Some effects of vertical resolution on modelling forced planetary waves with a time‐dependent model     

J.‐G. Desmarais  J. Derome 《大气与海洋》2013,51(2):212-225

Abstract

Previous studies by Nakamura (1976) and Kirkwood and Derome (1977) have shown that the use of a relatively low vertical resolution in a numerical model of the atmosphere can lead to a poor representation of the forced stationary planetary waves. In the present study the consequences of this result on short‐term numerical forecasts are investigated. This is done by performing forecast experiments using a low resolution linear β‐plane model that is initialized with data extracted from the steady forced solution of the high resolution (reference) version of the model. The deviation of the low resolution forecast from the initial state, which can be interpreted as the forecast error due to insufficient vertical resolution, is examined as a function of time.

It is shown that the short‐range forecast error is dominated by a westward propagating external mode and that in time some of the eastward moving internal modes gain in importance.  相似文献   

Stable carbon isotopic evidence for climate change across the late Pleistocene to early Holocene from Lesotho,southern Africa     

P. ROBERTS  J. A. LEE‐THORP  P. J. MITCHELL  C. ARTHUR 《第四纪科学杂志》2013,28(4):360-369

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Preferred orientation distribution of shock‐induced planar microstructures in quartz and feldspar     

Lidia Pittarello  Ludovic Ferrire  Jean‐Guillaume Feignon  Gordon R. Osinski  Christian Koeberl 《Meteoritics & planetary science》2020,55(5):1082-1092

Shocked quartz and feldspar grains commonly exhibit planar microstructures, such as planar fractures, planar deformation features, and possibly microtwins, which are considered to have formed by shock metamorphism. Their orientation and frequency are typically reported to be randomly distributed across a sample. The goal of this study is to investigate whether such microstructures are completely random within a given sample, or whether their orientation might also retain information on the direction of the local shock wave propagation. For this work, we selected samples of shatter cones, which were cut normal to the striated surface and the striation direction, from three impact structures (Keurusselkä, Finland, and Charlevoix and Manicouagan, Canada). These samples show different stages of pre‐impact tectonic deformation. Additionally, we investigated several shocked granite samples, selected at different depths along the drill core recovered during the joint IODP‐ICDP Chicxulub Expedition 364 (Mexico). In this case, thin sections were cut along two orthogonal directions, one parallel and one normal to the drill core axis. All the results refer to optical microscopy and universal‐stage analyses performed on petrographic thin sections. Our results show that such shock‐related microstructures do have a preferred orientation, but also that relating their orientation with the possible shock wave propagation is quite challenging and potentially impossible. This is largely due to the lack of dedicated experiments to provide a key to interpret the observed preferred orientation and to the lack of information on postimpact orientation modifications, especially in the case of the drill core samples.  相似文献   

Ice‐jam flood risk assessment and mapping          下载免费PDF全文

Karl‐Erich Lindenschmidt  Apurba Das  Prabin Rokaya  Thuan Chu 《水文研究》2016,30(21):3754-3769

In northern regions, river ice‐ jam flooding can be more severe than open‐water flooding causing property and infrastructure damages, loss of human life and adverse impacts on aquatic ecosystems. Very little has been performed to assess the risk induced by ice‐related floods because most risk assessments are limited to open‐water floods. The specific objective of this study is to incorporate ice‐jam numerical modelling tools (e.g. RIVICE, Monte‐Carlo simulation) into flood hazard and risk assessment along the Peace River at the Town of Peace River (TPR) in Alberta, Canada. Adequate historical data for different ice‐jam and open‐water flooding events were available for this study site and were useful in developing ice‐affected stage‐frequency curves. These curves were then applied to calibrate a numerical hydraulic model, which simulated different ice jams and flood scenarios along the Peace River at the TPR. A Monte‐Carlo analysis was then carried out to acquire an ensemble of water level profiles to determine the 1 : 100‐year and 1 : 200‐year annual exceedance probability flood stages for the TPR. These flood stages were then used to map flood hazard and vulnerability of the TPR. Finally, the flood risk for a 200‐year return period was calculated to be an average of $32/m²/a ($/m²/a corresponds to a unit of annual expected damages or risk). Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Quantifying the P–T–t conditions of north–south Lhasa terrane accretion: new insight into the pre‐Himalayan architecture of the Tibetan plateau          下载免费PDF全文

O. M. Weller  M. R. St‐Onge  M. P. Searle  D. J. Waters  N. Rayner  S. Chen  S.‐L. Chung  R. M. Palin 《Journal of Metamorphic Geology》2015,33(1):91-113

An integrated field, petrological and geochronological study of the Basong Tso region of south‐eastern Tibet has constrained the timing and P–T conditions of north–south Lhasa terrane accretion and provides new insight into the tectonothermal evolution of the Tibetan plateau. Two distinct high‐grade metamorphic belts are recognized in the region: a southern belt (the Basong Tso complex) that consists of sheared schist and orthogneiss; and a northern belt (the Zhala complex) that comprises paragneiss and granite. Combined pseudosection modelling and U–Pb geochronology of monazite and zircon indicates that the Basong Tso complex records peak metamorphic conditions of 9 ± 0.5 kbar and 690 ± 25 °C at c. 204–201 Ma, whereas the Zhala complex experienced peak metamorphic conditions of 5.0 ± 1.0 kbar and 740 ± 40 °C at c. 198–192 Ma. Microstructural analysis suggests that the two belts share a common early prograde history, after which the Basong Tso complex attained peak conditions following rapid burial, and the Zhala complex approached peak conditions along an isobaric path. Overall it is inferred that the Basong Tso and Zhala complexes represent the lower and upper structural levels of an evolving orogen that underwent Barrovian‐type metamorphism following collision (M1), followed by Buchan‐style overprinting at higher structural levels due to heat advection by syn‐tectonic granites (M2). Mylonitization (sensu lato) of the Basong Tso complex and juxtaposition of the two units occurred after attainment of peak conditions. The dominance of Mesozoic regional metamorphism across most of the Tibetan plateau indicates that Cenozoic crustal thickening processes, where present, are only manifested at depth.  相似文献   

Contaminant transport and biodegradation in saturated porous media: model development and simulation     

Song‐Bae Kim 《水文研究》2005,19(20):4069-4079

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Postglacial chironomid assemblage succession in northernmost Ungava Peninsula,Canada     

Émilie Saulnier‐Talbot  Reinhard Pienitz 《第四纪科学杂志》2010,25(2):203-213

Sediment cores spanning the postglacial period were recovered from two coastal freshwater basins located 300 km apart in northernmost Ungava (Nunavik, Canada). A basal date from the sequence recovered near Wakeham Bay suggests that the region was ice‐free by as early as 9600 cal. a BP. The initial development of both investigated lacustrine ecosystems was characterised by chironomid assemblages strongly dominated by the Subtribe Tanytarsina. These early postglacial assemblages showed greatly reduced diversity but much greater abundance than during subsequent periods of lake evolution. An abrupt and distinct turnover in sedimentary chironomid assemblage composition and productivity, marked by a switch to a dominance of Orthocladiinae, occurred around 6 ka BP. This turnover likely corresponds with a significant disturbance in the regional environment, which could be linked to the final disappearance of the last remnants of the Laurentide Ice Sheet. These findings, based on the first palaeolimnological investigations undertaken in northernmost Ungava, provide new insights into lateglacial and postglacial faunal recolonisation patterns in aquatic ecosystems of the eastern Canadian Arctic. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Evaluation of typhoon‐induced rainfall using nonparametric Monte Carlo simulation and locally weighted polynomial regression     

Tae‐Suk Oh  Young‐Il Moon  Hyun‐Han Kwon 《水文研究》2011,25(11):1765-1777

Typhoons in Korea are the major causes of natural disasters in the Korean peninsula. In this study, rainfall generated by typhoons was quantitatively analysed using various statistical methods. First, the frequency analysis of rainfall induced by typhoons was carried out to calculate the design rainfall. Second, the frequency analysis of simulated rainfall derived by nonparametric Monte Carlo simulation (NMCS) was performed to evaluate the uncertainty of rainfall caused by typhoons. Third, the regression relationship between the physical characteristic factors of typhoons and rainfall was established by locally weighted polynomial regression (LWPR), and the characteristic factors of typhoons were simulated. The simulated characteristic factors were then used to estimate rainfall and to calculate the design rainfall by typhoons. Comparative analyses of design rainfalls as estimated using various statistical methods were performed. The LWPR showed good performance in terms of reproducing typhoon characteristics. Therefore, the combined NMCS and LWPR method suggested in this study can be used as a supplementary technique for assessing extreme rainfall with climate change and reflected variability. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The stability of sapphirine + quartz: calculated phase equilibria in FeO–MgO–Al2O3–SiO2–TiO2–O     

K. TAYLOR‐JONES  R. POWELL 《Journal of Metamorphic Geology》2010,28(6):615-633

The presence in rocks of coexisting sapphirine + quartz has been widely used to diagnose conditions of ultra‐high‐temperature (UHT) metamorphism (>900 °C), an inference based on the restriction of this assemblage to temperatures >980 °C in the conventionally considered FeO–MgO–Al₂O₃–SiO₂ (FMAS) chemical system. With a new thermodynamic model for sapphirine that includes Fe₂O₃, phase equilibra modelling using thermocalc software has been undertaken in the FeO–MgO–Al₂O₃–SiO₂–O (FMASO) and FeO–MgO–Al₂O₃–SiO₂– TiO₂–O (FMASTO) chemical systems. Using a variety of calculated phase diagrams for quartz‐saturated systems, the effects of Fe₂O₃ and TiO₂ on FMAS phase relations are shown to be considerable. Importantly, the stability field of sapphirine + quartz assemblages extends down temperature to 850 °C in oxidized systems and thus out of the UHT range.  相似文献   

Intertidal gastropod assemblages shaped by key environmental variables across the northern Persian Gulf and the Gulf of Omanss     

Fatemeh Amini‐Yekta  Mohammad Reza Shokri  Abdolvahab Maghsoudlou  Hassan Rajabi‐Maham 《Marine Ecology》2019,40(3)

Variations in environmental factors can alter the species distribution pattern in intertidal rocky shores. The Persian Gulf (PG) and the Gulf of Oman (GO) vary substantially with respect to environmental and oceanographic conditions. The abundance and biodiversity of intertidal rocky gastropods in five locations across the northern PG and the GO were compared, and the environmental variables underlying the distribution pattern of these organisms were investigated. A total of 67 gastropod species were identified. The largest average density (294 ind./m²) and diversity (N = 43) for gastropods occurred in the Hotel Lipar station (LIP) located in Chabahar Bay in the GO. Clypeomorus bifasciata (107.43 ind./m²) followed by Cerithium caeruleum (94.67 ind./m²) were the most abundant species. Planaxis sulcatus and Siphonaria spp. occurred in all locations during both sampling occasions. Species richness and abundance of gastropods showed significant differences between LIP and remaining locations. A significant difference was found in assemblage structure across locations. In general, the species richness and density in the locations at GO were significantly larger than those locations in the PG, suggesting that the harsh environmental condition in the PG might be the forcing factor for this diminish. Distinct grouping was observed in both assemblage structure and species composition between locations in the PG and the GO. The spatial and temporal distribution patterns of gastropods assemblages were significantly correlated with variation in salinity and substrate rugosity.  相似文献