Exploitable wave energy assessment based on ERA-Interim reanalysis data—A case study in the East China Sea and the South China Sea

Wave energy resources assessment is a very important process before the exploitation and utilization of the wave energy. At present, the existing wave energy assessment is focused on theoretical wave energy conditions for interesting areas. While the evaluation for exploitable wave energy conditions is scarcely ever performed.Generally speaking, the wave energy are non-exploitable under a high sea state and a lower sea state which must be ignored when assessing wave energy. Aiming at this situation, a case study of the East China Sea and the South China Sea is performed. First, a division basis between the theoretical wave energy and the exploitable wave energy is studied. Next, based on recent 20 a ERA-Interim wave field data, some indexes including the spatial and temporal distribution of wave power density, a wave energy exploitable ratio, a wave energy level, a wave energy stability, a total wave energy density, the seasonal variation of the total wave energy and a high sea condition frequency are calculated. And then the theoretical wave energy and the exploitable wave energy are compared each other; the distributions of the exploitable wave energy are assessed and a regional division for exploitable wave energy resources is carried out; the influence of the high sea state is evaluated. The results show that considering collapsing force of the high sea state and the utilization efficiency for wave energy, it is determined that the energy by wave with a significant wave height being not less 1 m or not greater than 4 m is the exploitable wave energy. Compared with the theoretical wave energy, the average wave power density, energy level, total wave energy density and total wave energy of the exploitable wave energy decrease obviously and the stability enhances somewhat. Pronounced differences between the theoretical wave energy and the exploitable wave energy are present. In the East China Sea and the South China Sea, the areas of an abundant and stable exploitable wave energy are primarily located in the north-central part of the South China Sea, the Luzon Strait,east of Taiwan, China and north of Ryukyu Islands; annual average exploitable wave power density values in these areas are approximately 10–15 k W/m; the exploitable coefficient of variation(COV) and seasonal variation(SV)values in these areas are less than 1.2 and 1, respectively. Some coastal areas of the Beibu Gulf, the Changjiang Estuary, the Hangzhou Bay and the Zhujiang Estuary are the poor areas of the wave energy. The areas of the high wave energy exploitable ratio is primarily in nearshore waters. The influence of the high sea state for the wave energy in nearshore waters is less than that in offshore waters. In the areas of the abundant wave energy, the influence of the high sea state for the wave energy is prominent and the utilization of wave energy is relatively difficult. The developed evaluation method may give some references for an exploitable wave energy assessment and is valuable for practical applications.     

植被覆盖区高精度遥感地貌场景分类数据集

地貌数据集是实现地貌自动分类和加深对地貌形态学认识的重要支撑数据之一。当前缺乏高精度地貌成因类数据集,制约了地貌遥感自动解译的发展。本文在中国东北地区以沟—弧—盆体系为主的天山—兴蒙造山系中,针对强烈的构造运动和新生代以来的火山作用、流水作用形成的地貌成因类型,制作了构造地貌、火山熔岩地貌和流水地貌3类场景数据集（GOS10m）。数据集覆盖面积约5000 km²,包括哨兵2号可见光遥感影像、SRTM1 DEM及基于DEM提取的7个地貌形态参数（山体晕渲图、坡度、DEM局部平均中值、标准偏差、坡向—向北方向偏移量、坡向—向东方向偏移量和相对偏离平均值）。单张样本图为64像素×64像素,空间分辨率为10 m。采用多模态深度学习神经网络对数据进行训练并分类,平均测试精度可达到82.63%,表明构建的数据集具有较高的质量。可为地貌成因遥感自动分类研究以及推动遥感地貌智能解译的向前发展,提供数据集支撑。     

Operational Data Assimilation System for the Kuroshio South of Japan: Reanalysis and Validation

We describe an operational ocean data assimilation system for the Kuroshio and its validation using a nine-year reanalysis (historical run from 1993 to 2001) dataset of upper-ocean state estimation in the North Pacific. The horizontal structure of volume transport of the Ryukyu Current System (RCS) is shown from the reanalysis: The RCS is connected to the flow of the subtropical gyre, and its volume transport gradually increases from south-east of Okinawa (5–10 Sv) to the east of Amami-Ohshima Island (20 Sv). Comparing the reanalysis with independent observations on the southeast slope of the Amami-Ohshima Island indicates that the root mean square differences (RMSDs) are 0.076 (0.037) m/s in the period of December 1998 to November 1999 (November 1999 to November 2000) respectively. The reanalysis field has a bias (3.1 Sv) of the volume transport of the RCS and the RMSD (3.5 Sv) which is larger than the observed variability (2.81 Sv). Surface velocity and the Kuroshio axis south of Japan are also examined. Comparison of the reanalysis and ADCP data gave maximum RMSD of 0.749 (0.271) m/s in the strong (weak) current regions, respectively. The annual mean value of the axis error is 19 km in 1998. The RMSD of the error is at most 50 km, in 294 cases in the observation period, which is smaller than the observed root mean square variability of the axis (64 km). This revised version was published online in July 2006 with corrections to the Cover Date.     

空间位置信息的多源POI数据融合

为从2个来源不同的POI数据集合中准确找出用于融合的对应对象,在国外研究成果的基础上提出1种改进方案,该方案在空间位置属性的基础上利用非空间属性相似度来提高结果融合集的准确性。技术路线如下:首先对2个POI数据集合实施空间位置方法找出对应对象组成的初步融合集,然后使用低阈值的名称属性相似度方法排除由空间位置方法找出的错误对应对象,最后使用高阈值的名称属性相似度方法找出空间位置方法未能找出的对应对象。用多组POI数据集合测试改进方案,结果表明融合集的准确率、召回率以及F1值都有明显提高。     

菲律宾海盆深层温盐结构与环流变化特征研究

基于ECCO2 (Estimating the Circulation and Climate of the Ocean)、 GLORYS12V1 (Global Ocean Reanalysis and Simulations)、ORA-S5 (Ocean ReAnalysis)三种海洋再分析数据,对比研究了菲律宾海盆深层温盐及环流的季节和年际变化特征。结果表明:三种数据显示的海盆深层温盐季节变化特征基本一致,在3 000～4 000 m水深区域,海水呈春夏两季高温低盐而秋冬季低温高盐特性,4 000 m以下海水温盐季节变化很小;沿西边界,温度与内部有明显差异且季节变化幅度相对较大。沿西边界的输运季节变化特征表现为10月至次年4月输运向南,5—9月输运向北,并且在8月份达最大值;表明存在沿西边界的流动,即菲律宾海盆与南端西卡罗林海盆(West Caroline Basin)之间存在季节性水体交换。海盆深层海水温盐年际变化也十分显著,但不同数据显示的变化特征存在较大差异。EOF和相关分析显示,三种再分析数据的深层位温与ENSO均存在一定相关性,ECCO2的深层位温变化与ENSO的相关性最强。由于长期观测数据较少,再分析数据的结果难以验证,因此目前对年际变化特征的研究仍具有很大的不确定性。     

两次台风衍生龙卷的环境背景和雷达特征对比分析

利用ECMWF高分辨率再分析资料及广州多普勒天气雷达资料,对1522号台风"彩虹"外围衍生的广州番禺龙卷和1806 号台风"艾云尼"外围衍生的广州南沙龙卷进行对比分析,同时还挑选了一个未发生龙卷的台风做外围环境参数对比.结果表明:两次强龙卷都发生在登陆台风的东北象限,中低空急流明显、低层辐合、高层辐散在珠江三角洲地区叠...     

北半球温带气旋的变化

许多学者对近半个世纪以来温带气旋的频数、强度和路径的年际、年代际变化等特征进行了研究,并探讨了温带气旋变化与大气环流的关系,试图揭示气候变暖背景下温带气旋变化的可能原因。较为一致的研究结论是：在全球变暖背景下,北半球气旋活动的变化显示出在中纬度明显减少,而在高纬度增加的趋势,意味着气旋的路径已经明显地北移。研究还表明,气旋活动的变化与对流层斜压性、急流以及北大西洋涛动、海温梯度等因素有关。     

Using reanalysis‐driven regional climate model outputs for hydrology modelling

Bias correction methods are usually applied to climate model outputs before using these outputs for hydrological climate change impact studies. However, the use of a bias correction procedure is debatable, due to the lack of physical basis and the bias nonstationarity of climate model outputs between future and historical periods. The direct use of climate model outputs for impact studies has therefore been recommended in a few studies. This study investigates the possibility of using reanalysis‐driven regional climate model (RCM) outputs directly for hydrological modelling by comparing the performance of bias‐corrected and nonbias‐corrected climate simulations in hydrological simulations over 246 watersheds in the Province of Québec, Canada. When using RCM outputs directly, the hydrological model is specifically calibrated using RCM simulations. Two evaluation metrics (Nash–Sutcliffe efficiency [NSE] and transformed root mean square error [TRMSE]) and three hydrological indicators (mean, high, and low flows) are used as criteria for this comparison. Two reanalysis‐driven RCMs with resolutions of 45 km and 15 km are used to investigate the scale effect of climate model simulations and bias correction approaches on hydrology modelling. The results show that nonbias‐corrected simulations perform better than bias‐corrected simulations for the reproduction of the observed streamflows when using NSE and TRMSE as criteria. The nonbias‐corrected simulations are also better than or comparable with the bias‐corrected simulations in terms of reproducing the three hydrological indicators. These results imply that the raw RCM outputs driven by reanalysis can be used directly for hydrological modelling with a specific calibration of hydrological models using these datasets when gauged observations are scarce or unavailable. The nonbias‐corrected simulations (at a minimum) should be provided to end users, along with the bias‐corrected ones, especially for studying the uncertainty of hydrological climate change impacts. This is especially true when using an RCM with a high resolution, since the scale effect is observed when the RCM resolution increases from a 45‐km to a 15‐km scale.     

1979-2010年中国流域水汽含量变化

为进一步丰富对中国上空水汽含量与可降水量气候平均状态及其变化的认识,利用日本气象中心的再分析资料,计算得到中国平均水汽含量分布图和各个季节水汽含量分布图。以再分析资料为基础计算得到的分布图与以探空资料为基础得到的分布图进行比较,可验证二者的合理性和不足之处。以流域为单元,分析了1979-2010年中国大陆区流域含量变化,结果表明:中国各流域年平均可降水量的年际变化都不大,变差系数都小于0.1;年际变化最大的处于中国西北地区的流域,变差系数都大于0.06;年平均可降水量呈显著增加的流域有北疆、塔里木内流区、河西走廊及阿拉善地区、柴达木内流区和羌塘内流区,呈显著减少的流域有东南诸河和内蒙古内流区,其他流域变化不显著。     

基于ERA5再分析数据的中国邻近海域极端波高特征分析

极端波浪对沿海地区基础设施有着深远的影响,了解它们的变化规律是进行海岸带风险分析和灾害预防的基础。文章基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasting,ECMWF)第五代再分析数据集(ECMWF reanalysis v5,ERA5),对中国邻近海域1979~2018年间极端波高展开时空特征分析,并统计了40 a厄尔尼诺系数,利用广义极值分布(generalized extreme value,GEV)函数探究了近40 a厄尔尼诺现象对我国海域极端波高的影响,结果显示:统计1979~2018年整个研究区域前2%极端波浪年均值在6~10 m间浮动,且整体趋势递增,在四季趋势变化中,春夏极端波高增长趋势较秋冬高,且波动明显,在年际极端波高变化趋势中有较大波动时大多伴随着厄尔尼诺或是拉尼娜现象的发生,结合厄尔尼诺现象对GEV分布中位置参数的影响分布图和极端波高年、季节际趋势变化分布图,厄尔尼诺现象影响大的地区极端波高大多呈现增长趋势,表明厄尔尼诺现象对极端波高有较高影响。