An Intercomparison of Large-Eddy Simulations of the Stable Boundary Layer   总被引：2，自引：27，他引：2  

Robert J. Beare  Malcolm K. Macvean  Albert A. M. Holtslag  Joan Cuxart  Igor Esau  Jean-Christophe Golaz  Maria A. Jimenez  Marat Khairoutdinov  Branko Kosovic  David Lewellen  Thomas S. Lund  Julie K. Lundquist  Anne Mccabe  Arnold F. Moene  Yign Noh  Siegfried Raasch  Peter Sullivan 《Boundary-Layer Meteorology》2006,118(2):247-272

Results are presented from the first intercomparison of large-eddy simulation (LES) models for the stable boundary layer (SBL), as part of the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study initiative. A moderately stable case is used, based on Arctic observations. All models produce successful simulations, in as much as they generate resolved turbulence and reflect many of the results from local scaling theory and observations. Simulations performed at 1-m and 2-m resolution show only small changes in the mean profiles compared to coarser resolutions. Also, sensitivity to subgrid models for individual models highlights their importance in SBL simulation at moderate resolution (6.25 m). Stability functions are derived from the LES using typical mixing lengths used in numerical weather prediction (NWP) and climate models. The functions have smaller values than those used in NWP. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL.  相似文献   

Titanium isotopic compositions of well‐characterized silicon carbide grains from Orgueil (CI): Implications for s‐process nucleosynthesis     

Gary R. Huss  Julie B. Smith 《Meteoritics & planetary science》2007,42(7-8):1055-1075

Abstract— We have measured the titanium isotopic compositions of 23 silicon carbide grains from the Orgueil (CI) carbonaceous chondrites for which isotopic compositions of silicon, carbon, and nitrogen and aluminum‐magnesium systematics had been measured previously. Using the 16 most‐precise measurements, we estimate the relative contributions of stellar nucleosynthesis during the asymptotic giant branch (AGB) phase and the initial compositions of the parent stars to the compositions of the grains. To do this, we compare our data to the results of several published stellar models that employ different values for some important parameters. Our analysis confirms that s‐process synthesis during the AGB phase only slightly modified the titanium compositions in the envelopes of the stars where mainstream silicon carbide grains formed, as it did for silicon. Our analysis suggests that the parent stars of the >1 μm silicon carbide grains that we measured were generally somewhat more massive than the Sun (2–3 M_⊙) and had metallicities similar to or slightly higher than solar. Here we differ slightly from results of previous studies, which indicated masses at the lower end of the range 1.5–3 M_⊙ and metallicities near solar. We also conclude that models using a standard ¹³C pocket, which produces a good match for the main component of s‐process elements in the solar system, overestimate the contribution of the ¹³C pocket to s‐process nucleosynthesis of titanium found in silicon carbide grains. Although previous studies have suggested that the solar system has a significantly different titanium isotopic composition than the parent stars of silicon carbide grains, we find no compelling evidence that the Sun falls off of the array defined by those stars. We also conclude that the Sun does lie on the low‐metallicity end of the silicon and titanium arrays defined by mainstream silicon carbide grains.  相似文献   

Accumulation,solid partitioning and remobilisation of 99Tc in subtidal and intertidal sediments in the Irish Sea     

Paul Finegan  Luis León Vintró  Peter I. Mitchell  Dominique Boust  Aurélien Gouzy  Peter J. Kershaw  Julie A. Lucey 《Continental Shelf Research》2009,29(16):1995-2010

Recent studies have shown that accumulation of ⁹⁹Tc in seabed sediments labelled by authorised radioactive liquid discharges into the NE Irish Sea from the Sellafield reprocessing complex is greater than previously thought. In this paper, new data on ⁹⁹Tc concentration profiles in subtidal and intertidal sediments from the eastern and western Irish Sea are provided with a view to elucidating the processes responsible for the incorporation and retention of ⁹⁹Tc in the seabed. The data show that substantial amounts of ⁹⁹Tc have accumulated in the fine-grained subtidal sediments off the Cumbrian coast, particularly after increased releases from Sellafield following the commissioning of the Enhanced Actinide Removal Plant (EARP) in 1994. In all the cores taken in this area, ⁹⁹Tc has been found to be present to depths in excess of 30 cm. Analysis of ¹³⁷Cs and ²⁴¹Am profiles, together with other supporting geochemical data, show a high degree of homogenisation of the sediments down to these depths as a result of physical and biological processes, and confirm that incorporation of ⁹⁹Tc into the sediment compartment is actually the result of mixing and reworking, rather than active sediment accumulation. In contrast, active deposition of material transported from this mixed pool of sediment appears to be the dominant mechanism controlling ⁹⁹Tc profiles in intertidal areas close to the Sellafield discharge outfall.Data obtained from the analysis of subtidal sediment cores from the western Irish Sea mud basin suggest that similar mixing processes to those occurring in the subtidal sediments of the eastern Irish Sea are also active in this area. Time-series data on ⁹⁹Tc concentrations in surficial sediments from this basin, gathered in the period 1988–2004, inclusive, show a clear increase in concentrations, by a factor of ～2, between samples collected pre-EARP and post-EARP. The constancy of ⁹⁹Tc concentrations in surface sediments throughout the 1980s and the early-1990s suggests that little redissolution and export of ⁹⁹Tc occurred over this extended period. A similar observation applies to the post-EARP period, when concentrations remained relatively constant despite the reported steady decrease in ⁹⁹Tc concentrations in the overlying waters.This apparent lack of remobilisation is consistent with data from sequential extraction analyses, which indicate that the bulk of the ⁹⁹Tc is strongly bound to non-labile geochemical phases, with only a small proportion associated with exchangeable and acido-soluble phases. Further, these analyses show that ⁹⁹Tc is not associated with oxygen-sensitive and highly-reactive acid-volatile sulphides (AVS) to any significant extent.  相似文献   

Investigation of diurnal and seasonal galactic cosmic ray variations on quiet days in two mid latitude stations     

K.C. Okpala  F.N. Okeke 《Astroparticle Physics》2011,34(12):878-885

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Statistical tests of chondrule sorting     

Seth A. TEITLER  Julie M. PAQUE  Jeffrey N. CUZZI  Robert C. HOGAN 《Meteoritics & planetary science》2010,45(7):1124-1135

Abstract– The variation in sizes of chondrules from one chondrite to the next is thought to be due to some sorting process in the early solar nebula. Hypotheses for the sorting process include chondrule sorting by mass and sorting by some aerodynamic mechanism; one such aerodynamic mechanism is the process of turbulent concentration (TC). We present the results of a series of statistical tests of chondrule data from several different chondrites. The data do not clearly distinguish between various options for the sorting parameter, but we find that the data are inconsistent with being drawn from lognormal or (three‐parameter) Weibull distributions in chondrule radius. We also find that all but one of the chondrule data sets tested are consistent with being drawn from the TC distribution.  相似文献   

Ground-based observations of time variability in multiple active volcanoes on Io     

Julie A. Rathbun  John R. Spencer 《Icarus》2010,209(2):625-630

Since before the beginning of the Galileo spacecraft’s Jupiter orbital tour, we have observed Io from the ground using NASA’s Infrared Telescope Facility (IRTF). We obtained images of Io in reflected sunlight and in-eclipse at 2.3, 3.5, and 4.8 μm. In addition, we have measured the 3.5 μm brightness of an eclipsed Io as it is occulted by Jupiter. These lightcurves enable us to measure the brightness and one-dimensional location of active volcanoes on the surface. During the Galileo era, two volcanoes were observed to be regularly active: Loki and either Kanehekili and/or Janus. At least 12 other active volcanoes were observed for shorter periods of time, including one distinguishable in images that include reflected sunlight. These data can be used to compare volcano types and test volcano eruption models, such as the lava lake model for Loki.  相似文献   

Late Pliocene to Early Quaternary extensional detachment in the La Paz–El Cabo area (Baja California Sur, Mexico): implications on the opening of the Gulf of California and the mechanics of oblique rifting     

Laurent Geoffroy  Julie Pronost 《地学学报》2010,22(1):64-69

We demonstrate that Pliocene to Early Quaternary sedimentary formations in Baja California Sur (Mexico) were deposited syn-tectonically over a major detachment associated with the exhumation of Mesozoic crust. The detachment dips to the ENE and is associated with E–W stretching. This large extensional structure strikes almost parallel to the general trend of the Gulf of California and extension is oblique to the East-Pacific seafloor-spreading direction. Crustal-scale stretching in this area was still active after the beginning of seafloor spreading c.  3.6 Ma ago. The detachment is capped by Late Pleistocene–Holocene alluvial sediments the deposition of which seems to be partly syn-tectonic and controlled by minor stretching subparallel to the present-day North American–Pacific kinematic vector. We discuss the implications of our observations on strain partitioning during opening of the California Gulf as well as on the structure of the Gulf of California margin.  相似文献   

Pattern scaling: Its strengths and limitations,and an update on the latest model simulations     

Claudia Tebaldi  Julie M. Arblaster 《Climatic change》2014,122(3):459-471

We review the ideas behind the pattern scaling technique, and focus on its value and limitations given its use for impact assessment and within integrated assessment models. We present estimates of patterns for temperature and precipitation change from the latest transient simulations available from the Coupled Model Inter-comparison Project Phase 5 (CMIP5), focusing on multi-model mean patterns, and characterizing the sources of variability of these patterns across models and scenarios. The patterns are compared to those obtained from the previous set of experiments, under CMIP3. We estimate the significance of the emerging differences between CMIP3 and CMIP5 results through a bootstrap exercise, while also taking into account the fundamental differences in scenario and model ensemble composition. All in all, the robustness of the geographical features in patterns of temperature and precipitation, when computed as multi-model means, is confirmed by this comparison. The intensity of the change (in both the warmer and cooler areas with respect to global temperature change, and the drier and wetter regions) is overall heightened per degree of global warming in the ensemble mean of the new simulations. The presence of stabilized scenarios in the new set of simulations allows investigation of the performance of the technique once the system has gotten close to equilibrium. Overall, the well established validity of the technique in approximating the forced signal of change under increasing concentrations of greenhouse gases is confirmed.  相似文献   

Analyzing seismic imagery in the time–amplitude and time–frequency domains to determine fluid nature and migration pathways: A case study from the Queen Charlotte Basin,offshore British Columbia     

Mathieu J. Duchesne  E. Julie Halliday  J. Vaughn Barrie 《Journal of Applied Geophysics》2011,73(2):111-120

Combining time–amplitude and time–frequency information from seismic reflection data sets of different resolutions allows the analysis of anomalous reflections from very-shallow to great subsurface depths. Thus, it can enhance the imaging of subsurface features which have a frequency-dependent reflectivity such as gas. Analysing seismic data of different resolution in the time–amplitude and time–frequency domains is a powerful method to determine hydrocarbon migration pathways from deep reservoirs to the seafloor. This interpretation method has been applied to the formerly-glaciated offshore Queen Charlotte Basin hosting several seafloor pockmarks and mounds associated with the leakage of underlying hydrocarbon reservoirs. Low-frequency shadows observed in the time–frequency domain provide evidence of different resolutions that several anomalous reflection amplitudes may be attributed to the occurrence of gas. The seismic imagery shows that gas uses a fault to migrate from deep reservoirs included in Upper Mesozoic strata towards secondary reservoirs located along the fault plane into Neogene layers. Once gas reaches a porous cut-and-fill succession, migration changes from structurally- to stratigraphically-controlled before gas leaks through unconsolidated Quaternary sediments forming the shallow subsurface to eventually seep at the seafloor where pockmarks and carbonate mounds are formed.  相似文献   

Extreme value modelling of daily areal rainfall over Mediterranean catchments in a changing climate     

Yves Tramblay  Luc Neppel  Julie Carreau  Emilia Sanchez‐Gomez 《水文研究》2012,26(25):3934-3944

Heavy rainfall events during the fall season are causing extended damages in Mediterranean catchments. A peaks‐over‐threshold model is developed for the extreme daily areal rainfall occurrence and magnitude in fall over six catchments in Southern France. The main driver of the heavy rainfall events observed in this region is the humidity flux (FHUM) from the Mediterranean Sea. Reanalysis data are used to compute the daily FHUM during the period 1958–2008, to be included as a covariate in the model parameters. Results indicate that the introduction of FHUM as a covariate can improve the modelling of extreme areal precipitation. The seasonal average of FHUM can improve the modelling of the seasonal occurrences of heavy rainfall events, whereas daily FHUM values can improve the modelling of the events magnitudes. In addition, an ensemble of simulations produced by five different general circulation models are considered to compute FHUM in future climate with the emission scenario A1B and hence to evaluate the effect of climate change on the heavy rainfall distribution in the selected catchments. This ensemble of climate models allows the evaluation of the uncertainties in climate projections. By comparison to the reference period 1960–1990, all models project an amplification of the mean seasonal FHUM from the Mediterranean Sea for the projection period 2070–2099, on average by +22%. This increase in FHUM leads to an increase in the number of heavy rainfall events, from an average of 2.55 events during the fall season in present climate to 3.57 events projected for the period 2070–2099. However, the projected changes have limited effects on the magnitude of extreme events, with only a 5% increase in the median of the 100‐year quantiles. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献