Single point mooring system modal parameter identification based on empirical mode decomposition and time-varying autoregressive model

A method based on empirical mode decomposition (EMD) and time-varying autoregressive (TVAR) model is proposed here to identify the modal parameters of time-varying systems, such as the Floating Production Storage and Offloading (FPSO) single point mooring system. For the EMD–TVAR method, the original signal is decomposed into a finite number of ‘intrinsic mode functions’ (IMFs) by the EMD. Each IMF can be represented as a TVAR model. Then, the time-varying modal parameters i.e., instantaneous frequency (IF) and modal dumping, can be obtained by the basis functions expansion method. The proposed EMD–TVAR method has good results in two experiments compared with the Huang–Hilbert transformation and Short Time Fourier Transform method, and it has been used to analysis the modal parameters of FPSO single point mooring system successfully. The system's time-varying characteristic and its frequency distribution can be known from the modal analysis results.     

一种考虑PMX与PMY之间相关性的极移预报新方法

提出采用多元回归模型（MAR）与最小二乘（LS）组合进行极移预报。该模型考虑极移PMX和PMY的LS拟合残差之间的相关性,采用PMX残差和PMY残差一起构建预报模型进行残差预报。通过与LS+AR预报结果的对比表明,LS+MAR模型的预报结果更优。此外,通过与EOP_PCC预报结果的对比也说明,LS+MAR模型的短期极移预报精度能够达到国际先进水平。     

一种基于频谱分析和AR补偿的对流层延迟预报模型

利用实测天顶对流层延迟值（ZTD）,在无气象参数条件下,提出一种对流层延迟建模与预报方法。首先利用频谱分析,得到ZTD时间序列周期特性,并在此基础上对ZTD进行建模,给出模型参数计算方法。然后,基于频谱分析模型拟合ZTD,并与实测值进行比较分析。最后,将分析得到的拟合残差用AR模型进行改正并预报。结果表明,基于频谱分析和AR补偿的ZTD改正预报模型能够满足不同测试环境下的需求,精度达到cm级。     

基于多源证据估算气候敏感度最新研究进展:IPCC AR6解读

本文依据政府间气候变化专门委员会(IPCC)第六次评估报告(AR6)第一工作组(WGI)报告第七章的内容,详细解读了基于多源证据对气候敏感度的估算,这些证据包括:过程理解、仪器记录、古气候数据和萌现约束。得到的结论是,多源证据支持平衡态气候敏感度(ECS)的中心估计值接近3 ℃,可能区间为2.5～4.0 ℃,非常可能区间为2.0～5.0 ℃;瞬态气候响应(TCR)的最佳估值为1.8 ℃,可能区间为1.4～2.2 ℃,非常可能区间为1.2～2.4 ℃。与之前历次IPCC评估报告相比,AR6关于气候敏感度的估算最为重要的创新之处为,它没有将气候模式结果当作唯一证据,而是仅仅给出第六次国际耦合模式比较计划(CMIP6)结果并与基于多源证据的综合评估结果进行了对比。通过对比发现,CMIP6关于ECS与TCR的平均值均高于第五次国际耦合模式比较计划(CMIP5)和AR6的综合评估结果。相比CMIP6,AR6综合了多个证据线有效地缩小了ECS的不确定范围。     

AR模型中AO类异常值探测及其在GPS卫星钟差预报中的应用

基于EM算法,提出一种AR模型中AO类异常值(additive outlier)探测的算法。该算法可同时进行AR模型拟合与AO类异常值探测,并可有效地解决成片AO类异常值探测时所产生的掩盖和淹没问题。最后,将本文算法应用于GPS卫星钟差预报之中。本文算法可以准确探测出钟差历史观测序列中的AO类异常值,并可对卫星钟差进行精确预报。     

Analysis of the decadal and interdecadal variations of the east asian winter monsoon as simulated by 20 coupled models in IPCC AR4

Using the output data of 20 coupled climate models used in IPCC AR4 and observational data from NCEP, the capability of the models to simulate the boreal winter climatology of the East Asian sea level pressure, 850-hPa wind, and surface air temperature; the decadal variations of the East Asian winter monsoon (EAWM) intensity and EAWM-related circulation, and the interdecadal variations of EAWM-related circulation are systematically evaluated. The results indicate that 16 models can weakly simulate the declining trend of the EAWM in the 1980s. More than half of the models produce relatively reasonable decadal variations of the EAWM-related circulation and the interdecadal differences of EAWM-related circulation between the boreal winters of 1960-1985 and 1986-1998, including the weakened Siberian high, Aleutian low, and East Asian trough, the enhanced Arctic oscillation and North Pacific oscillation, and a deepened polar vortex. It is found that the performance of the multi-selected-model ensemble in reproducing the spatial distribution of the variations is encouraging, although the variational amplitudes are generally smaller than the observations. In addition, it is found that BCCR-BCM2.0, CGCM3.1-T63, CNRM-CM3, CSIRO-MK3.0, GISS-ER, INM-CM3.0, and MRI-CGCM2.3.2 perform well in every aspect.     

东亚夏季风水汽输送带及其对中国大暴雨与洪涝灾害的影响

东亚夏季风每年给中国东部地区带来充沛的降水，是中国水资源的主要来源，同时也常常给中国造成严重的洪涝灾害。东亚夏季风水汽输送的强度、影响范围和持续性在极端暴雨过程中起着关键的作用。这支夏季风气流的水汽输送带可称为东亚季风水汽输送带，与国际上近期提出的"大气河"概念相近，但又不完全相同。东亚夏季风水汽输送带是东亚夏季风最具地区性的特征，也是东亚地区夏季大暴雨和洪涝的制造者。本文根据近百年来的资料，综合评述了东亚夏季风水汽输送带的特征和形成原因，并以海河、黄河、淮河与长江近百年最强的5次持续大暴雨过程为例，分析了季风水汽输送带的重要作用。最后，提出气候变暖可以通过4个方面影响全球水循环，包括气候变暖后大气可容纳更多的水汽、大气环流发生变化、辐射强迫改变以及气溶胶影响的区域性等，这些变化都会对季风水汽输送带产生重要影响。     

IPCC AR6报告解读：地下水

地下水已成为满足全球农业生产和生活用水需求的重要来源,也是实现联合国2030年可持续发展议程的关键资源。地下水的数量和质量会直接或间接地受到气候变化的影响。IPCC第六次评估报告（AR6）第二工作组报告对全球和区域历史时期及未来地下水变化趋势进行了评估。报告指出：(1)自21世纪初以来,由于地下水灌溉用水量增加,全球许多国家和地区地下水储量呈现下降趋势。(2)在气候变化背景下,地下水开采量将持续增加,包括全球主要含水层中不可再生的地下水。(3)在热带和半干旱地区,气候变化引起强降水发生频率加快,导致地下水补给量呈增加趋势;在高寒地区,受气候变化影响地下水主要补给期从春季向冬季演变,由于融雪周期和融雪量的减少造成高寒地区春季地下水补给量减少。在地下水退化区域开展渐进式生态修复,是应对气候变化和保障水安全的重要措施。     

On the use of maximum entropy/autoregressive spectrum in harmonic analysis of time series

The maximum entropy (ME) spectrum, or its equivalent form of the autoregressive (AR) spectrum, has been used as a tool for harmonic analysis of time series in geophysics. This paper critically examines its usage in estimating the amplitude and the exponential decay rate of a harmonic function. The argument is based upon Prony's relation, which relates a complex-conjugate pair of poles for the AR model of the time series on one hand, to the complex frequency of one harmonic component in the time series on the other. It is found that: (i) the ME spectrum can be used as an estimator for the decay rate in a way similar to the Fourier spectral analysis; (ii) the ME spectrum contains no information whatsoever about the amplitude, contrary to what has been claimed and practiced in geophysical applications.