Influences of climate change on California and Nevada regions revealed by a high-resolution dynamical downscaling study     

Lin-Lin Pan  Shu-Hua Chen  Dan Cayan  Mei-Ying Lin  Quinn Hart  Ming-Hua Zhang  Yubao Liu  Jianzhong Wang 《Climate Dynamics》2011,37(9-10):2005-2020

In this study, the influence of climate change to California and Nevada regions was investigated through high-resolution (4-km grid spacing) dynamical downscaling using the WRF (Weather Research & Forecasting) model. The dynamical downscaling was performed to both the GFS (Global forecast model) reanalysis (called GFS-WRF runs) from 2000?C2006 and PCM (Parallel Climate Model) simulations (called PCM-WRF runs) from 1997?C2006 and 2047?C2056. The downscaling results were first validated by comparing current model outputs with the observational analysis PRISM (Parameter-elevation Regressions on Independent Slopes Model) dataset. In general, the dominant features from GFS-WRF runs and PCM-WRF runs were consistent with each other, as well as with PRISM results. The influences of climate change on the California and Nevada regions can be inferred from the model future runs. The averaged temperature showed a positive trend in the future, as in other studies. The temperature increases by around 1?C2°C under the assumption of business as usual over 50?years. This leads to an upward shifting of the freezing level (the contour line of 0°C temperature) and more rain instead of snow in winter (December, January, and February). More hot days (>32.2°C or 90°F) and extreme hot days (>37.8°C or 100°F) are predicted in the Sacramento Valley and the southern parts of California and Nevada during summer (June, July, and August). More precipitation is predicted in northern California but not in southern California. Rainfall frequency slightly increases in the coast regions, but not in the inland area. No obvious trend of the surface wind was indicated. The probability distribution functions (PDF) of daily temperature, wind and precipitation for California and Nevada showed no significant change in shape in either winter or summer. The spatial distributions of precipitation frequency from GFS-WRF and PCM-WRF were highly correlated (r?=?0.83). However, overall positive shifts were seen in the temperature field; increases of 2°C for California and 3°C for Nevada in summer and 2.5°C for California and 1.5°C for Nevada in winter. The PDFs predicted higher precipitation in winter and lower precipitation in the summer for both California and Nevada.  相似文献   

Middle Eocene diatoms from Whitecliff Bay, Isle of Wight, England: stratigraphy and preservation     

Alex De Jonghe  Malcolm B. Hart  Stephen T. Grimes  Alex G. Mitlehner  Gregory D. Price  Christopher W. Smart 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(3):472-483

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The initial impact of the tobacco buyout program     

Hart JF 《Geographical review》2011,101(3):447-457

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Venus Express observations of ULF and ELF waves in the Venus ionosphere: Wave properties and sources     

C.T. Russell  H. Leinweber  R.A. Hart  H.Y. Wei  R.J. Strangeway  T.L. Zhang 《Icarus》2013

Electrical activity in a planetary atmosphere enables chemical reactions that are not possible under conditions of local thermodynamic equilibrium. In both the Venus and terrestrial atmospheres, lightning forms nitric oxide. Despite the existence of an inventory of NO at Venus like the Earth’s, and despite observations of the signals expected from lightning at optical, VLF, and ELF frequencies, the existence of Venus lightning still is met with some skepticism. The Venus Express mission was equipped with a fluxgate magnetometer gradiometer system sampling at rates as high as 128 Hz, and making measurements as low as 200 km altitude above the north polar regions of Venus. However, significant noise levels are present on the Venus Express spacecraft. Cleaning techniques have been developed to remove spacecraft interference at DC, ULF, and ELF frequencies, revealing two types of electromagnetic waves, a transverse right-handed guided mode, and a linearly polarized compressional mode. The propagation of both types of signals is sensitive to the magnetic field in ways consistent with propagation from a distant source to the spacecraft. The linearly polarized compressional waves generally are at lower frequencies than the right-handed transverse waves. They appear to be crossing the usually horizontal magnetic field. At higher frequencies above the lower hybrid frequency, waves cannot enter the ionosphere from below when the field is horizontal. The arrival of signals at the spacecraft is controlled by the orientation of the magnetic field. When the field dips into the atmosphere, the higher frequency guided mode above the lower hybrid frequency can enter the ionosphere by propagating along the magnetic field in the whistler mode. These properties are illustrated with examples from five orbits during Venus Express’ first year in orbit. These properties observed are consistent with the linearly polarized compressional waves being produced at the solar wind interface and the transverse guided waves being produced in the atmosphere.  相似文献   

Petrogenesis of Sierra Nevada plutons inferred from the Sr, Nd, and O isotopic signatures of mafic igneous complexes in Yosemite Valley, California     

Wendy R. Nelson  Michael J. Dorais  Eric H. Christiansen  Garret L. Hart 《Contributions to Mineralogy and Petrology》2013,165(2):397-417

Mafic complexes in the central Sierra Nevada batholith record valuable geochemical information regarding the role mafic magmas play in arc magmatism and the generation of continental crust. In the intrusive suite of Yosemite Valley, major and trace element compositions of the hornblende-bearing gabbroic rocks from the Rockslides mafic complex and of the mafic dikes in the North America Wall are compositionally similar to high-alumina basalt. Of these rocks, two samples have higher Ni and Cr abundances as well as higher ε_Nd values than previously recognized for the intrusive suite. Plagioclase crystals in rocks from the North America Wall and the Rockslides have prominent calcic cores and sharply defined sodic rims, a texture commonly associated with mixing of mafic and felsic magmas. In situ analyses of ⁸⁷Sr/⁸⁶Sr in plagioclase show no significant isotopic difference from the cores to the rims of these grains. We propose that the high ⁸⁷Sr/⁸⁶Sr (~0.7067) and low ε_Nd (~?3.4) of bulk rocks, the homogeneity of ⁸⁷Sr/⁸⁶Sr in plagioclase, and the high δ¹⁸O values of bulk rocks (6.6–7.3 ‰) and zircon (Lackey et al. in J Petrol 49:1397–1426, 2008) demonstrate that continental crust was assimilated into the sublithospheric mantle-derived basaltic precursors of the mafic rocks in Yosemite Valley. Contamination (20–40 %) likely occurred in the lower crust as the magma differentiated to high-alumina basalt prior to plagioclase (and zircon) crystallization. As a consequence, the isotopic signatures recorded by whole rocks, plagioclase, and zircon do not represent the composition of the underlying lithospheric mantle. We conclude that the mafic and associated felsic members of the intrusive suite of Yosemite Valley represent 60–80 % new additions to the crust and include significant quantities of recycled ancient crust.  相似文献   

Lithium isotope systematics of lavas from the Cook–Austral Islands: Constraints on the origin of HIMU mantle     

Lui-Heung Chan  John C. Lassiter  Erik H. Hauri  Stanley R. Hart  Jerzy Blusztajn 《Earth and Planetary Science Letters》2009,277(3-4):433-442

Radiogenic isotope variations in lavas from the Cook–Austral volcanic chain have delineated three distinct mantle sources: a HIMU component, a depleted component (DM), and an enriched component (EM). To better constrain the mantle sources for South Pacific hot spot volcanism, we determined lithium isotopic compositions of lavas from Raivavae, Rapa, Mangaia and Tubuai of the volcanic chain. The study includes whole rock and mineral analyses. In general, δ⁷Li of most olivines resemble bulk rock composition whereas clinopyroxenes are variably lighter. This implies that clinopyroxene is more susceptible to diffusion-induced fractionation, in agreement with previous studies. Olivine δ⁷Li values span a narrower range than whole rock values, and do not extend to the very heavy compositions previously reported in HIMU bulk lavas. This discrepancy likely reflects alteration of bulk lavas, and suggests that Li-isotope analyses of bulk lavas should be interpreted with caution. Olivines from HIMU lavas have heavy δ⁷Li values (up to 6.2‰), and extend beyond the range reported for fresh MORB. Correlations between Li-isotopes and radiogenic isotopes suggest that the heavy δ⁷Li values in HIMU olivines are a source characteristic and not the result of post-magmatic alteration. Although the Li-isotope composition of recycled, dehydrated oceanic crust is currently under debate, our results suggest that HIMU lavas derive from a source containing recycled dehydrated oceanic crust, and that the “heavy” Li-isotope signature of altered oceanic crust is partially preserved during passage through the subduction factory.  相似文献   

Late Pleistocene to Holocene sedimentation and hydrocarbon seeps on the continental shelf of a steep,tectonically active margin,southern California,USA   总被引：1，自引：0，他引：1  

Amy E. Draut  Patrick E. Hart  Thomas D. Lorenson  Holly F. Ryan  Florence L. Wong  Ray W. Sliter  James E. Conrad 《Marine Geophysical Researches》2009,30(3):193-206

Small, steep, uplifting coastal watersheds are prolific sediment producers that contribute significantly to the global marine sediment budget. This study illustrates how sedimentation evolves in one such system where the continental shelf is largely sediment-starved, with most terrestrial sediment bypassing the shelf in favor of deposition in deeper basins. The Santa Barbara–Ventura coast of southern California, USA, is considered a classic area for the study of active tectonics and of Tertiary and Quaternary climatic evolution, interpretations of which depend upon an understanding of sedimentation patterns. High-resolution seismic-reflection data over >570 km² of this shelf show that sediment production is concentrated in a few drainage basins, with the Ventura and Santa Clara River deltas containing most of the upper Pleistocene to Holocene sediment on the shelf. Away from those deltas, the major factor controlling shelf sedimentation is the interaction of wave energy with coastline geometry. Depocenters containing sediment 5–20 m thick exist opposite broad coastal embayments, whereas relict material (bedrock below a regional unconformity) is exposed at the sea floor in areas of the shelf opposite coastal headlands. Locally, natural hydrocarbon seeps interact with sediment deposition either to produce elevated tar-and-sediment mounds or as gas plumes that hinder sediment settling. As much as 80% of fluvial sediment delivered by the Ventura and Santa Clara Rivers is transported off the shelf (some into the Santa Barbara Basin and some into the Santa Monica Basin via Hueneme Canyon), leaving a shelf with relatively little recent sediment accumulation. Understanding factors that control large-scale sediment dispersal along a rapidly uplifting coast that produces substantial quantities of sediment has implications for interpreting the ancient stratigraphic record of active and transform continental margins, and for inferring the distribution of hydrocarbon resources in relict shelf deposits.  相似文献   

Gases and trace elements in soils at the North Silver Bell deposit, Pima County, Arizona — Discussion     

C.R.M. Butt  M.K.W. Hart  M.J. Gole 《Journal of Geochemical Exploration》1985,24(1):129-134

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Subglacial comminution in the deforming bed: Inferences from SEM analysis     

Kathryn C. Rose  Jane K. Hart 《Sedimentary Geology》2008,203(1-2):87-97

This study investigates the variations in erosional processes beneath Briksdalsbreen; a Norwegian valley glacier, with a thin coarse grained deforming bed. The subglacial zone was investigated in situ, close to the central glacial flow line (Site A) and close to the valley wall (Site B), via boreholes. The till was collected using two different sediment samplers and the bed was examined using a borehole video camera. In order to evaluate how representative borehole sampling was of the subglacial environment, the results from in situ subglacial samples were compared with random samples taken from an exposed subglacial surface in the glacier foreland, as well as a sample taken from the site after glacier retreat. The results indicated that the texture of the exposed subglacial surface was similar to in situ samples from subglacial Site B (close to the valley wall), and that the samples collected with the ‘small’ sediment sampler had the closest fit. SEM analysis revealed eroded quartz grains at both sites as a result of rotation (abrasion) and fracture. The samples from close to the valley wall were very poorly sorted, with evidence for rounding and preservation of pre-weathered surfaces, which suggest that a relatively simple pattern of erosion from crushing to rotation dominated. However, the till from the centre of the glacier was better sorted, more angular, and with few pre-weathered surfaces. We suggest that this results from a more complex glacial erosional history associated with greater strain and longer residence time within the deforming layer. When compared with other deformation tills, it was confirmed that there is a relationship between grain size and erosional style. Clay-rich tills show little comminution, fine sand-rich tills generate a significant silt component, whilst the coarse sand-rich tills at Briksdalsbreen showed complex deformational styles but no significant silt component.  相似文献   

THE IMPACT OF A DIAGNOSTIC CLOUD SCHEME ON FORECASTS WITH A GLOBAL ATMOSPHERE MODEL          下载免费PDF全文

T. L. Hart  Zheng Qinglin  W. Bourke 《Acta Meteorologica Sinica》1990,4(1):38-50

Experiments were conducted to test the impact of a cloud diagnosis scheme in place of prescribed zonalaverage cloud on medium and long range integrations with the Australian Bureau of Meteorology ResearchCentre(BMRC)global atmosphere model.The cloud scheme was shown to improve the temperature bias inthe lower troposphere but there was deterioration in the upper troposphere,especially in the tropics,asso-ciated with underestimation of high cloud amount.Thirty day mean fields in a January integration showed greater amplitude in the Northern Hemisphereplanetary waves and a deeper Antarctic circumpolar trough than the control experiment or a simulation withno cloud.The results for the diagnosed cloud case agree more closely with corresponding observed fields.There was also some reduction in the zonal average zonal wind component reflecting the additional zonalasymmetry introduced by the diagnostic cloud scheme.Similar trends were also noted in medium and longrange forecasts for January and July conditions,although the impact on predictive skill was slight and insome cases detrimental.Areas for improving the diagnostic cloud scheme are noted.  相似文献