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101.
Non‐point source (NPS) pollution from agricultural land is increasing exponentially in many countries of the world, including India. A modified approach based on the conservation of mass and reaction kinetics has been derived to estimate the inflow of non‐point source pollutants from a river reach. Two water quality variables, namely, nitrate (NO3) and ortho‐phosphate (o‐PO4), which are main contributors as non‐point source pollution, were monitored at four locations of River Kali, western Uttar Pradesh, India, and used for calibration and validation of the model. Extensive water quality sampling was done with a total of 576 field data sets collected during the period from March 1999 to February 2000. Remote sensing and geographical information system (GIS) techniques were used to obtain land use/land cover of the region, digital elevation model (DEM), delineation of basin area contributing to non‐point source pollution at each sampling location and drainage map. The results obtained from a modified approach were compared with the existing mass‐balance equations and distributed modelling, and the performances of different equations were evaluated using error estimation viz. standard error, normal mean error, mean multiplicative error and correlation statistics. The developed model for the River Kali minimizes error estimates and improves correlation between observed and computed NPS loads. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
102.
Summary The motivation for this study came from recent results of an Atmospheric Model Inter-comparison Project (AMIP) coordinated by the Lawrence Livermore Laboratory at Livermore, California. That project included a review of seasonal monsoon simulations from 13 different atmospheric models over the world. Most of the models used a horizontal resolution of roughly 300 km. The seasonal monsoon simulations from these models varied significantly. The poor performance by these models stems in part from the use of the coarse resolution. The purpose of this note is to show that by using the same model physics and lower boundary conditions, such as snow/ice cover and sea surface temperatures, the use of the higher horizontal resolution does have a stronger positive impact on the skill of monthly rainfall when compared to a lower horizontal resolution. In this note we present the results of such a comparison between the horizontal resolutions of T42 and T170. These studies are carried out for the prescribed lower boundary specification of sea surface temperatures and snow/ice cover with the help of an Atmospheric General Circulation Model. Received August 16, 1999 Revised October 14, 1999  相似文献   
103.
The effect of a uniform transverse magnetic field on the free-convection and mass-transform flow of an electrically-conducting fluid past an infinite vertical plate for uniformly accelerated motion of the plate through a porous medium is discussed. The magnetic lines of force are assumed to be fixed relative to the plate. Expression for the velocity field and skin-friction are obtained by the Laplace transform technique. The influence of the various parameters, entering into the problem, on the velocity field and skin-friction is extensively discussed.  相似文献   
104.
An analytical study is performed to examine the effects of magnetic field on the free-convection and mass transfer flow through porous medium. The effects of various parameters on the velocity field are discussed by tables.  相似文献   
105.
Drilling at the barrage site of a hydropower project usually gives a reasonable picture of the sub-surface rock mass condition. However, when the overburden (OB) comprising river borne materials is very thick and the basement rock is deep, the drilling results become unreliable. In the present case, the depth to the granitic gneiss basement is 45m from the river level and the height of the proposed diversion barrage is only 24.5 m. For this reason, stripping of the overburden up to the basement is not considered feasible. Cross-borehole seismic tomography (CST) was carried out at the barrage site to investigate the inclusions and structure of the OB material in order to facilitate a foundation design suitable for permeable formation. Three sets of CST surveys were carried out up to a depth of 30 m between the three vertical boreholes that were prepared at the vertices of an equilateral triangle with a separation of 17.8 m. The tomograms precisely imaged the nature and disposition of the different constituents of the overburden material. A lens shaped low velocity layer (LVL) with seismic velocity Vp=2000–2500 ms?1 was mapped at a depth of 14.5m from the surface. Hence, it was recommended to shift the barrage axis by 50 m towards the downstream side of the proposed axis. The outcome of this study proved valuable for the designer who finalised the foundation design. Successful application of CST in OB characterisation has reiterated the need of such studies for barrage site investigations particularly in the Himalayan terrain.  相似文献   
106.
Size distribution of PM10 mass aerosols and its ionic characteristics were studied for 2 years from January 2006 to December 2007 at central Delhi by employing an 8-stage Andersen Cascade Impactor sampler. The mass of fine (PM2.5) and coarse (PM10?2.5) mode particles were integrated from particle mass determined in different stages. Average concentrations of mass PM10 and PM2.5 were observed to be 306 ± 182 and 136 ± 84 μg m?3, respectively, which are far in excess of annual averages stipulated by the Indian National Ambient Air Quality Standards (PM10: 60 μg m?3 and PM2.5: 40 μg m?3). The highest concentrations of PM10?2.5 (coarse) and PM2.5 (fine) were observed 505 ± 44 and 368 ± 61 μg m?3, respectively, during summer (June 2006) period, whereas the lower concentrations of PM10?2.5 (35 ± 9 μg m?3) and PM2.5 (29 ± 13 μg m?3) were observed during monsoon (September 2007). In summer, because of frequent dust storms, coarse particles are more dominant than fine particles during study period. However, during winter, the PM2.5 contribution became more pronounced as compared to summer probably due to enhanced emissions from anthropogenic activities, burning of biofuels/biomass and other human activities. A high ratio (0.58) of PM2.5/PM10 was observed during winter and low (0.24) during monsoon. A strong correlation between PM10 and PM2.5 (r 2 = 0.93) was observed, indicating that variation in PM10 mass is governed by the variation in PM2.5. Major cations (NH4 +, Na+, K+, Ca2+ and Mg2+) and anions (F?, Cl?, SO4 2? and NO3 ?) were analyzed along with pH. Average concentrations of SO4 2? and NO3 ? were observed to be 12.93 ± 0.98 and 10.33 ± 1.10 μg m?3, respectively. Significant correlation between SO4 2? and NO3 ? in PM1.0 was observed indicating the major sources of secondary aerosol which may be from thermal power plants located in the southeast and incomplete combustion by vehicular exhaust. A good correlation among secondary species (NH+, NO3 ? and SO4 2?) suggests that most of NH4 + is in the form of ammonium sulfate and ammonium nitrate in the atmosphere. During winter, the concentration of Ca2+ was also higher; it may be due to entrainment of roadside dust particles, traffic activities and low temperature. The molar ratio (1.39) between Cl? and Na+ was observed to be close to that of seawater (1.16). The presence of higher Cl? during winter is due to western disturbances and probably local emission of Cl? due to fabric bleaching activity in a number of export garment factories in the proximity of the sampling site.  相似文献   
107.
In this work, authors examine the variabilities of precipitation and surface air temperature (T2m) in Northeast China during 1948–2012, and their global connection, as well as the predictability. It is noted that both the precipitation and T2m variations in Northeast China are dominated by interannual and higher frequency variations. However, on interdecadal time scales, T2m is shifted significantly from below normal to above normal around 1987/1988. Statistically, the seasonal mean precipitation and T2m are largely driven by local internal atmospheric variability rather than remote forcing. For the precipitation variation, circulation anomalies in the low latitudes play a more important role in spring and summer than in autumn and winter. For T2m variations, the associated sea surface pressure (SLP) and 850-hPa wind (uv850) anomalies are similar for all seasons in high latitudes with significantly negative correlations for SLP and westerly wind anomaly for uv850, suggesting that a strong zonal circulation in the high latitudes favors warming in Northeast China. The predictability of precipitation and T2m in Northeast China is assessed by using the Atmospheric Model Inter-comparison Project type experiments which are forced by observed sea surface temperature (SST) and time-evolving greenhouse gas (GHG) concentrations. Results suggest that T2m has slightly higher predictability than precipitation in Northeast China. To some extent, the model simulates the interdecadal shift of T2m around 1987/1988, implying a possible connection between SST (and/or GHG forcing) and surface air temperature variation in Northeast China on interdecadal time scales. Nevertheless, the precipitation and T2m variations are mainly determined by the unpredictable components which are caused by the atmospheric internal dynamic processes, suggesting low predictability for the climate variation in Northeast China.  相似文献   
108.
In this study, the climate mean, variability, and dominant patterns of the Northern Hemisphere wintertime mean 200 hPa geopotential height (Z200) in a CMIP and a set of AMIP simulations from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Version 2 (CFSv2) are analyzed and compared with the NCEP/NCAR reanalysis. For the climate mean, it is found that a component of the bias in stationary waves characterized with wave trains emanating from the tropics into both the hemispheres can be attributed to the precipitation deficit over the Maritime continent. The lack of latent heating associated with the precipitation deficit may have served as the forcing of the wave trains. For the variability of the seasonal mean, both the CMIP and AMIP successfully simulated the geographical locations of the major centers of action, but the simulated intensity was generally weaker than that in the reanalysis, particularly for the center over the Davis Strait-southern Greenland area. It is also noted that the simulated action center over Aleutian Islands was southeastward shifted to some extent. The shift was likely caused by the eastward extension of the Pacific jet. Differences also existed between the CMIP and the AMIP simulations, with the center of actions over the Aleutian Islands stronger in the AMIP and the center over the Davis Strait-southern Greenland area stronger in the CMIP simulation. In the mode analysis, the El Nino-Southern Oscillation (ENSO) teleconnection pattern in each dataset was first removed from the data, and a rotated empirical orthogonal function (REOF) analysis was then applied to the residual. The purpose of this separation was to avoid possible mixing between the ENSO mode and those generated by the atmospheric internal dynamics. It was found that the simulated ENSO teleconnection patterns from both model runs well resembled that from the reanalysis, except for a small eastward shift. Based on the REOF modes of the residual data, six dominant modes of the reanalysis data had counterparts in each model simulation, though with different rankings in explained variance and some distortions in spatial structure. By evaluating the temporal coherency of the REOF modes between the reanalysis and the AMIP, it was found that the time series associated with the equatorially displaced North Atlantic Oscillation in the two datasets were significantly correlated, suggesting a potential predictability for this mode.  相似文献   
109.
Caribbean rainfall and associated regional-scale ocean–atmosphere anomalies are analyzed during and after warm pool (WP) and cold tongue (CT) El Niño (EN) events (i.e. from the usual peak of EN events in boreal winter to next summer from 1950 to 2011). During and after a CT event, a north–south dipolar pattern with positive (negative) rainfall anomalies over the northern (southern) Caribbean during the boreal winter tends to reverse in spring, and then to vanish in summer. On the contrary, during and after a WP event, weak rainfall anomalies during the boreal winter intensify themselves from spring, with anomalous wet conditions over most of the Caribbean basin observed during summer, except over the eastern coast of Nicaragua and Costa Rica. The Caribbean rainfall anomalies associated with WP and CT events are shaped by competition between at least four different, but interrelated, mechanisms; (1) the near-equatorial large-scale subsidence anomaly over the equatorial Atlantic linked to the zonal adjustment of the Walker circulation; (2) the extra-tropical wave-like train combining positive phase of the Pacific/North American mode and negative phase of the North Atlantic Oscillation; (3) the wind-evaporation-sea surface temperature (SST) positive feedback coupling warmer-than-normal SST with weaker-than-normal low level easterlies over the tropical North Atlantic; and (4) the air-sea coupling between the speed of low level easterlies, including the Caribbean low level jet, and the SST anomaly (SSTA) gradient between the Caribbean basin and the eastern equatorial Pacific. It seems that Caribbean rainfall anomalies are shaped mostly by mechanisms (1–3) during CT events from the boreal winter to spring. These mechanisms seem less efficient during WP events when the atmospheric response seems driven mostly by mechanism (4), coupling positive west-east SSTA gradient with weaker-than-normal low level easterlies, and secondary by mechanism (3), from the boreal spring to summer.  相似文献   
110.
Time series analysis has two goals, modeling random mechanisms and predicting future series using historical data. In the present work, a uni-variate time series autoregressive integrated moving average (ARIMA) model has been developed for (a) simulating and forecasting mean rainfall, obtained using Theissen weights; over the Mahanadi River Basin in India, and (b) simulating and forecasting mean rainfall at 38 rain-gauge stations in district towns across the basin. For the analysis, monthly rainfall data of each district town for the years 1901-2002 (102 years) were used. Theissen weights were obtained over the basin and mean monthly rainfall was estimated. The trend and seasonality observed in ACF and PACF plots of rainfall data were removed using power transformation (α=0.5) and first order seasonal differencing prior to the development of the ARIMA model. Interestingly, the ARIMA model (1,0,0)(0,1,1) 12 developed here was found to be most suitable for simulating and forecasting mean rainfall over the Mahanadi River Basin and for all 38 district town rain-gauge stations, separately. The Akaike Information Criterion (AIC), goodness of fit (Chi-square), R 2 (coefficient of determination), MSE (mean square error) and MAE (mea absolute error) were used to test the validity and applicability of the developed ARIMA model at different stages. This model is considered appropriate to forecast the monthly rainfall for the upcoming 12 years in each district town to assist decision makers and policy makers establish priorities for water demand, storage, distribution, and disaster management.  相似文献   
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