北京地区3500a来的气候与环境变迁——兼论昆明湖的沧桑

通过对北京颐和园昆明湖中沉积物的沉积特征的研究,结合历史记载,对昆明湖水域的形成时间和发展过程有了深入的了解,据此对北京地区3500a以来的气候与环境变迁作出了科学的划分,为探讨北京地区未来的气候变化趋势将会有所启迪。     

Land subsidence caused by groundwater exploitation in Suzhou City,China

Suzhou City, located at the lower reaches of the Yangtze River in southeastern Jiangsu Province, is one of the few cities in China which suffer from severe ground settlement. A research project was carried out to investigate this problem. Geological and hydrogeological studies show that there is a multi-layered aquifer system with three distinct, soft mud layers of marine and lagoonal origins. An examination of historical records of groundwater extraction, water levels, and ground settlement shows that the ground subsidence is associated with the continuously increasing groundwater extraction in the deep, confined aquifer. It is believed that the consolidation of the soft mud layers, especially the third layer which is thick and close to the main pumped aquifer, contributes to the ground settlement. A three-dimensional finite difference numerical model representing the multi-layered aquifer system was developed to study the ground settlement in response to groundwater extraction. By calibrating the model with both the measured groundwater level and ground settlement, the aquifer parameters were estimated. The model outputs fit reasonably well with the observed results, which indicates that the numerical model can reproduce the dynamic processes of both groundwater flow and soil consolidation. The hydraulic conductivity of the third mud layer near the center of the ground settlement has been reduced by over 30% in the last 14 years. The gradual deterioration in the hydraulic conductivity of the mud may have significant adverse effect on the sustainable groundwater resource of the deep confined aquifer, since the recharge from the shallow aquifers through the mud layer is the only source of water to the deep aquifer. An analysis of the spatial distributions of groundwater drawdown and ground settlement shows that the area with maximum drawdown is not necessarily the area with maximum ground settlement due to the occurrence of the soft mud layer. A simple reallocation in pumping rates on the basis of the spatial distribution of the thick mud layer could significantly reduce the ground settlement. Electronic Publication     

Pull-down basin in the central part of Japan due to subduction-induced mantle flow

The driving force for the basin subsiding against isostatic balance in and around Lake Biwa in the Kinki district, Japan is discussed. The lake region is characterized by strong negative Bouguer anomalies, especially by a steep horizontal gradient zone of gravity anomaly running along the western margin of the lake. The large negative anomaly (>50 mgal) cannot be explained by low-density sediments beneath it. A down-warping structure extending to the Moho depth should be taken into account. This conjecture has been strongly supported by a short-period receiver function imaging, which shows a clear offset of about 8 km for the Moho discontinuity under the steep gravity gradient zone.A question arises as to what is the driving force to create such a large down-warping structure. We consider that the subduction of the shallow-dipping slab under the region (Philippine Sea Slab) may cause crustal deformation by dragging the viscous mantle downward. In order to verify this model, we simulated the induced mantle flow due to the subduction of the Philippine Sea Slab and the pressure distribution on the crust–mantle boundary. This numerical experiment showed that the induced flow makes a strong negative pressure zone under the lake region if the slab has a vertical offset along the direction of subduction. This offset of the slab is consistent with plate models deduced from hypocentral distributions and Sp phases of the deep-focus earthquakes.     

中尺度自忆模式在强降水预报中的应用

根据大气自忆性原理提出的回溯时间积分格式应用于中尺度格点模式MM5,构建了中尺度自忆模式SMM5并做了短期强降水预报的实验.结果表明,SMM5模式与MM5模式相比,由于使用了多个时刻的场资料,预报精度有了明显的提高, SMM5预报的最大雨区的中心位置与降水量也比MM5更接近实际观测场.     

城市天气预报服务产品制作系统

利用FORTRAN和BASIC语言开发在WINDOWS．XX环境下运行的城市天气预报服务产品制作程序，包括报文采集、报文处理与翻译、报文检索与纠错、产品制作、产品输出与分发等内容，实现了大数量和多类型城市天气预报产品的自动制作。在保证准确、高效的专业预报服务中发挥了重要作用。     

多元判据综合评估中期天气客观相似预报模式

提出一个对多元判据综合评估的中期天气客观相似预报模式。模式应用同中期天气过程的时间—空间尺度相适应的经过时间滤波的大气环流背景为客观判据，比较全面地评估了预报时刻前后多层次、多要素的大气环流动态变化的相似，通过定义相似指数综合评估在多元判据下样本的相似程度，从相似时域的历史样本中找到较佳相似的中期过程，预测未来l～10天的中期天气过程。模式检验和预报试验表明该模式具有预报技巧。     

一次梅雨锋降水系统三维风场双、三雷达对比研究

2002年，“我国重大气候和天气灾害的形成机理与预测理论研究”项目首次启用三多普勒天气雷达组网对暴雨系统进行同步观测，作者使用MUSCAT技术对6月24日梅雨锋雨带上的一个中β系统进行了双、三多普勒雷达三维风场对比分析，表明大气中低层辐合线是此次暴雨系统的一个重要特征。     

河西走廊东部强雷暴天气分析与预报

根据1961～2000年武威站雷暴天气实况资料分析了河西走廊东部40年强雷暴天气发生的气候规律，并研究了河西走廊东部强雷暴天气发生的4种环流背景及4种主要天气条件，归纳总结出其短期预报着眼点，为雷暴天气预报业务系统的研制奠定了基础。     

南海各月月平均海流场的数值模拟

本文用一个区域三维、自由表面、斜压海洋模式对南海全年各月的三维平均流场进行了数值模拟，模拟得到的环境特征与己有的实测资料十分相近，这表明该模拟结果是可信的，该数值模拟也是成功的。     

一次强对流系列风暴个例的多普勒天气雷达资料分析

讨论了新一代（多普勒）天气雷达对2002年5月14日19:00至21:00影响湖南常德地区的3个对流风暴的探测情况，其中两个为超级单体，一个为飑线。观测到了与超级单体相联系的中气旋和龙卷式涡旋特征（TVS）。上述强对流系统产生了地面大风、大冰雹和龙卷等强烈天气，与雷达的探测相吻合。特别值得一提的是在中国首次探测到了三体散射（TBSS）和龙卷式涡旋特征（TVS）这两个分别指示大冰雹和龙卷的雷达回波特征，并得到了地面报告的印证。