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排序方式: 共有347条查询结果,搜索用时 15 毫秒
121.
Rebecca E. Eager Sethu Raman Teddy R. Holt Douglas Westphal Jeffrey Reid Jason Nachamkin Ming Liu Abdulla Al Mandoos 《Pure and Applied Geophysics》2007,164(8-9):1747-1764
A statistical evaluation of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) was performed over the Arabian Gulf region for the period, 1 August to 5 October, 2004. Verification skill scores of bias and root-mean-square error were estimated for surface variables and for vertical profiles to investigate any diurnal variations. The model predictions of boundary-layer heights are compared with the observations at Abu Dhabi, United Arab Emirates. The Middle East presents challenges to numerical weather prediction due to complex land-ocean-land mesoscale processes. An independent data set of surface measurements from 50 stations in the UAE was available from the Department of Water Resources Studies, Abu Dhabi for model verification. The results indicate a diurnal variation in the model errors. The errors are small considering the magnitudes of the observed variables. Errors in the coastal region can be attributed to the differences in the timing of the onset of sea and land breeze circulations in the simulations as compared to the observations. Errors are relatively smaller in the offshore locations. 相似文献
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How much does dry‐season fog matter? Quantifying fog contributions to water balance in a coastal California watershed
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The seasonally‐dry climate of Northern California imposes significant water stress on ecosystems and water resources during the dry summer months. Frequently during summer, the only water inputs occur as non‐rainfall water, in the form of fog and dew. However, due to spatially heterogeneous fog interaction within a watershed, estimating fog water fluxes to understand watershed‐scale hydrologic effects remains challenging. In this study, we characterized the role of coastal fog, a dominant feature of Northern Californian coastal ecosystems, in a San Francisco Peninsula watershed. To monitor fog occurrence, intensity, and spatial extent, we focused on the mechanisms through which fog can affect the water balance: throughfall following canopy interception of fog, soil moisture, streamflow, and meteorological variables. A stratified sampling design was used to capture the watershed's spatial heterogeneities in relation to fog events. We developed a novel spatial averaging scheme to upscale local observations of throughfall inputs and evapotranspiration suppression and make watershed‐scale estimates of fog water fluxes. Inputs from fog water throughfall (10–30 mm/year) and fog suppression of evapotranspiration (125 mm/year) reduced dry‐season water deficits by 25% at watershed scales. Evapotranspiration suppression was much more important for this reduction in water deficit than were direct inputs of fog water. The new upscaling scheme was analyzed to explore the sensitivity of its results to the methodology (data type and interpolation method) employed. This evaluation suggests that our combination of sensors and remote sensing allows an improved incorporation of spatially‐averaged fog fluxes into the water balance than traditional interpolation approaches. 相似文献
124.
Stefan Jung Soenke Brandt Rebecca Bast Erik E. Scherer Jasper Berndt 《Journal of Metamorphic Geology》2019,37(1):41-69
Migmatites comprise a minor volume of the high‐grade part of the Damara orogen of Namibia that is dominated by granite complexes and intercalated metasedimentary units. Migmatites of the Southern Central Zone of the Damara orogen consist of melanosomes with garnet+cordierite+biotite+K‐feldspar, and leucosomes, which are sometimes garnet‐ and cordierite‐bearing. Field evidence, petrographic observations, and pseudosection modelling suggest that, in contrast to other areas where intrusion of granitic magmas is more important, in situ partial melting of metasedimentary units was the main migmatite generation processes. Pseudosection modelling and thermobarometric calculations consistently indicate that the peak‐metamorphic grade throughout the area is in the granulite facies (~5 kbar at ~800°C). Cordierite coronas around garnet suggest some decompression from peak‐metamorphic conditions and rare andalusite records late, near‐isobaric cooling to <650°C at low pressures of ~3 kbar. The inferred clockwise P–T path is consistent with minor crustal thickening through continent–continent collision followed by limited post‐collisional exhumation and suggests that the granulite facies terrane of the Southern Central Zone of the Damara orogen formed initially in a metamorphic field gradient of ~35–40°C/km at medium pressures. New high‐precision Lu–Hf garnet‐whole rock dates are 530 ± 13 Ma, 522.0 ± 0.8 Ma, 520.8 ± 3.6 Ma, and 500.3 ± 4.3 Ma for the migmatites that record temperatures of ~800°C. This indicates that high‐grade metamorphism lasted for c. 20–30 Ma, which is compatible with previous estimates using Sm–Nd garnet‐whole rock systematics. In previous studies on Damara orogen migmatites where both Sm–Nd and Lu–Hf chronometers have been applied, the dates (c. 520–510 Ma) agree within their small uncertainties (0.6–0.8% for Sm–Nd and 0.1–0.2% for Lu–Hf). This implies rapid cooling after high‐grade conditions and, by implication, rapid exhumation at that time. The cause of the high geothermal gradient inferred from the metamorphic conditions is unknown but likely requires some extra heat that was probably added by intrusion of magmas from the lithospheric mantle, i.e., syenites that have been recently re‐dated at c. 545 Ma. Some granites derived from the lower crust at c. 545 Ma are the outcome rather than the cause of high‐T metamorphism. In addition, high contents of heat‐producing elements K, Th, and U may have raised peak temperatures by 150–200°C at the base of the crust, resulting in the widespread melting of fertile crustal rocks. The continuous gradation from centimetre‐scale leucosomes to decametre‐scale leucogranite sheets within the high‐grade metamorphic zone suggests that leucosome lenses coalesced to form larger bodies of anatectic leucogranites, thereby documenting a link between high‐grade regional metamorphism and Pan‐African magmatism. In view of the close association of the studied high‐T migmatites with hundreds of synmetamorphic high‐T granites that invaded the terrane as metre‐ to decametre‐wide sills and dykes, we postulate that crystallization of felsic lower crustal magma is, at least partly, responsible for heat supply. Late‐stage isobaric cooling of these granites may explain the occurrence of andalusite in some samples. 相似文献
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Malick Wade Guy Caniaux Yves duPenhoat Marcus Dengler Hervé Giordani Rebecca Hummels 《Ocean Dynamics》2011,61(1):1-20
A one-dimensional model is used to analyze, at the local scale, the response of the equatorial Atlantic Ocean under different
meteorological conditions. The study was performed at the location of three moored buoys of the Pilot Research Moored Array
in the Tropical Atlantic located at 10° W, 0° N; 10° W, 6° S; and 10° W, 10° S. During the EGEE-3 (Etude de la circulation
océanique et de sa variabilité dans le Golfe de Guinee) campaign of May–June 2006, each buoy was visited for maintenance during
2 days. On board the ship, high-resolution atmospheric parameters were collected, as were profiles of temperature, salinity,
and current. These data are used here to initialize, force, and validate a one-dimensional model in order to study the diurnal
oceanic mixed-layer variability. It is shown that the diurnal variability of the sea surface temperatures is mainly driven
by the solar heat flux. The diurnal response of the near-surface temperatures to daytime heating and nighttime cooling has
an amplitude of a few tenths of degree. The computed diurnal heat budget experiences a net warming tendency of 31 and 27 W m−2 at 0° N and 10° S, respectively, and a cooling tendency of 122 W m−2 at 6° S. Both observed and simulated mixed-layer depths experience a jump between the nighttime convection phase and the
well-stabilized diurnal water column. Its amplitude changes dramatically depending on the meteorological conditions occurring
at the stations and reaches its maximum amplitude (~50 m) at 10° S. At 6° and 10° S, the presence of barrier layers is observed,
a feature that is clearer at 10° S. Simulated turbulent kinetic energy (TKE) dissipation rates, compared to independent microstructure
measurements, show that the model tracks their diurnal evolution reasonably well. It is also shown that the shear and buoyancy
productions and the vertical diffusion of TKE all contribute to the supply of TKE, but the buoyancy production is the main
source of TKE during the period of the simulation. 相似文献
130.
Autumn J. Oczkowski F. Graham Lewis Scott W. Nixon H. Lee Edmiston Rebecca S. Robinson Jeffrey P. Chanton 《Estuaries and Coasts》2011,34(5):993-1005
Apalachicola Bay lies at the mouth of the Apalachicola River, where seasonally variable freshwater inflows and shifting winds
have long been thought to contribute to the support of an unusually productive and commercially important oyster fishery.
Links between the river and productivity have been shown to lie in salinity-induced reductions in oyster predators and oyster
disease as well as organic supplements from an extensive floodplain. Several studies have also indicated that nitrogen (N)
and phosphorous (P) carried by the river are important in fertilization of bay primary production. While there is concern
that upstream water withdrawals may impact the fishery, the importance of riverine N to oyster diets remains unclear. We measured
N and carbon (C) stable isotopes (δ15N, δ13C) in macroalgae, surface-water nitrate, and surface sediments, which showed a gradient from enriched riverine δ15N values to more depleted values in the Gulf of Mexico. In contrast, δ13C of particulate matter is depleted in the river and enriched offshore. Oyster stable isotope values throughout Apalachicola
Bay are more complex, but are dominated by freshwater inputs and reflect the variability and hydrodynamics of the riverine
inflows. 相似文献