人工防雹作业浅析

1引言人工防雹[1],是对将要降雹的冰雹云施加人工影响,以减少和避免冰雹灾害。目前,人工防雹作业在理论和实践上都取得了很大的进展,积累了宝贵的经验,成为群众所愿意接受的减灾手段,受到各地有关部门的大力支持。防雹作业后,冰雹的密度、质量、个体减小,减轻了雹灾程度。冰雹云内存在着雷电和强大的升降气流,给观测和试验研究带来了困难,人工防雹至今仍处于试验研究阶段[4]。随着科学技术的发展,人们对雹云认识的深入,人工防雹工作必将为人类作出更大的贡献。2冰雹的预报冰雹预报有下面几种主要方法。有天气图方法、点聚图、T-LnP图及高…     

Phosphorus retention and release by sediments in the eutrophic Mai Po Marshes, Hong Kong

This study examined the phosphorus retention and release characteristics of sediments in the eutrophic Mai Po Marshes in Hong Kong. Results of chemical fractionation show that the sum of inorganic P pools exceeded 50% of the total sediment P content, with the redox-sensitive iron-bound P (Fe(OOH) approximately P) being the dominant P fraction. Given the considerable average Fe(OOH) approximately P concentration of 912 microg g(-1), Mai Po sediments demonstrated a great potential to release bioavailable P under low sediment redox potentials. This was further supported by the high mean anaerobic P flux of 31.8 mg m(-2)d(-1) recorded in Mai Po sediment cores, indicating the role of bottom sediments as a net P source. Although sediments in Mai Po had appreciable Langmuir adsorption maxima (1642-3582 mg kg(-1)), the high zero equilibrium P concentrations (0.02-0.51 mg L(-1)) obtained suggest that sediment sorption processes would contribute to sustaining the eutrophic conditions in overlying water column even with a further reduction in external P load. Concerted efforts should be made to reduce internal loading of P, especially under reducing conditions, to complement the implementation of zero discharge policy for Deep Bay for effective eutrophication abatement and long-term water quality improvement in the Mai Po Marshes.     

The distributions of particulate heavy metals and its indication to the transfer of sediments in the Changjiang Estuary and Hangzhou Bay,China

Particulate heavy metals (Cu, Pb, Cd) were measured following intensive sampling in June and October 1994 at 70 stations in the Changjiang Estuary and Hangzhou Bay, China. In the study area, particulate Cu and Pb have a similar level that is higher than the concentration of particulate Cd. Cu, Pb and Cd concentrations in suspended sediments are higher than those in bed load. In the middle of Hangzhou Bay, heavy metal concentrations in suspended sediments and bed load are similar. This may be the result of the frequent exchange between them, which is due to the strong dynamic condition. A negative relationship was observed between concentrations of heavy metals in bed load and bulk density. Fine-grained sediments were the main carriers of heavy metals. Sedimentary dynamics dominate the fate of heavy metals in these sites. The distributions of metals (especially Cu) in suspended sediments can indicate the transfer of sediments in this area.     

MM5模式在高性能系统FreeBSD上的移植及其与RHAS 4的性能比较

MM5模式系统常被用在气象科研和天气预报当中,通常运行在商业版本的Unix/Linux系统上,对非商业版本的类Unix系统并不太友好。文章详细介绍了MM5V3.7在高性能免费Unix操作系统FreeBSD 6.0上的移植及其应注意的问题,并通过一个个例分别在FreeBSD 6.0和Red Hat Advanced Server 4(RHAS 4)上的运行来比较其效率。通过对比发现,FreeBSD的性能要比通常所用的Linux系统有较大的提高,这对于改善实际业务中的时间迫切性问题有很大的意义。     

PN断面东海黑潮的地转经验模态分析

基于东海PN断面近50年的历史水文数据,本文中作者应用一种斜压流函数空间投影的方法分析冲绳海槽北部黑潮水团的季节性和年代际变异.诊断生成的地转经验模态(GEM)显示黑潮中层水的盐度在夏季相对较低,春季达到最高.通过比较1987年之后CTD数据生成的GEM场与1987年之前BOttle数据生成的GEM场,得以证实黑潮的年代际变化特征,即黑潮表层水近20年来温度升高而盐度减小,同时发现黑潮热带水具有盐度增加而中层水具有盐度减小的趋势.