The role of some regional factors in the assessment of well yields from hard-rock aquifers of Fennoscandia     

Helge?HenriksenEmail author 《Hydrogeology Journal》2003,11(6):628-645

The attributes of about 13,600 hard-rock water wells were arranged in three profiles parallel to gradients of typical regional factors. These factors are thought to be of importance to groundwater yield from wells in the Fennoscandian crust and were subjected to a statistical analysis. The regional factors comprise annual rate of postglacial crustal uplift and annual average precipitation, whereas soil type, soil depth, and bedrock type are considered sub-regional and local factors. There is no clear trend in well yield along the regional gradients. The results of the statistical analysis indicate that for the typical regional variables, the rate of postglacial uplift and average annual precipitation explain not more than 11% of the observed variation in well yields. Some of these factors, and other factors not included in this study, work in opposite directions and may cancel each other out. It is concluded that other, more local factors, such as well depth, proximity to fracture-related lineaments and topography, have a greater influence on well yields in this area.

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Resumen Se ha recogido los atributos de aguas subterráneas con 13.600 años de antigüedad en tres perfiles perpendiculares a los gradientes de los factores regionales típicos, las cuales son captadas por pozos perforados en rocas duras. Se cree que estos factores tienen importancia en el rendimiento de los pozos realizados en la corteza de Fenoscandia, y han sido analizados estadísticamente. Los factores regionales comprenden la tasa anual de alzamiento postglacial y la precipitación media anual, mientras que el tipo y la profundidad del suelo, y el tipo de roca madre, son tratados como factores sub-regionales y locales. No se aprecia una tendencia clara en el rendimiento de los pozos a lo largo de los gradientes regionales. Los resultados del análisis estadístico indican que, para las variables regionales típicas, la tasa de alzamiento postglacial y la precipitación media anual explican como mucho el 11,2% de las variaciones observadas en el rendimiento de los pozos. Algunos de estos factores, así como otros no incluidos en el estudio, son de signo opuesto y pueden llegar a compensarse. Se concluye que factores diferentes, de escala más local, tales como la proximidad a lineamientos correlacionados con fracturas o la topografía, pueden afectar de forma más importante al rendimiento de los pozos en esta zona.

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Résumé Les propriétés d'environ 13,600 puits d'extraction d'eau souterraine dans le socle ont été réparties selon trois profils disposés perpendiculairement aux gradients de facteurs régionaux typiques. Ces facteurs sont considérés comme étant importants pour les rendements des puits dans le bouclier fenno-scandien et ont été soumis à une analyse statistique. Les facteurs régionaux sont le taux de soulèvement postglaciaire et les précipitations moyennes annuelles, alors que le type et l'épaisseur de sol, le type de substratum sont des facteurs sub-régionaux et locaux. Il n'existe pas de tendance dans le rendement des puits selon les gradients régionaux. Les résultats de l'analyse statistique indiquent que pour les variables régionales typiques, le taux de soulèvement postglaciaire et les précipitations moyennes annuelles n'expliquent pas plus de 11,2% de la variation observée du rendement des puits. Certains de ces facteurs, ainsi que d'autres non pris en compte dans cette étude, jouent dans des directions opposées et peuvent s'annuler l'un l'autre. En conclusion, d'autres facteurs, plus locaux, tels que la proximité de linéaments corrélés aux fractures et la topographie peuvent avoir une grande importance pour le rendement des puits dans cette région.

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Operator splitting methods for degenerate convection–diffusion equations II: numerical examples with emphasis on reservoir simulation and sedimentation     

Helge Holden  Kenneth Hvistendahl Karlsen  Knut-Andreas Lie 《Computational Geosciences》2000,4(4):287-322

We present an accurate numerical method for a large class of scalar, strongly degenerate convection–diffusion equations. Important subclasses are hyperbolic conservation laws, porous medium type equations, two-phase reservoir flow equations, and strongly degenerate equations coming from the recent theory of sedimentation–consolidation processes. The method is based on splitting the convective and the diffusive terms. The nonlinear, convective part is solved using front tracking and dimensional splitting, while the nonlinear diffusion part is solved by an implicit–explicit finite difference scheme. In addition, one version of the implemented operator splitting method has a mechanism built in for detecting and correcting unphysical entropy loss, which may occur when the time step is large. This mechanism helps us gain a large time step ability for practical computations. A detailed convergence analysis of the operator splitting method was given in Part I. Here we present numerical experiments with the method for examples modelling secondary oil recovery and sedimentation–consolidation processes. We demonstrate that the splitting method resolves sharp gradients accurately, may use large time steps, has first order convergence, exhibits small grid orientation effects, has small mass balance errors, and is rather efficient.  相似文献   

Reconstruction of Northern Hemisphere 500 hPa geopotential heights back to the late 19th century   总被引：2，自引：0，他引：2  

D.-Y. Gong  H. Drange  Y.-Q. Gao 《Theoretical and Applied Climatology》2007,90(1-2):83-102

Summary In this study the authors have developed a statistical method and have reconstructed Northern Hemisphere 500 hPa heights back to the late 19th century using one temperature and three sea level pressure (SLP) data sets. First, the relationship between ERA40 500 hPa heights and surface temperature and SLP was screened using stepwise multiple regression based on the calibration period of 1958–2002 (1998/2000 according to the availability of SLP data). All selected predictors (temperature and SLP) were significant and their variance contribution was greater than 1%. On average, there were 8.1 variables retained in the final regression equations. Second, the regression equations were applied to compute the 500 hPa height through to the late 19th century for the whole Northern Hemisphere. As the SLP and temperature coverage improved over time, the number of predictors decreased by about 1 in the most recent periods, and the root mean squared error decreased by about 0.8 m. A leave-one-out cross-validation method was used to test the skill and stability of the regression models. The reduction of error during the cross-validation period of 1958–1997 varied from 0.33 to 0.56, depending on the SLP data. Reconstructions were also checked using NCEP/NCAR 500 hPa heights from January 1949 to December 1957, and compared with the historical reconstruction over Europe. Reconstructions show high consistency with these independent data sets. Generally, the reconstruction provides a valuable opportunity to analyze, as well as to validate climate simulations of the variability in free atmosphere circulations over the past one hundred years.  相似文献   

Inception of the Northern European ice sheet due to contrasting ocean and insolation forcing   总被引：1，自引：0，他引：1  

Bjørg Risebrobakken  Trond Dokken  Eystein Jansen  Yongqi Gao  Helge Drange 《Quaternary Research》2007,67(1):128-135

About 115,000 yr ago the last interglacial reached its terminus and nucleation of new ice-sheet growth was initiated. Evidence from the northernmost Nordic Seas indicate that the inception of the last glacial was related to an intensification of the Atlantic Meridional Overturning Circulation (AMOC) in its northern limb. The enhanced AMOC, combined with minimum Northern hemisphere insolation, introduced a strong sea-land thermal gradient that, together with a strong wintertime latitudinal insolation gradient, increased the storminess and moisture transport to the high Northern European latitudes at a time when the Northern hemisphere summer insolation approached its minimum.  相似文献   

Global and regional surface cooling in a warming climate: a multi-model analysis     

Iselin Medhaug  Helge Drange 《Climate Dynamics》2016,46(11-12):3899-3920

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Gravity currents down canyons: effects of rotation     

Jarle Berntsen  Elin Darelius  Helge Avlesen 《Ocean Dynamics》2016,66(10):1353-1378

The flow of dense water in a V-shaped laboratory-scale canyon is investigated by using a non-hydrostatic numerical ocean model with focus on the effects of rotation. By using a high-resolution model, a more detailed analysis of plumes investigated in the laboratory (Deep-Sea Res I 55:1021–1034 2008) for laminar flow is facilitated. The inflow rates are also increased to investigate plume structure for higher Reynolds numbers. With rotation, the plumes will lean to the side of the canyon, and there will be cross-canyon geostrophic currents and Ekman transports. In the present study, it is found that the cross-canyon velocities are approximately 5 % of the down-canyon velocities over the main body of the plume for the rotational case. With rotation, the flow of dense water through the body of the plume and into the plume head is reduced. The plume head becomes less developed, and the speed of advance of the head is reduced. Fluid parcels near the top of the plume will to a larger extent be left behind the faster flowing dense core of the plume in a rotating system. Near the top of the plume, the cross-canyon velocities change direction. Inside the plume, the cross-flow is up the side of the canyon, and above the interface to the ambient there is a compensating cross-flow down the side of the canyon. This means that parcels of fluid around the interface become separated. Parcels of fluid around the interface with small down-canyon velocity components and relative large cross-canyon components will follow a long helix-like path down the canyon. It is found that the entrainment coefficients often are larger in the rotational experiments than in corresponding experiments without rotation. The effects of rotation and higher inflow rates on the areal patterns of entrainment velocities are demonstrated. In particular, there are bands of higher entrainment velocities along the lateral edges of the plumes in the rotational cases.  相似文献   

A multi-model comparison of Atlantic multidecadal variability     

Jin Ba  Noel S. Keenlyside  Mojib Latif  Wonsun Park  Hui Ding  Katja Lohmann  Juliette Mignot  Matthew Menary  Odd Helge Otterå  Bert Wouters  David Salas y Melia  Akira Oka  Alessio Bellucci  Evgeny Volodin 《Climate Dynamics》2014,43(9-10):2333-2348

A multi-model analysis of Atlantic multidecadal variability is performed with the following aims: to investigate the similarities to observations; to assess the strength and relative importance of the different elements of the mechanism proposed by Delworth et al. (J Clim 6:1993–2011, 1993) (hereafter D93) among coupled general circulation models (CGCMs); and to relate model differences to mean systematic error. The analysis is performed with long control simulations from ten CGCMs, with lengths ranging between 500 and 3600 years. In most models the variations of sea surface temperature (SST) averaged over North Atlantic show considerable power on multidecadal time scales, but with different periodicity. The SST variations are largest in the mid-latitude region, consistent with the short instrumental record. Despite large differences in model configurations, we find quite some consistency among the models in terms of processes. In eight of the ten models the mid-latitude SST variations are significantly correlated with fluctuations in the Atlantic meridional overturning circulation (AMOC), suggesting a link to northward heat transport changes. Consistent with this link, the three models with the weakest AMOC have the largest cold SST bias in the North Atlantic. There is no linear relationship on decadal timescales between AMOC and North Atlantic Oscillation in the models. Analysis of the key elements of the D93 mechanisms revealed the following: Most models present strong evidence that high-latitude winter mixing precede AMOC changes. However, the regions of wintertime convection differ among models. In most models salinity-induced density anomalies in the convective region tend to lead AMOC, while temperature-induced density anomalies lead AMOC only in one model. However, analysis shows that salinity may play an overly important role in most models, because of cold temperature biases in their relevant convective regions. In most models subpolar gyre variations tend to lead AMOC changes, and this relation is strong in more than half of the models.  相似文献   

Nannoplankton successions in the northern Red Sea during the last glaciation (60 to 14.5 ka BP): Reactions to climate change   总被引：1，自引：0，他引：1  

Heiko-Lars Legge  Jrg Mutterlose  Helge W. Arz  Jürgen Ptzold 《Earth and Planetary Science Letters》2008,270(3-4):271-279

Due to its restricted connection with the Indian Ocean, the desert-enclosed Red Sea is extremely sensitive to global sea level changes and thus ideally suited for paleoceanographic studies of what occurred during the last glaciation. The understanding of its glacial history is, however, still limited. A serious obstacle to obtain satisfactory paleoecological information has been the rarity of microfossil proxy species caused by high salinities. Here, we present a continuous and well-dated calcareous nannoplankton record from the northern Red Sea, covering the interval from 60–14.5 ka BP. Our investigation shows that the composition of the calcareous nannoplankton community varied between  32 ka BP and 14.5 ka BP in response to rapid environmental changes which are closely correlated to climatic fluctuations described from the North Atlantic region. Heinrich events H3, H2 and H1 are dominated by Emiliania huxleyi. Gephyrocapsa oceanica and especially Gephyrocapsa ericsonii are abundant between H3–H2 and H2–H1. A less pronounced response of the calcareous nannoplankton to the high latitudinal climatic oscillations is documented prior to  32 ka BP, suggesting that a strong atmospheric coupling between the northern Red Sea and the North Atlantic realm was established in the late Marine Isotope Stage 3. In contrast to the previously held view of a sea level related salinity increase as the major cause for changes of the plankton communities within the glacial Red Sea, we interpret the documented variations as being caused by local hydrographic changes under the atmospheric control from the extratropics. Temperature changes and especially variations of the water stratification appear to be critical selective factors for the calcareous nannoplankton composition.  相似文献   

Habitat Selection and Ecology of Two Speleophilic Gobiid Fishes(Pisces: Gobiidae) from the Western Mediterranean Sea     

Jürgen Herler  Robert A. Patzner  Harald Ahnelt&  Helge Hilgers 《Marine Ecology》1999,20(1):49-62

The life habits and microhabitat selection of speleophilic gobiid fishes were investigated on the Balearic Island of Ibiza (western Mediterranean Sea). Corcyrogobius liechtensteini (Kolombatović, 1891) was the most frequent species within submarine crevices, cavities and caves. Didogobius splechtnai Ahnelt & Patzner, 1995 co-occurred with C. liechtensteini in several cases but showed a clear spatial separation based on a different microhabitat preference. The microhabitat selection of both species was confirmed by habitat-choice experiments in anaquarium. Corcyrogobius liechtensteini was frequent in depths between 5 m and 25 m and attained abundances of 14.2 individuals · m⁻². This species inhabited the ceilings and upper parts of the walls within the caves. D. splechtnai was mainly found between 7 m and 11 m and showed abundances of approximately 2 indivi-duals · m⁻². This species occupied the fine sediment bottoms in the innermost parts of crevices and caves. The growth and the maximum age of both species were determined by length-frequency distributions. The overall sex ratio from catches of three different years are given for C. liechtensteini .  相似文献   

The response of the North Pacific Decadal Variability to strong tropical volcanic eruptions   总被引：5，自引：2，他引：3  

Tao Wang  Odd Helge Otter?  Yongqi Gao  Huijun Wang 《Climate Dynamics》2012,39(12):2917-2936

In this study, the effects of volcanic forcing on North Pacific climate variability, on interannual to decadal time scales, are examined using climate model simulations covering the last 600?years. The model used is the Bergen Climate Model, a fully coupled atmosphere–ocean general circulation model. It is found that natural external forcings, such as tropical strong volcanic eruptions (SVEs) and variations in total solar irradiance, play an important role in regulating North Pacific Decadal Variability (NPDV). In response to tropical SVEs the lower stratospheric pole–to–equator temperature gradient is enhanced. The North polar vortex is strengthened, which forces a significant positive Arctic Oscillation. At the same time, dipole zonal wind anomalies associated with strong polar vortex propagate downward from the lower stratosphere. Through positive feedbacks in the troposphere, the surface westerly winds across the central North Pacific are significantly weakened, and positive sea level pressure anomalies are formed in the North Pacific. This anomalous surface circulation results in changes in the net heat fluxes and the oceanic advection across the North Pacific. As a result of this, warm water converges in the subtropical western North Pacific, where the surface waters in addition are heated by significantly reduced latent and sensible heat fluxes from the ocean. In the eastern and high–latitude North Pacific the ocean loses more heat, and large–scale decreases in sea surface temperatures are found. The overall response of this chain of events is that the North Pacific enters a negative phase of the Pacific decadal oscillation (PDO), and this negative phase of the PDO is maintained for several years. It is thus concluded that the volcanic forcing plays a key role in the phasing of the PDO. The model results furthermore highlight the important role of troposphere–stratosphere coupling, tropical–extratropical teleconnections and extratropical ocean–atmosphere interactions for describing NPDV.  相似文献