非线性微分-代数子系统的初始化高增益观测器设计

针对一类大系统中的非线性微分-代数子系统,研究其状态观测问题,提出了一种初始化高增益观测器设计方案.首先,通过一个非线性微分同胚变换,实现了系统的等价变换;然后针对等价系统,给出了初始化状态观测器设计,使得观测误差是指数收敛的;最后,给出一个数值仿真算例.仿真结果验证了该方法的有效性.     

Dynamic analogue initialization for ensemble forecasting

This paper introduces a new approach for the initialization of ensemble numerical forecasting: Dynamic Analogue Initialization (DAI). DAI assumes that the best model state trajectories for the past provide the initial conditions for the best forecasts in the future. As such, DAI performs the ensemble forecast using the best analogues from a full size ensemble. As a pilot study, the Lorenz63 and Lorenz96 models were used to test DAI’s effectiveness independently. Results showed that DAI can improve the forecast significantly. Especially in lower-dimensional systems, DAI can reduce the forecast RMSE by ～50% compared to the Monte Carlo forecast (MC). This improvement is because DAI is able to recognize the direction of the analysis error through the embedding process and therefore selects those good trajectories with reduced initial error. Meanwhile, a potential improvement of DAI is also proposed, and that is to find the optimal range of embedding time based on the error’s growing speed.     

High resolution numerical weather prediction over the Indian subcontinent

In this study, the Florida State University Global Spectral Model (FSUGSM), in association with a high-resolution nested regional spectral model (FSUNRSM), is used for short-range weather forecasts over the Indian domain. Three-day forecasts for each day of August 1998 were performed using different versions of the FSUGSM and FSUNRSM and were compared with the observed fields (analysis) obtained from the European Center for Medium Range Weather Forecasts (ECMWF). The impact of physical initialization (a procedure that assimilates observed rain rates into the model atmosphere through a set of reverse algorithms) on rainfall forecasts was examined in detail. A very high nowcasting skill for precipitation is obtained through the use of high-resolution physical initialization applied at the regional model level. Higher skills in wind and precipitation forecasts over the Indian summer monsoon region are achieved using this version of the regional model with physical initialization. A relatively new concept, called the ‘multimodel/multianalysis superensemble’ is described in this paper and is applied for the wind and precipitation forecasts over the Indian subcontinent. Large improvement in forecast skills of wind at 850 hPa level over the Indian subcontinent is shown possible through the use of the multimodel superensemble. The multianalysis superensemble approach that uses the latest satellite data from the Tropical Rainfall Measuring Mission (TRMM) and the Defense Meteorological Satellite Program (DMSP) has shown significant improvement in the skills of precipitation forecasts over the Indian monsoon region.     

GRAPES-TCM台风模式的新涡旋初始化方案——原理和实施

在更新的GRAPES-TCM (Global/Regional Assimilation and Prediction System-Tropical Cyclone Model)台风模式架构下,引进与发展了一个新的涡旋初始化方案。该方案对台风涡旋进行极小化订正,减少了人为因素对台风涡旋结构的影响,所产生的涡旋满足特定的动力与热力平衡,且保持了与模式动力及热力的一致性。新的涡旋初始化方案能更精细地体现初始台风的强度与结构,强度更接近于观测,结构更为合理。试验表明其可以有效地改善台风路径与强度的预报精度。     

Evaluation of different versions of NCUM global model for simulation of track and intensity of tropical cyclones over Bay of Bengal

The global UK Met office Unified Model (UM) is currently operational at National Centre for Medium Range Weather Forecasting (NCMRWF), the global model named as NCUM. An inter-comparison of two different versions of NCUM has been carried out for simulating the track and intensity of Tropical Cyclones (TCs), which formed over the Bay of Bengal (BoB). For this purpose, two series of numerical experiments named as NCUM25 (New Dynamical core with NCUM N512 resolution) and NCUM17 (ENDGame core with NCUM N768 resolution and upgraded physics and data assimilation scheme) are carried out with seven different initial conditions (ICs) for two TCs. The results suggested that the location, intensity, and vertical structure of the TCs are reasonably well predicted by the NCUM17 over the NCUM25. The Direct Position Error (DPE) and landfall error of TCs are reduced in the NCUM17 in comparison to the NCUM25 for all initial conditions. The mean DPEs and intensity error are reduced by 21–41% and 18–21% in NCUM17 over NCUM25 in both the cases respectively. Improvements in mean landfall position errors are shown to range from 43 to 65% in the NCUM17 as compared to the NCUM25. The mean statistical skill scores for rainfall are considerably improved in NCUM17.     

全球海洋蒸发量年代际变化归因：动力因子分析

本文基于动力调整方法,利用客观分析海气通量（OAFlux）资料研究了1958～2016年全球海洋蒸发量变化及其动力作用和辐射强迫分量的变化,发现海洋蒸发量及其动力作用分量具有一致性年代际变化特征,特别是在20世纪70年代及90年代末期存在明显的年代际转折。进一步分析发现:主要动力因子有太平洋—北美遥相关型（PNA）、北极涛动（AO）、北大西洋涛动（NAO）、厄尔尼诺—南方涛动（ENSO）和阿留申低压（AL）,并受到太平洋年代际振荡（PDO）的影响,其中,1970年代末期的转折与PNA、PDO、ENSO和AL密切相关,而1990年代末期的转折还与NAO变化有关。动力作用分量的前六个模态解释方差达到67.5%,其中,低纬北太平洋和印度洋蒸发异常主要与海表温度（SST）及其引起的环流异常有关,南太平洋、中纬北太平洋和北大西洋蒸发异常与环流异常直接相关。ENSO与PDO在全球海洋蒸发量上的影响要大于NAO。单因子相关分析发现南方涛动指数（SOI）、NAO和PDO与海洋蒸发年代际变化密切相关。总体来说,动力作用分量在海洋蒸发的年代际变化中起主导作用,其中,以ENSO、NAO和PDO的影响最大。     

应用非线性振荡理论研究云南局地气温的演变规律

将描述局地气温变化的非线性振荡方程应用到云南省17个测站局地气温演变研究中,根据各测站1958年1月—2000年12月逐旬气温距平资料和反演理论获得具体描述各测站局地气温变化的非线性振荡方程。以经典非线性振荡理论为依据,研究了云南省17个测站的局地气温演变规律。结果表明,云南局地气温系统是弱的非线性系统;其演变的固有周期大致在6～10旬之间;在无外源强迫的条件下,云南局地气温振幅随时间增加总是衰减;考虑外源强迫的作用后,云南局地气温系统在其演变过程中只随外源强迫的振荡而振荡。应用反演获得的描述各测站局地气温变化的有外源强迫非线性振荡方程做出未来云南局地气温演变趋势预报,其平均预报准确率约为78．9％。说明该模型具有良好的预报能力和预报稳定性。     

强烈地震孕育与发生的地点、时间及强度预测的思考与探讨

进入21世纪以来,全球范围内强烈地震频频发生,势已进入到一个新的地震活动时期.我国大陆内部、周边和台湾岛内一系列强烈地震(MS≥6.5)的发生,特别是2008年5月12日汶川MS8.0大地震的突发与其震前的异常平静表明:地表与上地壳均未见有明显的或确切能构成短、临强烈地震预测的浅表层活动过程,大地震由深部壳、幔物质运动,即深层动力过程所致.基于对强烈地震孕育、发生和发展的初步研究提出:(1)面对强烈地震的预测必须强化震源深部介质和构造环境的研究与探索,以达对未来地震发生地点的预测.(2)在地震强烈活动地区长期坚守介质破裂效应及其派生物理响应的井中观测,即"抚模"震源区介质与结构的动态"脉搏",以达对地震发生时间的逐步逼近或预测.(3)深入剖析强烈地震活动区、带、点的深、浅层空间结构与动力过程,历史地震在地震活动地域的纵向和横向的分布特征及可靠前兆信息的同步性经验和统计效应与发展态势,以对未来强烈地震发生强度的估计.这三个方面均必须以地壳深部信息的采集和研究为前提,是地震学和地震预测深化研究与探索的必经之途！     

青藏高原及附近区域穿越对流层顶的质量和臭氧通量研究

利用等熵坐标下的Wei公式对青藏高原及附近地区穿越动力学和热力学定义下对流层顶的质量和臭氧通量的时空分布变化进行了计算分析。结果表明,采用这两种定义下的对流层顶时,穿越对流层顶的质量和臭氧通量都表现出在热带纬度带为TST通量,到了副热带则转换为STT通量。由于热力学定义下的对流层顶位置稍高,造成了穿越热力学对流层顶的质量和臭氧通量变化幅度大于动力学对流层顶的情况。另外,还发现在所研究的区域穿越对流层顶质量和臭氧通量交换具有明显的年代际变化特征,在1958—2001年时段内交换是先减弱后增强。青藏高原南部及南侧地区向上的质量和臭氧输送经历了逐渐减弱过程,青藏高原北部地区向下的质量和臭氧通量交换也表现为逐渐减弱的过程,这些区域作为通量输送的通道作用是在减弱的。而接近青藏高原西北侧的塔里木盆地附近的向上输送则是逐渐加强的,表明这一区域交换通道作用在青藏高原及附近地区的质量和臭氧交换过程中起着越来越重要的作用。     

乌拉泊水库大坝的抗震安全性评价

位于北天山地震带中段的乌拉泊水库工程场地，自有历史地震记载以来，影响场区的最大烈度是Ⅶ度。通过参考前人工作成果及数据对大坝及附属建筑进行了动力稳定性计算研究，探讨了造成坝体震害的原因，评价了水库大坝的抗震安全性。