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51.
Climate links and recent extremes in antarctic sea ice, high-latitude cyclones, Southern Annular Mode and ENSO 总被引:2,自引:0,他引:2
In this article, we study the climate link between the Southern Annular Mode (SAM) and the southern sea-ice extent (SIE), and discuss the possible role of stationary waves and synoptic eddies in establishing this link. In doing so, we have used a combination of techniques involving spatial correlations of SIE, eddy streamfunction and wind anomalies, and statistics of high-latitude cyclone strength. It is suggested that stationary waves may be amplified by eddy anomalies associated with high latitude cyclones, resulting in more sea ice when the SAM is in its positive phase for most, but not all, longitudes. A similar association is observed during ENSO (La Ni?a years). Although this synergy in the SAM/ENSO response may partially reflect preferential areas for wave amplification around Antarctica, the short extent of the climate records does not allow for a definite causality connection to be established with SIE. Stronger polar cyclones are observed over the areas where the stationary waves are amplified. These deeper cyclones will break up and export ice equatorward more efficiently, but the near-coastal regions are cold enough to allow for a rapid re-freeze of the resulting ice break-up. We speculate that if global warming continues this same effect could help reverse the current (positive) Antarctic SIE trends once the ice gets thinner, similarly to what has been observed in the Northern Hemisphere. 相似文献
52.
A detailed hydrogeological and hydrochemical study was carried out in Yamuna-Krishni sub-basin which is a part of the vast
central Ganga plain. Groundwater is the major source of water supply for agricultural, domestic and industrial uses. The excess
use of groundwater has resulted in depletion of water levels. The groundwater quality, too, has deteriorated in areas dominated
by industrial activity. This has led to the preparation of a groundwater vulnerability map in relation to contamination. Groundwater
vulnerability maps are valuable derivative maps that show, quantitatively or qualitatively, certain characteristics of the
sub-surface environment that determine vulnerability of groundwater to contamination. The modified DRASTIC method was used
to prepare vulnerability map. The parameters like depth to water, net recharge, aquifer media, soil media, impact of vadose
zone, hydraulic conductivity and land use pattern, owing to its bearing on groundwater regime, were considered to prepare
vulnerability map. The vulnerability index is computed as the sum of the products of weight and rating assigned to each of
the input considered as above. The vulnerability index ranges from 140 to 180, and is classified into four classes i.e. 140–150,
150–160, 160–170 and 170–180 corresponding to low, medium, high and very high vulnerability zones respectively. Using this
index, a groundwater vulnerability potential map was generated which shows that 7%, 40% and 53% of the study area falls in
low, medium and high to very high vulnerability zones respectively. The map, thus generated, can be used as a tool for protection
and management of aquifers from contamination. 相似文献
53.
Hafiz Muhammad Awais Rashid J. A. D. K. Wanigarathna L. C. Kurukulasuriya N. H. Priyankara A. M. N. Alagiyawanna Takeshi Saito Ken Kawamoto 《Environmental Earth Sciences》2017,76(11):396
This study aimed to develop a low-cost and effective clay liner material for solid waste landfills in Sri Lanka. A locally available clayey soil and its admixtures with 5 and 10% bentonite were examined for this purpose. Laboratory experiments to determine soil plasticity and swell index were carried out on the tested samples. Hydraulic conductivity (k) tests were carried out in the laboratory using water and an aqueous solution of CaCl2 on unconsolidated samples prepared by either dry or slurry packing and pre-consolidated samples with five different consolidation pressures (p) from 10 to 200 kPa. Measured liquid limits for tested admixtures increased with increasing bentonite contents and correlated well with measured values of the swell index. The difference in permeant solutions had little effect on measured k values for both unconsolidated and pre-consolidated samples. The hydraulic conductivities were highly affected by changing p, i.e., the k values decreased on two orders of magnitude as p increased from 10 to 200 kPa. The Kozeny–Carman equation, a theoretical permeability model that expresses the k-porosity relationship, was applied to measured data including reported values. Results showed the Kozeny–Carman equation captured well the porosity-dependent k values for tested soils and their admixtures with bentonite under a wide range of void ratios, suggesting that the Kozeny–Carman equation is a useful tool to estimate the magnitude of k values for differently compacted soil and its bentonite admixtures. 相似文献
54.
This study records length-weight relationships(LWRs)for eleven commercially important marine catfi sh species of the family Ariidae(sea catfi shes)and Plotosidae(eel catfi shes)from the northern Arabian Sea coast of Pakistan.The specimens were sampled from December 2014 to November 2015,using bottom trawls with various mesh sizes by commercial vessels.The species were Nemapteryx caelatus,Sciades sona,Arius gagora,Batrachocephalus mino,Netuma thalassina,N.bilineata,Osteogeneiosus militaris,Plicofollis dussumieri,P.tenuispinis,Plotosus limbatus,and P.lineatus.Of the eleven species,two species A.gagora and N.bilineata were recorded for the fi rst time and LWRs for four species A.gagora,N.bilineata,S.sona,and B.mino still have no data in the Fish Base database.In addition,new maximum length for each of the three species N.bilineata,O.militaris and B.m ino was also found. 相似文献
55.
Groundwater flow modelling of Yamuna-Krishni interstream,a part of central Ganga Plain Uttar Pradesh 总被引:4,自引:0,他引:4
Groundwater is a major source of water for agricultural and domestic requirements in western Uttar Pradesh. Due to increasing
agricultural requirements the abstraction of groundwater has increased manifold in the last two-to-three decades. The quaternary
alluvium hosts the aquifer in the region. The study area forms a part of Yamuna-Krishni interfluve. Although the area hosts
potential aquifers these have been adversely affected by poor management. For effective groundwater management of a basin
it is essential that a careful water balance study should be carried out. Keeping this in mind groundwater flow modelling
was attempted to simulate the behaviour of the flow system and evaluate the water balance. The groundwater flow modelling
was carried out. The horizontal flows, seepage losses from unlined canals, recharge from rainfall and irrigation return flows
were applied using different boundary packages available in Visual MODFLOW, Pro 4.1. The river-aquifer interaction was simulated
using the river boundary package. Hydraulic conductivity values were applied to specific zones and these ranged from 9.8 to
26.6m/day. Recharge due to rainfall and irrigation returns were assigned to respective zones. Pumping rates of 500m3/day, 1000m3/day, 1500m3/day, 2000m3/day and 2500m3/day were applied to appropriate areas of the model to simulate areas of stress. The zone budget shows a water balance deficit
for the period June 2006 to June 2007. The total recharge to the study area is 160.21 million m3 (Mcum). The groundwater draft through pumping is of the order of 233.56 Mcum, thus leaving a deficit balance of −73.35 Mcum.
The sensitivity of the model to input parameters was tested by varying the parameters of interest over a range of values,
monitoring the response of the model and determining the root mean square error of the simulated groundwater heads to the
measured heads. These analyses showed that the model is most sensitive to hydraulic conductivity and recharge parameters.
Three scenarios were considered to predict aquifer responses under varied conditions of groundwater bstraction. 相似文献
56.
57.
Ussif Rashid Sumaila Ahmed Khan Louise Teh Reg Watson Peter Tyedmers Daniel Pauly 《Marine Policy》2010
The life spans of demersal species of fishes occurring in deep-waters are much longer and their potential growth rates much lower than those of related shallow water species. As a result, deep-sea demersal fish species are more vulnerable to exploitation. This is because low growth rates relative to the available market discount rate for capital makes it desirable for fishing firms to mine, rather than sustainably exploit, these resources even in the absence of fisheries subsidies. However, it is common knowledge that governments around the world do provide subsidies to their fishing industries. The objective of this contribution is to estimate the global amount of subsidies paid to bottom trawl fleets operating in the high seas, i.e., outside of the Exclusive Economic Zones of maritime countries. Our study suggests that fisheries subsidies to these fleets stand at about US$152 million per year, which constitutes 25% of the total landed value of the fleet. Economic data for bottom trawlers suggest that the profit achieved by this vessel group is normally not more than 10% of landed value. The implication of this finding is that without subsidies, the bulk of the world's bottom trawl fleet operating in the high seas will be operating at a loss, and unable to fish, thereby reducing the current threat to deep-sea and high seas fish stocks. 相似文献
58.
Colombia has coasts on both the Atlantic and Pacific Oceans, but its marine fisheries are limited by the relatively small size of commercially important stocks. However, diverse fishery resources have traditionally been exploited by coastal communities, and industrial fisheries have grown in recent years with the intensification of tuna fishing in both oceans. The management of Colombia's fisheries has been hampered by frequent administrative changes, which has notably led to the disappearance of a part of the official landings data. We estimated total fisheries removals (reported plus discards and unreported catches) in the Colombian Atlantic and Pacific Oceans for the period 1950–2006. We used secondary sources of information to estimate missing data, and we estimated subsistence fishing and the unreported by-catches of the shrimp and tuna fisheries. We used available information on seafood prices to estimate the relative economic impact (gross revenues) of the small-scale and industrial sectors for the period 2000–2006. Our results suggest that for the period 1950–2006, the Colombian marine fisheries catches may have been almost twice the landings reported by FAO on behalf of the country (2.8 times higher in the Atlantic; 1.3 times higher in the Pacific). Although the total gross revenues of industrial fisheries were higher than those of the small-scale sector, the latter commanded higher gross revenues in the Atlantic in 2006. 相似文献
59.
By comparing the real reductions in fishing capacity of the European Union (EU) and the effects of technological efficiency, this paper presents the first comprehensive analysis since the creation of the Common Fisheries Policy (CFP). Using a standard methodology and a conservative value of ±4.4% for annual technological progress, the results obtained for tonnage indicated that the EU-13 fleet's fishing capacity was reduced by >4% for only three years (1991, 2004, and 2006) in the 1987–2006 period. 相似文献
60.
Bilal Rashid Astor-Lonice Bal Glyn J. J. Williams Ann H. Muggeridge 《Computational Geosciences》2012,16(2):409-422
The vorticity of the displacement velocity is used to derive dimensionless numbers that can be used to quantify the relative
importance of viscosity ratio, gravity, diffusion/dispersion and permeability heterogeneity on secondary hydrocarbon recovery.
Using this approach, a new objective measure of the impact of permeability and porosity heterogeneity on reservoir performance
is obtained. This is used, in conjunction with other dimensionless numbers, to analyse the relative impact of heterogeneity,
buoyancy effects, mobility ratio and dispersion on breakthrough time and recovery at 1 pore volume injected during first contact
miscible gas injection. This is achieved using results obtained from detailed simulation of miscible displacements through
a range of geologically realistic reservoir models. This study goes some way towards developing a unified mathematical framework
to determine under which flow conditions reservoir heterogeneity becomes more important than other physical processes. We
propose that comparison of these dimensionless numbers can be used to identify the key factors controlling recovery and thus
assist the engineer in determining appropriate enhanced oil recovery techniques to improve recovery. 相似文献