地理信息系统中几何特征不确定性的通用模型：从1维到N维

本文提出了描述地理信息系统中几何特征位置不确定性的一个通用模型，从１维到Ｎ维，在每１维中，ＧＩＳ中的特征被划分为点，线段及线性特征。由于ＧＩＳ中数据含有误差。这些特征在ＧＩＳ中位置未必与其现实世界中的真实位置一致，而其真实位置只是在围绕着ＧＩＳ中量测位置的某一个区域内，本文提出的模型给出了这些区域的统计描述。     

中国极端温度的群发性研究

从极端事件再现时间的角度研究了中国极端高、低温事件再现时间序列的长程相关性、群发性以及二者的关系。发现极端温度事件再现时间序列具有长程相关性,表征长程相关性的标度指数分布存在着明显的区域性特征,并与大气环流有关,当中国大陆在盛夏或隆冬稳定的西风环流控制下,极端温度的长程相关性较好,标度指数较大。通过定义极端事件的群发指数,对极端高、低温进行研究,发现具有长程相关性再现时间序列的极端温度呈现群发现象,且极端温度再现时间序列的标度指数和群发指数二者在空间分布上有较好的对应,极端温度再现时间序列的长程相关性可能是导致极端温度群发性的原因。从年际变化的角度看,极端高温Ⅰ级群发区域的群发指数增长趋于平缓,而极端低温Ⅰ级群发区域的群发指数有下降趋势,这与近几十年来全球变暖一致。在年代际尺度上,群发指数分布的演变特征明显,极端高温Ⅰ级群发区域总体面积变化不大,而极端低温Ⅰ级群发区域面积明显减少。因此,极端低温事件群发性减弱很可能是年代际气候变暖的主要原因。     

Potentials and limitations of modelling vertical distributions of root water uptake of an Austrian pine forest on a sandy soil

Root water uptake patterns are often studied with simulation models of the unsaturated soil water flow, as they are difficult to measure directly. Calibration of these models is not straightforward and causes uncertainties in simulated uptake distributions. In this paper we study how uncertainties in the calibration of the SWIF model affect uncertainty intervals in simulated uptake patterns of an Austrian pine stand (Pinus nigra var. nigra) on a sandy soil. After calibrating and validating SWIF with a large data set of more than 125 000 measured soil water contents over a three year period, uncertainty ranges in simulated soil water dynamics and root water uptake distributions were estimated with a Monte Carlo analysis. In general, uncertainties in root uptake patterns were small (typically <2 10⁻⁴ m³ m⁻³ day⁻¹) and were higher for trees with a shallow rooting system (0·8 m) than for trees with a deep rooting system (2·5 m). Uncertainties arose mainly from uncertainties in simulated soil water fluxes and from variations in the reduction of uptake during periods of drought. Uncertainties in soil water contents were far higher (typically 0·01 m³ m⁻³) than uncertainties in uptake, illustrating that uncertainties in uptake parameters and those in the distribution of water uptake hardly affect the modelling of soil water dynamics. Root water uptake models should therefore be validated against measured uptake distributions, which can be determined on sandy soils during dry periods with a high water use when soil fluxes are negligible to uptake. Copyright © 2000 John Wiley & Sons, Ltd.     

雷达资料同化频次对数值模拟效果影响的试验

采用中尺度数值天气预报模式WRF3.2, 研究了不同的同化时间间隔对2011年7月3~4日成都暴雨模拟的影响。结果表明, 同化了雷达资料后, 使初始场的水汽场、水平风场、垂直速度的分布更加接近实况;除温度场外, 同化频次越高对初始场的影响越大, 水平风场的增量值越大, 呈现的中小尺度信息越多, 更加接近“真实”大气;经过多次同化, 中低层风场的改变已经传递到高层, 引起了高层流场的调整;同化雷达反射率资料是有效的, 能够调整大气中的水汽分布。     

神农架红桦林的孢粉学研究

本文是在鄂西神农架山区的红桦林中,进行的孢粉组合与植被关系,及其森林植被历史的实验研究。在孢粉统计中、计算了各种类成分的百分频度、浓度、“R”值及其置信区间。论证了由华山松林——红桦林的植被变化过程,各种植物成分间的生态关系。实验证明,研究当地现代花粉与植物间数量关系,以校正化石花粉数值,对于用孢粉学方法研究历史时期的植被与环境,是至关重要的。     

一个海洋资料的客观分析方法和分析场的置信水平

这项工作提出了用于海洋资料的一个客观分析方法。这个方法是根据ＧａｕｓＭａｒｋｏｖ原理建立的。当给出一个待分析场中有限个资料点上的观测值时，使用这个方法可以得到相应物理量（如速度，流函数和温度等）的最小平方误差的线性估计场。在建立这个方法的过程中，也给出了计算ＲＭＳ误差的公式。使用这个方法还可以设计出有效的空间取样阵列。本文使用这个方法对海冰速度，海面风速和流函数等分别进行了分析，试验结果表明，这个方法简单、方便，得到了满意的结果     

Regularized joint inverse estimation of extreme rainfall amounts in ungauged coastal basins of El Salvador

A regularized joint inverse procedure is presented and used to estimate the magnitude of extreme rainfall events in ungauged coastal river basins of El Salvador: Paz, Jiboa, Grande de San Miguel, and Goascoran. Since streamflow measurements reflect temporal and spatial rainfall information, peak-flow discharge is hypothesized to represent a similarity measure suitable for regionalization. To test this hypothesis, peak-flow discharge values determined from streamflow recurrence information (10-year, 25-year, and 100-year) collected outside the study basins are used to develop regional (country-wide) regression equations. Peak-flow discharge derived from these equations together with preferred spatial parameter relations as soft prior information are used to constrain the simultaneous calibration of 20 tributary basin models. The nonlinear range of uncertainty in estimated parameter values (1 curve number and 3 recurrent rainfall amounts for each model) is determined using an inverse calibration-constrained Monte Carlo approach. Cumulative probability distributions for rainfall amounts indicate differences among basins for a given return period and an increase in magnitude and range among basins with increasing return interval. Comparison of the estimated median rainfall amounts for all return periods were reasonable but larger (3.2–26%) than rainfall estimates computed using the frequency-duration (traditional) approach and individual rain gauge data. The observed 25-year recurrence rainfall amount at La Hachadura in the Paz River basin during Hurricane Mitch (1998) is similar in value to, but outside and slightly less than, the estimated rainfall confidence limits. The similarity in joint inverse and traditionally computed rainfall events, however, suggests that the rainfall observation may likely be due to under-catch and not model bias.     

腾格里沙漠南缘风积物快组分光释光信号选择研究

光释光(OSL)信号衰减曲线不同时段信号积分的选择, 直接影响到能否有效提取快组分信号, 从而影响等效剂量(De)计算的准确性。本文根据腾格里沙漠南缘古浪县附近的两个剖面的6个风成沉积物的共193个单片的单片再生剂量法(SAR)测试结果, 将石英OSL衰减曲线分解成快、中、慢与背景信号三个组分。利用分解出的OSL快组分信号建立再生曲线, 求取每个单片对应的De值, 并与4组选择OSL衰减曲线上不同时段信号积分的SAR法所计算的De值对比。结果表明, 腾格里沙漠南缘风成沉积物的De值对信号区间选择方式较为敏感; 使用通道1~2(0~0.32 s)作为快组分信号区间, 通道3~7(0.32~1.12 s)作为背景信号区间的早期背景信号扣除法获得的De值与快组分法计算的De值较一致; 晚期背景信号扣除法由于受中组分信号的显著影响, 计算的De值与真实De值之间存在较大差异。     

中国大陆活动断裂大震复发间隔

通过重新编制活动断层定量参数数据库,利用中国大陆活动断裂定量资料评估了中国大陆活动断裂(段)的大震复发间隔,给出了青藏、新疆、华北3个构造区的大震复发间隔分布特征。研究结果表明,青藏高原活动断裂M7.5级以上大震复发间隔远小于华北和新疆。青藏高原从几100a到2000a,而华北和新疆则从2000a到5000a。大震复发间隔与断层滑动速率成反比,边界断裂的大震复发间隔通常比块体内部断裂短,比例关系大体为1:1.5—2.0。大震复发间隔与断裂性质相关,走滑断层的复发间隔小于逆走滑断层,逆走滑断层小于逆断层,比例关系大体为1:1.5—2.5。现有的定量数据汇编成果和大震复发间隔估计以及统计结果,既可作为地震危险性分析的重要参数,又可作为构造类比研究的参考信息。     

SPI drought class prediction using log-linear models applied to wet and dry seasons

A log-linear modelling for 3-dimensional contingency tables was used with categorical time series of SPI drought class transitions for prediction of monthly drought severity. Standardized Precipitation Index (SPI) time series in 12- and 6-month time scales were computed for 10 precipitation time series relative to GPCC datasets with 2.5° spatial resolution located over Portugal and with 112 years length (1902–2014). The aim was modelling two-month step class transitions for the wet and dry seasons of the year and then obtain probability ratios – Odds – as well as their respective confidence intervals to estimate how probable a transition is compared to another. The prediction results produced by the modelling applied to wet and dry season separately, for the 6- and the 12-month SPI time scale, were compared with the results produced by the same modelling without the split, using skill scores computed for the entire time series length. Results point to good prediction performances ranging from 70 to 80% in the percentage of corrects (PC) and 50–70% in the Heidke skill score (HSS), with the highest scores obtained when the modelling is applied to the SPI12. The adding up of the wet and dry seasons introduced in the modelling brought improvements in the predictions, of about 0.9–4% in the PC and 1.3–6.8% in the HSS, being the highest improvements obtained in the SPI6 application.