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D. Lu L. White R. S. Reddy P. J. Croft J. M. Medlin 《Meteorology and Atmospheric Physics》2006,94(1-4):153-165
Summary A numerical mesoscale model (COAMPS) is used to study some of the features associated with the evolution of the kinematic,
thermodynamic, and physical structure of the Alabama sea and bay breeze circulations and convections in weak shear environments
based on five cases from Medlin and Croft (1998). The general and expected features and evolution of sea and bay breeze circulations
are captured by the model simulations, including horizontal and vertical wind shifts, thermal contrast between land and water
surface, vertical stability over water and land, return currents and moisture increase. The relationship of the circulations
to specific synoptic flow regimes and local physiographic features was investigated. The sea breeze triggered convective cells
are confirmed to have a preferred location according to the flow regime and local conditions. This result can assist the forecasters
in understanding the anticipated convective cell initiation and development on a given day as related to sea and bay breeze
cells as well as improve the short-term forecast accuracy of the location of thunderstorm initiation based on routine observations
and subsequent convective activity. If local NWS office model a selective subset of cases then they can better visualize and
forecast those cases operationally. 相似文献
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Croft William Lee Shi Wei Sack Jörg-Rüdiger Corriveau Jean-Pierre 《Journal of Geographical Systems》2017,19(3):221-248
Journal of Geographical Systems - Given the large volumes of detailed data now being collected, there is a high demand for the release of this data for research purposes. In particular,... 相似文献
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Enrique Gaztañaga Rupert A. C. Croft 《Monthly notices of the Royal Astronomical Society》1999,309(4):885-904
We present predictions for the one-point probability distribution and cumulants of the transmitted QSO flux in the high redshift Lyman- α forest. We make use of the correlation between the Lyman- α optical depth and the underlying matter density predicted by gravitational instability theory and seen in numerical hydrodynamic simulations. We have modelled the growth of matter fluctuations using the non-linear shear‐free dynamics, an approximation which reproduces well the results of perturbation theory for the cumulants in the linear and weakly non-linear clustering regime. As high matter overdensities tend to saturate in spectra, the statistics of the flux distribution are dominated by weakly non-linear overdensities. As a result, our analytic approach can produce accurate predictions, when tested against N -body simulation results, even when the underlying matter field has root-mean-square fluctuations larger than unity. Our treatment can be applied to either Gaussian or non-Gaussian initial conditions. Here we concentrate on the former case, but also include a study of a specific non-Gaussian model. We discuss how the methods and predictions we present can be used as a tool to study the generic clustering properties of the Lyman- α forest at high redshift. With such an approach, rather than concentrating on simulating specific cosmological models, we may be in a position to directly test our assumptions for the Gaussian nature of the initial conditions, and the gravitational instability origin of structure itself. In a separate paper we present results for two-point statistics. 相似文献
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Duanjun Lu L. White R. S. Reddy Quinton L. Williams Paul J. Croft 《Meteorology and Atmospheric Physics》2011,111(3-4):75-90
Three models, MM5, COAMPS, and WRF, have been applied for the warm season in 2003 and the cool season in 2003?C2004 to evaluate their performances. All models run over the same domain area covering the north Gulf Mexico and southeastern United States (US) region with the same spatial resolution of 27?km. It was found that the temporal variations of the mean error distribution and strength at 24 and 36?h were rather weak for surface temperature, sea level pressure, and surface wind speed for all models. A warm bias in surface temperature forecasts dominated over land during the warm season, whereas a cool bias existed during the cool season. The MM5 and WRF produced negative biases of sea level pressure during the warm season and positive biases during the cool season while the COAMPS yielded a similar distribution of sea level pressure biases during both seasons. During both seasons, similar surface wind speed biases produced by each model included a high wind speed forecast over most areas by MM5 while the COAMPS and WRF yielded weak surface winds over the western Plains and stronger surface winds over the eastern Plains. Root-mean-squared errors revealed that the forecast of surface temperature, sea level pressure, and surface wind speed were degraded with the increase of forecast time. For rainfall evaluation, it was found that the MM5 underpredicted seasonal precipitation while the COAMPS and WRF overpredicted. The bias scores revealed that the MM5 yielded an underprediction of the coverage of precipitation areas, especially for heavier rainfall events. The MM5 presented the lower threat score at lighter rainfall events compared to the COAMPS and WRF. For moderate and heavier thresholds, all models lacked forecast accuracy. The WRF accuracy in predicting precipitation was heavily dependent upon the performance of the selected cumulus parameterization scheme. Use of the Grell?CDevenyi and Bette?CMiller?CJanjic schemes helps suppress precipitation overprediction. 相似文献
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Gabriel Altay Jörg M. Colberg Rupert A. C. Croft 《Monthly notices of the Royal Astronomical Society》2006,370(3):1422-1428
Alignments of galaxy clusters (the Binggeli effect), as well as of galaxies themselves have long been studied both observationally and theoretically. Here, we test the influence of large-scale structures and tidal fields on the shapes and alignments of cluster-size and galaxy-size dark matter haloes. We use a high-resolution N -body simulation of a Λ cold dark matter (ΛCDM) universe, together with the results of Colberg, Krughoff & Connolly, who identified filaments connecting pairs of clusters. We find that cluster pairs connected by a filament are strongly aligned with the cluster–cluster axis, whereas unconnected ones are not. For smaller, galaxy-size haloes, there also is an alignment signal, but its strength is independent of whether the halo is part of an obvious large-scale structure. Additionally, we find no measurable dependence of galaxy halo shape on membership of a filament. We also quantify the influence of tidal fields and find that these do correlate strongly with alignments of haloes. The alignments of most haloes are thus caused by tidal fields, with cluster-size haloes being strongly aligned through the added mechanism of infall of matter from filaments. 相似文献
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Young-Rae Kim Rupert A. C. Croft 《Monthly notices of the Royal Astronomical Society》2008,387(1):377-386
Using cosmological hydrodynamic simulations, we measure the mean transmitted flux in the Lyα forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel quasar separation distance can be fitted using a simple power-law form including the usual correlation function parameters r 0 and γ, so that . From the simulations, we find the relation between r 0 and quasar host mass, and formulate this as a way to estimate quasar host dark matter halo masses, quantifying uncertainties due to cosmological and IGM parameters, and redshift errors. With this method, we examine data for ∼9000 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 5, assuming that the effect of ionizing radiation from quasars (the so-called transverse proximity effect) is unimportant (no evidence for it is seen in the data). We find that the best-fitting host halo mass for SDSS quasars with mean redshift z = 3 and absolute G -band magnitude −27.5 is log M /M⊙ = 12.68+0.81 −0.67 . We also use the Lyman-Break Galaxy (LBG) and Lyα forest data of Adelberger et al. in a similar fashion to constrain the halo mass of LBGs to be log10 M /M⊙ = 11.41+0.54 −0.59 , a factor of ∼20 lower than the bright quasars. In addition, we study the redshift distortions of the Lyα forest around quasars, using the simulations. We use the quadrupole to monopole ratio of the quasar Lyα forest correlation function as a measure of the squashing effect. We find its dependence on halo mass difficult to measure, but find that it may be useful for constraining cosmic geometry. 相似文献
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The United States has the world’s largest coal reserves and Montana the highest potential for mega-mine development. Consequently,
a large-scale effort to convert coal to liquids (CTL) has been proposed to create a major source of domestic transportation
fuels from coal, and some prominent Montanans want to be at the center of that effort. We calculate that the energy efficiency
of the best existing Fischer–Tropsch (FT) process applied to average coal in Montana is less than 1/2 of the corresponding
efficiency of an average crude oil refining process. The resulting CO2 emissions are 20 times (2000%) higher for CTL than for conventional petroleum products. One barrel of the FT fuel requires
roughly 800 kg of coal and 800 kg of water. The minimum energy cost of subsurface CO2 sequestration would be at least 40% of the FT fuel energy, essentially halving energy efficiency of the process. We argue
therefore that CTL conversion is not the most valuable use for the coal, nor will it ever be, as long as it is economical
to use natural gas for electric power generation. This finding results from the low efficiency inherent in FT synthesis, and
is independent of the monumental FT plant construction costs, mine construction costs, acute lack of water, and the associated
environmental impacts for Montana.
相似文献
| Tad W. PatzekEmail: |