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61.
The present study is carried out to examine the performance of a regional atmospheric model in forecasting tropical cyclones
over the Bay of Bengal and its sensitivity to horizontal resolution. Two cyclones, which formed over the Bay of Bengal during
the years 1995 and 1997, are simulated using a regional weather prediction model with two horizontal resolutions of 165 km
and 55 km. The model is found to perform reasonably well towards simulation of the storms. The structure, intensity and track
of the cyclones are found to be better simulated by finer resolution of the model as compared to the coarse resolution. Rainfall
amount and its distribution are also found to be sensitive to the model horizontal resolution. Other important fields, viz.,
vertical velocity, horizontal divergence and horizontal moisture flux are also found to be sensitive to model horizontal resolution
and are better simulated by the model with finer horizontal grids. 相似文献
62.
Lake Bosumtwi is one of the most widely studied palaeoclimate archives in West Africa. Results from numerous AMS 14C dates of samples from four piston cores from Lake Bosumtwi show that an abrupt sedimentary transition from a mid-Holocene sapropel to calcareous laminated muds occurred at about 3200 cal yr B.P. High-resolution analyses of the nitrogen isotopic composition of organic matter across this transition confirm its abrupt nature, and suggest that the change may signal a step toward increased aridity and intensified surface winds that affected western equatorial Africa from Ghana to the Congo basin. Northern and Eastern Africa experienced a similar abrupt shift toward aridity during the late Holocene, but at about 5000 cal yr B.P., a difference in timing that illustrates the regional nature of climate changes during the Holocene and the importance of feedback mechanisms in regulating Holocene climate variability. Furthermore, an abrupt change at about 3000 cal yr B.P. occurs at several sites adjacent to the tropical and subtropical Atlantic, which may hint at major changes in the surface temperatures of the tropical Atlantic and/or Pacific at this time. 相似文献
63.
统计1965年以来影响韶关的热带气旋发现,韶关出现暴雨不仅与热带气旋的路径、强度有关,而且与大气层结稳定度或冷空气的相互作用密切相关。由此结合实况、应用数值预报产品来制作热带气旋暴雨24小时预报。 相似文献
64.
采用MCE(Multi-Criteria Evaluation)方法,在台风路径客观综合预报方法研究与业务实验中,根据多家预报的主要结果进行综合评估分析,提出最佳客观综合预报结果以供决策者及预报员参照。取得初步结果:(1)对9711号台风进行了MCE客观综合决策方法的预报试验。结果表明,对于9711号台风生命史中几个关键点的预报,即登陆预报、台风转向北上预报及出海转向预报等以及全程预报,MCE方法取得较佳预报结果。(2)在综合平台上对近10年的疑难路径台风和2000年全年台风进行了MCE方法试验及多种预报结论的对比分析研究。MCE方法预报误差检验结果较好。(3)所提出的模拟预报员预报思维的联想智能模拟方法,以及可操作综合预警平台,为台风路径预报,包括分析、学习、回忆、对比、推理、联想直到形成综合预报结论提供了一个十分有用的工具。(4)讨论的自反馈函数对形成和推演多规则评估决策有一定的实用性。 相似文献
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68.
硬盘一旦出现故障,对每一个使用电脑的人来说简直就是一场灾难,因为硬盘里的数据比硬盘本身的价值更大,如何将其损失降到最低限度,这是非常值得研究的。 相似文献
69.
This work presents the temporal evolution and spatial distribution of nitrogen dioxide (NO2) measured with the help of passive diffusion tubes in different environments: rural, sub-urban, urban, at La Réunion Island in December 1997 and November 2000 (austral spring), respectively. NO2 concentration exhibits notable enhancement from 1997 to 2000. For instance, its mean concentration was 16 and 20 μg/m3 in December 1997 and November 2000, respectively, at La Réunion Island, especially in inhabited regions due to increase of local anthropogenic activities, mainly traffic circulation, in the absence of house heating and biomass burning. We also observe a net increase of pollutant levels by a factor two in rural/remote areas within 3 years, which is tied to the extension of inhabited areas and air-flows from enhanced local sources. The increase of atmospheric pollutants is mainly due to enhancement of anthropogenic activities (traffic) since the 1990s at La Réunion Island, which results from a constant increase of population and consequently, from a higher number of vehicles in circulation. Importantly, in cities like Saint-Denis, where traffic network has been subject to notable improvement (e.g. single to double lanes, etc.), pollutant levels exhibit little variability as in temperate continental latitudes. Semi-continuous NO2 concentration measured in parallel with ozone in November 2000 also showed that daytime photochemical ozone production is influenced by pollutant and precursor (NO2) levels at Saint-Denis, while nighttime ozone increase is mainly tied to dynamical processes. The November 2000 ozone diurnal pattern is notably different from that observed in September 1995, during which a daytime ozone loss was observed, pointing out that atmospheric conditions have been subject to notable changes, i.e., clean to moderately polluted, within a few years at La Réunion Island. The results presented here point out that the ‘source enhancement effect’ is superimposed on dynamical and photochemical processes to influence pollutants variability and hence atmospheric chemistry, in a quite ‘pristine’ tropical oceanic region. 相似文献
70.
M. C. Kim 《Journal of Geodesy》1997,71(12):749-767
The fundamental geometry of satellite ground tracks and their crossover problem are investigated. For idealized nominal ground
tracks, the geometry is governed by a few constant parameters whose variations lead to qualitative changes in the crossover
solutions. On the basis that the theory to locate crossovers has not been studied in sufficient detail, such changes are described
in regard to the number of crossover solutions in conjunction with their bifurcations. Employing the spinor algebra as a tool
for establishing the ground-track crossing condition, numerical methodologies to locate crossovers appearing in general dual-satellite
ground-track configurations are also presented. The methodologies are applied to precisely determined orbital ephemerides
of the GEOSAT, ERS-1, and TOPEX/POSEIDON altimeter satellites.
Received: 19 November 1996 / Accepted: 12 May 1997 相似文献