汕头近岸区的台风波浪 (二)后报台风波浪及其基本特征

本文采用《受陆岸影响浅水区台风风浪的推算方案》后报影响汕头近岸区的台风风浪，并以此与Ｔｈｏｍｐｓｏｎ关于波型的判据和合田良实的不同波型能量集中度的规定相结合，计算台风混合浪，经与现场实测资料相比较，效果良好；依４４年台风浪的后报结果，可以得到各场台风过程的波高，波能和主波向的变化以及后报台风较大浪时能随方向的分布     

南海东北部台风潮的数值后报及极值增水估计

本研究对近40年来影响南海东北部陆架海区的28次台风引起的风暴潮进行了数值后报,其中8个过程的沿岸后报增水值与实测值进行了比较,表明后报值与实测值符合良好,90%以上的最大增水值偏差在30厘米以下。为了得出本海区多年一遇的台风增水极值,在后报台风路径密集处选择了9个不同水深点,对每点取出各次台风下的最大增水值,然后用Weibull分布进行拟合,得出了各点的极值分布。     

应用九层全球大气格点模式进行跨季度短期气候预测系统性试验

利用中国科学院大气物理研究所9层大气环流模式（IAP9L AGCM）对夏季气候进行了30年（ 1970～1999年）集合回报试验,并采用统计学分析方法对跨季度夏季短期气候的可预测性问 题进行了初步探讨. 结果表明,该模式对对流层中、高层大气环流的预测能力强于低层,位 势高度场和表面气温的可预测性最大,而降水的可预测性则相对较小. 对流层中、高层位势 高度场的可预测性基本呈带状分布,越靠近赤道可预测性越高;而降水的可预测性基本局限 于赤道东太平洋及热带个别区域. 由此可见,降水的预测极为困难和复杂,订正系 统的研究和寻找新的预报物理因子非常重要.      

初始场的同化对短期气候预测的影响

基于已建立的三维变分资料同化系统(3D-VAR),利用大气环流模式(IAP9L2°×2.5°-AGCM),对同化和未同化2种初始场分别进行了17a(1988—2004年)的集合回报试验,并对试验结果进行了相关分析.结果表明:在热带地区,2组初始场下的集合回报结果差别很小,除热带外的中高纬地区差别较大,尤其是东亚地区;另外,大部分物理量场的17a异常空间相关系数的均值在同化后的初始场下也得到了提高,可能是因为同化的初始场包含了一段时间的大气信息,动力模式更加协调.     

大气初始场对短期气候数值预测的影响

利用中国科学院大气物理研究所发展的九层大气环流模式(简称IAP 9L2°×2.5°-AGCM)分析了大气初始场对短期气候数值预测的影响,分别从实际观测海温、海冰的外强迫和气候态海温、海冰的外强迫出发,进行两组集合回报试验,每组包含3个试验,分别将实时NCEP-Ⅱ资料和对NCEP-Ⅱ资料经5 d平滑、11 d平滑后的资料作为大气初始场,进行17 a(1988—2004年)集合回报试验,采用相关分析方法对试验结果进行对比分析。结果表明,比较相关系数定量检验出大气初始场对热带地区可预报性影响较小,而对中、高纬度地区影响很大。通过对6个试验中对应气象要素在对流层各层距平时间相关系数以及17 a空间异常相关系数均值比较分析发现对东亚(中国)地区夏季气候而言,NCEP-Ⅱ资料经5 d平滑后生成的大气初始场对应回报试验结果相对最好。     

Potential Predictability of Sea Surface Temperature in a Coupled Ocean--Atmosphere GCM

Using the Flexible Global Ocean--Atmosphere--Land System model (FGOALS) version g1.11, a group of seasonal hindcasting experiments were carried out. In order to investigate the potential predictability of sea surface temperature (SST), singular value decomposition (SVD) analyses were applied to extract dominant coupled modes between observed and predicated SST from the hindcasting experiments in this study. The fields discussed are sea surface temperature anomalies over the tropical Pacific basin (20^oS--20^oN, 120^oE--80^oW), respectively starting in four seasons from 1982 to 2005. On the basis of SVD analysis, the simulated pattern was replaced with the corresponding observed pattern to reconstruct SST anomaly fields to improve the ability of the simulation. The predictive skill, anomaly correlation coefficients (ACC), after systematic error correction using the first five modes was regarded as potential predictability. Results showed that: 1) the statistical postprocessing approach was effective for systematic error correction; 2) model error sources mainly arose from mode 2 extracted from the SVD analysis---that is, during the transition phase of ENSO, the model encountered the spring predictability barrier; and 3) potential predictability (upper limits of predictability) could be high over most of the tropical Pacific basin, including the tropical western Pacific and an extra 10-degrees region of the mid and eastern Pacific.     

Discontinuous hindcast simulations of estuarine bathymetric change: A case study from Suisun Bay,California

Simulations of estuarine bathymetric change over decadal timescales require methods for idealization and reduction of forcing data and boundary conditions. Continuous simulations are hampered by computational and data limitations and results are rarely evaluated with observed bathymetric change data. Bathymetric change data for Suisun Bay, California span the 1867–1990 period with five bathymetric surveys during that period. The four periods of bathymetric change were modeled using a coupled hydrodynamic-sediment transport model operated at the tidal-timescale. The efficacy of idealization techniques was investigated by discontinuously simulating the four periods. The 1867–1887 period, used for calibration of wave energy and sediment parameters, was modeled with an average error of 37% while the remaining periods were modeled with error ranging from 23% to 121%. Variation in post-calibration performance is attributed to temporally variable sediment parameters and lack of bathymetric and configuration data for portions of Suisun Bay and the Delta. Modifying seaward sediment delivery and bed composition resulted in large performance increases for post-calibration periods suggesting that continuous simulation with constant parameters is unrealistic. Idealization techniques which accelerate morphological change should therefore be used with caution in estuaries where parameters may change on sub-decadal timescales. This study highlights the utility and shortcomings of estuarine geomorphic models for estimating past changes in forcing mechanisms such as sediment supply and bed composition. The results further stress the inherent difficulty of simulating estuarine changes over decadal timescales due to changes in configuration, benthic composition, and anthropogenic forcing such as dredging and channelization.     

大气初始异常在跨季度短期气候预测中作用的研究

针对大气初始异常在跨季度短期气候预测中的可能作用,利用中国科学院大气物理研究所9层大气环流格点模式(简称IAP 9L-AGCM)对全球夏季气候进行了30年(1970～1999年)集合回报试验,系统地考察了基于大气初始异常条件下模式对跨季度短期气候异常的可预测性.结果表明,在热带、副热带及高纬都存在气候异常的可预测性区域,说明大气初始场异常本身对跨季度短期气候预测有很重要的影响.相对于全球来说,大气初始异常对跨季度短期气候预测的影响在东亚地区更为显著,其作用不可忽略.通过对典型年份的个例分析发现,在某些气候异常剧烈的特殊年份,春季大气初始异常在我国夏季气候形成中扮演着尤为重要的角色.     

Spring drought prediction based on winter NAO and global SST in Portugal

The aim of this paper is to test the ability of neural network approaches to hindcast the spring standardized precipitation index on a 6‐month time scale (SPI6) in Portugal, based on winter large‐scale climatic indices. For this purpose, the linkage of the spring SPI time series with the winter North Atlantic Oscillation (NAO) and the sea surface temperature (SST) was investigated by means of maps of the correlation coefficient for the period from October 1910 to September 2004. The results indicate that the winter NAO is a good predictor for the SPI6 of the spring (SPI6 finishing in April, May and June, SPI6_April, SPI6_May and SPI6_June, respectively) for the northern, central and southern regions of Portugal. The winter SST1 (area of the Mediterranean Sea) must only be considered for the northern region, and the winter SST3 (area of the North Atlantic between Iberia and North America) only for the southern region. Spatial maps of predictive SPI6 for April, May and June were created and validated. The neural models explained more than 81% of the total variance for the SPI6_April and SPI6_May and more than 64% of the total variance for the SPI6_June. Probability maps were also developed considering the values predicted by the neural methods for the spring months and all drought categories (moderate, severe and extreme). These maps indicating the probability of droughts can provide valuable support for the integrated planning and management of water resources throughout Portugal. Copyright © 2012 John Wiley & Sons, Ltd.     

Wave energy and clast transport in eastern Tasman Bay,New Zealand

Coarse‐gravel beaches are common features along the eastern margin of Tasman Bay, at the north end of South Island, New Zealand. Although these features have traditionally been interpreted as spits, contemporary incident wave energy appears too small to transport boulders and cobbles persistently along the beaches and platforms by longshore drift. An alternative explanation suggests that boulder beaches are essentially derived in situ from resistant bedrock, which lies seaward and was buried by gravel during the Holocene sea level rise. Wind, wave and clast size data from Cable Bay and the Nelson Boulder Bank were used to resolve this problem. Wave and wind data indicate that waves reaching these areas are derived locally in Tasman Bay, and are limited in size and energy. Hindcasting predicts a 4·7 m wave could propagate from Tasman Bay. However, during Cyclone Yalli, the most intense storm in nearly 40 years of wind records, the largest wave measured in the nearby area of Cable Bay was only 2·7 m high. Maximum orbital velocity on the seabed beneath a 4·7 m is calculated to be 2·9 m s^?1, which cannot initiate transport of clasts greater than 0·15 m in diameter. Clasts on the gravel platforms have average diameters greater than this, but some clasts may be as large as 1·0 m in diameter. By comparison, a swash run‐up method predicts that a wave 4·7 m high can transport clasts no larger than 0·3 m in diameter. These data and approximate calculations strongly suggest that the present wave environment in eastern Tasman Bay is not capable of consistently transporting clasts on the boulder platforms by longshore drift. Reduced sea levels in the pre‐Holocene period would further reduce wave energies available in Tasman Bay. Copyright © 2006 John Wiley & Sons, Ltd.