Spatial variability and interpolation of daily precipitation amount

Daily precipitation amounts show spatial variation over sub-continential regions. Point measurements, representative for regions of land, have to be interpolated towards unobserved locations. In this study four days in 1984 were selected to investigate the spatial variability of daily precipitation amount in North-western Europe in relation to the meteorological conditions. Data were interpolated using Kriging. Crossvalidation was used to compare interpolated values with measured values. Large differences in the spatial structure of daily precipitation amount are obsered as a result of different meterological conditions. Stratification of the study area into a coastal, a mountainous and an interior stratum proved to be successful, reducing the Mean Squared Error of Prediction with up to 55%.     

Effect of Moisture on Attraction Force in Beach Sand

Beach sands located above the sea water level exist in an unsaturated, rather than a fully saturated or dry state. Within the unsaturated zone, a steep excavated surface can be sustained for some unknown but finite time, and some slopes may remain stable for extended time periods due to capillary forces. These observations clearly indicate small but nonzero values for attraction strength (tensile strength and cohesion) in unsaturated beach sands, especially apparent but not confined to settings where there are low stress levels. Thus, experiments were carried out to quantify the magnitude of attraction strength in moist sands (D_r = 30%) and to examine the variation of these values as a function of moisture content and presence of a small amount of fines. Tensile strength, which is significantly different from zero, increases with increasing moisture content and fines. However, the influences of fines on the tensile strength are substantially dependent on the water content. Apparent cohesion strength is also identified in moist sands. A simple relationship between tensile strength and apparent cohesion is proposed using the obtained data. This study would help to further understand the phenomenon of stability of beach sands.     

Reference points for optimal fish stock management: A lesson to be learned from the Northeast Arctic cod stock

In the North Atlantic the Icelandic, the North Sea, and the Newfoundland cod stocks are currently overexploited. Overexploitation also characterised the Northeast Arctic cod stock, but effective management measures introduced in 1990 and the years thereafter have brought this stock within safe biological limits. The Northeast Arctic cod stock is transboundary and shared between Norway and Russia. As guidelines for a sound management strategy of this cod stock in the future, reference points for management are discussed. As a point of departure, a management strategy which fulfils the objectives for fishery policy stated by Norway is analysed. These objectives, focusing on sustainable harvesting, increased profitability and the role of the fishery as employer of labour in rural districts are fundamental in most of the world's fishery nations.The “optimal” strategy is defined as the one which fulfils these in the best way possible. The natural variations are discussed and the biological and economic yield's dependence upon the rate of exploitation are analysed. The analysis shows that the size of the spawning stock should be no less than 500 000 tonnes and that highest yield is obtained through a rate of exploitation of around 17–30% (equivalent to a fishing mortality of about 0.20–0.40). A spawning stock size of 500 000 tonnes should therefore serve as a “limit reference point” and a fishing mortality of about 0.20–0.40 should serve as a “target reference point” in the management of Northeast Arctic cod.The method described may be applied to other demersal stocks to help establish target and limit reference points in order to conduct a sound management.     

Implications of estimated and measured thermal conductivity for oceanic heat flow studies

Heat flow data provide constraints on the thermal structure and evolution of the oceanic lithosphere. Because precise determination of the heat flux requires that both the thermal gradient and the thermal conductivity be well determined we have examined the thermal conductivities used in a new Pacific Basin heat flow data set. 43% of the 1600 heat flow determinations rely on values estimated by various methods, rather than directly measured. Although the measured and estimated conductivities have comparable means, the measured conductivities have a standard deviation 50% larger than the estimated, suggesting that the estimated values underestimate the actual variation. We investigate the limitations of using such estimates by examining factors controlling the variations of measured conductivity values. We find that the variation between the closest adjacent sites increases with increasing separation, such that sites within 200 km are on average noticeably closer in conductivity than sites further apart. Contributing to this effect may be the variation of conductivity with lithology (with mean conductivity highest for carbonate oozes, intermediate for deep-sea clays, and least for siliceous oozes) and a possible trend of decreasing conductivity with increasing seafloor depth. Tests with the measured data suggest that the best method for estimating conductivity is using the mean value measured within 200 km. The mean of a larger geographical region is a somewhat poorer predictor, and using the oceanwide mean and the value at the nearest site are poorer still. Approximately 29% of the estimated values were not based on measurements from a reference site. For most others, the reference site was the nearest measurement from the same cruise, typically a large distance away. For those sites where conductivity was not measured, 78% had measured conductivity within 200 km and were reestimated using the local mean, whereas the remaining 22% were reestimated using the regional mean. The resulting change in the estimated conductivity averaged 9% using the local mean and 6% using the regional mean. We suggest that such a procedure be used to improve the utility of the heat flow data set, as an alternative to discarding the large fraction of the available data that does not incorporate measured conductivities.     

Organic carbon content/sedimentation rate relationship and its paleoenvironmental significance for marine sediments

Organic carbon content and sedimentation rate data may give information about the depositional environment of marine sediments. For sediments deposited under oxic deep-water conditions, a positive correlation exists between organic carbon content and sedimentation rate, with very high organic carbon values and high sedimentation rates typical for coastal upwelling areas. Under anoxic deep-water conditions, no such correlation exists. This relationship between (marine) organic carbon and sedimentation rate (the “OCSR diagram”) has been used to characterize the depositional environments of Deep-Sea Drilling Project/Ocean Drilling Program (DSDP/ODP) sediments of Late Cenozoic and Cretaceous age. Furthermore, the results are compared with organic carbon/sulfur data.     

Deep-water circulation in the Northeast Atlantic and climatic changes during the Late Neogene (DSDP Site 141)

Oxygen and carbon stable isotope data of Pyrgo murrhina and flux rates of calcium carbonate in the bio- and magnetostratigraphically dated sediment sequence at DSDP Site 141 were used for a reconstruction of the deep-water circulation in the Northeast Atlantic during Late Miocene and Pliocene times. A distinct change towards reduced advection of deep water recorded near 5.4 Ma is contemporaneous with the cessation of the outflow of the saline Mediterranean water into the Atlantic. During the Pliocene, between 4.5 and 2.75 Ma and between 2.1 and 1.8 Ma, North Atlantic Deep Water (NADW) circulation was sluggish and Site 141 possibly influenced by Antarctic Bottom Water (AABW). Near 2.75 Ma, the advection of well-oxidized NADW was strongly intensified. This change is related to an onset of major Arctic ice growth and/or a major cooling of NADW.     

Numerical study of the relaxation of one-dimensional gravitational systems: A reply

This paper is a response to Numerical Study of the Relaxation of One-Dimensional Gravitational Systems, by Luwelet al. (1984) hereafter referred to as (LSR). The subject of their work is a topic studied earlier by us (Wrightet al., 1982) hereafter referred to as (WMS). Each group has studied the dynamical evolution of this system by applying the Kolmogorov-Smirnov goodness of fit test to distributions of the density and velocity. The methods employed and conclusions reached by LSR concerning relaxation in this system are questioned. The earlier work of WMS is clarified.This article was scheduled to appear in the March issue ofAstrophysics and Space Science, along with the article Numerical Study of the Relaxation of One-Dimensional Gravitational Systems by Luwel, Severn, and Rousseeuw. Its Appearance in the September issue is due to an oversight at the time of making up the March issue.     

Stability of model performance and parameter values on two catchments facing changes in climatic conditions

Abstract

Hydrological models are often used for studying the hydrological effects of climate change; however, the stability of model performance and parameter values under changing climate conditions has seldom been evaluated and compared. In this study, three widely-used rainfall–runoff models, namely the SimHYD model, the HBV model and the Xin’anjiang model, are evaluated on two catchments subject to changing climate conditions. Evaluation is carried out with respect to the stability in their performance and parameter values in different calibration periods. The results show that (a) stability of model performance and parameter values depends on model structure as well as the climate of catchments, and the models with higher performance scores are more stable in changing conditions; (b) all the tested models perform better on a humid catchment than on an arid catchment; (c) parameter values are also more stable on a humid catchment than on an arid catchment; and (d) the differences in stability among models are somewhat larger in terms of model efficiency than in model parameter values.