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排序方式: 共有110条查询结果,搜索用时 375 毫秒
71.
72.
W.K. Peterson L. Andersson B. Callahan S.R. Elkington R.W. Winglee J.D. Scudder H.L. Collin 《Journal of Atmospheric and Solar》2009,71(16):1623-1629
Energetic O+ ions have important dynamic effects on the ring current. Insights into the effects of O+ on ring current dynamics have come primarily from models, not observations. Here, we discuss observations of O+ populations escaping from the ionosphere and their access to the plasma sheet and ring current. We review data establishing that a significant flux of O+ escapes the ionosphere during geomagnetically quiet intervals. We then estimate the relative magnitude of the O+ population in transit between the ionosphere and ring current during quiet intervals before geomagnetic storms. Our analysis suggests that dynamic reconfigurations of the magnetosphere during geomagnetic storms significantly alter the O+ transport paths from the ionosphere to the ring current. During these reconfigurations some of the pre-existing, quiet time, in-transit O+ populations are captured on magnetic field lines leading to the ring current. The prompt appearance of this O+ population in the ring current could modify the evolution of the ring current in the storm growth phase. Our analysis suggests that the consequences of an activity-dependent O+ transport path to the ring current should be systematically investigated. 相似文献
73.
Thomas Mathai A. K. Samadder M. L. Renjith K. N. Rajarama 《Marine Georesources & Geotechnology》2013,31(4):316-327
Deficiency in major port facilities off Orissa prompted the State Government to promote development of a port facility in the Subarnarekha river outflow sector utilizing the inland water network of Orissa coast canal and Contai canal. Marine and Coastal Surveys Division of Geological Survey of India carried out geotechnical feasibility surveys to explore possibilities of setting up a port facility in this sector. Bathymetry reveals smooth, parallel isobaths signifying gentle slopes with varying gradients. The East-West profile delineates a natural channel that could be dredged into a navigational channel. Sediments are dominantly sandy silt marginally varying either into silty sand or clayey silt. Geotechnical characteristics suggest a stable substratum ideal for developing the offshore port facility. Side-scan sonar surveys reveal a seafloor bereft of any hazardous rocks or reefs. The surveys espouse immense potential for developing this sector into an offshore port facility. 相似文献
74.
强对流风暴新一代雷达产品特征分析 总被引:9,自引:1,他引:8
利用濮阳、三门峡新一代天气雷达产品,结合卫星、探空、天气图、地面雨量等资料对2006年6月25日发生在河南省北部、西部和中部的强对流风暴过程进行分析发现:(1)此次强对流风暴表现为多个处于不同发展阶段的的强对流回波单体组成长80~400km、宽40km的NE-SW向中β对流回波带即飑线;(2)强对流风暴在发展旺盛期间,其前沿有雷暴出流边界;(3)低层强NW风推动对流回波带向前发展成弓型带状回波;(4)在强对流风暴前侧,紧挨雷暴出流边界内侧产生了一条弧线窄带速度线,随着雷暴出流边界远离强对流风暴主体,该弧线窄带速度线也远离大片的速度区,并逐渐消失;(5)不同性质的强对流天气,其基本反射率、回波顶高、垂直液态积分含水量时有差异.北部雷雨大风伴短时强降水的强对流天气,强中心基本反射率在53~63dBz,回波顶高9~14km,垂直液态积分含水量在38~48kg*m-1之间;而西部中部的雷雨大风伴随局部冰雹和短时强降水的强对流天气,强中心基本反射率在53~65dBz,回波顶高度11~16km,对应垂直液态积分含水量在48~63kg*m-1之间;(5)在强对流风暴发展旺盛时期一直有中气旋伴随,中气旋出现在强对流单体前侧或前侧的入流槽口处.强对流风暴的新一代雷达产品特征是强对流天气监测预警的重要参考依据. 相似文献
75.
Recent studies of the star formation region BBW 36 and associated molecular clouds are presented. The 12CO (1-0) observations, carried out with the 15-m SEST (Swedish-ESO) telescope (Cerro La Silla, Chile), revealed the existence
of cloud a, connected with BBW 36 and of cloud b, having elongation in SE-NW direction. A red-shifted molecular outflow with
velocity ∼+5 km/s (with respect to cloud a), having a direction parallel to the line of sight, was also observed. VLA observations
showed the presence of a source VLA 2 at 3.6 cm with an elongation in the N-S direction. It is suggested that the VLA 2 source
coincides with a dust disc (surrounding the object BBW 36). The star 3, which is one of the YSOs in the star-forming region
BBW 36 and is connected with a bright comma-like nebula, can be the source of the molecular outflow. The star 3 has very high
IR colors and is associated with an IRAS point source IRAS 07280-1829, which has IR colors, typical for an IRAS point source,
connected with a water maser. On the 2MASS K image of BBW 36 we can see the existence of a bright nebula; a group of stars
is embedded in that nebula, and among these stars there are stars with dust discs (or envelopes). On the 2MASS K image several
spiral jets are also present, some of them with a condensation at the end.
Published in Astrofizika, Vol. 51, No. 3, pp. 469–477 (August 2008). 相似文献
76.
针对中国北方海湾水库间歇来水、连续取水和沉积物动态释盐的特点,建立水量与盐分耦合的数学模型,以青岛拟建的沐官岛水库为例,探讨水位变化条件下混合型海湾水库库水盐分的影响因素、超标风险与达标条件。模拟结果表明,在水库水位连续降低条件下,毫米量级的日蒸发量对库水盐分的累积效应显著。在不利水文条件下,受沉积物释盐、水分蒸发与人工取水的影响,混合型海湾水库长期存在盐分超标的风险。与水位不变时相反,水位降低时库水盐分浓度随着取水量的增大而升高;因此,当库水盐分存在超标风险时,可以通过减少日取水量实现库水盐分达标。为保障安全供水,在海湾水库设计与运营管理阶段,均需要综合考虑水量-盐分因素进行水库的日取水量调算。 相似文献
77.
Our proposed three-dimensional dam breach model is tested using one field test from the European Community funded IMPACT project. Results show that this three-dimensional model accurately predicts the peak breach discharge and final breach width for this case. It is shown that the three-dimensional model is capable of simulating the breaches that develop in different locations along a hypothetical long non-cohesive dam while accounting for variations in the natural valley topography, including symmetrical and asymmetrical settings. Our results show that both the breach location and reservoir shape have a significant effect on the peak breach discharge and the outflow hydrograph shape. Different inflow hydrographs were found not to significantly change the peak breach discharge rate for the hypothetical reservoir and spillway. Comparisons with laboratory and field dam breach tests and one historically breached dam show that the real shape of the breach channel during the breach process is successfully modeled. 相似文献
78.
山东省主要生态环境地质问题与调查方法探讨 总被引:1,自引:0,他引:1
山东省主要生态地质环境问题--海(咸)水入侵、地下水超采漏斗、地面塌陷、地面沉降、地裂缝、地下水串层污染,主要是对地下水不合理开发造成的.从综合治理的需要出发,新一轮生态地质环境调查应包括地下水潜力调查、地下水环境质量调查、地下水环境保护区划、地下水调蓄条件调查、环境地质问题与灾害调查等内容.在调查方法上,要充分利用"3S"技术,要采用点、线、面结合的调查方法,要确定重点、典型区、带加深调研以带动面上的调查,并要针对各地不同情况有侧重的开展调查工作. 相似文献
79.
80.
Mark Barton 《大气与海洋》2017,55(3):144-154
Snow density is important information for a wide range of activities including avalanche control, marketing, building-code development, weather forecasting, and water supply forecasting. Extended recent high-quality datasets from the mountainous regions of the Pacific Northwest coastal area are rare. This paper presents a study of an unusually long and continuous (January 1990 to April 2016) manually collected dataset of fresh snowfall measurements for Whistler Mountain, British Columbia, Canada. The dataset consists of snowboard core measurements that were collected by Whistler–Blackcomb ski patrol staff twice daily for avalanche control and resort-marketing purposes. These records were collated, transcribed, quality controlled, and made computer accessible in this study. A discussion of the characteristics of the data collection site and an assessment of data reliability are presented. Two examples of the many purposes to which this high-quality dataset might be put were studied. Climatic teleconnections to winter (December–February) mean snow density were examined, which revealed a positive relationship to the quadratic form of the Pacific Decadal Oscillation pattern (i.e., PDO2). In addition, an analysis of daily snow density relationships to air mass types was performed, which suggested that higher (lower) densities are associated with maritime inflow (arctic outflow) conditions. Both of these relationships appear to be mediated by the positive correlation between snow density and air temperature.Based on the full dataset (N?=?1275 individual snow density measurements) for all months with measured snowfall, annual snowfall season (November to May) mean snow densities ranged from 77?kg?m?3 to 109?kg?m?3 with an overall mean of 91?kg?m?3, giving an overall snow-depth to water-depth ratio of 11:1. 相似文献