Temporal Characteristics of Pacific Decadal Oscillation (PDO) and ENSO and Their Relationship Analyzed with Method of Empirical Mode Decomposition (EMD)

1. IntroductionPacific Decadal Oscillation (PDO) is a long-termENSO-like variability of the North Pacific. It can becharacterized by the first principal component of EOFof the North Pacific SST (Zhu and Yang, 2003; Tren-berth, 1990; Yang and Zhang, 2003). ENSO is thestrongest signal of annular change of global climatesystem (Trenberth, 1997). The spatial pattern of PDOis a wedge similar to El Nino. In the cool (warm)phases of PDO, the central and northwest Pacific is ofwarm (co…     

SVD方法在气象场诊断分析中的普适性

本文首次从理论上推导证明两个气象场的奇异值分解（ＳＶＤ）在气象场时空分布耦合信号的诊断分析中具有普适性。结果表明，两个场的ＳＶＤ求解准则不同于典型相关分析（ＣＣＡ），且ＣＣＡ模型可视为ＳＶＤ之特例，尤其当各个场经ＰＣＡ滤波后，其ＣＣＡ完全与ＳＶＤ等价。ＳＶＤ分析的结果不但可完全代替ＣＣＡ，且计算更简便，所得耦合信号的物理解释更清晰，特别适合于大尺度气象场的遥相关型研究。     

The Arctic and Antarctic Oscillations in the IPCC AR4 Coupled Models

This study evaluates the fidelity of Arctic and Antarctic oscillations (AO and AAO for short,respectively) in the coupled general circulation models participating in the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR4).The AO and AAO during 1970-1999 in 24 models are analyzed and compared with that in ERA-40 and NCEP-1.Models'performance is seasonally dependent,with best reproducibility of both spatial structure and trend in winter.In most models,the spatial pattern and temporal trend of AAO during this period are more delicately simulated than AO.After picking out models with better performance according to the Taylor diagram,we find that their ensemble mean can obviously improve models'reproducibility.The AO and AAO in the Special Report on Emission Scenarios (SRES) A1B Projection during the 21st century are also briefly analyzed.The results reveal that both the AO and AAO indices keep increasing during 1970-2099,with a steadier pace of AO than AAO.The spatial difference of sea level pressure between 2060 2089 and 1970-1999 shows decreased values in polar regions,and increased values in midlatitudes.The results manifest that the ozone recovery during the mid 21st century may not weaken such a trend.     

CMIP5模式对东太平洋ITCZ偶极子模态模拟能力的评估

本研究利用第五次国际间耦合模式比较计划(Coupled Model Intercomparison Project phase 5, CMIP5)中的24个模式的工业革命前控制试验(Pre-industrial Control, picontrol)模拟结果, 结合观测资料, 评估了24个CMIP5 模式对东太平洋热带辐合带偶极子(Eastern Pacific ITCZ dipole, EPID)降水模态的模拟能力, 并建立了其与模式对热带太平洋气候态模拟之间的联系。结果表明: 1) 绝大多数模式在北半球春季(2—4月)对EPID模态模拟能力较差, 主要原因在于CMIP5模式对热带辐合带(Intertropical Convergence Zone, ITCZ)的模拟偏差, 其中模拟效果较差的模式在2—4月的气候态降水分布在赤道以南, 且降水普遍偏强; 2) 对各模式的EPID模态选取的季节按照技巧评分最高进行调整后, 大部分模式能较好地模拟出EPID模态的空间分布特点, 技巧评分在0.6以上, 其中模拟效果好的模式(技巧评分大于0.7)中EPID模态出现的月份同时在中东太平洋气候态表现出“双ITCZ”特征, 且多模式集合结果的模拟误差小于绝大多数模式。     

锚固站对BDS自主导航精度的影响分析

介绍了自主导航的轨道确定及时间同步观测方程。以北斗仿真全星座为对象,通过采用仿真星间及卫星与地面锚固站间观测值,进行了60 d自主导航解算,分别探讨了锚固站数量及锚固站观测连续性对北斗卫星导航系统（BDS）3类卫星自主导航精度的影响。结果表明：锚固站数量及观测连续性对RERR及CERR无影响;加入1个锚固站即可显著改进URE结果精度,继续增加锚固站数量虽然可进一步提高URE精度但其改进效果有限;锚固站观测中断时间越长,其对应自主导航精度越低。因此,在BDS自主导航运行模式下应保持较高的锚固站观测频次以保证自主导航精度;另外,锚固站数量及观测连续性对北斗系统3类卫星自主导航精度的影响无显著差异。     

GNSS转发式欺骗干扰方法的改进

针对GNSS多天线转发式欺骗干扰在实际应用中,当干扰机与目标机距离大于一定范围时,将引起目标机钟差突跳,从而易被目标机检测和识别的缺陷,提出了基于干扰机阵列的转发式欺骗干扰新方法。干扰机阵列按照正六边形网型布设,可实现目标区域的无缝覆盖,并且灵活易拓展。不论目标机位于区域的任何位置,均有一个最优干扰机能够对其实施有效干扰。为了确定相邻干扰机的最优间距,本文在干扰机阵列不同间距下对具有钟差突跳自适应检测能力的目标机的干扰有效性进行了仿真研究。结论表明,综合考虑各种约束因素,相邻干扰机最优间距为17 km,满足该条件的干扰机阵列在实施欺骗干扰过程中,不会造成目标机钟差突跳,有效解决了该干扰方式易被目标机识别的问题。     

基于WalkGIS的地形数据建库加工整理模式

以1∶500基础地理信息数据加工整理模式为研究对象,对数据整理的技术要求和整理方法进行了清晰的阐述,总结出一套基于WalkGIS平台的基础地理信息数据库建库数据加工整理模式,为数据整理工作提供参考。     

风廓线雷达大气风场观测误差分析

依据风廓线雷达工作原理和风的计算公式,分析影响大气风场观测误差的主要因素,重点分析了雷达回波SNR对风的观测精度影响和GPS探空对比试验。结果表明:①风速观测精度主要取决于波束倾角、雷达技术参数和大气折射率结构常数C2n的垂直分布;风速及风速观测精度越大,风向观测精度越大。②在同种观测模式下,波束倾角与C2n越大,风场观测精度越高。③同一观测模式的SNR越大,风速观测误差越小;不同模式间的大气风场观测精度相差较大。④对比试验的风速风向相关性较好,但相对偏差较大,尤其低空更为明显。     

全极化SAR数据在地表覆盖/利用监测中的应用

SIR-C/X-SAR是运行在地球轨道上的第一个多波段(L、C、X)全极化(HH、VV、VH和HV)成像雷达系统,该系统具有极化测量和干涉测量功能。全极化雷达测量每一个像元的全散射矩阵,所获取的信息非常丰富。但是,由于这些极化合成图像具有较高的相关性,导致了图像信息提取精度的降低。本文基于新疆和田地区的SIR-CL波段全极化雷达数据,利用全散射矩阵的特点合成了HH-VV极化相关图像、极化度图像、目标增强图像和相位差图像。这些图像相关性小,地表覆盖信息丰富,提高了全极化SAR数据在实验区信息提取的准确度。     

Algorithm for Harmonic Tidal Analysis along T/P Tracks： Taking Differences of Observed Sea Surface Heights at Adjacent Points as Observations

An algorithm （differential mode） is presented for the improvement of harmonic tidal analysis along T/P tracks, in which the differences between the observed sea surface heights at adjacent points are taken as observations. Also, the observation equations are constrained with the results of the crossover analysis; the parameter estimations are performed at 0.1° latitude intervals by the least squares. Cycle 10 to 330 T/P altimeter data covering the China Sea and the Northwest Pacific Ocean （2°-50° N,105°-150° E） are adopted for a refined along-track harmonic tidal analysis, and harmonic constants of 12 constituents in 8 474 points are obtained, which indicates that the algorithm can efficiently remove non-tidal effects in the altimeter observations, and improve the precision of tide parameters. Moreover, parameters along altimetry tracks represent a smoother distribution than those obtained by traditional algorithms. The root mean squares of the fitting errors between the tidal height model and the observations reduce from 11 cm to 1.3 cm.