichte Beobachtungen der Intensität der direkten Sonnenstrahlung, die während der fünfjährigen Periode 1927 bis 1931 von der Solarkonstanten-Beobachtungsgruppe der Smithsonian Institution in Brukkaros angestellt wurden. Das andere ist eine Parallelregistrierung der globalen und der diffusen Strahlung auf Horizontalfläche in Windhoek, wo im Strahlungsnetz des Weather Bureau von Südafrika seit August 1951 eine Station in Betrieb ist. Es wird auch über die in diesem Strahlungsnetz angewandten instrumentellen Einrichtungen berichtet.Für Brukkaros werden nicht nur verschiedene Gesichtspunkte der grundlegenden Intensitätsmessungen erörtert, sondern es wurde auch der Versuch gemacht, eine Serie der repräsentativen Größen für die Globalstrahlung zu berechnen, die von einer horizontalen Ebene zu jeder Zeit des Jahres von einem wolkenlosen Himmel erhalten werden. Weiterhin wurde eine vorläufige Untersuchung über die Trübung und die Absorptions- und Reflexionseigenschaften der Atmosphäre über diesem subtropischen Steppenhochland durchgeführt. Speziell das Material von Windhoek wurde einer statistischen Analyse unterzogen und in einigen zusammenfassenden Darstellungen wurden die wesentlichen Resultate der Registrierungen herausgearbeitet. Zwischen den Ergebnissen der beiden Stationen wird eine Vergleichung durchgeführt und es werden die allgemeinen Züge des Strahlungsklimas des Landes abgeleitet.Da es sich hierbei offenbar um eine erste zusammenfassende Untersuchung über die Verteilung der Sonnenstrahlung in einer Trockenzone von Afrika handelt, werden Einzelheiten erörtert, denen speziell im Hinblick auf eine zukünftige Ausnützung der Sonnenenergie eine besondere Bedeutung zugeschrieben werden muß. Die gute Übereinstimmung der zwei deutlich verschiedenen Beobachtungsreihen verleiht ihrer Deutung einen hohen Grad von Zuverlässigkeit.

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Résumé L'auteur analyse deux séries d'enregistrements du rayonnement solaire obtenues sur le haut plateau du Sud-Ouest africain; l'une comprend 6000 mesures de l'intensité du rayonnement solaire direct faites de 1927 à 1931 par un groupe d'observateurs de la constante solaire de la Smithsonian Institution à Brukkaros et publiées récemment; l'autre comprend un enregistrement parallèle du rayonnement global et diffus sur une surface horizontale à Windhoek où se trouve une station de rayonnement du Weather Bureau de l'Afrique du Sud depuis août 1951. Il décrit l'appareillage utilisé dans ce réseau pour l'étude du rayonnement.Pour Brukkaros, l'auteur ne se borne pas à discuter les mesures d'intensité de base, mais il tente de calculer une série de grandeurs représentatives du rayonnement global reçu par une surface horizontale à tout moment de l'année par ciel sans nuages. Il étudie provisoirement le trouble atmosphérique et les propriétés absorbantes et réfléchissantes de l'atmosphère de ce haut plateau semi-désertique subtropical. Le matériel de Windhoek spécialement a été soumis à l'examen statistique et les résultats essentiels des enregistrements mis en évidence par quelques condensés. Il compare ensuite les résultats des deux stations et esquisse le climat radiatif du pays.Dans cette première synthèse de la distribution du rayonnement dans une région sèche d'Afrique on mentionne aussi des détails importants pour l'utilisation future de l'énergie solaire. Le bon accord de ces deux séries différentes de mesures leur confère un degré élevé de crédibilité.

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With 9 Figures.  相似文献   

Assessment of the Uncertainties in the NO2 and O3 Measurements by Visible Spectrometers     

M. Koike  Y. Kondo  W.A. Matthews  P.V. Johnston  H. Nakajima  A. Kawaguchi  H. Nakane  I. Murata  A. Budiyono  M. Kanada  N. Toriyama 《Journal of Atmospheric Chemistry》1999,32(1):121-145

The column amounts of nitrogen dioxide (NO2) and ozone (O3) were measured using a visible spectrometer based on the twilight zenith-sky technique at two observatories located at similar latitudes in the northern part of Japan separated by a distance of 150 km. The measurements began in April 1991 at the Moshiri Observatory (44.4°N, 142.3°E) and in April 1994 at the Rikubetsu Observatory (43.5°N, 143.8°E). Since weather conditions and the possible influence from tropospheric pollution were not always identical at these two observatories, the overall accuracy of the measurements was studied comparing these data sets. The first year data obtained at a solar zenith angle of 90 degrees indicated that the NO2 slant column values at sunrise and sunset agreed within 0.36 and 0.54 × 1016 cm-2, respectively, corresponding to 5 % (June) and to 12 % (December) of the columns. The O3 values agreed within 0.76 × 1019 cm-2, corresponding to 4 % (March) 6 % (August) of the columns, although a part of the difference was systematic. The O3 column amounts were also compared to those obtained by the Dobson spectrometer at Sapporo (43.5°N, 143.8°E), whose latitude is similar to these observatories. When an air mass factor of 17.5 was used, the two-year Moshiri vertical column values agreed with the Dobson direct sun values to within 15 Dobson Units, or 3 6 % of the column. The difference between the two values was found to be due partly to the change in the air mass factor caused by seasonal and day-to-day changes in the shape of the O3 vertical profiles. These results confirm the reliability of the NO2 and O3 measurements by visible spectrometers at these sites for the Network for the Detection of Stratospheric Change (NDSC).  相似文献   

Multi-wavelength observations of the onset phase of a coronal mass ejection     

Innes  D.E.  Inhester  B.  Srivastava  N.  Brekke  P.  Harrison  R.A.  Matthews  S.A.  Noëns  J.C.  Schmieder  B.  Thompson  B.J. 《Solar physics》1999,186(1-2):337-361

The structure and dynamics of the initial phases of a coronal mass ejection (CME) seen in soft X-ray, extreme ultraviolet and optical emission are described. The event occurred on the SW limb of the Sun in active region AR 8026 on 9 April 1997. Just prior to the CME there was a class C1.5 flare. Images taken with the Extreme Ultraviolet Imaging Telescope (EIT) reveal the emergence of a candle-flame shaped extreme ultraviolet (EUV) cavity at the time of the flare. Yohkoh images, taken about 15 min later, show that this cavity is filled with hot X-ray emitting gas. It is most likely that this is the site of the flare. Almost simultaneous to the flare, an H surge or small filament eruption occurs about 50 arc sec northwards along the limb from the EUV cavity. At both the site of the core of the hot, EUV cavity and the filament ejection are X-ray jets. These jets seem to be connected by hot loops near their bases. Both jets disappear within a few minutes of one another.Clear evidence of the CME first appeared in the Large Angle Spectrometric Coronagraph (LASCO) and EIT images 40 min after the flare and onset of the filament ejection. It seems to come from a region between the two X-ray jets. This leads to the speculation that magnetic field reconnection near one footpoint of a loop system triggers reconnection near its other footpoint. The loop system is destabilized and ultimately gives rise to the CME. This possibility is supported by magnetic field and H images taken when the active region was at disk center which show that the active region had a double bipole structure with dark H filaments between the bipoles.  相似文献   

Announcement     

K. Matthews  G. Neugebauer  P.D. Nicholson 《Icarus》1982,50(1):126-135

Maps of the ring system of Uranus, as seen in reflected sunlight at a wavelength of 2.2 μm, are presented for May 1978 and July 1979. Large azimuthal brightness variations revealed by these maps are consistent with the variable width established for the ? ring from occultation studies and support the existing elliptical model for this ring. An upper limit of ～0.010 is placed on the normal optical depth of any broad (～5000 km wide) axisymmetric ring component. There exists, however, an unexplained east-west asymmetry in the May 1978 map. In addition, multiaperture broadband infrared photometry of Uranus is reported, from which the geometric albedo of the planet at wavelengths of 1.25, 1.65, and 2.2 μm and the geometric albedo of the rings at 2.2 μm are derived.  相似文献   

The role of land surface dynamics in glacial inception: a study with the UVic Earth System Model   总被引：5，自引：2，他引：3  

K. J. Meissner  A. J. Weaver  H. D. Matthews  P. M. Cox 《Climate Dynamics》2003,21(7-8):515-537

The first results of the UVic Earth System Model coupled to a land surface scheme and a dynamic global vegetation model are presented in this study. In the first part the present day climate simulation is discussed and compared to observations. We then compare a simulation of an ice age inception (forced with 116 ka BP orbital parameters and an atmospheric CO₂ concentration of 240 ppm) with a preindustrial run (present day orbital parameters, atmospheric [CO₂] = 280 ppm). Emphasis is placed on the vegetations response to the combined changes in solar radiation and atmospheric CO₂ level. A southward shift of the northern treeline as well as a global decrease in vegetation carbon is observed in the ice age inception run. In tropical regions, up to 88% of broadleaf trees are replaced by shrubs and C₄ grasses. These changes in vegetation cover have a remarkable effect on the global climate: land related feedbacks double the atmospheric cooling during the ice age inception as well as the reduction of the meridional overturning in the North Atlantic. The introduction of vegetation related feedbacks also increases the surface area with perennial snow significantly.  相似文献   

Influence of aquifer properties on phytoremediation effectiveness     

Matthews DW  Massmann J  Strand SE 《Ground water》2003,41(1):41-47

Recent research has shown that planting deep-rooted trees, such as poplar, can take up and degrade important ground water pollutants such as trichloroethylene (TCE) as they transpire water from the capillary fringe of shallow contaminated aquifers. The effect of hydrogeologic factors on the minimum plantation area needed to prevent downgradient migration of contaminated ground water is not well known. Accordingly, the objective of this research was to identify the hydrogeologic parameters that control phytoremediation effectiveness. We used a numerical ground water flow model to evaluate the effect that natural variations in hydrogeologic parameters and growing season duration have on the minimum plantation area required for capture. We found that the plantation area that was needed to completely capture a ground water contamination plume was directly proportional to aquifer horizontal hydraulic conductivity, saturated thickness, and ground water gradient. The plantation area needed for capture increased nonlinearly with increasing plume width, aquifer anisotropy, and decreasing growing season duration. The plantation area needed for capture was generally insensitive to aquifer-specific yield and storativity. Steady-state simulations can be used to predict the plantation area needed for capture in many applications. A particularly important finding of this work is that evapotranspiration fluxes through plantations appropriately sized to contain the plume substantially exceeded the ground water flux through the plume itself.  相似文献   

Butterfly pitch-angle distributions observed by ISEE-1     

Theodore A. Fritz  Mohamed Alothman  Jyotirmoyee BhattacharjyaDavid L. Matthews  Jiasheng Chen 《Planetary and Space Science》2003,51(3):205-219

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Meteorological monitoring of an active volcano: Implications for eruption prediction     

Jenni Barclay  Jade E. Johnstone  Adrian J. Matthews   《Journal of Volcanology and Geothermal Research》2006,150(4):241-358

Rainfall data collected on and around the Soufriere Hills Volcano, Montserrat between 1998 and 2003 were analysed to assess the impact on primary volcanic activity, defined here as pyroclastic flows, dome collapses, and explosions. Fifteen such rainfall-triggered events were identified. If greater than 20 mm of rain fell on a particular day, the probability of a dome collapse occurring on that day increased by a factor of 6.3% to 9.2%, compared to a randomly chosen day. Similarly, the probability of observing pyroclastic flows and explosions on a day with > 20 mm of rainfall increased by factors of 2.6 and 5.4, respectively. These statistically significant links increased as the rainfall threshold was increased. Seventy percent of these rainfall-induced dome collapse episodes occurred on the same calendar day (most within a few hours) as the onset of intense rainfall, but an extra 3 occurred one or two calendar days later. The state of the volcano was important, with the rainfall–volcanic activity link being strongest during periods of unstable dome growth and weakest during periods of no dome growth or after a recent major collapse.Over 50% of the heavy rain days were associated with large-scale weather systems that can potentially be forecast up to a few days ahead. However, the remaining heavy rain days were associated with small-scale, essentially unpredictable weather systems. There was significant variability in the amount of rainfall recorded by different rain gauges, reflecting topographic variations around the volcano but also the inherent small-scale variability within an individual weather system. Hence, any monitoring/warning program is recommended to use a network, rather than just a single gauge. The seasonal cycle in rainfall was pronounced, with nearly all the heavy rain days occurring in the May–December wet season. Hence, the dome was at its most vulnerable at the beginning of the wet season after a period of uninterrupted growth. Interannual variability in rainfall was related to tropical Pacific and Atlantic sea surface temperature anomalies, and holds out the prospect of some limited skill in volcanic hazard forecasts at even longer lead times.  相似文献   

Communicating academic geography—the continuing challenge     

Jon Shaw  Judith Matthews 《Area》1998,30(4):367-372

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