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121.
Seth W. Bigelow Michael J. Papaik Caroline Caum Malcolm P. North 《Climatic change》2014,123(2):215-224
Large trees (>76 cm breast-height diameter) are vital components of Sierra Nevada/Cascades mixed-conifer ecosystems because of their fire resistance, ability to sequester large amounts of carbon, and role as preferred habitat for sensitive species such as the California spotted owl. To investigate the likely performance of large trees in a rapidly changing climate, we analyzed growth rings of five conifer species against 20th century climate trends from local weather stations. Over the local station period of record, there were no temporal trends in precipitation, but maximum temperatures increased by 0.10 to 0.13 °C/decade (summer and autumn), and minimum temperatures increased by 0.11 to 0.19 °C/decade in all seasons. All species responded positively to precipitation, but more variation was explained by a significant positive response to minimum winter temperatures. High maximum summer temperature adversely affected growth of two species, and maximum spring temperatures in the year prior to ring formation were negatively associated with growth of one species. The strong coherent response to increasing minimum temperatures bodes well for growth of large trees in Sierra/Cascades region mixed conifer forest under continued climatic warming, but these trees will still be under threat by the increased fire intensity that is a indirect effect of warming. 相似文献
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Omar Benazzouz Luis M. Pinheiro Luis M. A. Matias Alexandra Afilhado Daniel Herold Seth S. Haines 《Mathematical Geosciences》2018,50(5):569-584
The positioning of ocean bottom seismometers (OBS) is a key step in the processing flow of OBS data, especially in the case of self popup types of OBS instruments. The use of first arrivals from airgun shots, rather than relying on the acoustic transponders mounted in the OBS, is becoming a trend and generally leads to more accurate positioning due to the statistics from a large number of shots. In this paper, a linearization of the OBS positioning problem via the multilateration technique is discussed. The discussed linear solution solves jointly for the average water layer velocity and the OBS position using only shot locations and first arrival times as input data. 相似文献
126.
Grass hedges are narrow strips of stiff‐stemmed vegetation used to control erosion and sediment delivery. When planted on the contour, the hydraulic resistance of the vegetation slows runoff, creates ponding, and promotes sediment deposition. When tillage is performed between grass hedges, soil may be thrown against the vegetation, where it settles to form a berm within the hedge. Tillage‐induced berms divert part of runoff, causing it to flow alongside the hedge without crossing it. Such flow partitioning created by grass hedges was measured on experimental plots located on silt loam loess soil near Holly Springs, Mississippi, USA, where hedges planted at the bottom of 5%, 22.1‐m‐long slopes evolved berms averaging 0.13 m in height. They diverted about 80% of the runoff for events smaller than 5 mm and about 50% for large events. A two‐dimensional model was developed to determine overland flow patterns over complex terrains, accounting for oriented roughness created by tillage corrugations, crop rows, and larger features such as berms and vegetative barriers. The model was used to reproduce the flow partition observed in the field experiments and to determine how berm height and slope steepness and length affected runoff redistribution. Numerical simulations indicated that for most runoff events, ponded runoff depths were not high enough to overtop the berm but rather crossed the berms through cracks and gaps, represented in the model as small triangular weirs. The model also was applied to a 6.0‐ha watershed in Western Iowa, USA, where nine grass hedges were planted across 12–16% slopes. Computed dynamic flow properties showed that berms increased the amount of runoff flowing laterally upslope of the hedges and that a large portion of the runoff crossed the vegetative strips at a few locations and with high flow depths, increasing the risk of development of ephemeral gullies. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
127.
Rogier A.Windhorst Nimish P.Hathi Seth H.Cohen Russell E.Ryan Robert W.O’Connell Patrick J.McCarthy 《中国天文和天体物理学报》2010,10(9)
We present a large sample of candidate galaxies at z ≈ 7-10,selected in the Hubble Ultra Deep Field using the new observations of the Wide Field Camera 3that was recently installed on the Hubble Space Telescope.Our sample is composed of 20 z850-dropouts(four new discoveries),15 Y105-dropouts(nine new discoveries)and 20 J125-dropouts(all new discoveries).The surface densities of the z850-dropouts are close to what was predicted by earlier studies,however,those of the Y105-and J125-dropouts are quite unexpected.While no Y105-or J125-dropouts have been found at AB < 28.0 mag,their surface densities seem to increase sharply at fainter levels.While some of these candidates seem to be close to foreground galaxies and thus could possibly be gravitationally lensed,the overall surface densities after excluding such cases are still much higher than what would be expected if the luminosity function does not evolve from z~7 to 10.Motivated by such steep increases,we tentatively propose a set of Schechter function parameters to describe the luminosity functions at z ≈ 8 and 10.As compared to their counterpart at z ≈ 7,here L*decreases by a factor demanded by the existing observations,they are allowed and seem to agree with the data better than other alternatives.If these luminosity functions are still valid beyond our current detection limit,this would imply a sudden emergence of a large number of low-luminosity galaxies when looking back in time to z ≈ 10,which,while seemingly exotic,would naturally fit in the picture of the cosmic hydrogen reionization.These early galaxies could easily account for the ionizing photon budget required by the reionization,and they would imply that the global star formation rate density might start from a very high value at z ≈ 10,rapidly reach the minimum at z ≈ 7,and start to rise again towards z ≈ 6.In this scenario,the majority of the stellar mass that the universe assembled through the reionization epoch seems still undetected by current observations at z ≈ 6. 相似文献
128.
Spartina alterniflora leaf litter bundles were placed in a North Carolina salt marsh to study the effects of environmental heterogeneity on decomposition and animal colonization. Sediment type (mud vs. sand), tidal inundation zone (near bay, mid-marsh and upper marsh) and Spartina growth form (tall vs. short) were studied. Tidal zone had the greatest effect on decomposition rate. The main effects of sediment type and growth form were not significant. All treatments affected animal distribution patterns in the leaf bundles. Nearly all common taxa were more common on mud than sand. Most taxa showed a strong association with one tidal zone. Half of the taxa were associated with one of the Spartina growth forms. Many interactions among the treatments were also significant.This study demonstrates the significance of environmental heterogeneity in a Spartina marsh both for litter decomposition and animal distributions. 相似文献
129.
Subsistence in coastal fisheries policy: What's in a word? 总被引:1,自引:2,他引:1
Consideration of subsistence fishing activities seems particularly relevant to coastal fisheries policy, yet formal recognition of subsistence fishing is often absent from associated policy frameworks. A critical problem is the very meaning of the term “subsistence.” A review of the literature on subsistence, dominated until recently by North American research, reveals a schism between interpretations emphasizing material aspects of subsistence and interpretations highlighting cultural aspects. The North American literature on the subject is heavily influenced by a focus on Arctic indigenous populations emphasizing cultural survival. Ultimately, subsistence can be a matter of survival in the belly, the soul, or both. International case studies suggest that different interpretations of subsistence are appropriate in different circumstances, and that appropriate policy can be fashioned only after the local context of subsistence is understood. 相似文献
130.
Domain choice in an experimental nested modeling prediction system for South America 总被引:1,自引:0,他引:1
S. A. Rauscher A. Seth J.-H. Qian S. J. Camargo 《Theoretical and Applied Climatology》2006,86(1-4):229-246
Summary The purposes of this paper are to evaluate the new version of the regional model, RegCM3, over South America for two test
seasons, and to select a domain for use in an experimental nested prediction system, which incorporates RegCM3 and the European
Community-Hamburg (ECHAM) general circulation model (GCM). To evaluate RegCM3, control experiments were completed with RegCM3
driven by both the NCEP/NCAR Reanalysis (NNRP) and ECHAM, using a small control domain (D-CTRL) and integration periods of
January–March 1983 (El Ni?o) and January–March 1985 (La Ni?a). The new version of the regional model captures the primary
circulation and rainfall differences between the two years over tropical and subtropical South America. Both the NNRP-driven
and ECHAM-driven RegCM3 improve the simulation of the Atlantic intertropical convergence zone (ITCZ) compared to the GCM.
However, there are some simulation errors. Irrespective of the driving fields, weak northeasterlies associated with reduced
precipitation are observed over the Amazon. The simulation of the South Atlantic convergence zone is poor due to errors in
the boundary condition forcing which appear to be amplified by the regional model.
To select a domain for use in an experimental prediction system, sensitivity tests were performed for three domains, each
of which includes important regional features and processes of the climate system. The domain sensitivity experiments were
designed to determine how domain size and the location of the GCM boundary forcing affect the regional circulation, moisture
transport, and rainfall in two years with different large scale conditions. First, the control domain was extended southward
to include the exit region of the Andes low level jet (D-LLJ), then eastward to include the South Atlantic subtropical high
(D-ATL), and finally westward to include the subsidence region of the South Pacific subtropical high and to permit the regional
model more freedom to respond to the increased resolution of the Andes Mountains (D-PAC). In order to quantify differences
between the domain experiments, measures of bias, root mean square error, and the spatial correlation pattern were calculated
between the model results and the observed data for the seasonal average fields. The results show the GCM driving fields have
remarkable control over the RegCM3 simulations. Although no single domain clearly outperforms the others in both seasons,
the control domain, D-CTRL, compares most favorably with observations. Over the ITCZ region, the simulations were improved
by including a large portion of the South Atlantic subtropical high (D-ATL). The methodology presented here provides a quantitative
basis for evaluating domain choice in future studies. 相似文献