Meteorological observations 2006 and ground temperature variations over 12-year at the Sermilik Station,Ammassalik Island,Southeast Greenland

Geografisk Tidsskrift, Danish Journal of Geography 108(1):153–161, 2008

Meteorological stations have been in operation since 1993 at the Sermilik Research Station (65°40′N, 38°10′W), Ammassalik Island, Southeast Greenland. This note presents meteorological observations for the calendar year 2006 from the two meteorological stations: Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.). The year 2006 record is not complete due to a temporal break down of Station Coast (from end-of June through beginning of August). Special focus is given to ground temperature measurements at the meteorological Station Nunatak (1994–2006) 0.1 and 0.3 m below the surface. Data are presented to illustrate the intra- and inter-annual temperature variability and possible trends in the upper part of the soil.     

Autumn atmospheric response to the 2007 low Arctic sea ice extent in coupled ocean–atmosphere hindcasts

The autumn and early winter atmospheric response to the record-low Arctic sea ice extent at the end of summer 2007 is examined in ensemble hindcasts with prescribed sea ice extent, made with the European Centre for Medium-Range Weather Forecasts state-of-the-art coupled ocean–atmosphere seasonal forecast model. Robust, warm anomalies over the Pacific and Siberian sectors of the Arctic, as high as 10°C at the surface, are found in October and November. A regime change occurs by December, characterized by weaker temperatures anomalies extending through the troposphere. Geopotential anomalies extend from the surface up to the stratosphere, associated to deeper Aleutian and Icelandic Lows. While the upper-level jet is weakened and shifted southward over the continents, it is intensified over both oceanic sectors, especially over the Pacific Ocean. On the American and Eurasian continents, intensified surface Highs are associated with anomalous advection of cold (warm) polar air on their eastern (western) sides, bringing cooler temperatures along the Pacific coast of Asia and Northeastern North America. Transient eddy activity is reduced over Eurasia, intensified over the entrance and exit regions of the Pacific and Atlantic storm tracks, in broad qualitative agreement with the upper-level wind anomalies. Potential predictability calculations indicate a strong influence of sea ice upon surface temperatures over the Arctic in autumn, but also along the Pacific coast of Asia in December. When the observed sea ice extent from 2007 is prescribed throughout the autumn, a higher correlation of surface temperatures with meteorological re-analyses is found at high latitudes from October until mid-November. This further emphasises the relevance of sea ice for seasonal forecasting in the Arctic region, in the autumn.     

Characterization of fractured reservoirs using a consistent stiffness‐permeability model: focus on the effects of fracture aperture

In this paper we propose a method for the characterization of naturally fractured reservoirs by quantitative integration of seismic and production data. The method is based on a consistent theoretical frame work to model both effective hydraulic and elastic properties of fractured porous media and a (non‐linear) Bayesian method of inversion that provides information about uncertainties as well as mean (or maximum likelihood) values. We model a fractured reservoir as a porous medium containing a single set of vertical fractures characterized by an unknown fracture density, azimuthal orientation and aperture. We then look at the problem of fracture parameter estimation as a non‐linear inverse problem and try to estimate the unknown fracture parameters by joint inversion of seismic amplitude versus angle and azimuth data and dynamic production data. Once the fracture parameters have been estimated the corresponding effective stiffness and permeability tensors can be estimated using consistent models. A synthetic example is provided to clearly explain and test the workflow. It shows that seismic and production data complement each other, in the sense that the seismic data resolve a non‐uniqueness in the fracture orientation and the production data help to recover the true fracture aperture and permeability, because production data are more sensitive to the fracture aperture than the seismic data.     

Assessment of climate change and associated impact on selected sectors in Poland

The present paper offers a brief assessment of climate change and associated impact in Poland, based on selected results of the Polish–Norwegian CHASE-PL project. Impacts are examined in selected sectors, such as water resources, natural hazard risk reduction, environment, agriculture and health. Results of change detection in long time series of observed climate and climate impact variables in Poland are presented. Also, projections of climate variability and change are provided for time horizons of 2021–2050 and 2071–2100 for two emission scenarios, RCP4.5 and RCP8.5 in comparison with control period, 1971–2000. Based on climate projections, examination of future impacts on sectors is also carried out. Selected uncertainty issues relevant to observations, understanding and projections are tackled as well.     

Visco-Elastic Waves in Rock-Like Composites

The subject of this paper is the treatment of rocks - and, especially, fluid-saturated and partially saturated reservoir rocks, as composite visco-elastic media. By this we mean to study and partially answer the question of how the effective material (frequency-dependent and complex-valued stiffness/density) parameters can be estimated from a knowledge of the constituents of the rocks, their volume fractions, the statistical distribution of sizes, shapes, orientations and positions of the individual particles (minerals of quartz, clay, etc.) and cavities (pores, cracks, etc.); in addition to parameters related to the fluid and its ability to flow, at the scale of the microstructure as well as that of the wavelength (assumed to be long compared to the scale-size of the microstructure).Our approach is to develop and combine a theory of stochastic waves with established results for the micromechanics of defects in solids, as well as state-of-the-art models of wave-induced fluid flow. Specifically, we first derive an exact formal expression for the effective material parameters in terms of a dynamic T-matrix for the material, which satisfies a single integral equation of the Lippmann-Schwinger type (known from quantum scattering theory), but formulated in an abstract vector space, associated with the combination of the strain and velocity fields into a more general state vector . Inclusions-based models are developed on the basis of standard many-body techniques, known from the static T-matrix approach as well as nuclear collision theory. The t-matrix of a low-aspect-ratio spheroidal crack is expressed in terms of the familiar displacement discontinuity parameters of Hudson, via the so-called K-tensor, which is of interest in itself, for example, when connecting cracks to pores (in the presence of multiple solid constituents) on the basis of an expression for the t-matrix of a communicating cavity.The present theory can in principle be used beyond the Rayleigh limit, but explicit estimates of the effective material parameters have so far been derived only under the assumption that (scattering attenuation can be ignored) the wavelength is large compared to the scale-size of a representative volume element. Starting with the dynamic equations of motion, we show that the behaviour of the mean wave in the Rayleigh limit is indeed determined by the effective stiffness tensor associated with a static theory of composites, in conjunction with the spatially averaged density for the heterogeneous material as a whole. Thus, we have provided justification to the procedure we used in a series of related papers, where we started out with the static equilibrium condition and employed the elastic/visco-elastic correspondence principle. Numerical examples (dealing with the effects of randomly oriented cracks on the isotropic velocity and attenuation spectra of a dual porosity model of clay-sand mixtures, and the effects of spatial distribution on the anisotropic attenuation spectra of fully aligned cracks that are partially saturated with two different fluids) will be provided in order to complement those in our earlier papers.     

A poly morphological landform approach for hydrogeological applications in heterogeneous glacial sediments

The ‘poly morphological (PM) concept’ is used to assess geological heterogeneity in glacial sediments and to evaluate groundwater recharge to aquifers, especially those underlying clay till. The novelty of the PM concept is that it enhances the knowledge of, especially, heterogeneity of till units in geological models by using superimposed geomorphological units with typical sediment types related to the individual landforms. The PM concept is demonstrated through the construction of a poly morphological map for Zealand in Denmark and an aggregated map comparing clay-till-thickness distribution within individual PM types. The hydrogeological applicability of the PM concept was tested with a physical-based distributed 3D hydrological model. The aggregated PM map was compared with fracture and redox conditions at 21 field sites to evaluate the PM-type correlation to: (1) till thickness, (2) thickness of the reduced-till zone, and (3) depth to the zone with fracture spacing >1 m The results show that the till thickness is a critical parameter for the formation of fracture networks in clay till, and that fracture density decreases in till thicker than 8–10 m. However, the amount of data is still inadequate for statistically proving the PM concept.     

Unmanned aerial vehicle observations of water surface elevation and bathymetry in the cenotes and lagoons of the Yucatan Peninsula,Mexico

Observations of water surface elevation (WSE) and bathymetry of the lagoons and cenotes of the Yucatán Peninsula (YP) in southeast Mexico are of hydrogeological interest. Observations of WSE (orthometric water height above mean sea level, amsl) are required to inform hydrological models, to estimate hydraulic gradients and groundwater flow directions. Measurements of bathymetry and water depth (elevation of the water surface above the bed of the water body) improve current knowledge on how lagoons and cenotes connect through the complicated submerged cave systems and the diffuse flow in the rock matrix. A novel approach is described that uses unmanned aerial vehicles (UAVs) to monitor WSE and bathymetry of the inland water bodies on the YP. UAV-borne WSE observations were retrieved using a radar and a global navigation satellite system on-board a multi-copter platform. Water depth was measured using a tethered floating sonar controlled by the UAV. This sonar provides depth measurements also in deep and turbid water. Bathymetry (wet-bed elevation amsl) can be computed by subtracting water depth from WSE. Accuracy of the WSE measurements is better than 5–7 cm and accuracy of the water depth measurements is estimated to be ~3.8% of the actual water depth. The technology provided accurate measurements of WSE and bathymetry in both wetlands (lagoons) and cenotes. UAV-borne technology is shown to be a more flexible and lower cost alternative to manned aircrafts. UAVs allow monitoring of remote areas located in the jungle of the YP, which are difficult to access by human operators.