南海中尺度波动现象研究进展

Kelvin波和Rossby波是经常出现于海洋中的边界波;南海的复杂岸线、陡变地形和热盐场时空结构的不均匀性具有形成强迫Kelvin波和地形Rossby波的条件。现有研究表明,南海大部分中尺度涡形成于东部一些较大岛屿附近;这些中尺度涡一旦形成后,就在β效应作用下向西移动并最终耗散于西边界,且其波动一般以Rossby波的形式向西传播。因此,南海环流的多涡结构与中尺度波动之间存在着一定的联系。在南海北部,中尺度涡主要由黑潮入侵和风应力旋度所诱生,而在南海南部而以风应力旋度为主要成因。提出了利用线性波动动力学模式来研究南海南部中尺度波动、分析风应力强迫所产生的中尺度波动特征和规律,并据此建立相应的数值模式来揭示该海区环流的动力学和热动力学机制的思路,以便了解该海区流场季节性变化与中尺度波动之间的内在关系。     

临近空间重力波强扰动的卫星观测研究进展

重点综述了近年来利用MODIS,AIRS,AMSU,MLS,DNB,COSMIC,HIRDLS以及SOFIE等卫星资料分析和研究大气重力波波动的若干研究进展,并简要概述了相关的地基观测结果以及数值模拟研究,列举了卫星观测与地基观测和数值模式在大气重力波分析中的联合应用结果。总的来说,卫星遥感资料在临近空间环境特性研究中发挥着重要作用,与其他资料联合起来可分析不同波源激发波动的尺度,不稳定条件与波动发生和波动形态的关系,波动在气候过程中的作用,波与波之间的相互作用以及波流相互作用等。     

南极海冰增加对全球7月气候的影响

采用了OSU两层大气环流模式进行数值试验, 研究了南极海冰增加的气候效应.试验中海温取为气候平均值, 南极海冰作为外强迫源影响大气, 大气响应完全是环流内部调整的结果.调整的途径首先是对外强迫的局地响应--南极下垫面的温度发生变化, 结果使得冬季南大洋绕极低压带的位置偏北、强度增加, 南半球大气以强经向环流为主, 绕极气旋强大活跃.这种变异主要以Rossby波列的形式影响到南半球的中高纬度, 再通过斜压的越赤道气流, 即经向热交换的变化影响到北半球的大气环流, 导致北半球夏季大气环流呈纬向分布, 极地冷空气活动减弱.大气环流的变异又影响到气候诸要素, 反映明显的是越赤道气流在印度洋上的加强和太平洋上的减弱, 使得西南季风加强, 东南季风减弱; 太平洋副高位置的偏北, 导致中国华北、华东和江淮流域少雨、高温, 北美中高纬度严重多雨和低温.     

简谐波在黏弹性介质中波动传播的应力场研究

得到了简谐波在具有Kelvin模型黏弹性介质中的外行扩散波与内行入射波应力场表达式。将波动在介质中的传播分为外行扩散波与内行入射波两部分,先得到简谐波在弹性介质中波动传播时外行扩散波与内行入射波各自的应力场,结合弹性波理论与黏弹性理论,分别得到了波动在Kelvin模型黏弹性介质中外行扩散波与内行入射波两部分的应力场,并将外行扩散波与内行入射波两部分的应力场分别表示为外行扩散波与内行入射波位移与速度场的表达式,其结果有利于波动理论在黏弹性介质中的应用     

洮儿河镇西站径流长期预报研究

利用1958～2004年洮儿河镇西站47a的径流量资料和同一时期的北太平洋海温及环流特征量资料，分析了北太平洋海温和大气环流变化与镇西站年径流的关系，建立了基于物理成因概念的多元线性回归预报模型，并利用该模型对镇西站2005年的最大洪峰流量和峰现时间做了预报。结果表明，最大洪峰流量和峰现时间模型对历史样本的拟合合格率可以达到76．2％和92．9％。2005年的最大洪峰流量和峰现时间的预报误差均在允许范围以内，为当年该地区的洪水资源利用和防洪减灾工作起到了重要作用。     

西太平洋次表层海温异常与北赤道流异常海温西传

通过对热带太平洋上层XBT温度资料分析,探讨了对厄尔尼诺(El Nino)事件发生起重要作用的西太平洋暖池区次表层海温变暖异常的变化规律,揭示了影响西太平洋暖池区次表层海温变暖异常的形成机制.分析表明:西太平洋暖池区的次表层海温异常变暖与赤道太平洋的北赤道流(10°N)的海温异常存在密切关系.在El Nino事件发生的前期,位于赤道中东太平洋的异常暖水沿北赤道流温跃层潜沉向西太平洋暖池区输送,在西太平洋暖池堆积并向赤道西太平洋扩展,当异常暖水达到一定强度,并在大气的强迫下,异常暖水沿温跃层东传至赤道中东太平洋并上浮于海面,最终导致El Nino事件的爆发.北赤道流的异常海温西传是导致西太平洋暖池区次表层海温异常的重要机制,是导致El Nino事件发生的关键.     

基于遗传算法的扩散波洪水演算参数的确定方法

大量的理论分析和实际洪水演算表明,扩散波方法是一种既具有足够精度又相对简单的一类洪水演算方法。以线性扩散波方程在自由下边界条件下的解析解为例,利用遗传算法来确定扩散波方程的参数。遗传算法和一般的优化算法不同,它具有全局寻优能力,一般能得到问题的最优解或准最优解,是一类优秀的非线性函数优化方法。实例计算结果表明,采用遗传算法所得到的参数精度较高,可以类推到其它水文模型的参数率定中去。     

二阶弹性波动方程高精度交错网格波场分离数值模拟

给出了一种等价的二阶弹性波动方程,以解决弹性波场中完全弹性波动方程不能完全分离耦合的纵、横波波场问题.应用高阶交错网格有限差分法求解该波动方程,并使用通量校正技术(FCT)进一步压制频散,采用均匀介质模型和层状介质模型进行波场分离数值试验,精确得到了混合波场、完全分离的纯纵波及纯横波波场.数值结果分析表明,本文方法在均匀介质情况下准确可靠,在分离后的纯纵、横波波场中可观察到较为丰富的能量转换信息,这对认识复杂弹性波的传播规律及弹性波理论具有重要意义.     

基于地球物理模型实验的波场特征

采用理论分析和物理模拟相结合的方法对地震剖面中的波场成份进行了综合研究,波动理论研究表明,地震剖面含有多种波场信息成份,组成了一个各种成份各具变化特征的复合波场,这种复合波场含有P波和PS波成份等。在物理模型中,采用了较先进的实验系统,设计了砂泥岩组成的三层地层模型,(20-280-1220)观测系统,采样率为0.25ms。实验得到了三层地层模型的地震剖面,对所获得的地震剖面进行了波场特征分析,实验地震剖面中含有多种波场成份(P波、PS波和面波等)。波场理论研究结果得到物理模型实验的证实,表明地震剖面属复合波场剖面。这种叠后地震剖面可直接用于进行叠后弹性参数反演等以挖掘更多的有效地质信息,提高勘探效果,扩大地震剖面的应用范围。     

海洋内波动力学

海洋内波的研究已有较长的历史。Stokes(1847)和Raleigh(1883)分别作了两层流体界面处的波动和连续层结流体中的内波理论研究。本世纪初(1902)Nansen第一次报告了有关海洋内波的观测结果。但由于观测技术限制和理论研究的困难,关于海洋内波的研究长期处于缓慢发展状态。 到了40年代,由于内波对潜艇活动和声纳功能的严重影响等原因促使人们重视海洋内波的观测与研究,而海洋调查仪器和资料分析方法的发展也使内波观测和分析快速发展起来。到了70年代初,在大量调查和研究的基础上,Garrett和Munk(1972,1975)提出大洋内波谱模型(在物理海洋学中被称为GM模型)。此模型假设大洋内波场可抽象成一平稳随机场,它具有水平均匀、水平各向同性、垂向对称性(即上传与下传波能相等)。内波可表示成在一定频率区间内各种频率、各种波数的自由传播的进行波之叠加。从当时所得观测资料看,此模型几乎普遍地适用于世界各大洋。     

海洋卫星测高技术和海洋地形试验TOPEX卫星计划

ＴＯＰＥＸ卫星是目前精度最高的海洋测高卫星，利用ＳＬＲ技术确定的ＴＯＰＥＸ卫星轨道径向精度达到２．８ｃｍ，这使它可以有效地监测全球的海洋地形。ＴＯＰＥＸ卫星主要用于全球的海面变化和洋流研究。利用ＴＯＰＥＸ资料可以得到新的地球引力场，海洋大地水准面和海潮模型。     

Hindcast/forecast of ENSO events based upon the redistribution of observed and model dynamic height in the Western Tropical Pacific, 1964–1986

Anomalous sea level, anomalous observed dynamic height (0/400 db) and anomalous model dynamic height are examined at the locations of 13 island sea level stations in the tropical Pacific for each bimonth of the four year period 1979 to 1982. Starting in 1981, the anomalous dynamic height data show off-equatorial Rossby waves propagated toward the W boundary of the Pacific basin. At the W boundary, the model Rossby wave activity was found to have excited coastally trapped Kelvin-Munk waves which transmitted the anomalous dynamic height equatorward. At the equator, coastally trapped wave activity excited eastward propagating equatorial Kelvin waves, yielding a pair of anomalous peaks in dynamic height variability in the E equatorial Pacific associated with the 1982–1983 ENSO event. The evolution of the peaks in dynamic height associated with the Rossby and Kelvin wave activity reflects the redistribution of observed upper-ocean heat content in the W tropical Pacific, providing a qualitative hindcast for the 1982–1983 ENSO event. In consequence of these results, and the results of a related study (Inoue et al. 1985), the redistribution of both observed and model heat content, as evidenced in dynamic height in the W Pacific during the 23-year period 1964–1985, is examined for its ability to hindcast and forecast ENSO events in this period. Complex EOF analysis is applied to the Onset Phase of ENSO events occurring in 1968–69, 1972–73, 1976–77, and 1982–83; it is used to determine the characteristic redistribution of heat content (dynamic height) prior to the Mature Phase of ENSO events. This analysis found both model and observed dynamic height in the N hemisphere to be characterized by wind-driven, westward propagating, baroclinic Rossby wave activity, having a remarkably stable period of 3 years over the 23-year period. The complex time series associated with these first spatial eigen-functions are used to construct observed and model hindcast indices that yield high values one year prior to the Mature Phase of ENSO events of the period. These indices achieve these values due to the incidence upon the Philippine coast in fall/winter of a positive anomaly in dynamic height propagating from the east at nondispersive Rossby long wave speeds.     

Vertical propagation of baroclinic Kelvin waves along the west coast of India

A linear, continuously stratified ocean model is used to investigate vertical propagation of remotely forced, baroclinic Kelvin waves along the Indian west coast. The extent of vertical propagation over the length of the coast is found to be an increasing function of the forcing frequency. Simulations show that, over the length of the Indian west coast, vertical propagation is limited at annual and semi-annual periods, but significant at periods shorter than about 120 days. This has two major consequences. First, the depth of subsurface currents associated with these frequencies varies substantially along the coast. Second, baroclinic Kelvin waves generated in the Bay of Bengal at periods shorter than about 120 days have negligible influence on surface currents along the north Indian west coast.     

北太平洋涡旋振荡研究进展

从观测事实和动力机制两方面,对近年发现的新的气候模态——北太平洋涡旋振荡（NPGO）的研究成果进行系统总结。NPGO的空间结构表现为北太平洋上海表高度异常（SSHA）的正负中心呈南北偶极子分布,当NPGO位于正位相时,南北涡流都加强,这种加强是由风应力旋度及风生涌流所驱动的。关于NPGO的机制研究发现,NPGO是中纬太...     

Surface wind speed probability distribution in the Southeast Pacific of Marine Stratus and Stratocumulus regions

Probability distributions of surface wind speeds (SWS) near coastal regions are needed for applications such as estimating offshore wind power and ocean surface fluxes and for offshore wind risk assessments. Ocean surface wind speed probability distribution (PDF) is characterized using three-year QuikSCAT and AIRS satellite observations in the southeast Pacific of marine stratus and stratocumulus (MSC) regions. Seasonal variation is removed from wind statistics. It was found that the observed SWS standard deviation has a linear positive relationship with its mean SWS; while the SWS skewness decreases with mean SWS in regimes of strong winds and increases with mean SWS in regimes of weak winds. A simple 1D conceptual model is developed near the Peruvian region, which successfully reproduces the observed relationship between higher moments of SWS and its mean value. The model based physical picture among ocean surface winds, SST, and marine boundary clouds are supported by three-year QuikSCAT surface wind observations and fifteen-year ERA40 re-analysis data. Model sensitive tests suggest that large-scale divergence, and strengths of momentum and cloud fluctuations have significant effects on the ocean SWS-PDF in marine stratus and stratocumulus regions.     

Sensitivity of MM5 and WRF mesoscale model predictions of surface winds in a typhoon to planetary boundary layer parameterizations

Sea surface winds and coastal winds, which have a significant influence on the ocean environment, are very difficult to predict. Although most planetary boundary layer (PBL) parameterizations have demonstrated the capability to represent many meteorological phenomena, little attention has been paid to the precise prediction of winds at the lowest PBL level. In this study, the ability to simulate sea winds of two widely used mesoscale models, fifth-generation mesoscale model (MM5) and weather research and forecasting model (WRF), were compared. In addition, PBL sensitivity experiments were performed using Medium-Range Forecasts (MRF), Eta, Blackadar, Yonsei University (YSU), and Mellor–Yamada–Janjic (MYJ) during Typhoon Ewiniar in 2006 to investigate the optimal PBL parameterizations for predicting sea winds accurately. The horizontal distributions of winds were analyzed to discover the spatial features. The time-series analysis of wind speed from five sensitivity experimental cases was compared by correlation analysis with surface observations. For the verification of sea surface winds, QuikSCAT satellite 10-m daily mean wind data were used in root-mean-square error (RMSE) and bias error (BE) analysis. The MRF PBL using MM5 produced relatively smaller wind speeds, whereas YSU and MYJ using WRF produced relatively greater wind speeds. The hourly surface observations revealed increasingly strong winds after 0300 UTC, July 10, with most of the experiments reproducing observations reliably. YSU and MYJ using WRF showed the best agreements with observations. However, MRF using MM5 demonstrated underestimated winds. The conclusions from the correlation analysis and the RMSE and BE analysis were compatible with the above-mentioned results. However, some shortcomings were identified in the improvements of wind prediction. The data assimilation of topographical data and asynoptic observations along coast lines and satellite data in sparsely observed ocean areas should make it possible to improve the accuracy of sea surface wind predictions.     

14MaB.P.澳大利亚板块对赤道太平洋影响的数值模拟

文章利用美国NASA的GISS海气耦合模式,研究了14MaB.P.时期与现代情景下的澳大利亚板块不同位置对赤道太平洋的影响。结果表明:14MaB.P.澳大利亚板块位置较现代偏南时,海洋次表层南赤道海水穿过印度尼西亚通道直接进入印度洋,注入赤道潜流的南赤道海水减少,使得赤道潜流主要来源于北赤道海水,造成赤道太平洋海温比现在冷,其中以赤道西太平洋海温降低幅度最大。而在海洋近表层赤道中东太平洋地区,由于进入海洋的净能量增加和西向风应力加强的共同作用,使得14MaB.P.时海温较之现代情景下要低0.2℃左右。此外,14MaB.P.澳大利亚板块较现代偏南时,赤道太平洋地区的降水量少于现代。     

Improvement in predictability of waves over the Indian Ocean

Accurate prediction of ocean surface waves is a challenging task with many associated difficulties. Availability of good quality wind and wave information from satellite platforms inspired the scientific community to assimilate such data in various spectral wave models for enhancing the accuracy of prediction. Over the Indian Ocean, which is the region of interest for the present study, wave heights in extreme situation can go up to 12–14 m, thereby increasing the probability of coastal hazards. This region is further governed by the southern ocean swells that propagate thousands of kilometers. These are, in general, not well captured by the spectral wave models. Therefore, assimilation of altimeter data in open ocean wave model WAM has been attempted with the aim of enhancing the quality of prediction of significant wave height. Further, simulated wave spectra have been assimilated in a coastal wave model SWAN. This assimilation has been found to significantly improve the prediction of the height of wind waves as well as swell waves. V. Bhatt and S. Surendran are former students of Meteorology and Oceanography Group, Space Applications Centre, ISRO, Ahmedabad.     

北太平洋副热带环流变异及其对我国近海动力环境的影响

我国东部陆架海和南海是国防安全的重要门户;位处第二岛链以西的副热带北太平洋既是各国争夺的重要海区,又是我国从近海走向大洋的重要通道.围绕"北太平洋副热带环流变异如何通过黑潮与我国近海动力环境之间相互作用"这一国际前沿科学问题,国家重点基础研究发展计划项目"北太平洋副热带环流变异及其对我国近海动力环境的影响"于2007年9月正式立项.该项目不仅有助于拓展和丰富海洋动力学理论,揭示我国近海及邻近大洋动力环境变异机制,提高预测能力,而且也将为维护我国国防安全和海洋权益,为可持续开发利用海洋资源提供海洋动力环境保障.该项目主要研究内容包括:①北太平洋副热带环流变异和调整机理;②黑潮与我国近海的能量与水体交换过程及机制;③北太平洋副热带环流变异与大气驱动力的耦合效应;④我国近海及邻近大洋动力环境变异的可预测性研究.拟解决的关键科学问题为:北太平洋副热带内区环流变异的机理及其对黑潮的影响;黑潮源头变异机理及其对吕宋海峡水交换的影响和黑潮变异机理及其对东部陆架海域动力环境的影响.