历史时期广东省旱涝变化及其层次分析

根据历史时期广东的旱涝灾害史料建立了该地区1480～1939年间旱涝指数序列,并采用小波分析、功率谱分析对该序列进行了研究。分析认为,从历史时期来看,广东的旱涝变化主要存在准7年、15年、23年左右的准周期,不同的历史时期主要影响周期不尽相同。旱涝指数的多尺度分析表明,广东在本世纪整体上将处于偏涝期,但自2000(±5)年已开始进入偏旱期,2010(±5)年左右达到最旱,这种偏旱状况将一致持续到2040(±5)左右,期间也会有较小强度的偏涝期出现。预计2040(±5)年之后广东将有较大强度的偏涝期出现,而且在未来几十甚至百年内的旱涝变化幅度有增大的趋势。由于高层次上的偏旱(涝)期常常包含有若干个低层次上的偏旱和偏涝期,因此在对未来气候变化趋势进行预测时,离开具体的时间尺度谈气候变化是没有意义的。     

山东近百年降水的层次结构及趋势诊断

本文采用子波变换的方法分析了山东烟台、济南、青岛近百年降水距平序列,结果表明：气候系统高层次（时间尺度大）的多（少）雨期是由若干中低层次的多雨期或少雨期组成,东部沿海地区的烟台、青岛气候层次为7,降水变化以准70年周期振荡显著,中西部地区的济南气候层次为6,以准11年周期振荡最为显著。在百年以上尺度上,我省未来20年内为降水多雨期或平水期,但还存在中小尺度的降水偏多偏少阶段,2000年以前降水以偏少为主。     

贵州威宁X波段双偏振雷达反射率因子的衰减订正分析

针对贵州威宁X波段双偏振雷达的衰减订正问题,在利用综合小波去噪方法对差分传播相移ФDP进行质量控制基础上,基于自适应衰减订正算法对雷达反射率因子ZH进行衰减订正分析,订正结果与昭通C波段新一代天气雷达进行对比,结果表明：（1）综合小波去噪能够有效去除ФDP存在的脉动和毛刺,保证ФDP的连续性和平滑度;（2）订正前后雷达反射率因子在距离雷达较近处（20-35 km）强度廓线基本重合,订正前后差别不大,随着对流区（雨区）距离的增加,电磁信号出现衰减,订正后反射率值加强,总体上订正后的反射率值比订正前高1-12 dB,其中在35～75 km距离范围内,订正后的反射率值达到50 dBz以上,雷达反射率因子更加接近真实情况;（3）使用综合小波去噪配合自适应衰减订正算法可以提高雷达反射率因子衰减订正的准确率,方法具有普适性,在今后科研业务中可以采用该订正方法以进一步提高对粒子相态识别、降水估测精度。     

1968—2017年湖南省冰雹时空分布特征

基于湖南省92个站点1968—2017年冰雹观测资料,采用回归分析、小波分析、主成分分析等方法,研究了湖南冰雹时空分布特征。结果表明,湖南近50年冰雹天气年际下降趋势显著,近20年来有记录的冰雹天气发生频次明显降低。湖南初次降雹的时间都集中在1—3月。冰雹月季变化显著,一年中以3月冰雹最多,2月的次之,从5月份起雹日骤然减少。春季是降雹最多的季节,占雹灾总数的56.06%,冬季的次之,夏季和秋季冰雹发生频率分别仅为全年的2.53%和0.69%。年冰雹日数主要存在4~5 a和19 a左右的振荡周期,20世纪90年代前还存在明显的9~10 a的振荡周期。各季节冰雹日数振荡周期不一。湖南冰雹空间分布呈自湘西北向湘东南递减的规律,年冰雹日数的空间分布特征与春季、冬季冰雹分布特征相似。湘北和湘中地区冰雹天气年际变化以下降趋势为主,湘南地区其气候趋势变化不明显。对湖南近50年冰雹日数进行主成分分析的前3个主要模态,在空间向量场上分别呈现出全省一致型、地势主导型和南北呼应型。     

Modeling of Wave Dispersion Using Continuous Wavelet Transforms

In the estimate of dispersion with the help of wavelet analysis considerable emphasis has been put on the extraction of the group velocity using the modulus of the wavelet transform. In this paper we give an asymptotic expression of the full propagator in wavelet space that comprises the phase velocity as well. This operator establishes a relationship between the observed signals at two different stations during wave propagation in a dispersive and attenuating medium. Numerical and experimental examples are presented to show that the method accurately models seismic wave dispersion and attenuation.     

中国大陆地震活跃期及平静期判断的新方法与应用

基于小波变换方法,提出了刻画地震活动周期的指标一周期系数,该系数为描述地震活动周期显著程度的一种量度。应用该方法对中国大陆地区1890～2002年22年左右与10年左右周期(活跃期与平静期组成一个周期)内地震活动周期系数的变化过程进行了分析,结果表明,中国大陆地区的地震活跃期及7．5级以上地震的发生时段处于22年周期系数曲线的下降过程中,而平静期则与周期系数曲线的上升过程相对应。10年左右的周期系数将活跃期与平静期进行了大致分离,从而为地震活跃期的开始与结束的判断提供了一种全新的研究思路与方法。研究表明,中国大陆已处于20世纪以来的“第5活跃期”的尾声。     

Wavelet bicoherence analysis of wind–wave interaction

A new technique in the analysis of wind–wave interaction, wavelet bicoherence, will be applied in this article. Wavelet bicohence has the ability to detect phase coupling and nonlinear interactions of the quadratic order with time resolution. It is used in this study to analyze wind–wave interaction during wave growth in a Mistral event. A selected record of simultaneously measured wind and wave data during Mistral is divided into five segments and the computations of the wavelet bicoherence are conducted for the whole record and for all divided segments. The results show that the phase coupling occurs between wind speed and wave height over a certain range of frequencies and that the range is different from one segment to another due to the non-stationary feature of the time series.     

Time-Dependent Spatial Wavenumber Spectra Derived from Merged Sea Surface Temperature Data

Monthly wavenumber spectra of sea surface temperatures (SST) have been estimated in two regions near the Kuroshio, in the recirculation and the Kuroshio Extension regions, using the merged SST product to determine the statistical parameter (spatial decorrelation scale) required for optimal interpolation of a high-resolution SST dataset. The two-dimensional wavelet transform was used for analysis. Estimates were made of daily mean and daily minimum SSTs. These do not significantly differ, which suggests that the same covariance matrix can be used for the daily mean and minimum in the merging procedure. The seasonality of wavenumber spectra is significant. There are also large differences between those in the recirculation region and in the Kuroshio Extension region. Therefore, it is recommended that the covariance matrix in the merging process for high-resolution SST dataset be defined as a function of time and space. Improvements of the merging methodology are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.