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881.
Theoretical survey of the NH+CH3 potential energy surface in relation to Titan atmospheric chemistry
This paper looks at the possibilities opened by reaction of NH with methyl radical. A general survey of the potential surface by ab initio Möller-Plesset (MP2) and density functional theory has been performed, including determination of transition states on the pathways considered and vibrational analysis of all stationary points. Energetical data have been obtained using coupled cluster molecular orbital methods (CCSD(T)). It is shown that HCN is not formed from these starting reactants, but that CH2NH, a possible precursor of tholins and of prebiotic compounds through hydration is the major product. 相似文献
882.
Groundwater targeting in a hard-rock terrain using fracture-pattern modeling, Niva River basin, Andhra Pradesh, India 总被引:1,自引:0,他引:1
In hard-rock terrain, due to the lack of primary porosity in the bedrock, joints, fault zones, and weathered zones are the
sources for groundwater occurrence and movement. To study the groundwater potential in the hard-rock terrain and drought-prone
area in the Niva River basin, southern Andhra Pradesh state, India, Landsat 5 photographic data were used to prepare an integrated
hydrogeomorphology map. Larsson's integrated deformation model was applied to identify the various fracture systems, to pinpoint
those younger tensile fracture sets that are the main groundwater reservoirs, and to understand the importance of fracture
density in groundwater prospecting. N35°–55°E fractures were identified as tensile and N35°–55°W fractures as both tensile
and shear in the study area. Apparently, these fractures are the youngest open fractures. Wherever N35°–55°E and N35°–55°W
fracture densities are high, weathered-zone thickness is greater, water-table fluctuations are small, and well yields are
high. Groundwater-potential zones were delineated and classified as very good, good to very good, moderate to good, and poor.
Electronic Publication 相似文献
883.
884.
The impact of realistic representation of sea surface temperature (SST) on the numerical simulation of track and intensity
of tropical cyclones formed over the north Indian Ocean is studied using the Weather Research and Forecast (WRF) model. We
have selected two intense tropical cyclones formed over the Bay of Bengal for studying the SST impact. Two different sets
of SSTs were used in this study: one from TRMM Microwave Imager (TMI) satellite and other is the weekly averaged Reynold’s
SST analysis from National Center for Environmental Prediction (NCEP). WRF simulations were conducted using the Reynold’s
and TMI SST as model boundary condition for the two cyclone cases selected. The TMI SST which has a better temporal and spatial
resolution showed sharper gradient when compared to the Reynold’s SST. The use of TMI SST improved the WRF cyclone intensity
prediction when compared to that using Reynold’s SST for both the cases studied. The improvements in intensity were mainly
due to the improved prediction of surface latent and sensible heat fluxes. The use of TMI SST in place of Reynold’s SST improved
cyclone track prediction for Orissa super cyclone but slightly degraded track prediction for cyclone Mala. The present modeling
study supports the well established notion that the horizontal SST gradient is one of the major driving forces for the intensification
and movement of tropical cyclones over the Indian Ocean. 相似文献
885.
This paper presents one of the first investigations into the geochemical enrichment of the middle and lower Mvoti river system.
Chemical elements are naturally present in aquatic sediments, but their concentrations tend to rise to potentially toxic levels
via both natural and anthropogenic processes. This study evaluated the concentrations of aluminum, arsenic, boron, barium,
cadmium, calcium, cobalt, chromium, copper, iron, lead, magnesium, manganese, molybdenum, nickel, phosphorous, selenium, silicon,
strontium, titanium, vanadium and zinc, using inductively coupled plasma optical emission spectroscopy. The levels of elements
present were used to assess their spatial distribution within the river and to determine the contamination factors and enrichment
factors for each element. The pollution load index (PLi) is another contributing parameter that was calculated to determine
the degree of pollution at each site. The results indicate that the sediments of the Mvoti are low to moderately polluted
and deteriorating with time (average PLi value of 5.19), and that a major contributing factor to this contamination is natural
sources. 相似文献
886.
887.
Construction, observation site and instrumentation are described of an 80-m meteorological observation tower, erected in Vlaardingen, The Netherlands, for studies in connection with air pollution problems along the Nieuwe Waterweg. From measurements made regularly in the period April 1967–April 1968 summaries are given of wind profile parameters and gustiness averages. Case histories are presented of an air pollution episode lasting several days, and of an hourly average wind direction difference of 120 ° over 70 m. 相似文献
888.
P. K. Pal W. J. Prakash P. K. Thapliyal C. M. Kishtawal 《Meteorology and Atmospheric Physics》1999,71(3-4):157-168
Summary ?A methodology has been developed to assimilate satellite-measured rainfall during the initial phase of model integration
for extended range monsoon prediction. The vertical profiles of latent heating corresponding to different rain rates have
been derived from the model statistics. These heating rates have been assimilated through nudging in the thermodynamics equation
of the model. This procedure of assimilating observed heating has corrected the simulation of heating location in the model
and consequently removed the anomalous sinking motion over Indian landmass. With the correction of vertical circulation, both
mean July rainfall over India and the distribution have improved. Interannual variability has been brought out for the years
1987 and 1988. In view of the availability of rainfall profile from Tropical Rain Measuring Mission (TRMM) there is a scope
of adopting this method of assimilating observed rainfall, for extended range monsoon prediction.
Received February 12, 1999/Revised May 4, 1999 相似文献
889.
Della Vecchia A. Ferrazzoli P. Wigneron J.-P. Grant J.P. 《Geoscience and Remote Sensing Letters, IEEE》2007,4(4):508-512
This letter describes recent advances in modeling forest emissivity at L-band. The formulation is based on a previously developed discrete model and includes a new representation of forest litter. Comparisons with multitemporal radiometric data collected in the framework of the ldquoBray 2004rdquo experiment, which was carried out within Les Landes forest, are shown and discussed. Input variables are given by using detailed ground measurements. In general, the model reproduces both absolute values and temporal variations of measured brightness temperature. The contribution of the litter to overall emission was found to be important. 相似文献
890.
David Mendes Enio P. Souza José A. Marengo Monica C. D. Mendes 《Theoretical and Applied Climatology》2010,100(3-4):239-250
A climatology of extratropical cyclones is presented. Extratropical cyclones, their main characteristics and their predominant tracks, as well as their interannual variability, affect weather in South America. For that purpose, a storm track database has been compiled by applying a cyclone tracking scheme to six-hourly sea level pressure fields, available from the National Center for Environmental Prediction–National Center for Atmospheric Research reanalyses II for the 1979–2003 period. The spatial distribution of the cyclogenesis frequency shows two main centers: one around Northern Argentina, Uruguay, and Southern Brazil in all seasons and the other near to the North Antarctic Peninsula. The lifetime of extratropical cyclones in the South American sector exhibits small seasonality, being typically of the order of 3.0 days during most of the year and slightly higher (3.5 days) in austral summer. The distance travelled by the cyclones formed in the South American sector tends to be smaller than the total paths found in other areas of the Southern Hemisphere. A k-mean clustering technique is used to summarize the analysis of the 25-year climatology of cyclone tracks. Three clusters were found: one storm-track cluster in Northeast Argentina; a second one west of the Andes Cordillera; and a third cluster located to the north of the Antarctic Peninsula (around the Weddell Sea). The influence of the Antarctic Oscillation (AAO) in the variability of extratropical cyclones is explored, and some signals of the impacts of the variability of the AAO can be observed in the position of the extratropical cyclones around 40°S, while the impacts on the intensity is detected around 55°S. 相似文献