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《African Journal of Marine Science》2013,35(1):159-171
Aircraft observations were used to investigate contrasting weather conditions over the northern edge of the warm Agulhas Current south of George, South Africa, during June 1989. A sea surface temperature front of 7°C over 10 km was observed near 35°S, 23°E. Surface-sensible and latent heat fluxes increased by a factor of five on the warm side. A deepening of the moist unstable layer was indicated by increased equivalent potential temperatures over the warm side. Most significantly, convectively generated turbulence, as inferred from variances in air pressure, increased exponentially with sea surface temperature and surface layer winds doubled south of 35°S. The sea state, initially smooth over the continental shelf, became rough seawards of the northern edge of the Agulhas Current. Numerical model simulations were performed to assess air-sea interactions. Model-simulated thermodynamic variables responded in close agreement with observations, but the increase in cross-frontal winds was not fully resolved. The aircraft observations provide evidence that the Agulhas Current affects the large-scale pressure field and may enhance the rain-bearing capacity of transient weather systems. 相似文献
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《African Journal of Marine Science》2013,35(3-4):705-712
Analysis of sea-level data obtained from the Atlantic Global Sea Level Observing System (GLOSS) sea-level station at Takoradi, Ghana, West Africa, clearly reveals a tsunami signal associated with the Mw = 9.3 Sumatra earthquake of 26 December 2004 in the Indian Ocean. The tsunami arrived at this location on 27 December 2004 at approximately 01:38 UTC (which is close to the expected tsunami arrival time at that site), after travelling for more than 24 hours. The first wave was negative (trough), in contrast with the South African stations where the first wave was mainly positive (crest). The dominant observed period at Takoradi was about 42 minutes. The maximum trough-to-crest wave height (41cm) was observed on 28 December at 00:15 UTC. There were two distinct tsunami 'bursts', separated in time by about 14 hours, the larger being the second burst. A small residual lowering of the sea level (～15cm) during the tsunami and for several days afterwards, and a delayed (～4.5 days) lowering of seawater temperature (up to ～4.5°C), was observed, possibly indicating the presence of internal waves through the Gulf of Guinea associated with propagating tsunami waves. The prominent tsunami signal found in the Takoradi record suggests that tsunami waves could also be found at other sites off the West African coast. 相似文献
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《The Cartographic journal》2013,50(2):76-103
AbstractInnovations for the British Army during World War I included use of a military geologist to compile 'water supply' maps and to guide well drilling. Between June 1915 and November 1918, W. B. R. King served as a staff lieutenant at General Headquarters of the British Expeditionary Force deployed on the Western Front. He pioneered British development of water supply maps for parts of Belgium and northern France, in several different styles and at scales of 1 : 100 000, 1 : 250 000 and 1 : 40 000. These assisted planning for advances into enemy-occupied territory or the development of water supply infrastructure within the region held ultimately by five British armies: in total about 1,500,000 men with some 500,000 horses and mules, each man/animal requiring on average 10 gallons (45 L) per day of potable water. The maps guided emplacement of over 470 military boreholes to supply drinking water to British forces, especially in provinces underlain by Cretaceous Chalk: Picardy and Artois. German forces also made use of military geologists at the Front, but in much greater number: up to about 300 in total. Water supply tasks were given high priority, and German water supply maps were finally standardized like other medium scale German geotechnical maps at 1 : 25 000. Six geologists were deployed with the American Expeditionary Force late in the war, and for their sector of the Front compiled at least two water supply maps at 1 : 80 000, and 11 at 1 : 50 000 that were supported by explanatory reports. Wartime imperatives thus generated expertise in hydrogeology that became available for civilian use post-war, and laid the foundation for further military development during World War II. 相似文献
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《制图学和地理信息科学》2013,40(3):137-154
From the 1880s until the 1970s, photomechanical techniques played an important role in map making. Images created by and for photography were manipulated to form the printing image(s) from which the map was reproduced in multiple copies. After experiments in mapmaking in the 1860s, photomechanical techniques gained acceptance by the 1880s and, thereafter, increasingly dominated mapmaking until their rapid decline after the 1970s, as the shift to computers and electronic technology occurred. When they replaced earlier manual methods in the nineteenth century, photomechanical techniques caused the tools and materials of map production and the roles of personnel to change. Control over image production shifted from the printer to the cartographer as pen-and-ink drafting and associated collage techniques developed in the early 1900s, and even more so when scribing came into general use in the 1960s. Having thus assumed more direct responsibility for the end product (the printed map), the cartographer also adopted methods of predicting and controlling its appearance, such as standardized tools and materials, drafting specifications, flow charting, and color proofing. Through the faster and cheaper production of maps whose graphic presentation of information was enhanced by tonal effects and color printing, photomechanical production techniques also contributed to the growth of the map trade and of map use during the twentieth century. 相似文献
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《制图学和地理信息科学》2013,40(2):141-157
Most urban green space research focuses on the social benefits of parks and recreational areas. However, in areas with high levels of resource deprivation and physical disorder, parks may function as criminal marketplaces. Parks in such areas may cease to provide net benefits to the surrounding community and instead serve as a vector for criminal activity. Parks in eastern Kansas City, Kansas, are examined in terms of the probability of criminal marketplaces and beneficial social contribution. Variables for resource deprivation and social disorder are calculated for the study area and compared to national aggregates to identify which parks may behave as criminal marketplaces. In such cases, parks should exhibit an inverse relationship between distance from a park and number of criminal offenses per acre. Evaluating the incidence of crime near parks using geographic information systems (GIS) buffer analysis, proximity analysis, and spatial statistics demonstrates that parks in areas of extreme resource deprivation do not serve beneficial social roles, and some parks contradict conventional criminal justice and urban economic theory. 相似文献
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《制图学和地理信息科学》2013,40(4):237-247
Modeling line or surface phenomena digitally involves two tasks: discretization of the phenomenon, which yields a finite set of data, and subsequent interpolation, which reconstructs the continuum. Many mathematical techniques exist for the latter task, and most methods require a number of parameters to be specified. The shape of digital line or surface models between the data points (that is, the local shape) and the information derived from these models both depend on the selected method and, possibly, on the specification of parameters. The reconstruction of the continuum thus introduces uncertainty. This paper examines the sources and effects of this type of uncertainty. For this purpose, the modeling of lines and surfaces is separated into an abstraction, an implementation, and measurement. The individual factors affecting uncertainty of local shape in each step are identified and discussed. The paper concludes that local shape uncertainty, unlike positional uncertainty of given data, cannot be numerically assessed. Instead, measures of plausibility have to be used to denote the quality of digital models of lines and surfaces. Finally, the concept and potential problems of future empirical investigations are discussed. 相似文献
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《制图学和地理信息科学》2013,40(3):141-150
Animation is an important method of communicating information that lends itself to cartographic display. Cartographers may be delinquent in their utilization of this technique. Meteorologists, medical researchers, and physical scientists, employing mini-, mainframe, and supercomputers, are creating today's most sophisticated animated maps and continue to develop high-quality systems for data display. Though today's cartographers are concerned with the geometric accuracy and computer automation of their map products, they may be overlooking current developments in spatiotemporal display within other disciplines. Creating a method to bridge the current animation gap between cartography and these disciplines has been the primary goal of this research. Since personal computers are the platforms most commonly available to cartographers, development of animated cartographic displays is feasible with this technology. As a result of this research, an interactive microcomputer-based animated map of U.S. surface temperatures was designed to help understand the rapid climatic change occurring during the 20th century. 相似文献
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《制图学和地理信息科学》2013,40(3):145-149
The Defense Mapping Agency, the National Ocean Service, and the U.S. Geological Survey each has earned a reputation among respective user communities as a leader in producing quality data and map products that meet the highest standards. With the increased use of GIS, user communities are rapidly expanding and have now begun to overlap. With adoption of SDTS as a Federal Information Processing Standard, all federal agencies are required to use the SDTS domestically. There is additionally an emerging need to unify efforts in the development of international standards. Existing standards need to be harmonized and future standards activities need to be linked more closely. This paper reviews the roles of each agency in developing spatial data and standards for exchange and outlines leadership activities in standards development that are currently underway. 相似文献
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