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941.
942.
Ahmed M. Yosri Mohamed A. Abd-Elmegeed Ahmed E. Hassan 《Arabian Journal of Geosciences》2016,9(10):567
Gravity Recovery and Climate Experiment (GRACE) level two (L2) data is used in estimating the groundwater storage changes (GWSC) in the Nubian Sandstone Aquifer System (NSAS). This set of data consists of spherical harmonics coefficients with specific degree and order. The GRACE data is de-correlated using a sixth degree polynomial in order to reduce the effect of the noise error resulting from the correlation between the spherical harmonics coefficients with the same degree parity. The GRACE estimates of GWSC are smoothed using Gaussian filter with half width of 1000 km. This half width is chosen in order to maximize the correlation between the GRACE estimates of GWSC and previous modeling results of the NSAS. The loss in groundwater storage occurring in each of the four countries sharing the NSAS is calculated to assess the sustainability of using the NSAS as a water resource in each country. The overarching finding in this study is that NSAS is losing its groundwater storage at a very high rate. Also, it is found that Egypt is the fastest in losing its groundwater storage from the NSAS. This loss of groundwater storage in Egypt may not necessarily be resulting from in-country extractions because of the trans-boundary nature of this aquifer. The GRACE-based estimates are found to be close to available data and previous modeling results of the NSAS. 相似文献
943.
Abbas-Ali A Bidokhti Maryam Gharaylou Nafiseh Pegahfar Samaneh Sabetghadam Maryam Rezazadeh 《Journal of Earth System Science》2016,125(2):431-442
Determination of dust loading in the atmosphere is important not only from the public health point of view, but also for regional climate changes. The present study focuses on the characteristics of two major dust events for two urban areas in Iran, Kermanshah and Tehran, over the period of 4 years from 2006 to 2009. To detect extreme dust outbreaks, various datasets including synoptic data, dust concentration, reanalysis data and numerical results of WRF and HYSPLIT models were used. The weather maps demonstrate that for these events dusts are mainly generated when wind velocity is high and humidity is low in the lower troposphere and the region is under the influence of a thermal low. The event lasts until the atmospheric stability prevails and the surface wind speed weakens. The thermal low nature of the synoptic conditions of these major events is also responsible for deep boundary layer development with its thermals affecting the vertical dust flux over the region. Trajectory studies show that the dust events originated from deserts in Iraq and Syria and transported towards Iran. The main distinction between the two types of mobilizations seems to affect the dust concentrations in the Tehran urban area. 相似文献
944.
The hybrid two-way coupled 3DEnsVar assimilation system was tested with the NCMRWF global data assimilation forecasting system. At present, this system consists of T574L64 deterministic model and the grid-point statistical interpolation analysis scheme. In this experiment, the analysis system is modified with a two-way coupling with an 80 member Ensemble Kalman Filter of T254L64 resolution and runs are carried out in parallel to the operational system for the Indian summer monsoon season (June–September) for the year 2015 to study its impact. Both the assimilation systems are based on NCEP GFS system. It is found that hybrid assimilation marginally improved the quality of the forecasts of all variables over the deterministic 3D Var system, in terms of statistical skill scores and also in terms of circulation features. The impact of the hybrid system in prediction of extreme rainfall and cyclone track is discussed. 相似文献
945.
Leistner G. M. E. 《GeoJournal》1981,2(2):85-93
It is widely held that the large majority of African countries are too small in terms of population and purchasing power to allow meaningful and rapid economic development to take place within the constraints of their domestic economies. Sub-regional groupings of states are called for in order to overcome the drawbacks of small size. Many attempt at establishing larger economic unions in Africa have failed. Particular interest therefore attaches to the southern African sub-region where South Africa, as the only industrial power south of the Sahara, functions as a powerhouse for neighbouring as well as more distant economies. The article provides a factual sketch of existing economic ties (infrastructure, trade, labour, tourism, finance and technology). Attention is paid to South Africa's efforts to create a constellation of states, and also to to the counter-measures of nine neighbouring states. 相似文献
946.
The mode of occurrence of gold in the Yata micro-disseminated gold deposit is ap-proached through chemical phase studies coupled with ore-dressing monitoring and micro-beam analysis.The results showed that gold occurred for the most part as ultra-microscopic particles adsorbed on the surfaces or fracture planes of pyrite and other sulphides.The proportions of gold of different occurrences were estimated solutions containing nanometer-sized gold particles were prepared following the hydrolysis-reduction procedure and the adsorption of nanometer-sized gold on ordinary sulphides and rocks was experimentally determined.It is evident that sulphides are good adsorbents of gold and this is consistent with geological observations. 相似文献
947.
A. K. Varma R. M. Gairola A. K. Mathur B. S. Gohil Vijay K. Agarwal 《Journal of Earth System Science》2002,111(3):247-256
In this paper, MSMR geophysical products like Integrated Water Vapour (IWV), Ocean Surface Wind Speed (OWS) and Cloud Liquid
Water (CLW) in different grids of 50, 75 and 150 kms are compared with similar products available from other satellites like
DMSP-SSM/I and TRMMTMI. MSMR derived IWV, OWS and CLW compare well with SSM/I and TMI finished products. Comparison of MSMR
derived CLW with that derived from TMI and SSM/I is relatively in less agreement. This is possibly due to the use of 37 GHz
in SSM/I and TMI that is highly sensitive to CLW, while 37 GHz channels are not available on MSMR. Monthly comparison of MSMR
geophysical products with those from TMI is all carried out for climatological purpose. The monthly comparisons were much
better compared to instantaneous comparisons. In this paper, details of the data analysis and comparison results are presented.
The usefulness of the MSMR vis-à-vis other sensors is also discussed. 相似文献
948.
To assess responses and recovery of salt marsh grass species, we manipulated external nutrient supply and removed shoots of
Spartina alterniflora or Spartina patens from fertilized and control plots in a Massachusetts marsh. The pulse-and-recovery experiment included treatments for 5 years,
and recovery for an additional 7 years. Responses of these potential competitors sensitively depended on local contingencies
of elevation and nutrient dose, and, moreover, the differences in outcomes were emphasized at longer time scales. Local contingencies
became manifest as differences in responsiveness and resiliency of the different grass species, with differing time courses
and longer-term outcomes as to what species were present. These features might explain the diverse results obtained in shorter-term
salt marsh experiments, and provide a view of the complex suite of species-specific and external environmental variables that
may control competitive interactions in general. 相似文献
949.
950.
Nitrate pollution of groundwater in Toyserkan,western Iran 总被引:3,自引:2,他引:3
Mohsen Jalali 《Environmental Earth Sciences》2011,62(5):907-913
A total of 95 groundwater samples were collected from Toyserkan, western Iran to assess the chemical composition and nitrate
(NO3
−) status of groundwater. The most prevalent water type is Ca–HCO3 followed by water types Ca–Mg–HCO3. In comparison with the World Health Organization (WHO) drinking water guideline of 50 mg l−1 for NO3
−, a total of nine wells (9.5%) showed higher concentrations. In 36% of samples (34) NO3
− concentration was low (<20 mg l−1), and in 53.7% of samples (51), in the range of 20–50 mg l−1. The samples were classified into four groups based on NO3
− and chloride (Cl−) concentrations. Of the samples, 40% were classified as group 4 and were relatively high in Cl− and NO3
− (Cl− > 47 mg l−1, NO3
− > 27 mg l−1). The high correlation between NO3
− and Cl− (r = 0.86, p < 0.01) is consistent with a manure source, resulting from the practice of adding salt to animal feed. Pollution of groundwaters
appeared to be affected by the application of inorganic fertilizer at greater than agronomic rates, Cl-salt inputs, and irrigation
practice. 相似文献