The rigorous adjustment of the global mean sea level budget during 2005-2015

Global mean sea level budget is rigorously adjusted during the period 2005-2015.The emphasis is to provide the best estimates for the linear rates of changes(trends)of the global mean sea level budget components during this period subject to the constraint:Earth’s hydrosphere conserves water.The newly simultaneously adjusted trends of the budget components suggest a larger correction for the global mean sea level trend implicated by the other budget components’trends under the budget constraint.The simultaneous estimation of the linear trends of the budget components subject to the constraint for closure improves their uncertainties and enables a holistic assessment of the global mean sea budget,which has implications for future sea level science studies,including the future Intergovernmental Panel on Climate Change(IPCC)Assessment Reports,and the US Climate Assessment Reports.

MEAN SEA LEVEL AND SEA SURFACE VARIABILITY OF NQRTHWEST PACIFIC OCEAN AND EASTERN CHINA SEAS FROM GEOSAT ALTIMETRY

Collinear analysis technique is widely used for determining sea surface variability with Geosat altimeterdata from its Exact Repeat Mission(ERM).But most of the researches have been only on global scaleor in oceans deeper than 2000 m.In shallow shelf waters this method is hampered by the inaccuracy ofocean tide data supplied with Geosat Geophysical Data Records(GDRs).This work uses a modified collinearanalysis technique characterized by simultaneous separation of mean sea level and ocean tide with theleast squares method,to compute sea surface variability in the Northwest Pacific Ocean and eastern ChinaSeas.The mean sea level map obtained contains not ouly bathymetric but also dynamic features such asamphidromes,indicating considerable improvement over previous works.Our sea surface variability mapsshow clearly the main current system,the well-known Zhejiang coastal upwelling,and a northern East Chi-na Sea meso-scale eddy in good agreement with satellite sea surface temperature(SST)observation and

An analysis on the mean sea level change of the seas adjacent to Korea

Monthly changes of sea level recorded on the seas adjacent to Korea (the Huanghai Sea, the East ChinaSea and the East As) are investigated. The major influences on the spatial and temporal variation of mean sea level arequantitatively identified. A set of modes of monthly air pressure variation over the Huanghai Sea, East China Sea andEast Sea for the period of 1978-1992 is obtained. Each monthly air pressure distribution can be precisely defined bylinear combination of these modes. Hence, the set of air pressure series can be replaced by a set of time varying coefficents, where each coefficient describes the contribution of a particular mode to a given air pressure distribution. A selected set of the modal coefficients is then added to a multiple Fegresion model, consisting of a trend, monthly wind stress and tidal term, in an attempt to represent the effect of meteorological variations on monthly mean sea level on the seas adjacent to Korea. It is found that although the model may account for over 90% of the observed mean sea level variance, there still remains a high correlation between the residuals, hence identifying a regional variation for further study.

Mean Sea Level Changes near Weizhou Island from 1969 to 2010

Tidal data from Weizhou, Zhapo, and Shanwei stations between 1969 and 2010 and from five gauging stations in the western Pacific Ocean provided by PSMSL, and the global mean sea level data recorded between December 1992 and December 2010 by TOPEX and Jason satellites were compiled and analyzed. The results show that the perennial mean sea level near Weizhou Island is 211.7 cm(relative to the water gauge zero), and the relative mean sea level rising rate is 2.2 mm yr-1 from 1969 to 2010, which is consistent with the relative mean sea level rising rate recorded at other gauging stations in the western Pacific regions and with the global mean sea level rising rate. The absolute mean sea level rising rate at Weizhou Island is 3.0 mm yr-1 from 1993 to 2010, also conforming with the global mean sea level rising rate(3.1±0.4 mm yr-1) during the same time period. The highest annual tide level at Weizhou Island has a rising rate of 4.6 mm yr-1 and shows a 20-year quasi-periodic variation from 1966 to 2010. The primary cause of the mean sea level rising is global warming.

Performance of CMIP6 models in simulating the dynamic sea level:Mean and interannual variance

本研究采用卫星测高数据与第六次国际耦合模式比较计划(CMIP6)海平面动力进行对比,重点针对40S-40N地区的动力海平面(DSL),评估了模式对其平均态与年际变率的综合模拟能力,结果表明,对于DSL平均态的模拟,模式与观测结果非常吻合,模式之间的差异较小.其中,副热带北大西洋是模拟偏差和模式间差异较为显著的区域,对于DSL年际变率的模拟,模式之间保持较高的一致性,但是,模式与观测结果存在明显差异,模式普遍低估了DSL的年际方差;其中,误差大值区域出现在副热带西边界流附近,模式分辨率会影响CMIP6对中小尺度海洋过程的重现能力,这可能是导致CMIP6历史模拟出现误差的原因之一.

Improving the understanding of the influencing factors on sea level based on wavelet coherence and partial wavelet coherence

Relationship between sea level change and a single climate indicator has been widely discussed.However,few studies focused on the relationship between monthly mean sea level(MMSL)and several key impact factors,including CO_(2) concentration,sea ice area,and sunspots,on various time scales.In addition,research on the independent relationship between climate factors and sea level on various time scales is lacking,especially when the dependence of climate factors on Nino 3.4 is excluded.Based on this,we use wavelet coherence(WC)and partial wavelet coherence(PWC)to establish a relationship between MMSL and its influencing factors.The WC results show that the influence of climate indices on MMSL has strong regional characteristics.The significant correlation between Southern Hemisphere sea ice area and MMSL is opposite to that between Northern Hemisphere sea ice area and MMSL.The PWC results show that after removing the influence of Nino 3.4,the significant coherent regions of the Pacific Decadal Oscillation(PDO),Dipole Mode Index(DMI),Atlantic Multidecadal Oscillation(AMO),and Southern Oscillation Index(SOI)decrease to varying degrees on different time scales in different regions,demonstrating the influence of Nino 3.4.Our work emphasizes the interrelationship and independent relationship between MMSL and its influencing factors on various time scales and the use of PWC and WC to describe this relationship.The study has an important reference significance for selecting the best predictors of sea level change or climate systems.

The global mean sea level rise,still accelerated

Subject Code:D06A collaborative study partly sponsored by the National Natural Science Foundation of China indicates that the global mean sea level is still accelerated rising,with much of the increase from the accelerated Greenland ice sheet melting during 1993—2014.The work is coauthored by Prof.Chen Xianyao(陈显尧)

The impact of mean dynamic topography on a sea-level anomaly assimilation in the South China Sea based on an eddy-resolving model

The sea-level anomaly (SLA) from a satellite altimeter has a high accuracy and can be used to improve ocean state estimation by assimilation techniques. However, the lack of an accurate mean dynamic topography (MDT) is still a bothersome issue in an ocean data assimilation. The previous studies showed that the errors in MDT have significant impacts on assimilation results, especially on the time-mean components of ocean states and on the time variant parts of states via nonlinear ocean dynamics. The temporal-spatial differences of three MDTs and their impacts on the SLA analysis are focused on in the South China Sea (SCS). The theoretical analysis shows that even for linear models, the errors in MDT have impacts on the SLA analysis using a sequential data assimilation scheme. Assimilation experiments, based on EnOI scheme and HYCOM, with three MDTs from July 2003 to June 2004 also show that the SLA assimilation is very sensitive to the choice of different MDTs in the SCS with obvious differences between the experimental results and observations in the centre of the SCS and in the vicinity of the Philippine Islands. A new MDT for assimilation of SLA data in the SCS was proposed. The results from the assimilation experiment with this new MDT show a marked reduction (increase) in the RMSEs (correlation coefficient) between the experimental and observed SLA. Furthermore, the subsurface temperature field is also improved with this new MDT in the SCS.

Period components in the monthly mean sea level variations in the Pacific Ocean

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Research on the spectral analysis and testmethod of period signals in monthly mean sea level

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Characteristics of extratropical cyclone variability in the Northern Hemisphere and their response to rapid changes in Arctic sea ice

Extratropical cyclones are critical weather systems that affect large-scale weather and climate changes at mid-high latitudes.However,prior research shows that there are still great difficulties in predicting extratropical cyclones for occurrence,frequency,and position.In this study,mean sea level pressure(MSLP)data from the European Centre for Medium-Range Weather Forecasts(ECMWF)reanalysis(ERA5)are used to calculate the variance statistics of the MSLP to reveal extratropical cyclone activity(ECA).Based on the analysis of the change characteristics of ECA in the Northern Hemisphere,the intrinsic link between ECA in the Northern Hemisphere and Arctic sea ice is explored.The results show that the maximum ECA mainly occurs in winter over the mid-high latitudes in the Northern Hemisphere.The maximum ECA changes in the North Pacific and the North Atlantic,which are the largest variations in the Northern Hemisphere,are independent of each other,and their mechanisms may be different.Furthermore,MSLP is a significant physical variable that affects ECA.The North Atlantic Oscillation(NAO)and North Pacific Index(NPI)are significant indices that impact ECA in the North Atlantic and North Pacific,respectively.The innovation of this paper is to explore the relationship between the activity of extratropical cyclones in the Northern Hemisphere and the abnormal changes in Arctic sea ice for the first time.The mechanism is that the abnormal changes in summer-autumn and winter Arctic sea ice lead to the phase transition of the NPI and NAO,respectively,and then cause the occurrence of ECA in the North Pacific and North Atlantic,respectively.Arctic sea ice plays a crucial role in the ECA in the Northern Hemisphere by influencing the polar vortex and westerly jets.This is the first exploration of ECAs in the Northern Hemisphere using Arctic sea ice,which can provide some references for the in-depth study and prediction of ECAs in the Northern Hemisphere.

Effect of Sea Level Variation on Tidal Characteristic Values for the East China Sea

Tidal waves in the East China Sea are simulated numerically with POM(Princeton Ocean Model) model for normal mean sea level, 30 cm higher, 60 cm higher, and 100 cm higher, respectively, and the simulated result is compared with the harmonic analysis result of hourly sea level data from 19 tide gauges for more than 19 years. It is indicated that the long-term mean sea level variation affects notably tidal waves in this region. Generally, the tidal amplitude increases when the mean sea level rises, but this relationship may be inverse for some sea areas. The maximal variation of tidal amplitude takes place in the zones near the Fujian coast and the Zhejiang coast, rather than the shallowest Bohai Sea. The maximum increase of M2 amplitude can exceed about 15 cm corresponding to the 60 cm rise of the mean sea level along the Fujian coast. The other regions with large variations of tidal amplitude are those along the Jiangsu coast, the south-east coast of Shandong, and the south-east coast of Dalian. The propagation of tidal waves is also related to mean sea level variation, and the tidal phase-lag decreases generally when the mean sea level rises. Almost all the regions where the tidal phase-lag increases with rising mean sea level are close to amphidromic points, meanwhile the spatial area of such regions is very small. Because the influence of mean sea level variation upon tidal waves is spatially marked, such spatial effect should be considered in calculation of the tidal characteristic value and engineering water level. In the region where the amplitudes of the major tidal constituents increase, the probable maximum high water level becomes higher, the probable maximum low water level becomes lower, and both design water level andcheck water level increase obviously. For example, the design water level at Xiamen increases by 13.5 cm due to the variation of tidal waves when the mean sea level rises 60 cm, the total increase of design water level being 73.5 cm.

Adapting cities to sea level rise： A perspective from Chinese deltas

在最近的年里，在中国三角洲城市和邻近的区域里加强 waterlogging，盐水侵入，沼泽地损失，和生态系统降级产生了紧迫的需要创造被适合到合并海水平上升的两现在和将来的气候的一种城市的形式。然而，改编计划举起是慢的。因为城市的形式的模式以减少或加强它的影响的方法与吝啬的海水平上升(MSLR ) 交往，这是特别地不幸的。当前有二个主要障碍，在逮捕与设计从温暖的全球气候 geomorphologic MSLR 设计和海面升降的 MSLR 设计填写了的 MSLR 的参考计划的改编的实现是重要的，并且使全面风险成为对 MSLR 设计的评价。现在的评论在印射如下使这些城市适应 MSLR 设计的中国三角洲城市，然后一个观点上的 MSLR 设计和他们的风险评价途径显示出最近的进步六个方面。1 ) geomorphologic MSLR 设计被自然构造沉淀设计贡献，由人为的 geomorphologic 的 MSLR 设计变化。前者需要在一个全球框架被更新。后者由陆路被积累从地下的水弄空的沉淀，河床的侵蚀从归因于分水岭的构造的沉积供应衰落引起的水水平秋天建水坝，人工的沙挖掘，由包括陆地开垦设计工程的水水平加薪，深水路规定，并且新鲜的水水库。2 ) 由人为的 geomorphologic 控制 MSLR 设计变化。3 ) IPCC AR5 RCP MSLR 情形被期望在中国三角洲上被预测到本地海面升降的 MSLR 设计。4 )? MSLR 设计需要被匹配到一本本地举起资料。5 ) 与半分析的水动力学，河口隧道网络，系统动力学和改编点数字的地区性的河海的当模特儿的途径是观点。6 ) 计划到 MSLR 设计的改编要求对洪水的风险的一个全面风险评价，新鲜的水供应缺乏，沿海的侵蚀，沼泽地损失，中国三角洲城市和邻近的区域里的港口和水路的 siltation。

The global mean sea surface model WHU2013

The mean sea surface(MSS) model is an important reference for the study of charting datum and sea level change. A global MSS model named WHU2013, with 20? 20 spatial resolution between 80S and 84N, is established in this paper by combining nearly 20 years of multi-satellite altimetric data that include Topex/Poseidon(T/P), Jason-1, Jason-2, ERS-2,ENVISAT and GFO Exact Repeat Mission(ERM) data, ERS-1/168, Jason-1/C geodetic mission data and Cryosat-2 low resolution mode(LRM) data. All the ERM data are adjusted by the collinear method to achieve the mean along-track sea surface height(SSH), and the combined dataset of T/P, Jason-1 and Jason-2 from 1993 to 2012 after collinear adjustment is used as the reference data. The sea level variations in the non-ERM data(geodetic mission data and LRM data) are mainly investigated, and a combined method is proposed to correct the sea level variations between 66S and 66N by along-track sea level variation time series and beyond 66S or 66N by seasonal sea level variations. In the crossover adjustment between multi-altimetric data, a stepwise method is used to solve the problem of inconsistency in the reference data between the high and low latitude regions. The proposed model is compared with the CNES-CLS2011 and DTU13 MSS models, and the standard derivation(STD) of the differences between the models is about 5 cm between80S and 84N, less than 3 cm between 66S and 66N, and less than 4 cm in the China Sea and its adjacent sea. Furthermore, the three models exhibit a good agreement in the SSH differences and the along-track gradient of SSH following comparisons with satellite altimetry data.

Determination of the Absolute Rate of Sea Level by Using GPS Reference Station and Tide Gauge Data

The absolute rate of mean sea level of Xiamen area is derived from the data of Xiamen tide gauge station and Xiamen GPS fiducial station of crustal movement observation network of China(CMONC). The height variation is discussed deeply in this paper. It is shown that height has periodic variations. So the rate of vertical land movement can not be precisely obtained only from several GPS campaigns. It is pointed out that the vertical crustal movement of tide gauge station should be monitored by using long-term continuous GPS observations.

Combination of Tsoft and ET34-ANA-V80 software for the preprocessing and analysis of tide gauge data in French Polynesia

Since 2008 a network of five sea-level monitoring stations was progressively installed in French Polynesia.The stations are autonomous and data,collected at a sampling rate of 1 or 2 min,are not only recorded locally,but also transferred in real time by a radio-link to the NOAA through the GOES satellite.The new ET34-ANA-V80 version of ETERNA,initially developed for Earth Tides analysis,is now able to analyze ocean tides records.Through a two-step validation scheme,we took advantage of the flexibility of this new version,operated in conjunction with the preprocessing facilities of the Tsoft software,to recover co rrected data series able to model sea-level variations after elimination of the ocean tides signal.We performed the tidal analysis of the tide gauge data with the highest possible selectivity(optimal wave grouping)and a maximum of additional terms(shallow water constituents).Our goal was to provide corrected data series and modelled ocean tides signal to compute tide-free sea-level variations as well as tidal prediction models with centimeter precision.We also present in this study the characteristics of the ocean tides in French Polynesia and preliminary results concerning the non-tidal variations of the sea level concerning the tide gauge setting.

极端干旱条件下珠江口东江三角洲咸潮上溯响应规律研究

2021年珠江东江流域遭遇1956年以来最严重干旱,上游控制断面博罗站年均径流较多年平均减少了64.5%。在此极端干旱条件下,2021-2022年枯水期珠江口东江三角洲遭遇了有记录以来的最强咸潮上溯,严重威胁到区域供水安全。本文基于2009-2022年东江三角洲各水厂含氯度数据,利用交叉小波和小波相干分析识别了咸潮上溯与径流、潮汐、外海含氯度及海平面波动等影响因素间的相位关系与共变周期,揭示了极端干旱条件下东江三角洲咸潮上溯的主控因素及含氯度峰值交替变化的原因。研究发现,2021-2022年枯水期东江三角洲咸潮上溯主要影响因素为潮汐与伶仃洋湾内含氯度,其次为外海海平面波动,三种因素对东江三角洲咸潮上溯影响的时间尺度相互交织。5~9d的周期变化主要受外海海平面波动影响;14.8d的变化周期主要由大小潮及伶仃洋湾内含氯度控制;28~32d的周期变化主要影响因素为伶仃洋湾内含氯度。东江三角洲含氯度峰值交替变化的原因主要为伶仃洋湾内含氯度与潮汐间存在相位差(相关系数r=0.73,显著性水平P<0.01),并叠加外海海平面波动上升的影响(r=0.31,P<0.01)。本文可为东江三角洲咸潮预报及流域调度提供一定借鉴。

南海沿海港口航道图深度基准面计算与评估

《海道测量规范》(GB 12327—2022)正式实施,按照新规范评估南海沿海港口航道图深度基准面值,能为海洋垂直基准的维护提供数据支持。对广州海事测绘中心辖区17个长期水位站长于2年的水位数据、长期站邻近的28个短期、临时水位站数据进行潮汐分析,评估了长期水位站的L值及深度基准面保证率,分析了短期、临时水位站平均海面、深度基准面的传递精度。结果表明:17个长期水位站3种算法深度基准面保证率均超过98%,保证了航行的安全性;不同方法确定的深度基准面L值互差,53%的长期水位站超过10 cm,7%短期、临时水位站超过15 cm,11%短期、临时水位站两种方法L值中数与原采用值差值超过15 cm,亟需修正南海沿海港口航道图深度基准值。

基于局部均值分解和交叉小波的全球平均海平面变化与ONI指数多尺度特征研究

为研究全球平均海平面与ENSO(El Niño-Southern Oscillation)的相关性问题,本文提出了一种结合局部均值分解和交叉小波原理的分析方法,揭示全球平均海平面和ENSO的影响机理和因果关联。利用全球平均海平面的时间序列进行局部均值分解得到PF分量和余量,表示海平面变化的高频分量、低频分量和趋势分量。剔除高频分量的影响,利用最小二乘线性拟合趋势分量,得到1991—2000年的全球平均海平面上升速率为3.6 mm/a。接着对PF的低频分量进行距平变换再与ONI指数(Oceanic Niño Index,ONI)分别进行Morlet连续小波变换得到小波功率谱,再将变换的连续小波分别进行交叉小波变换得到交叉小波功率谱和凝聚谱,通过交叉小波功率谱和交叉小波凝聚谱揭示信号在时频空间的能量共振和协方差分布规律,其中交叉小波功率谱体现了共同的高能量区的相关性,交叉小波凝聚谱体现了共同的低能量区的相关性。结果表明,该方法能在多尺度上分析海平面的变化,并能分析ONI指数与全球平均海平面的关系,可为全球平均海平面演变规律分析和预测等方面提供有力工具。

重力场模型在长江口岛礁垂直基准建立中的应用

为了获取长江口外岛礁三维基准,探索岛礁垂直基准确定方法,基于长江口GNSSC级控制网成果,利用高阶全球重力场模型EGM2008、EIGEN-6C4采用“移去-恢复”法,计算长江口区域高程异常,建立两种重力场模型的高程异常修正模型,推算长江口外岛礁正常高;通过实例验证了构建EGM2008、EIGEN-6C4的修正模型的可用性,经推算正常高,呈现EIGEN-6C4模型计算正常高精确度优于EGM2008模型;通过长期验潮站基于平均海平面最小二乘高程传递方法推算岛礁正常高,验证了采用重力场模型推算正常高外符合性。