西南地区秋季干旱的年代际转折及其可能原因分析   总被引：2，自引：0，他引：2  

张顾炜  曾刚  倪东鸿  周国兵 《大气科学》2016,40(2):311-323

采用1961~2012年中国气象局753站降水和温度资料、NCEP/NCAR全球大气再分析资料、NOAA海表温度资料等,应用观测统计分析和全球大气环流模式NCAR CAM5.1数值模拟,基于标准化降水蒸散指数(SPEI),对我国西南秋季干旱的年代际转折及其可能原因进行了分析。观测分析结果表明:(1)西南秋季干旱的主要分布型为全区一致型;西南秋季SPEI在1994年发生年代际突变,突变后(前)为偏旱(涝)期。(2)西南秋季偏旱期的主要环流特征是,西太平洋副热带高压位置偏西、面积偏大、强度偏强,南支槽偏弱,西南地区存在下沉运动。(3)热带东印度洋-西太平洋的海表温度年代际升高对西南秋季SPEI在1994年发生年代际突变有重要作用,该关键海区海表温度异常升高,一是会使秋季西南地区500 hPa高度场偏高,南支槽减弱;二是产生偏强的Hadley环流,使得我国西南地区存在下沉运动;三是会在西太平洋激发气旋性环流,使我国西南地区被偏北气流控制,削弱了向我国西南地区的水汽输送,容易造成该地区的秋季干旱。应用NCAR CAM5.1全球大气环流模式进行了关键海区海表温度年代际变化的敏感性试验,验证了观测分析结果,即秋季关键海区海表温度年代际升高对西南秋季年代际变旱有重要作用。  相似文献   

Assimilation of Doppler weather radar observations in a mesoscale model for the prediction of rainfall associated with mesoscale convective systems     

S. Abhilash  Someshwar Das  S. R. Kalsi  M. Das Gupta  K. Mohankumar  J. P. George  S. K. Banerjee  S. B. Thampi  D. Pradhan 《Journal of Earth System Science》2007,116(4):275-304

Obtaining an accurate initial state is recognized as one of the biggest challenges in accurate model prediction of convective events. This work is the first attempt in utilizing the India Meteorological Department (IMD) Doppler radar data in a numerical model for the prediction of mesoscale convective complexes around Chennai and Kolkata. Three strong convective events both over Chennai and Kolkata have been considered for the present study. The simulation experiments have been carried out using fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) mesoscale model (MM5) version 3.5.6. The variational data assimilation approach is one of the most promising tools available for directly assimilating the mesoscale observations in order to improve the initial state. The horizontal wind derived from the DWR has been used alongwith other conventional and non-conventional data in the assimilation system. The preliminary results from the three dimensional variational (3DVAR) experiments are encouraging. The simulated rainfall has also been compared with that derived from the Tropical Rainfall Measuring Mission (TRMM) satellite. The encouraging result from this study can be the basis for further investigation of the direct assimilation of radar reflectivity data in 3DVAR system. The present study indicates that Doppler radar data assimilation improves the initial field and enhances the Quantitative Precipitation Forecasting (QPF) skill.  相似文献   

涌浪静校正技术在海洋单道地震资料处理中的应用   总被引：4，自引：0，他引：4  

李丽青  徐华宁  舒虎 《物探与化探》2007,31(4):339-343

分析了海洋地质调查单道地震资料中存在的同相轴跳动、记录延时、记录提前等问题，指出浪涌是造成同相轴跳动的重要原因，提出利用涌浪静校正技术解决问题的思路，即利用互相关统计法，计算涌浪对每道造成的时移量，作为静校正量，以消除地震剖面上同相轴抖动现象。根据涌浪静校正的原理将地层分为3类：平滑型、起伏型和崎岖型，针对不同类型地质条件进行了关键参数的试验。结果表明，对于平滑型、起伏型地层互相关统计法有良好的效果；对于崎岖型，效果较差，需要慎重使用和选取处理参数。笔者给出关键参数的选取原则和应用静校正技术中应注意的事项。  相似文献   

Long-term trends and regime shifts in sea surface temperature on the continental shelf of the northeast United States     

Kevin D. Friedland  Jonathan A. Hare 《Continental Shelf Research》2007

We investigated sea surface temperature (SST) variability over large spatial and temporal scales for the continental shelf region located off the northeast coast of the United States between Cape Hatteras, North Carolina, and the Gulf of Maine using the extended reconstruction sea surface temperature (ERSST) dataset. The ERSST dataset consists of 2°×2° (latitude and longitude) monthly mean values computed from in situ data derived from the International Comprehensive Ocean Atmosphere Data Set (ICOADS). Nineteen 2°×2° bins were chosen that cover the shelf region of interest between the years of 1854 and 2005. Mean annual and range of SST were examined using dynamic factor analysis to estimate trends in both parameters, while chronological clustering was used to determine temporal SST patterns and breakpoints in the time series that are believed to signal regime shifts in SST. Both SST and SST trend analysis show that interannual variability of SST fluctuations shows strong coherence between bins, with declining SST at the beginning of the last century, followed by increasing SST through 1950, and then rapidly decreasing between 1950 and mid-1960s, with somewhat warmer SST thereafter to present. Annual SST range decreases in a seaward direction for all bins, with strong coherence for interannual variability of range fluctuations between bins. The trend in SST range shows a decreasing range at the beginning of the last century followed by an increase in range from 1920 to the late-1980s, remaining high through present with some spatial variability. A more detailed spatial analysis was conducted by grouping the data into 7 regions using principal component analysis. We analyzed regional trends in mean annual SST, seasonal SST range (summer SST−winter SST), and normalized SST minima and maxima. Both the summer and winter seasons were also analyzed using the length of each season and amplitude of the warming and cooling season, respectively, along with the spring warming and fall cooling rates. Trends in all of the parameters were examined after low-pass filtering using a 10-point convolution filter (n=10 years) and regime shifts were identified using the sequential t-test analysis of regime shifts (STARS) method. The analysis shows some difference between regions in the timing of minimum SST with minima being reached 1 month earlier in the south (February) relative to more northern regions (March). Regional annual SST range decreased in a seaward direction. Amplitude of summer warming and the length of summer have shown fluctuations with recent years showing stronger warming and longer summers but generally not exceeding past levels. Overall, the difference in SST range, with recent larger values may be the most significant finding of this work. SST range changes have the potential to disrupt species important to local fisheries due to combinations of differing temperature tolerances, changes in reproduction potential, and changes in the distributional range of species.  相似文献   

A closer look at regime shifts based on coastal observations along the eastern boundary of the North Pacific     

Laurence C. Breaker 《Continental Shelf Research》2007

At least six regime shifts have been reported in the North Pacific since 1920. They occurred in 1925, 1939, 1946, 1976–1977, 1989 and 1999. The major change in 1976–1977 corresponds to a regime shift that is now widely accepted as a canonical event since it had a significant impact on virtually all climatic and ecosystem indicators. We seek to determine if daily sea surface temperature (SST) from Pacific Grove, in central California, and Scripps Pier, in southern California, and coastal observations from several other locations along the west coast of North America can be used to detect and resolve these events. Cumulative sums (CUSUMs) were initially calculated to enhance the detection process. The CUSUM trajectories during the 1976–1977 event at Pacific Grove and Scripps Pier were distinctive, highly correlated, and in phase. The turning point patterns from this event were then used to search for other events that have been reported since 1920. Turning point patterns very similar to the 1976–1977 event were detected in 1946 and 1989. The events in 1925 and 1939 were generally similar, but the CUSUM patterns for the event in 1999 departed significantly from the other events. Further examination of the 1976 and 1989 events revealed inflection points in the CUSUMs near the beginning and end of each transition that correspond to critical values or extrema in the original data. The inflection points and/or critical values provide an improved basis for determining the duration of these events.  相似文献   

基于速度模型的相移插值偏移     

赵宪生  罗运先  梁桂蓉 《物探化探计算技术》2004,26(1):1-4

实现复杂波场高精度、高效率的成像处理是广大地球物理工作者追求的目标。但由于受到实际波场速度因素的影响，许多波场成像方法难以达到预期的效果。采用基于初始速度模型的相移插值偏移方法，经理论模型与实际资料处理结果表明，可提高高陡构造复杂波场的成像精度及效率。  相似文献   

An investigation of the tipping term as a prognostic tool in short-range thunderstorm forecasting     

M. W. Sleigh  C. G. Collier   《Atmospheric Research》2004,69(3-4):185-198

A nowcasting system, GANDOLF, was operated by the Met Office and the University of Salford during the Sydney 2000 Forecast Demonstration Project (FDP). The purpose of this project was to test and evaluate the current state-of-the-art in nowcasting technology, and initial verification by the University of Salford has shown GANDOLF's performance to be poor. The system uses a conceptual model of the life cycle of an idealised convective cell to forecast the evolution of radar-observed storms in an object-oriented fashion. Analysis has shown the implementation of the model to be inadequate due in part to its reliance on relatively low resolution NWP model forecasts rather than the use of conceptual modelling itself. The advent of very high resolution three dimensional wind fields produced by four dimensional variational analysis (4DVAR) modelling techniques offers a way of circumventing many of the problems inherent in GANDOLF, and such data have been obtained for the cases during which GANDOLF was operational. These were produced by the National Center for Atmospheric Research's VDRAS system, which was also operated during the FDP, as part of the three-dimensional US Autonowcast system. The wind data allowed the calculation of time series of the three-dimensional tipping term field, which, it is suggested, can be used as a prognostic tool in automated convection nowcasting. This paper summarises the theoretical background of the tipping term in the context of severe storms, and presents the results of a number of tests performed on the data. The conclusions of these tests indicate that the tipping term may be a useful prognostic tool. Observations of the increasing asymmetry in the tipping term couplet predicted by theory as convection reaches its maximum intensity may offer a way of improving objective analysis of the life cycle of cells.  相似文献   

地球暖化促进植物迁移与入侵   总被引：15，自引：1，他引：15  

钟永德  李迈和 《地理研究》2004,23(3):347-356

在当今快速的全球气候变化 ,特别是快速而急剧的地球暖化情况下 ,现有植物及其系统被迫 :1)重新适应这种变化了及仍在变化着的环境条件 ;2 )往高海拔及极地方向迁移寻找合适的生存环境 ;或者 3)因其迁移的速度赶不上气候变化的速度而消亡。同时 ,气温升高和降水模式 (包括降水量及其分配 )的变化 ,以及与此相关联的干扰型式 (包括干扰种类、强度及延续时间 )的变化 ,一方面将使现有植物及其生态系统对外来生物的抗性弱化 ,另一方面将激活外来物种的活性 ,导致外来生物的快速扩散与大规模入侵 ,进而排挤和“杀死”当地乡土种 ,减少生物多样性 ,改变原有生态系统的组成、结构和功能 ,最终导致严重的社会经济与生态环境问题。在制定域、国家及全球经济与环境政策时 ,应充分考虑到这些问题 ,以防患于未然  相似文献   

Acoustic waves generated from seismic surface waves: propagation properties determined from Doppler sounding observations and normal-mode modelling     

Juliette Artru  Thomas Farges  Philippe Lognonné 《Geophysical Journal International》2004,158(3):1067-1077

  相似文献   

预处理共轭梯度法在VVP三维风场反演中的应用   总被引：1，自引：0，他引：1       下载免费PDF全文

张少波  胡明宝  张鹏 《气象科学》2004,24(3):303-308

本文从VVP(Volume Velocity Processing)方法的原始方程出发，进行三维风场反演的实验，在分析体积中心点反演十个变量，对病态矩阵的求解采用了预处理共轭梯度方法。通过对实测资料的分析，结果表明：预处理共轭梯度方法能较好的处理矩阵的病态问题，反演的水平二维风场、散度项和变形项结果比较合理，散度项和形变项量级都在10^-6～10^-3之间，水平速度和垂直速度量级在10^-1～10^1之间。  相似文献