Linear correlations between Florida Current volume transport and surface speed with Miami sea-level and weather during 1964-70

Summary. The 1964-70 Florida Current data of Niiler & Richardson are examined for linear correlation with observed sea-level and weather, because their data provide an independent test of similar correlations reported in Maul et al. Seventy-five values of directly measured volume transport and 67 values of surface speed from Niiler & Richardson's unevenly spaced data are correlated with available daily mean values of Miami Beach sea-level, Bimini sea-level, Bimini-Miami Beach sea-level difference, and Miami weather (barometric pressure, air temperature, and north and east components of wind speed). Statistical frequency distribution of transport and of surface speed suggest variability that is not dominated by annual and/or semiannual cycles. Volume transport is most highly correlated with Bimini minus Miami Beach sea-level difference, and surface speed is most highly correlated with inverted Miami Beach sea-level. Including certain weather variables results in statistically significant improvements in linear multivariate modelling of transport and surface speed from sea-level; the standard errors are ± 2.6 sverdrup and ±10 cms⁻¹ respectively. Linear correlation coefficients and multivariate regression parameters from Niiler & Richardson's data are in agreement with those from Maul et al. , except that the standard error of estimating volume transport from sea-level is smaller in Maul et al. , apparently because of smaller errors in the direct measurements.     

On mean sea-level along the Brazilian coast

Summary. (Part 1) Fourier analyses of mean monthly sea-level data from Belém, Fortaleza, Salvador and Imbituba, ports on the Brazilian coast, are made with simultaneous data of air temperature, sea surface atmospheric pressure, atmospheric precipitation and evaporation. Results show that the mean monthly sea-levels of ports below Recife's latitude show peaks in February-March and April-May which are apparently related to the seasonal temperature changes and the combined action of precipitation, winds and oceanographic large-scale changes. The port of Belém showed a stronger semi-annual seasonal component, which seems to be related to the alternate southern and northern hemispheres' influences of the atmospheric precipitation. (Part 2 of the paper presented at the Symposium concerned the longer term changes of sea-level, including an analysis of principal components. These subjects will be treated in a separate paper.)     

Long-period variations of sea-level in Australasia

Summary. The ability of the Australian sea-level monitoring network is assessed in the investigation of long-period sea-level signals. Through the character of coastal long waves, seasonal variations in level and inter-annual level anomalies, the importance of the south coast of the Continent is identified as a coherent indicator of large-scale marine and atmospheric teleconnections. The source of the sea-level signal is investigated by the tracing of progressive features, by the numerical modelling of wind stress over the Southern Ocean, by the modelling of the effect of monsoonal rains over the Indian Ocean and the mass transport through the Indonesian Strait. These features are related to the ENSO cycle which for the first time is linked, inter alia , with Southern Ocean mechanisms.     

Low-frequency sea-level fluctuations along the coasts of Namibia and South Africa

Summary. Sea-level records at nine ports along the coasts of Namibia and South Africa are used to establish the existence of coastal trapped disturbances in sea-level as a response to the passage of synoptic weather systems. Using spectral analysis the characteristics and spatial variability of the sea-level fluctuations are identified. The results of cross-correlation analyses performed on sea-level data at adjacent ports for two periods during 1982 are discussed in detail to examine the propagation of coastal trapped waves round the coast.     

The application of geodetic radio interferometric surveying to the monitoring of sea-level

Summary. Under project IRIS (International Radio Interferometric Surveying) geodesists are using Very Long Baseline Interferometry (VLBI) to monitor polar motion to 1-2 ms of arc and UT1 to 0.05-0.10 ms, and to develop a global geodynamic network to detect and study centimetre level displacements of reference points associated with large-scale phenomena such as tectonic plate motion and glacial rebound. Differential positioning techniques using the signals broadcast by the satellites of the Global Positioning System (GPS) are being used to study finer scale phenomena, such as localized subsidence, and economically to relate these specialized surveys to the geodynamic network. Including tide gauge stations in this system will make it possible to detect motions of specific gauges and correct or delete the measurements from those gauges when computing changes in sea-level. The National Oceanic and Atmospheric Administration (NOAA) has selected several tide gauges on the east and west coasts of the United States, and initial epoch GPS surveys to tie the gauges to VLBI observations have already begun. Other countries participating in project IRIS are planning similar activities. In addition to providing a globally based land reference datum for the tide gauge measurements, the IRIS polar motion and UT1 time series may contribute directly to monitoring and interpreting global sea level changes. Changes in the volume and distribution of ice masses result in long-term motions of the axis of rotation, and sea-level changes affect the length of day (lod). The IRIS time series will certainly have the resolution required to detect the expected polar motion and changes in lod, and a properly designed global VLBI/GPS network should allow the ice/sea-level effects to be separated from crustal dynamics effects.     

长江三角洲地区海面-地面系统模型构建与试验

本文从海面-地面系统研究的视角出发,介绍了由滑动底界计算、分段沉积速率计算、古地面高程计算和模拟结果验证等四个基本模块构成的海面—地面系统模型的基本构架,阐明了该模型的数据分类系统、基本功能目标及其实现的技术系统。初步建成的该系统模型,可以通过对海面变化、沉积作用、地壳运动等多种控制参数的调控,自动生成相应控制条件下任意指定时刻或时间段的二维、三维古地形图等多种形式的图件,因而可以用以对三角洲平原古地貌和海陆关系演变历史进行动态演示,并且为专业人员开展三角洲古环境反演研究和虚拟实验提供一种新的平台。根据长江三角洲地区的实际资料,运用该模型对最近一万年以来的海面—地面变化过程进行了初步的模拟试验,从模型输出的分层设色古地形图和三维彩色地貌晕渲图来看,效果良好。     

基于GIS的辽河三角洲潜在海平面上升淹没损失评估

辽河三角洲是海平面上升的主要脆弱区。本文以GIS为平台 ,以盘锦市 1∶10 0 0 0 0地形图和土地利用图作为底图 ,结合社会经济统计数据 ,获得地面 1km× 1km范围高程值以及评估单元基础数据 ,并计算出在没有防护、不同潮位背景、海平面上升不同高度的条件下 ,辽河三角洲未来海平面上升将淹没的土地面积、受灾人口和经济损失、生态损失 ,以及不同土地利用类型的淹没面积及相应的经济价值。可为制定区域减灾防灾战略提供科学依据     

基于SSA和MGF的海面变化长期预测及对比

海面变化预测受到建模思路、方法选择、数据长度及数据质量等因素的影响,导致了海面变化预测的不确定性。本文以国内6个验潮站自20世纪50年代以来的月平均潮位序列为基础,采用奇异谱分析(SSA)与均值生成函数(MGF)模型相结合的方案,以各站位最初20余年数据为基础建立预测模型,以后续年份的实测数据进行了多方案对比验证及检验。预测试验显示MGF模型具有较高的预测精度,并表现出较好的长期预测的稳定性特点。以SSA去噪序列为基础,应用MGF模型预测了各站位至2050年的月尺度海面值,年均值计算结果表明至2050年海面波动上升的幅度不超过20cm,海面变化速率同样表现出阶段性和波动性。与前人相关研究成果对比表明,本文所采用的SSA与MGF相结合的预测结果具有可比性,在方法原理和验证结果上看具有较好的长期预测潜力。     

Fully normalized spherical cap harmonics: application to the analysis of sea-level data from TOPEX/POSEIDON and ERS-1

We introduce two sets of fully normalized harmonics for the spectral analysis of functions defined on a spherical cap. The harmonics are the products of Fourier functions and the fully normalized associated Legendre functions of non-integer degree. Using Sturm-Liouville theory for boundary-value problems, we present two convenient and stable formulae for computing the zeros of the associated Legendre functions that form two sets of orthogonal functions. Formulae for the stable numerical evaluation of the fully normalized associated Legendre functions of non-integer degree that avoid the gamma function are also derived. The result from the expansions of sea-level anomaly from altimetry into Set 2 fully normalized cap harmonics shows fast convergence of the series, and the degree variances decay rapidly without aliasing effects. The zero-degree coefficients (Set 2) of sea-level anomaly from TOPEX/ POSEIDON (T/P) and ERS-1 indicate an El Niño event during 1993 January-1993 July, and a La Niño event during 1993 November-1994 July, although the ERS-1 result is less obvious. Ocean circulations over the South China Sea and the Kuroshio area are clearly identified with the low-degree expansions of sea-surface topography (SST) from T/P and ERS-1. A cold-core eddy of 4° in diameter centred at 17.5°N, 118 E was detected with the expansion of SST from T/P cycle 47, and a property of the cap harmonics is used to compute this eddy's kinetic energy. The kinetic energy is at a low in winter and high in summer, and its variation seems to be periodic with an amplitude of 0.4 m² S^-2.     

冬季北大西洋海温年际、年代际变化与中国气温的关系

利用NCEP/NCAR月平均再分析资料(1951~2001年)海洋表面月平均温度资料、500 hPa月平均高度场以及中国160站月平均气温资料,采用旋转方差极大正交旋转法(REOF)和小波变换等方法研究了冬季大西洋中低纬海表温度分布的主要模态及其与中国冬季气温的关系。结果表明,冬季北大西洋中部海表温度异常主要表现为2个基本模态,其中反映冬季大西洋20°~50°N区域海表温度异常的第二特征模态,在年际、年代际变化关系上与中国冬季平均气温关系非常密切。进一步研究表明,冬季北大西洋中部海表温度异常,可激发欧亚EU型环流,致使中国冬季气温异常。     

宁夏冬季气温的变化及同期500hPa环流特征量的变化特征

通过近40多年来宁夏冬季气温的变化进行了研究,结果表明:宁夏冬季气温总趋势是变暖的,冬季平均气温在1985年前后发生突变,突变后升温最明显的是中部干旱带;宁夏冬季气候变暖与大区域有不同之处,1967-1990年宁夏冬季升温过程,最低气温是主要的,但1990年以后宁夏冬季的变暖,并不完全是由于最低气温的变暖而形成,最高气温的变暖也是20世纪90年代以来宁夏冬季气候变暖的重要特征;宁夏极端气温变化具有明显阶段性特征,80年代末期以后极端最低气温的变率明显增大;冬季北半球500 hpa极涡面积、亚洲西风环流指数、东亚大槽位置、西太平洋副热带高压强度与宁夏冬季平均气温有较为一致的年代际气候特征;小波分析发现,以上环流特征量与宁夏冬季平均气温存在相同的4年左右的主周期变化,且在时、频域上有较为一致的对应关系。     

The grade index model as a rationale for autogenic nonequilibrium responses of deltaic clinoform to relative sea-level rise

Grade index (G_index) is a dimensionless number given as the volume-in-unit-time ratio of subaerial allocation to both subaerial and subaqueous allocations of sediment supplied to a delta from upstream. It was originally proposed for understanding the effect of basin water depth on the morphodynamics of delta distributary channels under stationary relative sea level. We here examine how rising relative sea level modulates the G_index, using geometrical reasoning and numerical simulations. We find that the grade index model can account for autoretreat of the deltaic shoreline, autodrowning of the whole system, and autobreak of the deltaic sedimentation, all of which are the consequences of autogenic nonequilibrium responses to steadily rising relative sea level. The regressive-to-transgressive threshold (i.e. the onset of autoretreat) is crossed when the delta plain's dimensionless basal area (A_t*) encounters a critical value that is expressed in terms of G_index: regression and transgression are sustained when A_t* is below and above the threshold, respectively. The mode of transgression depends on the slope conditions. If the hinterland slope (γ) is steeper than the foreset slope (β), both A_t* and G_index decrease as the relative sea-level rises. Eventually, the depositional system experiences autodrowning when A_t* = G_index = 0. If γ < β; on the other hand, both A_t* and G_index increase. This latter slope condition eventually causes autobreak of the deltaic sedimentation, afterward of which A_t* = G_index = 1. The grade index model is useful for interpreting and predicting the stratigraphic responses of natural deltaic clinoforms in conditions of rising relative sea level.     

末次盛冰期以来中国湖泊记录对环流系统及气候类型的响应

为了探讨中国长时间尺度湖泊时空演变规律和潜在的驱动机制,本文在柯本气候分区和中国季风—非季风区的划分基础上,对中国34个有明确数据的典型湖泊运行CCSM 3.0气候模拟系统和水量能量平衡模型模拟其水位变化,同时利用NCEP/NCAR再分析资料对中国按水汽输送划分的季风区进行验证。结果表明,末次盛冰期以来中国湖泊演化主要受千年尺度大气环流的驱动影响,在各个柯本气候区内没有明显的规律性。末次盛冰期以来,在季风区中国湖泊演化主要有早中全新世湖泊水位相对较高以及末次盛冰期和早全新世湖泊水位均较高2种演变规律;在东亚干旱区主要有中晚全新世期间湖泊水位相对较高以及末次盛冰期和中全新世湖泊水位均较高2种演变规律。本文为中国过去气候变化及湖泊演化机制研究提供新的证据,同时为人类全面认识末次盛冰期以来湖泊水位变化提供了新的视角。