地形横向密度扰动对于区域大地水准面建模的影响

分别利用Helmert和KTH法模拟试算了不同地形起伏区域内横向密度扰动对于大地水准面的影响。结果表明,在地形起伏较小的平原或丘陵地带,横向密度扰动的影响一般不会超过cm级,在精度允许的范围内可以忽略其影响;在地形起伏较大的山区,横向密度扰动的影响可达cm甚至dm级,对于cm级大地水准面精化而言,需要考虑其影响。此外,基于Helmert与KTH法解算的结果在地形起伏剧烈的山区差异较大,由于Helmert法计算地形效应时忽略了外区地形质量的影响,其解算结果可能存在偏差。总体而言,在地形起伏剧烈的山区建模时,需利用多种计算方法基于实测数据分别进行试算,通过计算的变密度大地水准面与实测的GPS水准数据进行比较分析,得到适合该区域的大地水准面建模方法。     

A Climatology Model for Forecasting Typhoon Rainfall in Taiwan

The continuous torrential rain associated with a typhoon often caused flood, landslide or debris flow, leading to serious damages to Taiwan. Thus, a usable scheme to forecast rainfall amount during a typhoon period is highly desired. An analysis using hourly rainfall amounts taken at 371 stations during 1989–2001 showed that the topographical lifting of typhoon circulation played an important role in producing heavier rainfall. A climatology model for typhoon rainfall, which considered the topographical lifting and the variations of rain rate with radius was then developed. The model could provide hourly rainfall at any station or any river basin for a given typhoon center. The cumulative rainfall along the forecasted typhoon track was also available. The results showed that the R² value between the model estimated and the observed cumulative rainfall during the typhoon period for the Dan-Shui (DSH) and Kao-Ping (KPS) River Basins reached 0.70 and 0.81, respectively. The R² values decreased slightly to 0.69 and 0.73 if individual stations were considered. However, the values decreased significantly to 0.40 and 0.51 for 3-hourly rainfalls, indicating the strong influence of the transient features in producing the heavier rainfall. In addition, the climatology model can only provide the average conditions. The characteristics in individual typhoons should be considered when applying the model in real-time operation. For example, the model could give reasonable cumulative rainfall amount at DSH before Nakri (2002) made landfall on Taiwan, but overestimated the rainfall after Nakri made landfall and weakened with significant reduction in convection.     

Differences and dynamics of multidimensional poverty in rural China from multiple perspectives analysis

Journal of Geographical Sciences - Absolute poverty was completely eliminated in China in 2020. However, poverty measured by income does not fully reflect the actual situation. This paper analyses...     

菜州浅滩地貌特征及演化

莱州浅滩是山东半岛北部著名的海岸地貌,位于刁龙嘴外,呈Nw—SE向延伸,浅滩众多,水道纵横,地貌状况复杂。目前对菜州浅滩的形成过程、沉积特征少有研究,或只针对某一方面有所论述。通过实地调查,并对资料进行分析,研究了莱州浅滩的沉积物分布特征、矿物组成、地貌特征、储砂量和演化过程,认为波浪作用是莱州浅滩形成的主要动力,控制着研究区地貌形态分布和莱州浅滩演化趋势。通过以上研究,结合莱州浅滩现状,指出了其目前在开发与保护中存在的问题,并提出了合理开发利用的建议。     

2016年北京地区一次雷暴大风的观测研究

利用常规气象观测资料、风廓线资料、北京观象台多普勒天气雷达产品、多普勒雷达变分同化分析系统（VDRAS）的反演资料和地面自动气象站客观分析资料,对2016年7月27日北京地区出现的一次雷暴大风天气的环境条件特征、风暴结构特征及演变机制进行了分析。结果显示：本次雷暴大风天气过程出现在弱天气尺度强迫环境中,较好的热力不稳定增强机制促使线状对流发展为弓形回波,形成雷暴大风天气。探空曲线中低层接近于干绝热的环境温度直减率和下沉对流有效位能突增等现象,对预报大风天气有较好的指示意义。上游雷暴的冷池出流与山前偏南暖湿气流在北京西部形成了明显的风向辐合,在强烈的扰动温度梯度和地形抬升的共同作用下,位于地面辐合抬升最强处触发新生单体并迅速发展。新生单体与风暴主体合并下山过程中,由于地形作用抬升了冷池出流高度,与平原地区偏南暖湿气流形成显著的不稳定层结,产生显著的扰动温度梯度,触发不稳定能量使雷暴在下山过程中强度增强。多普勒雷达产品上也表现为强的反射率因子核,并出现回波悬垂和有界弱回波区等特征,速度产品上可看到一对明显的端点涡旋。在冷池不断加强和端点涡旋对后入气流不断加速的共同作用下,后侧入流气流加强成为后侧入流急流,在低仰角速度产品上表现为显著的大风区。后侧入流气流将环境中的干冷空气夹卷进入云体,通过蒸发作用产生负浮力,使冷空气加速下沉,加之降水粒子的拖曳作用,最终造成剧烈的地面大风。     

全球季风槽

根据先前的研究总结出,全球有22个地形槽,其中只有3个行星尺度的季风槽和6个半岛尺度的季风槽。全球季风系统是由行星尺度季风槽和半岛尺度季风槽组成的。活动于热带北太平洋、热带北大西洋和热带南印度洋的赤道辐合带是太阳辐射随季节强迫下位置发生变化的行星尺度季风槽。半岛尺度季风槽起源于区域海陆地形和随季节变化的海陆热力对比和干湿(降水)转换。在北半球夏季,亚洲-西北太平洋地区受到4个半岛尺度季风槽和1个行星尺度季风槽的影响。其他2个半岛尺度的季风槽位于南非和印度尼西亚-西澳大利亚地区。     

A mesoscale analysis of heavy rain caused by frontal and topographical heterogeneities on Taiwan Island

The prevailing mesoscale model MM5 (V3) is used to simulate a heavy rain case caused by interaction between a move-in front and topographical heterogeneities on Taiwan Island. It is found that both thermodynamic and dynamic fields along the front are heterogeneous in time and space. The heterogeneity becomes more significant as the effect of topography is added on. The heterogeneous distribution of physical variables along the front is the main reason for the heterogeneous frontal rain band; the optimum cooperation of the low level and upper level jet is another reason for the development of the rain band.Topography can strengthen the rainfall and causes extremely heavy rain cells. Updraft induced by topography extends to a rather low level, while the uplifted air by frontal circulation can reach to higher levels.The quasi-steady topographic circulation overlaps the frontal circulation when the front moves over Taiwan Island; the advantageous cooperation of various mesoscale conditions causes the large upward velocity on the windward side of the island.