Application of an error statistics estimation method to the PSAS forecast error covariance model     

Runhua YANG  Jing GUO  Lars Peter RIISH?JGAARD 《大气科学进展》2006,23(1):33-44

In atmospheric data assimilation systems, the forecast error covariance model is an important component. However, the paralneters required by a forecast error covariance model are difficult to obtain due to the absence of the truth. This study applies an error statistics estimation method to the Pfiysical-space Statistical Analysis System （PSAS） height-wind forecast error covariance model. This method consists of two components： the first component computes the error statistics by using the National Meteorological Center （NMC） method, which is a lagged-forecast difference approach, within the framework of the PSAS height-wind forecast error covariance model; the second obtains a calibration formula to rescale the error standard deviations provided by the NMC method. The calibration is against the error statistics estimated by using a maximum-likelihood estimation （MLE） with rawindsonde height observed-minus-forecast residuals. A complete set of formulas for estimating the error statistics and for the calibration is applied to a one-month-long dataset generated by a general circulation model of the Global Model and Assimilation Office （GMAO）, NASA. There is a clear constant relationship between the error statistics estimates of the NMC-method and MLE. The final product provides a full set of 6-hour error statistics required by the PSAS height-wind forecast error covariance model over the globe. The features of these error statistics are examined and discussed.  相似文献   

Net circulation and salinity variations in an open-ended Swedish fjord system     

Göran Björk  Olof Liungman  Lars Rydberg 《Estuaries and Coasts》2000,23(3):367-380

Water circulation and salinity variations above sill levels in the Orust Tjöm fjords on the Swedish west coast, are investigated by means of hydrographic observations and a process-oriented box model. This fjord system, which is situated in the outer part of the Baltic estuary, consists of several basins separated by a number of sills and narrow passages. In contrast to most fjords, it is connected to the sea at both ends. Current measurements at different locations indicate a net, counterclockwise (mainly northward) circulation with an average of about 100 m³ s^?1. Model results and analyses of observations show that this net subtidal through-flow is primarily forced by the difference in steric height between the open ends. Salinity variations in the coastal waters give rise to density driven currents, mainly from the south which dominate the fjord exchange at large. The subtidal net circulation may be important for the properties in the northern parts of the system, particularly during periods of reversal. Validation against measurements shows that the model captures variations in the net circulation, as well as variations of the basin salinities above sill level. A seven-year model run, using monthly hydrographic data as forcing, yielded that the net circulation was counterclockwise during 81% of the time with a long-term average flow of about 70 m³ s^?1. Tidal choking in the narrow, northern end increases the flow resistance substantially, thereby decreasing the net through-flow.  相似文献   

高原泥炭记录揭示的全新世季风快速变化   总被引：5，自引：0，他引：5  

鲜锋  周卫健  于学峰  卢雪峰  A J T Jull  Lars G Franzén 《海洋地质与第四纪地质》2006,26(1):41-45

利用青藏高原东北缘的泥炭沉积记录,重建了该地区全新世冬、夏季风快速波动历史,清晰地识别出9次可与北大西洋浮冰碎屑事件及低纬海面降温事件相对比的气候干冷事件。总有机碳含量频谱分析揭示的1 428、512、2552、17 a气候准周期,表明中纬度地区百年至千年尺度气候韵律的存在,全新世气候快速变化具有全球性。  相似文献   

Application of a mass-balance model to predict PCDD/F turnover in a Baltic coastal estuary     

O. Magnus Karlsson  J. Mikael Malmaeus  Sarah Josefsson  Karin Wiberg  Lars Håkanson 《Estuarine, Coastal and Shelf Science》2010

A dynamical, process-based mass-balance model was applied to quantify the transports of polychlorinated-p-dibenzodioxins and dibenzofurans (PCDD/Fs) to, within and from the Kallrigafjärden Bay, a coastal estuary in the Baltic Sea, and to predict the PCDD/F levels in the water and sediments of the bay. Before the modelling, a one-year sampling programme was implemented in 2007–2008 to measure the flows of PCDD/Fs in tributaries entering the system, the fluxes from the adjacent sea and the levels in water, sediment and fish within the estuary. The collected data set was used as input data to the model and for validation purposes.  相似文献   

Fishing institutions: Addressing regulative,normative and cultural-cognitive elements to enhance fisheries management     

Maricela de la Torre-Castro  Lars Lindström 《Marine Policy》2010

Institutional approaches in natural resource management in general and in fisheries in particular seldom address cultural aspects or social institutions like kinship. In this study, a broad institutional approach is used to investigate the institutionalization of small-scale fisheries and seaweed farming in a seagrass dominated bay in Zanzibar. Regulative, normative and cultural-cognitive institutions and their rapid/slow moving properties are analyzed. The results show that dynamics of cooperation and conflict between different institutional elements and the balance of forces among actors are crucial to understand fisheries management dynamics. Regulations are, despite their importance, insufficient to promote sound management if they are not backed up by norms and cultural-cognitive institutions. Fisheries management would benefit by broadening the institutional perspective to increase the efficiency of management and to avoid blueprint solutions. The study shows that gaining knowledge about the wide institutional setting takes time but the investment is worth it in the long run.  相似文献   

Exhumed hydrocarbon traps in East Greenland: A comment on Andrews et al. (2020)     

Flemming G. Christiansen  Jørgen A. Bojesen-Koefoed  Stefan Piasecki  Lars Stemmerik  Jens Therkelsen 《Basin Research》2020,32(5):1234-1238

In a recent study, Andrews et al. (2020) describe “exhumed hydrocarbon traps” in North-East Greenland. The basic premise for their interpretation is that dark-coloured, pyrobitumen-bearing sandstones represent the remnants of once buried petroleum reservoirs. We do not see the necessary field or analytical evidence to support a model that has strong implications for resource evaluations. Andrews et al. (2020) have not considered previous published information on diagenetic and thermal maturity history of the area. A more probable model would include the intrusion of dykes and sills into a sedimentary succession with immature petroleum source rocks and reservoir-quality sandstones. The heating caused rapid generation of petroleum components and local hydrothermal circulation systems in adjacent porous sandstones. Any petroleum was rapidly destroyed leaving essentially only black grain-coatings and minor particles of pyrobitumen—essentially in one short-lived continuous process. The existence of new plays in the North Atlantic as proposed by Andrews et al. (2020) is in our opinion not substantiated as this requires analytical data from unaltered oils from the less mature parts of the sedimentary succession and considerations of thermal maturity and basin evolution. To draw conclusions that have a serious impact on resource evaluations based on the dark colouration of sandstones without comprehensive analytical data is, in our opinion, ill advised.  相似文献   

Vertical mixing in the Baltic Sea and consequences for eutrophication - A review   总被引：1，自引：0，他引：1  

Jan Hinrich Reissmann  Hans Burchard  Rainer Feistel  Eberhard Hagen  Hans Ulrich Lass  Volker Mohrholz  Günther Nausch  Lars Umlauf  Gunda Wieczorek 《Progress in Oceanography》2009,82(1):47-80

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Predictive permeability variations in a Hermod sand reservoir,Stine Segments,Siri Field,Danish North Sea     

Jesper Stokkendal  Henrik Friis  Johan B. Svendsen  Mette Lise K. Poulsen  Lars Hamberg 《Marine and Petroleum Geology》2009

The Hermod sand of the Stine Segments, Siri Field, Danish North Sea, displays large permeability variations (1–600 mD). These permeability variations represent horizontal layering in the reservoir, largely formed by diagenetic processes. They have a significant impact on reservoir performance, because horizontal producers in fairly thin reservoirs (∼30 m) are protected against bottom-water influx and can produce water-free for long periods of time.  相似文献   

Vertical movements of "escaped" farmed Atlantic salmon (Salmo salar L.)--a simulation study in a western Norwegian fjord     

Skilbrei  Ove T.; Holst  Jens Christian; Asplin  Lars; Holm  Marianne 《ICES Journal of Marine Science》2009,66(2):278-288

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Monocular 3D scene reconstruction at absolute scale     

Christian Wöhler  Pablo d’Angelo  Lars Krüger  Annika Kuhl  Horst-Michael Groß 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(6):529-540

In this article we propose a method for combining geometric and real-aperture methods for monocular three-dimensional (3D) reconstruction of static scenes at absolute scale. Our algorithm relies on a sequence of images of the object acquired by a monocular camera of fixed focal setting from different viewpoints. Object features are tracked over a range of distances from the camera with a small depth of field, leading to a varying degree of defocus for each feature. Information on absolute depth is obtained based on a Depth-from-Defocus approach. The parameters of the point spread functions estimated by Depth-from-Defocus are used as a regularisation term for Structure-from-Motion. The reprojection error obtained from bundle adjustment and the absolute depth error obtained from Depth-from-Defocus are simultaneously minimised for all tracked object features. The proposed method yields absolutely scaled 3D coordinates of the scene points without any prior knowledge about scene structure and camera motion. We describe the implementation of the proposed method both as an offline and as an online algorithm. Evaluating the algorithm on real-world data, we demonstrate that it yields typical relative scale errors of a few per cent. We examine the influence of random effects, i.e. the noise of the pixel grey values, and systematic effects, caused by thermal expansion of the optical system or by inclusion of strongly blurred images, on the accuracy of the 3D reconstruction result. Possible applications of our approach are in the field of industrial quality inspection; in particular, it is preferable to stereo cameras in industrial vision systems with space limitations or where strong vibrations occur.  相似文献