Assessing the effects of post‐pine beetle forest litter on snow albedo     

Rita Winkler  Sarah Boon  Barbara Zimonick  Karen Baleshta 《水文研究》2010,24(6):803-812

The effect of forest litter on snow surface albedo has been subject to limited study, mainly in the hardwood‐dominated forests of the northeastern United States. Given the recent pine beetle infestation in Western North America and associated increases in litter production, this study examines the effects of forest litter on snow surface albedo in the coniferous forests of south‐central British Columbia. Measured changes in canopy transmittance provide an indication of canopy loss or total litterfall over the winter of 2007–2008. Relationships between percent litter cover, an index of albedo, snow depth, and snow ablation during the 2008 melt season are compared between a mature, young, and clearcut coniferous stand. Results indicate a strong feedback effect between canopy loss and subsequent enhanced shortwave transmittance, and litter accumulation on the snow surface from that canopy loss. However, this relationship is confounded by other variables concurrently affecting albedo. While results suggest that a relatively small percent litter cover can have a significant effect on albedo and ablation, further research is underway to extract the litter signal from that of other factors affecting albedo, particularly snow depth. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Frequency and directional evaluation of the ocean data gathering program (ODGP) wave spectra at Hibernia     

Barbara‐Ann Juszko  Ross Graham 《大气与海洋》2013,51(3):441-456

Abstract

The frequency and directional wave‐modelling capability of the Ocean Data Gathering Program (ODGP) deep water spectral wave model is assessed through comparison with WAVEC data gathered at Hibernia. Both qualitative and quantitative analyses indicate better agreement with observations during storms and with the wind‐driven component of the wave spectra. There is statistically poor modelling of the swell. A coherence analysis on derived wave vectors indicates that the ODGP model does not simulate geophysical variability with time‐scales less than about 30 h for overall spectral energy and less than 24 h for wave energy of frequency greater than 0.6 rad s^?1 (0.095 Hz). The signals associated with swell waves are incoherent at nearly all time‐scales.  相似文献   

Latitudinal variations in Jovian stratospheric temperature     

R.D. Cess  Barbara E. Carlson  John Caldwell  I.G. Nolt  F.C. Gillett  A.T. Tokunaga 《Icarus》1981,46(2):249-255

Ground-based observations of Jupiter show that the planet's stratospheric and tropospheric thermal emission are anticorrelated. The observations can possibly be explained by latitudinal variations in cloud altitude. These variations cause differential stratospheric heating by sunlight which is reflected off the clouds and then absorbed within the stratosphere by visible and near-infrared bands of methane.  相似文献   

Hannibal and The Alps: unravelling the invasion route     

W.C. Mahaney  Barbara Kapran  Pierre Tricart 《Geology Today》2008,24(6):223-230

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Summaries of presentations during the sixth Workshop of the International Association of Phytoplankton Ecology and Taxonomy,Mondsee, Austria, 15–25 September 1986     

H. R. Bürgi  Gerhild Deisinger  M. Dokulil  Barbara Hickel  Utsa Pollingher  Hedy Kling  Pertti Eloranta  Eugen Rott  Peter Pfister  Maria Moustaka  Ivan S. Heaney  Eugen Rott  A. E. Bailey-Watts  Jorgen Kristiansen  Asbjorn Skogstad 《Aquatic Sciences - Research Across Boundaries》1987,49(3):375-392

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Fluoride in the Ground Water of Northeastern Ohio     

Robert G. Corbett  Barbara M. Manner 《Ground water》1984,22(1):13-17

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Evidence for the influence of fCH 4 on the crystallinity of disseminated carbon in greenschist facies rocks,Rhode Island,USA     

Robert P. Wintsch  Anne F. O'Connell  Barbara L. Ransom  Mark J. Wiechmann 《Contributions to Mineralogy and Petrology》1981,77(3):207-213

Disseminated carbon has been extracted from 19 samples of arkosic rocks from the chlorite, biotite and garnet zones in the Narragansett basin, and analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD of these samples yields only the (002) peak which may be as much as four times wider than the silicon internal standard peak and is always skewed to low angles 2θ. All (002) peaks were digitized and the four moments calculated. The results suggest that width at half-height (W_1/2) provides a poorer estimate of peak shape than coefficients of skewness and kurtosis. The positive correlation of these coefficients with grain size determined by SEM in the range of 0.1–100 μm suggest a direct relationship between peak shape and grain size. No variable measured in this study correlates with metamorphic grade. However, W_1/2, skewness and kurtosis of the (002) diffraction peak of the carbonaceous material in the biotite and garnet zones correlates inversely with modal carbon. This suggests that the volatilization reaction: C+2H₂=CH₄ may be an important step in the mechanism of graphitization. Variable fugacities of H₂ and CH₄ and/or variable permeabilities may be responsible for the non-uniform development of graphite crystallinity in the greenschist facies rocks in Rhode Island.  相似文献   

Spatially smoothed seismicity modeling of seismic hazard in Slovenia     

Janez K. Lapajne  Barbara Sket Motnikar  Blaz Zabukovec  Polona Zupancic 《Journal of Seismology》1997,1(1):73-85

A progress report on the mapping effort for construction of a peak ground acceleration (PGA) map of Slovenia for 475-year return period for rock and firm soil is presented. The methodology is similar to that recently applied in Central and Eastern United States. It is based on historical seismicity spatially smoothed to different length scales. The procedure is described by Frankel (1995). He uses the characteristic earthquake recurrence relationship and in his firt version four different seismicity models. We also use four seismicity models. But instead of characteristic earthquake recurrence, we use the doubly truncated exponential magnitude-frequency relationship; no evidence of characteristic earthquakes in Slovenia has been found yet. Three of our models are similar to Frankel's first three models. Model 1 uses spatially smoothed activity rate based on magnitude 3.7 and above events since 1880. Model 2 deals with spatially smoothed activity rate based on magnitude 5.0 abd above events since 1690. Model 3 smoothes the observed activity over the entire region; it represents a uniform seismicity zone. Frankel skipped this model in his latest version (Frankel et al. 1996). In model 4, we introduce a new approach of calculating seismic activity rate taking into account released seismic energy. The ground motion attenuation model of Pugliese and Sabetta (1989) is used for all models. PGA maps for models 1, 2, 3 and 4 have been calculated, and a weighted mean map derived from them. A map of model 1 has been compared with the corresponding source zone map; the two maps do not differ significantly. A worst-case map derived from all four models has also been produced.  相似文献   

A comparison of methods for detection of phosphate limitation in microalgae   总被引：6，自引：0，他引：6  

John Beardall  Tom Berman  Phil Heraud  Medina Omo Kadiri  Brett R. Light  Graeme Patterson  Simon Roberts  Barbara Sulzberger  Emel Sahan  Urs Uehlinger  Bayden Wood 《Aquatic Sciences - Research Across Boundaries》2001,63(1):107-121

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Settlement patterns of brachyuran megalopae in a Louisiana estuary     

Barbara E. Hasek  Nancy N. Rabalais 《Estuaries and Coasts》2001,24(6):796-807

Artificial substrate collectors were used to sample settled brachyuran megalopae in Terrebonne Bay, Louisiana, northern Gulf of Mexico. Three taxa,Callinectes sapidus, Uca spp., andRhithropanopeus harrisii, were the most common settlers. Settlement occurred almost year-round, although settlement densities were highest in late summer and early fall. In 1990, all three taxa had several simultaneous settlement peaks; in 1991, one simultaneous settlement peak occurred. FewerC. sapidus andUca spp. settled in 1991 than in 1990, but settlement abundance ofR. harrissii was similar between years. Local weather events, such as heavy precipitation, may have influenced the lower abundances ofC. sapidus andUca spp. in 1991. The megalopae ofC. sapidus andUca spp., which re-invade the estuary from higher salinity offshore waters where larval development occurs, may have been more affected by the lower 1991 estuarine salinity values than the larvae ofR. harrissii, which are retained within the estuary throughout larval development. Settlement ofC. sapidus andUca spp. was correlated with maximum tidal height, tidal amplitude, salinity, temperature, and lunar phase. In 1990, settlement ofC. sapidus was correlated with lunar declination cycles; settlement peaks occurred during equatorial minimum amplitude tides. The settlement ofR. harrisii was associated with tidal amplitude and lunar phase. Associations between environmental variables and settlement of megalopae were not consistent between the two years sampled. The opposing or reinforcing effects of various environmental variables on settlement, e.g., tidal height and rainfall, are superimposed on long-term hydrologic cycles so that dramatically altered cycles of settlement occur among years.  相似文献