Mapping with Ag/Au ratios of mineralized rocks and ores as a parameter reveals that the deep fractures in the Gangdise block control the distribution of the high value regions which may represent the shallow zones of strongly mineralized areas. The variance gradient regions with large Ag/Au ratio may represent the boundaries between strongly mineralized areas and weakly mineralized areas. In the middle part of the Gangdise block, gold and silver mineralization centers mainly distribute along the NW extending Coqen-Xigaze region, NE extending Yangbajain region and E-W extending Lhasa-Gongbogyamda region. The gold and silver mineralized rocks and ores may have been slightly denuded in the west of the middle Gangdise block, and the denudation in the east, however, may be stronger. The primary gold and silver prospect in the west may be better than in the east.
In view of the large quantities of areas,complex landform and dynamic change of resources and environ-ment in China,China has already funded abundantly a series of macro remote sensing investigation projects in land use cover change(LUCC) since 1990.Supported by the achievements of such projects,Chinese resources,environmental and remote sensing database(CRERS) was created.In this paper,we standardized the LUCC dataset of CRERS at scale of 1km,which facilitated the study of spatial features of LUCC in China.The analysis on the spatial features of LUCC and their causes of formation in China are based on the CRERS supported by the technologies of Geographic Information System(GIS) .The whole research was based on the grade index of land use,ecological environmental index and index of population density.Based on the correlation analysis,we found that the special features of LUCC were closely related with those of ecological environment and population density,which resulted form that areas with better ecological environ-ment and high production potential of land were easy and convenient for human being to live,which,furthermore,led to the aggravation of excessive exploitation of land resources there. 相似文献
1 INTRoDUCTIONIt is well known that solar proton flares are maiuly correlated with strong, bright H. flares,in particular, with two ribbon flares. Ellison et al. (l961) were the first to draw attelltion tothe faCt that all cosndc-ray flares had the typical two-ribbon shape. Then, Svestka and Simon(1976) drew uP the "Catalog of Solar Particle Evellts, 195ty1969", and using this Catalog,Dodson and Hedeman could safely identify the flare sources for 50 proton events. Out of the 50idellti… 相似文献
1. IntroductionDuring June and July, from the mid-lower reachesof the Yangtze River basin in China to southern Japan,a precipitation zone with intensive torrential rain ap-pears and lasts for two to three weeks. This phe-nomenon is called the "mei-yu" in … 相似文献
Tropical–extratropical climate interactions are studied by idealized experiments with a prescribed 2°C SST anomaly at different
latitude bands in a coupled climate model. Instead of focusing on intrinsic climate variability, this work investigates the
mean climate adjustment to remote external forcing. The extratropical impact on tropical climate can be as strong as the tropical
impact on extratropical climate, with the remote sea surface temperature (SST) response being about half the magnitude of
the imposed SST change in the forcing region. The equatorward impact of extratropical climate is accomplished by both the
atmospheric bridge and the oceanic tunnel. About two-thirds of the tropical SST change comes from the atmospheric bridge,
while the remaining one-third comes from the oceanic tunnel. The equatorial SST increase is first driven by the reduced latent
heat flux and the weakened poleward surface Ekman transport, and then enhanced by the decrease in subtropical cells’ strength
and the equatorward subduction of warm anomalies. In contrast, the poleward impact of tropical climate is accomplished mainly
by the atmospheric bridge, which is responsible for extratropical temperature changes in both the surface and subsurface.
Sensitivity experiments also show the dominant role of the Southern Hemisphere oceans in the tropical climate change.
CCR contribution number 829; DAS-PKU contribution number 002. 相似文献
Summary This paper presents a trend coefficient as a characteristic index with which to investigate the 1951–1998 secular trend variation
(STV) of northern 500-hPa height on a seasonal basis. Evidence suggests that low (high) latitude 500 hPa geopotential height
displays a remarkably positive (negative) trend; the positive anomaly of the height is maintained over NW Africa, the western
Mediterranean Sea and North Africa, mid-Pacific at lower latitudes, Lake Baikal and area to the east and NW North America;
the height drops significantly over the Aleutians and North Pacific, the area to the south of the Greenland and NE North America
and the sector to the north of the Arabian Sea. Further, analysis of abrupt change shows that the 500-hPa circulations experience
noticeable sudden change twice, once around the early 1960s and again in 1976, during which period the height exhibits great
differences between the Pacific and Atlantic. In the first period it drops (rises) over the mid-Atlantic at lower latitudes
(NW Africa); in the second period the height rises (drops) over the mid-Pacific at lower latitudes and Lake Baikal (the North
Pacific). Statistical tests indicate that in the 1976 case the low-latitude positive abrupt change is even more noticeable
compared to the negative of the North Pacific, thus representing a large-scale jumping event of the northern 500-hPa height.
Received April 9, 1999/Revised October 15, 1999 相似文献