Improving NWP through radar rainfall-driven land surface parameters: A case study on convective precipitation forecasting

In this study we investigate the effect of forcing the land surface scheme of an atmospheric mesoscale model with radar rainfall data instead of the model-generated rainfall fields. The goal is to provide improved surface conditions for the atmospheric model in order to achieve accurate simulations of the mesoscale circulations that can significantly affect the timing, distribution and intensity of convective precipitation. The performance of the approach is evaluated in a set of numerical experiments on the basis of a 2-day-long mesoscale convective system that occurred over the US Great Plains in July 2004. The experimental design includes multiple runs covering a variety of forcing periods. Continuous data integration was initially used to investigate the sensitivity of the model’s performance in varying soil state conditions, while shorter time windows prior to the storm event were utilized to assess the effectiveness of the procedure for improving convective precipitation forecasting. Results indicate that continuous integration of radar rainfall data brings the simulated precipitation fields closer to the observed ones, as compared to the control simulation. The precipitation forecasts (up to 48 h) appear improved also in the cases of shorter integration periods (24 and 36 h), making this technique potentially useful for operational settings of weather forecasting systems. A physical interpretation of the results is provided on the basis of surface moisture and energy exchange.     

Curie point depth from spectral analysis of aeromagnetic data from Cerro Prieto geothermal area,Baja California,México

Using aeromagnetic data acquired in the area from the Cerro Prieto geothermal field, we estimated the depth to the Curie point isotherm, interpreted as the base of the magnetic sources, following statistical spectral-based techniques. According to our results the Curie point isotherm is located at a depths ranging from 14 to 17 km. Our result is somewhat deeper than that obtained previously based only in 2-D and 3-D forward modeling of previous low-quality data. However, our results are supported by independent information comprising geothermal gradients, seismicity distribution in the crust, and gravity determined crustal thickness. Our results imply a high thermal gradient (ranging between 33 and 38 °C/km) and high heat flow (of about 100 mW/m²) for the study area. The thermal regime for the area is inferred to be similar to that from the Salton trough.     

Rainfall network design using kriging and entropy

The spatial distribution of rainfall is related to meteorological and topographical factors. An understanding of the weather and topography is required to select the locations of the rain gauge stations in the catchment to obtain the optimum information. In theory, a well‐designed rainfall network can accurately represent and provide the needed information of rainfall in the catchment. However, the available rainfall data are rarely adequate in the mountainous area of Taiwan. In order to provide enough rainfall data to assure the success of water projects, the rainfall network based on the existing rain gauge stations has to be redesigned. A method composed of kriging and entropy that can determine the optimum number and spatial distribution of rain gauge stations in catchments is proposed. Kriging as an interpolator, which performs linear averaging to reconstruct the rainfall over the catchment on the basis of the observed rainfall, is used to compute the spatial variations of rainfall. Thus, the rainfall data at the locations of the candidate rain gauge stations can be reconstructed. The information entropy reveals the rainfall information of the each rain gauge station in the catchment. By calculating the joint entropy and the transmitted information, the candidate rain gauge stations are prioritized. In addition, the saturation of rainfall information can be used to add or remove the rain gauge stations. Thus, the optimum spatial distribution and the minimum number of rain gauge stations in the network can be determined. The catchment of the Shimen Reservoir in Taiwan is used to illustrate the method. The result shows that only seven rain gauge stations are needed to provide the necessary information. Copyright © 2007 John Wiley & Sons, Ltd.     

Spatial and temporal characteristics of droughts in the western part of Bangladesh

Spatial and temporal characteristics of droughts in the western part of Bangladesh have been analysed. Standardized precipitation index method is used to compute the severity of droughts from the rainfall data recorded in 12 rainfall gauge stations for the period of 1961–1999. An artificial neural network is used to estimate missing rainfall data. Geographic Information System (GIS) is used to map the spatial extent of droughts of different severities in multiple time scales. Critical analysis of rainfall is also carried to find the minimum monsoon and dry months rainfall require in different parts of the study area to avoid rainfall deficit. The study shows that the north and north‐western parts of Bangladesh are most vulnerable to droughts. A significant negative relationship between multiple ENSO index and rainfall is observed in some stations. Analysis of seasonal rainfall distribution, rainfall reliability and long‐term rainfall trend is also conducted to aid prediction of future droughts in the area. Copyright © 2007 John Wiley & Sons, Ltd.     

A cascade approach to continuous rainfall data generation at point locations

High-resolution temporal rainfall data sequences serve as inputs for a range of applications in planning, design and management of small (especially urban) water resources systems, including continuous flow simulation and evaluation of alternate policies for environmental impact assessment. However, such data are often not available, since their measurements are costly and time-consuming. One alternative to obtain high-resolution data is to try to derive them from available low-resolution information through a disaggregation procedure. This study evaluates a random cascade approach for generation of high-resolution rainfall data at a point location. The approach is based on the concept of scaling in rainfall, or, relating the properties associated with the rainfall process at one temporal scale to a finer-resolution scale. The procedure involves two steps: (1) identification of the presence of scaling behavior in the rainfall process; and (2) generation of synthetic data possessing same/similar scaling properties of the observed rainfall data. The scaling identification is made using a statistical moment scaling function, and the log–Poisson distribution is assumed to generate the synthetic rainfall data. The effectiveness of the approach is tested on the rainfall data observed at the Sydney Observatory Hill, Sydney, Australia. Rainfall data corresponding to four different successively doubled resolutions (daily, 12, 6, and 3 h) are studied, and disaggregation of data is attempted only between these successively doubled resolutions. The results indicate the presence of multi-scaling behavior in the rainfall data. The synthetic data generated using the log–Poisson distribution are found to exhibit scaling behaviors that match very well with that for the observed data. However, the results also indicate that fitting the scaling function alone does not necessarily mean reproducing the broader attributes that characterize the data. This observation clearly points out the extreme caution needed in the application of the existing methods for identification of scaling in rainfall, especially since such methods are also prevalent in studies of the emerging satellite observations and thus in the broader spectrum of hydrologic modeling.     

临近基坑既有建筑物地基的抗剪强度指标取值问题

基坑开挖不仅改变了半无限空间体边界条件,卸载时还会引起周围地层移动,导致既有建筑物地基承载力的附加损失。在临近基坑既有建筑物地基承载力计算中,其抗剪强度参数的选取有别于斜坡上地基计算参数的常规取值方法。通过探讨临近基坑既有建筑物地基抗剪强度指标的取值问题,建议以地基土的完全软化强度与残余抗剪强度的平均值作为临近基坑既有建筑物地基抗剪强度指标,并据此估算了临近基坑既有建筑物地基承载力。所得结果与斜坡上地基承载力的试验值和理论解对比分析后显示出其具有一定的合理性。所建议的抗剪强度指标取值方法,还有待于试验的进一步验证。     

文山州降雨侵蚀力时空分布规律浅析

降雨是导致土壤侵蚀的主要动力因素,降雨侵蚀力反映降雨引起土壤侵蚀的潜在能力。利用文山州内21个雨量代表站月降雨资料,估算文山州降雨侵蚀力,对该地区降雨侵蚀力的年内分布、年际变化特征和空间分布变化规律进行分析。结果表明：文山州降雨侵蚀力空间分布基本与降雨一致,山区为高值区,坝区为低值区;降雨侵蚀力主要集中在汛期（5～10月）,各月的差异大于降雨量的差异;文山州降雨侵蚀力长期变化为略减小趋势但不显著,年际变化较年降雨量年际变化显著。     

“两权分离”方法解决海域勘界中的历史遗留问题

“坚持尊重历史,注重现实的原则”是福建省海域勘界的三大总体原则之一．在海域勘界过程中,常出现海域历史归属和现实的海域开发利用不在同一行政区的历史遗留问题,协调好二者的矛盾冲突关系到海域勘界工作的顺利进行．本研究以泉州湾和东山湾的2条海域勘界线的工作实例,就如何利用“管辖权”和“使用权”分离的方法来解决海域勘界管辖中历史遗留的问题进行阐述．     

Estimation of precipitation condensation latent heat in rainy season over Qinghai-Tibet Plateau

The basic data for this research comprise the outgoing long-wave radiation(OLR) data observed by the United States National Oceanic and Atmospheric Administration(NOAA) series satellites from June 1974 through December 2005 over the area of 75°-105°E and 25°-40°N(totaling 91 grid zones when the horizontal resolution is 2.5° longitude by 2.5° latitude) and the monthly rainfall data recorded,from 1961 through 2005,by 93 conventional meteorological stations on the Qinghai-Tibet Plateau.Based on the research of the relation between rainfall and OLR and climate regionalization,a mathematic model was established for each region and grid zone,which is applied to estimate the monthly rainfall and then to estimate the monthly latent heat resulting from the condensation of precipitation year by year from 1961 through 2005.The results indicated that the multi-year average precipitation is 401.5 mm and the condensation latent heat is 18.55×1020 J in the eastern part of the Qinghai-Tibet Plateau;the increasing rate of condensation latent heat is 0.218×1020J/10a in the recent 45 years;that is to say,it will increase 1.2 percent in each decade.Furthermore,the total condensation latent heat and its variation rate in the Qinghai-Tibet Plateau are slightly larger than in the east to the plateau.