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Summary The problem of the reconstruction of mean summer temperatures from proxy data on a rigorous statistical basis is addressed:
Cross spectral analysis is used for evaluating the suitability of linear transfer models between proxy data and temperature,
the linear model is estimated from the data of a calibration period and it is verified using the data of a different period.
Strict statistical tests are applied at every step of the analysis. Three examples using the proposed method are given: the
reconstruction of mean April–July temperatures at Basel from grape harvest data in NE France (1484–1768), mean April–September
temperatures at Basel from late wood density of trees from the Swiss Prealps (1270‐1768), and mean April–September temperatures
at Great St. Bernhard from the late wood proxy too (1270–1850). The grape harvest data give a very good reconstruction, the
resulting temperatures from 1500–1768 are documented. The late wood data fails to give a good reconstruction.
With 11 Figures 相似文献
Die Rekonstruktion von Temperaturreihen aus Proxydaten in Mitteleuropa
Zusammenfassung Es wird das Problem der Rekonstruktion von mittleren Sommertemperaturen aus sogenannten Proxydaten untersucht. Sehr viel Wert wird auf die statistische Signifikanz der Rekonstruktion gelegt. Kreuzspektralanalyse wird benutzt, um die Verwendungsf?higkeit eines linearen Modells als Transfermodell zwischen Temperatur und Proxydaten zu ermitteln. Die Parameter des linearen Transfermodells werden aus den Daten der sogenannten Eichperiode abgesch?tzt und die damit für eine unabh?ngige Periode rekonstruierten Temperaturen werden mit gemessenen verglichen. In jedem Schritt der Analyse werden strikte statistische Tests durchgeführt, um die Ergebnisse zu untermauern. Die Methode wird an drei Beispielen erprobt: die mittlere April–Juli Temperatur in Basel wird mit Hilfe von Weinlesedaten von NE-Frankreich für die Zeit (1484–1768) rekonstruiert, die mittlere April–September Temperatur in Basel und am Gro?en Bernhard wird mit Sp?tholzdichtewerten der Schweizer Voralpen verglichen. Die Weinlesedaten ergeben eine sehr gute Rekonstruktion und die Temperaturreihe für den Zeitraum 1500–1768 wird dokumentiert. Die Sp?tholzdichten liefern keine gute Temperaturrrekonstruktion.
With 11 Figures 相似文献
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Mauro Cacace Guido Blöcher Norihiro Watanabe Inga Moeck Nele Börsing Magdalena Scheck-Wenderoth Olaf Kolditz Ernst Huenges 《Environmental Earth Sciences》2013,70(8):3585-3602
Fluid flow in low-permeable carbonate rocks depends on the density of fractures, their interconnectivity and on the formation of fault damage zones. The present-day stress field influences the aperture hence the transmissivity of fractures whereas paleostress fields are responsible for the formation of faults and fractures. In low-permeable reservoir rocks, fault zones belong to the major targets. Before drilling, an estimate for reservoir productivity of wells drilled into the damage zone of faults is therefore required. Due to limitations in available data, a characterization of such reservoirs usually relies on the use of numerical techniques. The requirements of these mathematical models encompass a full integration of the actual fault geometry, comprising the dimension of the fault damage zone and of the fault core, and the individual population with properties of fault zones in the hanging and foot wall and the host rock. The paper presents both the technical approach to develop such a model and the property definition of heterogeneous fault zones and host rock with respect to the current stress field. The case study describes a deep geothermal reservoir in the western central Molasse Basin in southern Bavaria, Germany. Results from numerical simulations indicate that the well productivity can be enhanced along compressional fault zones if the interconnectivity of fractures is lateral caused by crossing synthetic and antithetic fractures. The model allows a deeper understanding of production tests and reservoir properties of faulted rocks. 相似文献
56.
Eren Ucar Eirik Keilegavlen Inga Berre Jan Martin Nordbotten 《Computational Geosciences》2018,22(4):993-1007
Simulating the deformation of fractured media requires the coupling of different models for the deformation of fractures and the formation surrounding them. We consider a cell-centered finite-volume approach, termed the multi-point stress approximation (MPSA) method, which is developed in order to discretize coupled flow and mechanical deformation in the subsurface. Within the MPSA framework, we consider fractures as co-dimension one inclusions in the domain, with the fracture surfaces represented as line pairs in 2D (face pairs in 3D) that displace relative to each other. Fracture deformation is coupled to that of the surrounding domain through internal boundary conditions. This approach is natural within the finite-volume framework, where tractions are defined on surfaces of the grid. The MPSA method is capable of modeling deformation, considering open and closed fractures with complex and nonlinear relationships governing the displacements and tractions at the fracture surfaces. We validate our proposed approach using both problems, for which analytical solutions are available, and more complex benchmark problems, including comparison with a finite-element discretization. 相似文献
57.
Multivariate statistics are used to investigate sensitivity of the tropical atmospheric circulation to scenario-based global
land cover change (LCC), with the largest changes occurring in the tropics. Three simulations performed with the fully coupled
Parallel Climate Model (PCM) are compared: (1) a present day control run; (2) a simulation with present day land cover and
Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 greenhouse gas (GHG) projections;
and (3) a simulation with SRES A2 land cover and GHG projections. Dimensionality of PCM data is reduced by projection onto
a priori specified eigenvectors, consisting of Rossby and Kelvin waves produced by a linearized, reduced gravity model of
the tropical circulation. A Hotelling T
2 test is performed on projection amplitudes. Effects of LCC evaluated by this method are limited to diabatic heating. A statistically
significant and recurrent signal is detected for 33% of all tests performed for various combinations of parameters. Taking
into account uncertainties and limitations of the present methodology, this signal can be interpreted as a Rossby wave response
to prescribed LCC. The Rossby waves are shallow, large-scale motions, trapped at the equator and most pronounced in boreal
summer. Differences in mass and flow fields indicate a shift of the tropical Walker circulation patterns with an anomalous
subsidence over tropical South America. 相似文献
58.
Summary Previous studies have highlighted the crucial role of sea surface temperature (SST) anomalies in the tropical Atlantic region
in forcing the summer monsoon rainfall over subsaharan West Africa. Understanding the physical processes, relating SST variations
to changes in the amount and distribution of African rainfall, is a key factor in improving weather and climate forecasts
in this highly vulnerable region.
Here, we present sensitivity experiments from a regional climate model with prescribed warmer tropical SSTs, according to
enhanced greenhouse conditions at the end of the 21st century. This dynamical downscaling approach provides information about
the nonlinear response of the atmosphere to oceanic heating. It has been suggested that the response is at least partly accounted
for by the linear theory of tropical dynamics, involving a Kelvin and Rossby wave response to a tropical heat source. We compute
the major modes of the linear Matsuno-Gill model for geopotential height and horizontal wind components and project the simulated
response patterns onto these linear modes, in order to evaluate to which extent the simple linear theory may explain the SST-induced
climate anomalies over Africa. A multivariate Hotelling T2 test is used to evaluate whether these anomalies are statistically significant.
Forcing the regional climate model by warmer SSTs leads to substantial climate anomalies over tropical Africa: Rainfall is
increases over the Guinea Coast region (GCR) and tropical East Africa, but decreases over the Congo Basin and the Sahel Zone
(SHZ). At the 850 hPa level, a trough develops over southern West Africa and the Gulf of Guinea, and is associated with stronger
surface wind convergence over the GCR. These changes in the atmospheric dynamics strongly project onto the leading modes of
the linear Matsuno-Gill model at various zonal wave numbers. The corresponding atmospheric heating pattern is highly reminiscent
of the simulated nonlinear model reponse. The T2 test statistics reveal that the SST forcing induces a statistically significant climate anomaly over tropical Africa if the
climate state vector is reduced by projecting the simulated data onto the leading 10 linear modes. It is also shown that the
linear response prevails in a long-term simulation with more realistic lower and lateral boundary conditions. Thus, linear
tropical dynamics are assumed to be a major physical process on the ground of the prominent SST-African rainfall relationship. 相似文献
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