MAP /GIS的简介及其在地质研究中的应用分析

本文概要介绍了MAP /GIS系统的构成、功能特点及适用范围,并着重分析了MAP /GIS系统中的空间分析和地图编辑功能在地质研究中的实际应用和发展前景,以便拓宽地质研究视野,为地质研究人员提供先进的信息处理、综合研究、 综合循环开发手段和工具,提高科研效率并促进地质科学的发展。     

Larmor radius effects on the instability of a stratified partially-ionized plasma in the presence of Hall currents and magnetic resistivity

Instability of a stratified layer of a partially-ionized plasma has been investigated in the simultaneous presence of the effects of Hall currents, magnetic resistivity, finite Larmor radius (FLR), and viscosity. The ambient magnetic field is assumed to be uniform and acting along the vertical direction. The solution is shown to be characterized by a variational principle, based on it the solution has been obtained for a plasma in which the density is stratified exponentially along the vertical. It is found that the viscosity, friction with neutrals, and FLR have all stabilizing influence on the growth rate of the unstable mode of disturbance. Magnetic resistivity and Hall currents are, however, found to have a destabilizing influence.     

Meridional oscillations in an idealized ocean-atmosphere system,Part I: uncoupled modes

Meridional, linear, and free modes of global, primitive-equation, ocean-atmosphere models were analyzed to see if they contain multi-year, especially decadal ( 10–30 years), oscillation time scale modes. A two-layer model of the global ocean and a two-level model of the global atmosphere were formulated. Both models were linearized around axially-symmetric basic states containing mean meridional circulations. The linearized perturbation system was solved as an eigenvalue problem. The operator matrix was discretized in the north-south direction with centered finite differences. Uncoupled, meridional modes of oscillation of the ocean and the atmosphere models were calculated. Calculations were performed at three grid spacings (5°, 2.5° and 1.25°) and for two types of basic states (symmetric and asymmetric). Uncoupled, free oceanic modes in the presence of mean meridional circulations have oscillation time scales ranging from two years to several centuries. Such low frequency meridional modes do not exist in the ocean model if there are no mean meridional circulations. A large number of oceanic modes are grouped around decadal oscillation time scales. All the oceanic modes have neutral growth rates. The spatial structures of some of the oceanic modes are comparable to observed spatial structures of sea surface temperature variations in the Pacific Ocean. Most years to decades variability of meridional modes of the ocean model is contained in tropical and midlatitude modes. Some oceanic modes with years to decades periods have standing oscillations in the tropics and poleward propagation of zonal velocity and layer thickness outside the tropics. Uncoupled, free atmospheric modes in the presence of mean meridional circulations have oscillation time scales ranging from a week to several decades. Such low-frequency meridional modes do not exist in the atmospere model if there are no mean meridional circulations. A large number of modes are grouped around intraseasonal time scales. Unlike the oceanic modes, the atmospheric modes are weakly unstable. Most of the intraseasonal variability of atmospheric modes is contained in tropical, midlatitude, and polar modes. Atmospheric modes with oscillation periods longer than about one year have global extent. Meridional ocean-atmospheric modes exist in the models wherever there are mean meridional circulations, i.e., tropical, midlatitude, polar, and global. Oceanic and atmospheric eigenvectors have symmetric (assymetric) latitudinal structures if their basic states are symmetric (asymmetric) around the equator. For both models, models calculated at coarser than 2.5° grid spacing do not accurately represent low-frequency variability. Scale analysis shows taht advection by tge basic state meridional velocities is the primary cause of the meridional oscillations on time scales longer than two years in the ocean model and longer than a few weeks in the atmosphere model. Meridional modes of the coupled ocean-atmosphere models are the subject of a subsequent paper.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil     

Spatial mobility in India: evolving patterns,emerging issues and implications

"This study examines the patterns of spatial mobility in India as expressed at the inter-state level for the post-Independence period. Comparing these patterns with those which had been evolving throughout the colonial period the paper probes into the processes of dislocation of people in the context of India's development strategy.... The analysis points out the complex interrelationships with the nature of socio-economic development and suggests alternatives for stemming distress migration from the backward regions."     

Intraseasonal zonal wind fluctuations seen through Indian radiosonde observations

Summary Twice-daily radiosonde records for Calcutta, Madras, Nagpur, New Delhi, Trivandrum, and Visakhapatnam have been quality checked and analyzed for intraseasonal activity in the summer monsoon. The records for all six cities end on 30 June 1978 and are 17–27 years long.Spectra were estimated by smoothing periodograms and by using the maximum entropy method (MEM), which entails fitting an autoregressive (AR) model. We show how confidence limits can be placed on an average of MEM spectral estimates using the Central Limit Theorem and how this helps pick the orders of the AR models to be tried. We donot favor use of Akaike's Final Prediction Error in choosing the model order, because it can grossly underestimate the AR model order needed to resolve low frequency peaks.MEM spectra of zonal wind based on thirtieth order AR models have large peaks around 30 day time scales. 10–20 day activity is identifiable but is much less prominent. On average, 3–5 day time scales are part of the spectral continuum and do not have a significant spectral peak.Time-height diagrams of filtered zonal wind show that a deep layer of the troposphere acts in phase on 30–50 day time scales over India. The shortest vertical length scale is over southern India and the longest is over northern India. Vertical phase propagation is irregular except over Nagpur, where it is generally upward. Empirical orthogonal functions indicate that vertically in phase activity has more variance (kinetic energy) than the first baroclinic mode.With 10 Figures     

Ocean Model Simulation of Southern Indian Ocean Surface Currents

The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N-60°S and 30°E-120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.     

Migration of scheduled caste population in rural Bist Doab (Punjab)

Using primary data collected from 5 villages in the Bist Doab, this study analyzes migration patterns of the scheduled caste population in rural areas of this region of Punjab. During 1971-1981, the rural scheduled caste population recorded a growth rate of 28.37% as compared to the corresponding growth rate of 13.32% among the rural nonscheduled castes. The proportion of the scheduled caste population showed striking intervillage variations from 52.85% in Khark Balhra to 87.45% in Bhoyapur. It was found that the rate of in-migration of the general population was quite low; the scheduled castes were no exception. Male in-migration has been primarily due to economic reasons; female in-migration was due largely to the change of marital status. It is only in Bhoyapur that about 44% of male in-migrants came as a result of rehabilitation programs undertaken by the state government after 1947. In all the villages, the scheduled caste males have out-migrated at a far slower pace than their nonscheduled caste counterparts. Economic reasons for males and marriage for females are almost the only 2 determinants of out-migration. Scheduled caste males and females differ from each other not only in terms of their motives for migration, but also with respect to the distance of the move; compared to the short distance migration among females, males experience relatively long range migration. Scheduled caste and nonscheduled caste difference is widest in terms of gross emigration; emigration among the scheduled castes is small in volume and more recent in origin. This is directly related to their meager incomes, low literacy rates, and lack of awareness of opportunities.     

An investigation of the relationship between sub‐Saharan rainfall and global sea surface temperatures

Abstract

The relationship between sea surface temperature (SST) and rainfall index anomalies over sub‐Saharan Africa for the 15‐year period, 1970–84, has been examined. The objectively analysed monthly mean SST data were used for the global oceans between 40°S and 60°N. The rainfall data consist of annual mean rainfall indices for the Sahel and Soudan belts over north Africa.

An Empirical Orthogonal Function analysis of the SST data has been carried out for the Atlantic, Indian and global ocean regions. The results show that the most dominant eigenmode, EOF1, is characterized by warming over the central eastern Pacific, cooling over the eastern mid‐latitude Pacific and warming over the entire Atlantic and Indian ocean basins. The second EOF for the Atlantic Ocean SST analysis shows a dipole (north‐south see‐saw) pattern. The third EOF for the Atlantic SST analysis has the same sign over the entire Atlantic basin. Global SST EOF2 and EOF3 correspondió Atlantic SST EOF3 and EOF2, respectively.

The correlation between the sub‐Saharan annual rainfall index, which mainly represents the summer season rainfall from June to September, and SST EOFs shows that EOF1 has statistically significant monthly correlations for the Sahel and Soudan regions and that the warm El Niño‐like phases of SST EOF1 correspond to drought conditions. This result suggests that the large‐scale SST anomalies may be responsible for a significant component of the observed vacillation of sub‐Saharan rainfall. Some preliminary GLA GCM simulation results that support the above findings are also presented.     

Analytical models for the groundwater tidal prism and associated benthic water flux

The groundwater tidal prism is defined as the volume of water that inundates a porous medium, forced by one tidal oscillation in surface water. The pressure gradient that generates the prism acts on the subterranean estuary. Analytical models for the groundwater tidal prism and associated benthic flux are presented. The prism and flux are shown to be directly proportional to porosity, tidal amplitude, and the length of the groundwater wave; flux is inversely proportional to tidal period. The duration of discharge flux exceeds the duration of recharge flux over one tidal period; and discharge flux continues for some time following low tide. Models compare favorably with laboratory observations and are applied to a South Atlantic Bight study area, where tide generates an 11-m³ groundwater tidal prism per m of shoreline, and drives 81 m³ s?^?1 to the study area, which describes 23% of an observational estimate. In a marine water body, the discharge component of any oscillatory benthic water flux is submarine groundwater discharge. Benthic flux transports constituents between groundwater and surface water, and is a process by which pollutant loading and saltwater intrusion may occur in coastal areas.