Preface     

Gordon McBean  Erik Rasmussen 《Dynamics of Atmospheres and Oceans》1987,10(4)

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A review of mathematical models of river planform changes     

Erik Mosselman 《地球表面变化过程与地形》1995,20(7):661-670

Different mathematical models of river planform changes exist or are being developed. They are reviewed here by discussing a two-dimensional depth-averaged model, various meander models and a model for the braided Brahmaputra-Jamuna River in Bangladesh. Much emphasis is placed on topics where further research is needed. It is concluded that the models help in understanding the underlying processes, but cannot yet be considered generally valid and easy-to-use software packages. In the hands of experienced geomorphologists or river engineers, however, some of the models do already form valuable tools which allow better predictions of future river planforms.  相似文献   

Nonlinear Adjustment of GPS Observations of Type Pseudo-Ranges     

Joseph L. Awange  Erik W. Grafarend 《GPS Solutions》2002,5(4):80-96

The nonlinear adjustment of GPS observations of type pseudo-ranges is performed in two steps. In step one a combinatorial minimal subset of observations is constructed which is rigorously converted into station coordinates by means of Groebner basis algorithm or the multipolynomial resultant algorithm. The combinatorial solution points in a polyhedron are reduced to their barycentric in step two by means of their weighted mean. Such a weighted mean of the polyhedron points in ℝ³ is generated via the Error Propagation law/variance-covariance propagation. The Fast Nonlinear Adjustment Algorithm (FNon Ad Al) has been already proposed by Gauss whose work was published posthumously and Jacobi (1841). The algorithm, here referred to as the Gauss-Jacobi Combinatorial algorithm, solves the over-determined GPS pseudo-ranging problem without reverting to iterative or linearization procedure except for the second moment (Variance-Covariance propagation). The results compared well with the solutions obtained using the linearized least squares approach giving legitimacy to the Gauss-Jacobi combinatorial procedure. ? 2002 Wiley Periodicals, Inc.  相似文献   

Die entwicklungsprobleme im “nordkalottgebiet” Schwedens Development problems in the northernmost parts of Sweden Les problèmes de développement dans la région suédoise de la “calotte du nord”     

Erik Bylund 《Geoforum》1971,2(1):37-46

Sweden's high economic and social standard has been gained through a hard past and present structural rationalization process in the economy. This process has had the regional consequence that Norrland and especially its northernmost parts have met with considerable difficulties in maintaining services and full employment. A large number of farmers and forest workers migrated southward. Swedish location policy after 1965 aims at creating one or two growth poles in northern Norrland; Luleå and its neighbouring towns of Piteå and Boden appear to have good prerequisites. However, Umeå has the strongest population increase, a result of the newly established university which has developed very rapidly. It appears that the growth potentials in northern Norrland are greatest on the coast. Long distances, a widely spread population, and a bad urban structure with too many small communities and no big expansive ones make the inland of northern Norrland the greatest regional-political problem in Sweden.  相似文献   

1983–2003 decaying rate of deflation at Askja caldera: Pressure decrease in an extensive magma plumbing system at a spreading plate boundary     

Erik Sturkell  Freysteinn Sigmundsson  Ragnar Slunga 《Bulletin of Volcanology》2006,68(7-8):727-735

New deformation data from the Askja volcano, Iceland, show that the volcano's caldera has been deflating continuously for over 20 years, and confirm that the rate of subsidence is slowing down. The decay in subsidence rate can be fitted with a function of the form e ^{− t / τ} , where τ is 39 years. Reanalysis of GPS data from 1993–1998 show that these data can be fitted with a model calling for two Mogi point sources, one shallow, and another one much deeper (16.2 km depth). Pressure decrease occurs in both sources. The deeper source is responsible for observed horizontal contraction towards Askja at distances that cannot be explained by the shallower source. Plate spreading of 19 mm/year distributed evenly over about 100-km-wide zone is also favoured by the data.  相似文献   

Present-day and future precipitation in the Baltic Sea region as simulated in a suite of regional climate models     

Erik Kjellström  Kimmo Ruosteenoja 《Climatic change》2007,81(1):281-291

Here we investigate simulated changes in the precipitation climate over the Baltic Sea and surrounding land areas for the period 2071–2100 as compared to 1961–1990. We analyze precipitation in 10 regional climate models taking part in the European PRUDENCE project. Forced by the same global driving climate model, the mean of the regional climate model simulations captures the observed climatological precipitation over the Baltic Sea runoff land area to within 15% in each month, while single regional models have errors up to 25%. In the future climate, the precipitation is projected to increase in the Baltic Sea area, especially during winter. During summer increased precipitation in the north is contrasted with a decrease in the south of this region. Over the Baltic Sea itself the future change in the seasonal cycle of precipitation is markedly different in the regional climate model simulations. We show that the sea surface temperatures have a profound impact on the simulated hydrological cycle over the Baltic Sea. The driving global climate model used in the common experiment projects a very strong regional increase in summertime sea surface temperature, leading to a significant increase in precipitation. In addition to the common experiment some regional models have been forced by either a different set of Baltic Sea surface temperatures, lateral boundary conditions from another global climate model, a different emission scenario, or different initial conditions. We make use of the large number of experiments in the PRUDENCE project, providing an ensemble consisting of more than 25 realizations of climate change, to illustrate sources of uncertainties in climate change projections.  相似文献   

Paleoceanographic evolution of the SW Svalbard margin (76°N) since 20,000 C yr BP     

Tine L. Rasmussen  Erik Thomsen  Simon Jessen  Nalân Koç 《Quaternary Research》2007,67(1):100-114

Two cores from the southwestern shelf and slope of Storfjorden, Svalbard, taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera, oxygen isotopes, and ice-rafted debris. The results show that over the last 20,000 yr, Atlantic water has been continuously present on the southwestern Svalbard shelf. However, from 15,000 to 10,000 ¹⁴C yr BP, comprising the Heinrich event H1 interval, the Bølling-Allerød interstades and the Younger Dryas stade, it flowed as a subsurface water mass below a layer of polar surface water. In the benthic environment, the shift to interglacial conditions occurred at 10,000 ¹⁴C yr BP. Due to the presence of a thin upper layer of polar water, surface conditions remained cold until ca. 9000 ¹⁴C yr BP, when the warm Atlantic water finally appeared at the surface. Neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of Atlantic water. Its warm core was merely submerged below the cold polar surface water.  相似文献   

Analysis and modeling of the seasonal South China Sea temperature cycle using remote sensing   总被引：1，自引：0，他引：1  

Daniel J. Twigt  Erik D. De Goede  Ernst J. O. Schrama  Herman Gerritsen 《Ocean Dynamics》2007,57(4-5):467-484

The present paper describes the analysis and modeling of the South China Sea (SCS) temperature cycle on a seasonal scale. It investigates the possibility to model this cycle in a consistent way while not taking into account tidal forcing and associated tidal mixing and exchange. This is motivated by the possibility to significantly increase the model’s computational efficiency when neglecting tides. The goal is to develop a flexible and efficient tool for seasonal scenario analysis and to generate transport boundary forcing for local models. Given the significant spatial extent of the SCS basin and the focus on seasonal time scales, synoptic remote sensing is an ideal tool in this analysis. Remote sensing is used to assess the seasonal temperature cycle to identify the relevant driving forces and is a valuable source of input data for modeling. Model simulations are performed using a three-dimensional baroclinic-reduced depth model, driven by monthly mean sea surface anomaly boundary forcing, monthly mean lateral temperature, and salinity forcing obtained from the World Ocean Atlas 2001 climatology, six hourly meteorological forcing from the European Center for Medium range Weather Forecasting ERA-40 dataset, and remotely sensed sea surface temperature (SST) data. A sensitivity analysis of model forcing and coefficients is performed. The model results are quantitatively assessed against climatological temperature profiles using a goodness-of-fit norm. In the deep regions, the model results are in good agreement with this validation data. In the shallow regions, discrepancies are found. To improve the agreement there, we apply a SST nudging method at the free water surface. This considerably improves the model’s vertical temperature representation in the shallow regions. Based on the model validation against climatological in situ and SST data, we conclude that the seasonal temperature cycle for the deep SCS basin can be represented to a good degree. For shallow regions, the absence of tidal mixing and exchange has a clear impact on the model’s temperature representation. This effect on the large-scale temperature cycle can be compensated to a good degree by SST nudging for diagnostic applications.  相似文献   

Alkaline ultramafic lamprophyres and associated carbonatite dykes from the Kalix area,northern Sweden     

Peter Kresten  Erik åhman  Arild O. Brunfelt 《International Journal of Earth Sciences》1981,70(3):1215-1231

Alkahne ultramafic lamprophyres and associated carbonatite dykes form north-south trending dyke swarms. The lamprophyres are sub-divided into micaceous, picritic and breccia varieties. Carbonatites sensu stricto (beforsites) occur very subordinate.The dykes of the Kalix area show great similarities to petrographically related rocks from other Scandinavian occurrences (Sokli, Alnö and Fen). Major differences are found in their tectonic setting (regularly striking dyke swarms) and the REE-pattern (distinctly negative cerium anomalies).The following petrogenetic model is advanced for the Kalix dykes: (1) partial melting of upper mantle material, (2) Intrusion into a crustal magma chamber, fractional crystallization, (3) Interactions between crystallized material and the volatile phase (light REE depletion, oxidation of cerium), (4) Intrusion in fracture zones under horizontal tension.

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Zusammenfassung Alkalin-ultrabasiscbe Lamprophyre und begleitende KarbonatitgÄnge bilden nordsüdlidi streichende GangschwÄrme. Die Lamprophyre zeigen gewisse Ähnlichkeiten zu alnöitischen und kimberlitischen Gesteinen; sie wurden unterteilt in glimmerreiche und pikritische Lamprophyre sowie Brekzien. Karbonatite im engeren Sinn treten nur sehr untergeordnet auf; sie sind als Beforsite charakterisiert.Die Ganggesteine des Kalix-Gebiets weisen gro\e Ähnlichkeiten mit petrographiscb verwandten Gesteinen von anderen skandinavischen Vorkommen (Sokli, Alnö und Fen) auf. GrundsÄtzliche Unterschiede finden sich vor allem im tektonischen Auftreten (ziemlich konstant streichende GangschwÄrme) und im Verteilungsmuster der seltenen Erden (deutlich negative Cer-Anomalien).Die Bildung der Kalix-GÄnge wird folgenderweise erklÄrt: (1) Partielle Aufschmelzung des oberen Mantels, (2) Intrusion der Schmelze in eine krustale Magmakammer, gefolgt von fraktionierter Kristallisation, (3) Reaktion zwischen vorzugsweise kristallisiertem Material und der volatilen Phase (Entarmung an leichten seltenen Erden, Oxidation des Cers), (4) Intrusion in Bruchzonen, die horizonteller Dehnung ausgesetzt sind.

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Résumé Des lamprophyres alcalins ultrabasiques accompagnés de carbonatites forment des essaims de dykes de direction nord-sud. Les lamprophyres se subdivisent en variétés micacée, picritique ainsi que brÊchique. Les carbonatites sensu stricto sont rares et sont plutÔ des beforsites.Les dykes de la région de Kalix présentent de grandes similitudes avec des roches pétrographiquement apparentées d'autres localités Scandinaves (Sokli, Alnö et Fen). Les différences essentielles sont dues à leur situation tectonique (essaims de dykes de direction régulière) ainsi qu'à la distribution des Terres Rares (anomalie négative distincte de cérium).Le modèle pétrogénétique suivant est proposé pour les dykes de Kalix: (1) fusion partielle de matériau du manteau supérieur, (2) intrusion dans une chambre magmatique de l'écorce et cristallisation fractionnée, (3) interaction entre le material déjà cristallisé et la phase volatile (appauvrissement des éléments légers des Terres Rares, oxydation du cérium), (4) intrusion le long de zones de fracture dans des conditions d'extension horizontale.

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Risø 1978: Further investigations into the effects of local terrain irregularities on tower-measured wind profiles     

Ernest W. Peterson  Peter A. Taylor  Jørgen Højstrup  Niels Otto Jensen  Leif Kristensen  Erik L. Petersen 《Boundary-Layer Meteorology》1980,19(3):303-313

Observations of flow over complex terrain taken at Risø during June–July 1978 and numerical studies confirm earlier findings that small variations in surface elevation have significant effects on mean wind profiles. Measured shear stresses in the nonequilibrium region of the flow are consistent with theory but quite different from those obtained assuming simple flux-profile relationships. These findings imply that flux-profile relationships can be quite complicated over other than simple homogeneous terrain.  相似文献