Improvement of 6–15 Day Precipitation Forecasts Using a Time-Lagged Ensemble Method简

A time-lagged ensemble method is used to improve 6-15 day precipitation forecasts from the Beijing Climate Center Atmospheric General Circulation Model,version 2.0.1.The approach averages the deterministic predictions of precipitation from the most recent model run and from earlier runs,all at the same forecast valid time.This lagged average forecast （LAF） method assigns equal weight to each ensemble member and produces a forecast by taking the ensemble mean.Our analyses of the Equitable Threat Score,the Hanssen and Kuipers Score,and the frequency bias indicate that the LAF using five members at time-lagged intervals of 6 h improves 6-15 day forecasts of precipitation frequency above 1 mm d-1 and 5 mm d-1 in many regions of China,and is more effective than the LAF method with selection of the time-lagged interval of 12 or 24 h between ensemble members.In particular,significant improvements are seen over regions where the frequencies of rainfall days are higher than about 40％-50％ in the summer season; these regions include northeastern and central to southern China,and the southeastem Tibetan Plateau.     

Decadal Variations of Intense Tropical Cyclones over the Western North Pacific during 1948–2010简

Using Joint Warning Typhoon Center （JTWC） best track data during the period 1948-2010, decadal and interdecadal changes of annual category 4 and 5 tropical cyclone （TC） frequency in the western North Pacific basin were examined. By allowing all of the observed TCs in the JTWC dataset to move along the observed TC tracks in a TC intensity model, the annual category 4 and 5 TC frequency was simulated. The results agreed well with observations when the TC intensity prior to 1973 was adjusted based on time-dependent biases due to changes in measurement and reporting practices. The simulated and adjusted time series showed significant decadal （12-18 years） variability, while the interdecadal （18-32 years） variability was found to be statistically insignificant. Numerical simulations indicated that changes in TC tracks are the most important factor for the decadal variability in the category 4 and 5 TC frequency in the western North Pacific basin, while a combined effect of changes in SST and vertical wind shear also contributes to the decadal variability. Further analysis suggested that the active phase of category 4 and 5 TCs is closely associated with an eastward shift in the TC formation locations, which allows more TCs to follow a longer journey, favoring the development of category 4 and 5 TCs. The active phase corresponds with the SST warming over the tropical central and eastern Pacific and the eastward extension of the monsoon trough, thus leading to the eastward shift in TC formation locations.     

近百余年来全球气温长期变化趋势分析

利用来自NCDC（美国国家气候数据中心）的温度数据,采用一元线性回归方法、功率谱分析方法、MK（Mann-Kendall）检验方法,分析了近百余年来（1891—2011年）全球温度偏差的长期变化趋势。结果表明：（1）1891—2011年期间,全球温度偏差整体上以0.0068℃/a的速度显著性逐年线性递增,该递增趋势在各个季节都有显著体现,其中逐1月（0.0072℃/a）、逐4月（0.0072℃/a）温度偏差的递增趋势稍强于逐年递增趋势,逐7月（0.0064℃/a）、逐10月（0.0061℃/a）温度偏差的递增趋势略弱于逐年递增趋势。（2）近百余年来,全球气温偏差主要存在两次较为显著的递增阶段：1910—1944年、1981—2011年。（3）近百余年期间,全球温度偏差存在显著的2a,2.4～2.5a,2.85～6.15a,8.9a的变化周期,以及80a左右的长周期震荡。（4）近百余年期间,全球温度偏差无显著突变,MK检验发现：1911—2011年,全球温度偏差表现出较为明显的递增趋势,也与全球变暖大背景相吻合。     

Debris flow hazard assessment using set pair analysis models: Take Beichuan county as an example

Assessment of debris flow hazards is important for developing measures to mitigate the loss of life and property and to minimize environmental damage. Two modified uncertainty models, Set Pair Analysis （SPA） and modified Set Pair Analysis （mSPA）, were suggested to assess the regional debris flow hazard. A ease study was conducted in seven towns of the Beichuan county, Sichuan Province, China, to test and compare the application of these two models in debris flow hazard assessment. The results showed that mSPA only can fit for value-variables, but not for non value-variable assessment indexes, Furthermore, as for a given assessment index xi, mSPA only considers two cases, namely, when grade value increases with xi and when grade value decreases with xi. Thus, mSPA can not be used for debris flow hazard assessment but SPA is credible for the assessment because there are no limitations when using SPA model to assess the debris flow hazard. Therefore, in this study SPA is proposed for assessing debris flow hazard.     

精密单点定位中相位偏差估计与修正方法研究

本文针对相位偏差对精密单点定位(Precise Point Positioning,PPP)的影响,分析了PPP模型中相位偏差估计的原则,并给出了宽巷和L1相位偏差的估计方法;对相位偏差小数提取过程中整数不一致以及偏差小数值存在正负差异的两个问题进行了修正。算例从相位偏差时间和空间一致性两方面进行了分析,结果表明宽巷相位偏差具有较高的时间和空间一致性,单个站点相位偏差与其均值最大差值为0.050周;L1相位偏差受无电离层模糊度影响较为严重,其空间一致性较宽巷相位偏差稍差些,但基本控制在0.180周以内,可用于PPP模糊度的相位偏差改正。     

基于上覆岩层结构理论的矿山三维地质模型修正方法

矿山三维地质建模是目前矿山地质学和测绘学科的一个研究热点,由于原始数据的松散性和不均匀性,滞后数据也不精确,导致模型的精确度较低。依据覆岩结构理论,结合相关力学模型,通过岩石应力反算出断裂处岩石的厚度,为矿山三维地质模型的修正提供一种新的方法。经实际应用与检验,能够提高模型的精确度,更接近客观实体。     

地球重力场模型在平面控制网中的应用

现在精密工程测量中GPS与全站仪的共用是普遍存在的事实,这必然存在法线系统与垂线系统的转换问题,以往由于重力场模型精度较低,未能充分顾及到这种差别,而利用现有最新的地球重力场模型,能较精确地计算垂线偏差并将其应用于精密工程测量。本文提出了顾及垂线偏差的GPS与全站仪的精密数据处理方法,通过"三差改正"将全站仪观测值转化为法线系统下的观测值,与GPS数据统一处理,利用某隧道算例验证了地球重力场模型对平面控制网数据处理的影响不容忽视。     

南京长江四桥引桥悬臂拼装测量技术

以分段施工桥梁——南京长江四桥引桥施工控制为例,针对悬臂拼装过程中的线形控制问题,明确施工过程中的主要控制内容及相应的精度控制目标,着重对施工控制网的建立、架桥机挠度检测、几何控制数据基础的选择、梁段定位测量、误差修正等内容进行研究。以最终线形控制结果为依据,评价所用测控方法,为今后悬臂拼装施工技术在类似工程中的应用提供参考。     

联合多代卫星测高数据建立高分辨率浙江近海垂线偏差模型

联合多代卫星测高数据,研究共线平均理论,在时域上削弱测高数据短波误差影响。基于EGM2008重力场模型及DTU10海面地形模型,采用沿轨迹加权最小二乘方法,确定浙江近海2.5′×2.5′分辨率格网点垂线偏差子午分量ξ和卯酉分量η,将所得计算结果与EGM96、EGM2008、ITG-Grace2010s模型值进行比较。结果表明:浙江近海垂线偏差模型与EGM2008模型的精度较为相近,在子午圈及卯酉圈上的RMS分别为±0.15320″、±0.63061″。     

加乘性混合误差模型参数估计方法及其应用

扩展乘性误差模型的参数估计方法至加乘性混合误差模型,推导了其参数最小二乘、加权最小二乘参数估计,并在偏差分析的基础上推导了偏差改正加权最小二乘估计。模拟计算和分析验证了偏差改正加权最小二乘适用于加乘性混合误差模型的大地测量数据处理,具有二阶近似无偏性,且精度较高。