Sediment budgeting: A case study in the Katiorin drainage basin,Kenya

The primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in Kenya. Results indicated that transfer of sediments (‘inputs’) from primary source areas was minor in comparison to changes in storage. The major sediment source area within the Katiorin drainage basin was the colluvial hillslope zone. The net change in storage within this zone was approximately 2100 Mg yr^?1. Surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments. Sediment storage within the in-channel reservoir increased by 60 Mg yr^?1, which was minor when compared to the total store of sediment in this reservoir. During 1986, the channel network stored only a small fraction ( < 3 per cent) of the sediment delivered from the hillslope subsystem. Therefore, the in-channel reservoir had limited influence on sediment conveyance to the basin outlet. These data indicate that a static equilibrium condition cannot be assumed within the Katiorin drainage basin. Such an assumption would result in erosion estimates of approximately 5.5 mm yr^?1 for the entire basin (based on a sediment output of 7430 Mg km^?2 yr^?1 and a measured bulk density of 1.35 Mg m^?3). However, this masked the actual rates of 1.2 to 7.1 mm yr^?1 in subbasin primary source areas, and rates of 0.6 to 17 mm yr^?1 for colluvial material in the various subbasins. The extreme accelerated erosion rates resulted from minimal ground vegetation, steep slopes, soil crust formation, an erodible substrate, and a well-integrated drainage network for rapid conveyance of sediments from the hillslope subsystem to the basin outlet.     

青藏高原冬春积雪和地表热源影响亚洲夏季风的研究进展

青藏高原冬春积雪和地表热源的气候效应是青藏高原气候动力学的两个重要内容。大量资料分析和数值试验研究均表明这两个因子对亚洲季风有一定的预测意义,本文对此做了比较系统的回顾和总结,并进一步比较了青藏高原积雪和地表热源影响东亚和南亚夏季降水的异同。结果表明,东亚夏季降水在年际和年代际尺度上均存在"三极型"和"南北反相"型的空间分布特征,高原春季地表热源在年代际和年际尺度上主要影响东亚夏季降水"三极型"模态;在年代际尺度上它是中国东部出现"南涝北旱"格局的重要原因,而高原冬季积雪的作用相反。另一方面,高原冬季积雪在年际和年代际尺度上对印度夏季风降水的预测效果均要优于高原地表热源。无论是空间分布还是时间演变特征,高原冬季积雪与春季地表热源整体上均无统计意义上的显著联系。不断完善高原地面观测网和改进模式在高原地区的模拟性能,将是进一步深入理解高原积雪和地表热源影响亚洲季风物理过程和机制的关键所在。     

1991年江淮暴雨时期的能量和水汽循环研究

通过对 1991年 5～ 7月江淮暴雨期全球范围的水汽输送和不同降水过程中江淮暴雨区及其临近区域的水汽收支和视热源和视水汽汇的计算分析得到了以下结论 :( 1)从水汽输送的机制来看 ,一方面 ,有大量的水汽以定常涡动的方式从孟加拉湾及南海输送到中国江淮地区 ;另一方面 ,江淮地区的瞬变涡动水汽向北输出 ,这可能与江淮地区频繁活动的α和β中尺度系统有关 ,它们将江淮地区汇集的充沛的水汽除了大部分以降水形式降下外 ,剩余部分继续向水汽较少的高纬地区输出 ,以维持全球水汽的平衡。( 2 )在降水过程中 ,局地蒸发项在水汽的供应中或再循环中十分重要 ,其数值一般为降水量的 13 ～ 12 ,这与1998年的降水情况相似。( 3 )在降水过程中 ,暴雨区的水汽主要是从南边界和西边界流入的 ,东边界和北边界则流出 ,并且水汽的流入、流出主要在中低层进行。 (a)在流入边界上 ,水汽通量的垂直分布存在差异 ,暴雨区西边界和南边界的水汽流入的垂直差异可能与其所在的地理位置有密切关系。 (b)对于暴雨区 ,不同强度的降水过程水汽的主要来源有所不同。( 4)在 5次降水过程中 ,视热源和视水汽汇的较大值对应降水的大值区 ,表明了水汽凝结加热对大气加热所起的主要作用。梅雨期降水 ,以对流性降水为主 ,对流活动随季节变化     

2006年以来《气象与减灾研究》期刊评价指标分析

对2006年以来《气象与减灾研究》的多项期刊评价指标进行统计分析,并对期刊稿源及网站建设情况进行细致调查。结果表明：1） 自2006年更名以来,期刊发展较快,然而期刊的进一步发展已经遇到“瓶颈”,即缺乏长期稳定的优质稿源;2） 拓宽优质稿源是期刊进一步发展的首要任务;3） 编辑部须重视期刊网站的建设、维护及更新,为读者、作者提供优质服务,以利期刊更好发展。     

地震供能、储能与放能机制的研究

“双向应变结构”是孕育和发生地震可能的供能、储能与放能的一种机制。它既能缓慢地储存弹性势能与重力势能而孕育地震,又能突然快速地释放弹性势能与重力势能而发生地震。由于地震发生时孕震体是(原应变的)应变逆转的自破裂过程,因此当初始破裂发生后,在破裂的前沿区,地震剪切应力在原有应力集中的基础上,还会再次产生一个突然快速增强(使破裂加速)到快速减弱(使破裂减速到停止)的过程,即产生“应变逆转破裂效应”。这样,不仅会大大增加地震破裂前沿区的剪切应力,而且还会大大减小破裂中的阻力,可能使地震发生中的断层强度佯谬得到解释。“双向应变结构”破裂发生地震的具体物理机制,印证了震源体断层运动的复杂性：既产生了剪切错动的破裂运动,又产生了单向的拉张与单向的压缩运动,同时还产生了整体的膨胀与整体的压缩运动。     

一种基于定向技术的Ad Hoc路由协议

基于MAC层的定向技术&提出了一种适合于Ad hoc无线网络的协议APRP协议,协议考虑了MAC层和网络层信息的共享和交互,改进了动态源路由协议DSR的路由发现和路由维护机制.采用NS2工具对协议性能进行了仿真研究,结果表明APRP协议不仅可以利用定向技术能量利用率的优势,而且还能较好地保持节点移动情况下的吞吐量,降低端到端数据包延时和路由开销     

关于热带大气低频振荡的一个简单模式与数值模拟

本文首先从观测事实分析了热带大气的低频振荡现象，然后从理论上加以研究。为此，本文建立了一个包括触发热源和CISK机制的三维线性模式，用此模式讨论了热带大气低频振荡的性质、结构、传播和动力学机制。从模式的计算结果得到了周期为30d左右以大约9 m/s的速度向东传播的低频振荡现象，这种振荡为Kelvin波型的响应和向西传播的Rossby波型的响应的结合。计算还表明，这种振荡的周期与触发热源的周期关系不大，这说明了热带大气的低频振荡是大气自身的固有振荡，它是大尺度运动与对流凝结加热相互作用的结果。     

NATURE OF PRECIPITATION AND ACTIVITY OF CUMULUS CONVECTION DURING THE 1991 MEIYU SEASON OF CHANGJIANG-HUAIHE RIVER BASIN*

Seasonal variability regarding the nature of precipitation and the activity of cumulus convection during the 1991 Meiyu season of Changjiang-Huaihe River Basin(Jianghuai)has been investigated by calculating apparent heat source/apparent moisture sink and analyzing TBB(cloud-top blackody radiation temperature)data.It is found that three periods of strong ascending motion during the Meiyu season lead to three episodes of heavy rain,and the latent heat due to the precipitation is of the sole heat source of the atmosphere.The nature of precipitation shows distinct seasonal variability,from frontal precipitation of the first episode to the extremely strong convective precipitation of the third episode.TBB field of East Asia may well reflect not only the intensity of convection and rainfall,but also the movement of rain belt and convection belt.In the whole Meiyu season.convection belt mainly stays in Jianghuai.but may shift within the domain of East Asia.Its locating in Jianghuai or not determines the maintenance or break of Meiyu.In the third episode,the narrow convection belt over Jianghuai is mainly caused by southwest monsoon which takes moist and convective atmosphere from tropical ocean.     

Mapping runoff generating areas using AGNPS-VSA model

ABSTRACT

In humid regions, surface runoff is often generated by saturation-excess runoff mechanisms from relatively small variable source areas (VSAs). However, the majority of the current hydrologic models are based on infiltration-excess mechanisms. In this study, the AGricultural Non-Point Source Pollution (AGNPS) model was used to integrate the VSA concept using topographic wetness index (TWI). Both the original and AGNPS-VSA models were evaluated for a small agricultural field in Ontario, Canada. The results indicate that the AGNPS-VSA model performed better than original model. The AGNPS-VSA model predicted that only the saturated portion of the field with higher TWI values produced runoff, whereas the original AGNPS model showed uniform hydrologic response from the entire field. The results of this study are important for accurately mapping the locations of VSAs. This new model could be a powerful tool in identifying critical source areas for applying targeted best management practices to minimize pollutant loads to receiving waters.     

西藏地区雷暴与大气热源关系研究

利用1979～2008年NCEP/NCAR全球再分析月平均资料和雷暴记录资料, 运用相关分析和合成分析等方法分别对西藏地区大气热源和雷暴日数的关系以及热源强弱不同时期雷暴日数变化特征进行了分析。结果表明, 大气热源与雷暴日数存在着明显的正相关关系, 月相关系数高达0.86。在雷暴高发区的那曲东部、拉萨、日喀则中部、山南地区东北部和林芝地区西北部, 相关系数均超过了0.4。进一步分析表明, 当大气热源强值年时, 整个日喀则地区、拉萨地区、山南地区、那曲中西部和东部地区以及昌都地区中西部, 雷暴日数是偏多的。当大气热源偏弱时, 雷暴日数在日喀则中部地区减少最为明显, 其次在日喀则南木林县东北部和林芝西北部地区。