短期集合预报技术在梅雨降水预报中的试验研究

数值预报的误差来源于初始场和模式的误差,集合预报技术是减小这些误差的有效方法。该文以MM5模式作为试验模式框架,模式的积云参数化方案分别取Anthes-Kuo、Grell、Kain-Fritsch和Betts-Miller方案,边界层参数化方案分别取MRF和Eta方案,通过组合4种积云参数化方案和两种边界层参数化方案产生8个集合成员,对1999年华东地区梅雨期间3个降水个例进行48 h集合预报试验。结果显示不同集合成员的预报结果各不相同,积云参数化方案对降水的影响比边界层参数化方案对降水的影响大;不同集合成员预报降水的偏差也各不相同,大多存在湿偏差,量级小的降水的湿偏差程度比量级大的降水的湿偏差程度小;对于不同个例,各成员中预报效果相对较好的成员是不同的,集合平均后可以得到一个比较稳定的预报结果;从集合预报结果中还能得到客观化和定量化的降水概率预报,它能对可能发生的天气现象发出信号。     

Holocene environmental change at Lake Njulla (999 m a.s.l.), northern Sweden: a comparison with four small nearby lakes alongan altitudinal gradient

We assess Holocene environmental change at alpine Lake Njulla(68°22N, 18°42E, 999 m a.s.l.) innorthernmost Sweden using sedimentary remains of chironomid head capsules anddiatoms. We apply regional calibration sets to quantitatively reconstruct meanJuly air temperature (using chironomids and diatoms) and lake-water pH(using diatoms). Both chironomids and diatoms infer highest temperatures(1.7–2.3°C above present-day estimates, includinga correction for glacio-isostatic land up-lift by0.6°C) during the early Holocene (c.9,500–8,500 cal. yrs BP). Diatoms suggest a decreasing lake-waterpH trend (c. 0.6 pH units) since the early Holocene. Usingdetrended canonical correspondence analysis (DCCA), we compare the Holocenedevelopment of diatom communities in Lake Njulla with four other nearby lakes(Lake 850, Lake Tibetanus, Vuoskkujávri, Vuolep Njakajaure) locatedalong an altitudinal gradient. All five lakes show similar initial DCCA scoresafter deglaciation, suggesting that similar environmental processes such ashigh erosion rates and low light availability associated with high summertemperature appear to have regulated the diatom community, favouring highabundances of Fragilaria species. Subsequently, the diatomassemblages develop in a directional manner, but timing and scale ofdevelopment differ substantially between lakes. This is attributed primarily todifferences in the local geology, which is controlling the lake-waterpH. Imposed on the basic geological setting, site-specific processessuch as vegetation development, climate, hydrological setting andin-lake processes appear to control lake development in northernSweden.     

修正的ECMWF质量通量积云参数化方案的预报试验

用一个有限区域业务预报模式，以１９９５年７—８月西北地区几次大范围的降水天气过程为试验个例，对经过修改的ＥＣＭＷＦ质量通量积云参数化方案和模式中的原Ｋｕｏ型积云参数化方案进行了共１３例４８ｈ的批量对比预报试验。结果显示：质量通量方案能给出比Ｋｕｏ型方案更合理的积云降水落区；质量通量方案对模式预报≥１０．０ｍｍ的降水有一定的改进，并提高了各种降水等级的预报效率评分值     

青藏高原春季积雪异常对亚洲季风降水影响的数值试验

该文利用一个移植和改进的ＣＯＬＡＡＧＣＭ谱模式，进行了青藏高原春季积雪异常对亚洲夏季风环流和降水影响的数值试验。试验结果指出：高原地区３月份积雪增多，亚洲地区６，７月的夏季风环流明显减弱，降水减少。     

吕梁地区分县降水逐日滚动T106产品释用系统

降水天气预报一直是各级气象台站工作的主要内容，如何能充分利用T106数值预报产品，制作更及时、准确的天气预报是气象工作者多年来探讨的主要课题之一。本系统旨在把T106数值预报产品与预报经验结合吕梁地区气候特点，对T106数值预报产品进行二次加工，制作出吕梁地区分县降水逐日滚动预报。     

Impact of imperfect rainfall knowledge on the efficiency and the parameters of watershed models

It is crucial to analyze the sensitivity of watershed (rainfall-runoff) models to imperfect knowledge of rainfall input, in order to judge whether or not they are reliable and robust, especially if they are to be used for operational purposes. In this paper, a new approach to sensitivity analysis is proposed, based on a comparison between the efficiency ratings and parameter values of the models and the quality of rainfall input estimate (GORE and BALANCE indexes, assessing the quality of rainfall time distribution and the total depth respectively). Data from three watersheds of increasing size (71, 1120, and 10700 km²), are used to test three watershed models of varying complexity (three-parameter GR3J model and six-parameter modified versions of TOPMODEL and IHACRES).

These models are able to cope with imperfect rainfall input estimates, and react to improvements in rainfall input accuracy by better performance and reduced variability of efficiency. Two different types of model behavior were identified: the models either benefit from improved rainfall data by producing more consistent parameter values, or they are unable to take advantage of the improvements. Although the watershed size seems to be immaterial, the smaller watersheds appear to need more precise areal rainfall estimates (a higher concentration of raingages) to ensure good modeling results.     

7Be在土壤侵蚀示踪中的应用研究进展

7Be是一种自然产生的放射性核素，由对流层和同温层大气中的氧和氮在宇宙射线作用下分裂生成，其半衰期为53．3天，7Be通过连续的干湿沉降作用到达土表，被土壤颗粒紧密吸附，其土壤环境化学行为与137Cs相似，因此，可以用于示踪某种特定土地利用方式或侵蚀事件下的土壤侵蚀作用的强度，空间分配以及季节性变化，7Be技术可与其它反映中长期土壤侵蚀的放射性核素（137Cs,210Pb)示踪技术相结合，共同表征某个流域的土壤侵蚀状况，对7Be示踪技术现有的土壤侵蚀速率定量估算模型进行了简述，并提出了各自的局限性及今后的研究方向。     

基于GIS不规则单元划分及其地质信息提取系统

地质单元（尤其是不规则单元）划分及地质信息提取是矿产资源定量预测的基础性工作，用通用型GIS软件完成这项工作时有许多限制。如何在较为成熟的商用GIS软件的基础上开发出专用于单元划分及信息提取的计算机系统，是更有效地进行矿产资源定量预测必须解决的问题。从这个目的出发，讨论GIS的不规则地质单元划分及地质信息提取系统的设计及实现过程。