Global circulation from SEASAT altimeter data

Abstract

A set of time‐averaged sea surface heights at 1° intervals, derived from the adjusted SEASAT altimeter data, and the GEML2 gravity field are used to estimate the long‐wavelength stationary sea surface topography. In order to reduce the leakage of energy in the estimated sea surface topography, the GEML2 field is augmented by the Rapp81 gravity field to generate geoidal undulations with wavelengths consistent with the ones of sea surface heights. These undulations are subtracted from the sea surface heights, and the resulting differences are subjected to filtering in order to recover sea surface topography with minimum wavelengths of 6000 km and an estimated accuracy of 20–25 cm. These estimates agree well with oceanographic and other satellite‐derived results.

The direction of current flow can be computed on a global basis using the spherical harmonic expansion of sea surface topography. This is done not only for the SEASAT/GEML2 estimates, but also using the recent dynamic topography estimates of Levitus. The results of the two solutions are very similar and agree well with the major circulation features of the oceans.     

HY-2A/GM高度计数据反演的初步海洋重力场

HY-2 A(Haiyang-2 A), launched in 2011, is the first ocean dynamic environment satellite of China and is equipped with a radar altimeter as one of the primary payloads. HY-2 A shifted the drift orbit in March 2016 and has been accumulating geodetic mission(GM) data for more than three years with 168-day cycle. In this paper, we present the preliminary gravity field inverted by the HY-2 A/GM data from March 2016 to December 2017 near Taiwan(21°–26°N, 119°–123°E). The gravity anomaly is computed by Inverse Vening Meinesz(IVM) formula with a onedimensional FFT method during remove-restore procedure with the EGM2008 gravity model as the reference field. For comparison, CryoSat-2 altimeter data are used to inverse the gravity field near Taiwan Island by the same method. Comparing with the gravity field derived from CryoSat-2, a good agreement between the two data sets is found. The global ocean gravity models and National Geophysical Data Center(NGDC) shipboard gravity data also are used to assess the performance of HY-2 A/GM data. The evaluations show that HY-2 A and CryoSat-2 are at the same level in terms of gravity field recovery and the HY-2 A/GM altimeter-derived gravity field has an accuracy of 2.922 mGal. Therefore, we can believe that HY-2 A will be a new reliable data source for marine gravity field inversion and has the potentiality to improve the accuracy and resolution of the global marine gravity field.     

GM测高数据反演中国近海及邻域精细重力场

综合对比4种波形重跟踪算法,选择改进阈值法处理Jason-1GM数据,联合波形重跟踪后的Geosat和ERS-1GM数据,沿轨2Hz重采样以提高数据空间分辨率。通过数据质量控制剔除粗差数据,考虑海表面地形的影响,基于移去-恢复法和维宁-曼齐兹公式反演了中国近海及邻近海域(0°~45°N,100°~140°E)1′×1′的精细重力场。船测数据检核表明反演结果在开阔海域精度约4mGal,近岸浅水区约10mGal,均优于DTU10和V21.1模型。     

Preliminary results of the global ocean tide derived from HY-2A radar altimeter data

The HY-2A satellite, which is equipped with a radar altimeter and was launched on August 16, 2011, is the first Chinese marine dynamic environmental monitoring satellite. Extracting ocean tides is one of the important applications of the radar altimeter data. The radar altimeter data of the HY-2A satellite from November 1, 2011 to August 16, 2014 are used herein to extract global ocean tides. The constants representing the tidal constituents are extracted by HY-2A RA data with harmonic analysis ...     

Pacific ocean circulation based on observation

A thorough understanding of the Pacific Ocean circulation is a necessity to solve global climate and environmental problems. Here we present a new picture of the circulation by integrating observational results. Lower and Upper Circumpolar Deep Waters (LCDW, UCDW) and Antarctic Intermediate Water (AAIW) of 12, 7, and 5 Sv (10⁶ m³s⁻¹) in the lower and upper deep layers and the surface/intermediate layer, respectively, are transported to the North Pacific from the Antarctic Circumpolar Current (ACC). The flow of LCDW separates in the Central Pacific Basin into the western (4 Sv) and eastern (8 Sv) branches, and nearly half of the latter branch is further separated to flow eastward south of the Hawaiian Ridge into the Northeast Pacific Basin (NEPB). A large portion of LCDW on this southern route (4 Sv) upwells in the southern and mid-latitude eastern regions of the NEPB. The remaining eastern branch joins nearly half of the western branch; the confluence flows northward and enters the NEPB along the Aleutian Trench. Most of the LCDW on this northern route (5 Sv) upwells to the upper deep layer in the northern (in particular northeastern) region of the NEPB and is transformed into North Pacific Deep Water (NPDW). NPDW shifts southward in the upper deep layer and is modified by mixing with UCDW around the Hawaiian Islands. The modified NPDW of 13 Sv returns to the ACC. The remaining volume in the North Pacific (11 Sv) flows out to the Indian and Arctic Oceans in the surface/intermediate layer.     

On performance of CryoSat-2 altimeter data in deriving marine gravity over the Bay of Bengal

Marine Geophysical Research - The utilization of sea areas adjacent to land has rapidly increased in recent years due to the expansion of economic activities from the land to the ocean. To secure...     

HY-2A卫星雷达高度计数据的全球统计评价及质量分析

自HY-2A卫星发射以来,针对HY-2A卫星雷达高度计产品的交叉定标、真实性检验及质量评估工作一直在持续开展。本文主要以HY-2A卫星高度计第44周期的IGDR产品数据为例,通过使用全球分布图、二维直方图和每日均值统计的方法完成了与Jason-2IGDR产品的比对验证,同时对主要环境校正参数及地球物理产品的数据质量稳定性进行了分析,结果显示高度计产品数据质量较稳定,此外利用HY-2A卫星升降轨交叉点海面高度差、与Jason-2卫星交叉点海面高度差以及沿轨海平面异常数据分析的方法进行了HY-2A卫星高度计观测系统的性能评估,结果显示,HY-2A卫星海面高度精度约为7.48cm,精度接近Jason-2,能满足海洋应用与科学研究的需要。     

基于CryoSat-2卫星测高数据的北极海冰体积估算方法

近30年来,北极海冰正发生着剧烈的变化。海冰体积是量化海冰变化的重要指标之一。本文以2015年CryoSat-2卫星测高数据和OSI SAF海冰类型产品为基础。提取了浮冰出水高度、积雪深度、海冰密集度、海冰类型等属性信息,通过数据内插、投影变换、栅格转换、空间重采样等工作将海冰属性信息统一为25 km×25 km分辨率的栅格数据集。根据流体静力学平衡原理,逐个估算栅格像元对应的海冰厚度值,将其与对应的海冰面积相乘,估算了北极海冰密集度大于75%海域的海冰体积,并分析了海冰厚度和体积的月变化和季节变化特征。用NASA IceBridge海冰厚度产品对反演的海冰厚度进行验证。结果表明二者相关系数为0.72,有较高的一致性。北极海冰平均厚度春季最大,夏季最小,分别约为2.99 m和1.77 m,最厚的海冰集中在格陵兰沿岸北部和埃尔斯米尔半岛以北海域。多年冰平均厚度大于一年冰。冬季海冰体积最大,约为23.30×103 km3,经过夏季的融化,减少了近70%。一年冰体积季节波动较大,而多年冰体积相对稳定,季节变化不明显。     

基于20a卫星高度计数据的黑潮变异特征

黑潮作为一支典型的西边界流,其路径变化特征及其相关的物理现象对于渔业和航海有着不可忽视的影响。本文基于改进的特征线方法,利用1992~2012年的高度计绝对动力地形数据提取了整个黑潮流区逐月的黑潮主轴和边界位置,并对沿轴速度、主流宽度、表层水体输运以及路径标准差等黑潮特征量进行了分析研究。结果表明,黑潮整体的沿轴速度在夏秋季较大,最大值可达0.95 m/s,而在冬季的速度较小;黑潮主流宽度在10、11月份达到最大值;黑潮表层水体输运在夏季最大,春秋两季次之,冬季最小。沿黑潮流路分区域对黑潮特征进行分析,结果表明,越往黑潮下游,其沿轴速度、主流宽度和表层水体输运越大,同时沿轴速度和表层水体输运量最大值出现的时间也越晚,黑潮主轴位置相对于其多年平均的偏离程度越大,且随时间波动也越强烈。     

A reduced-dynamics variational approach for the assimilation of altimeter data into eddy-resolving ocean models

A new method of assimilating sea surface height (SSH) data into ocean models is introduced and tested. Many features observable by satellite altimetry are approximated by the first baroclinic mode over much of the ocean, especially in the lower (but non-equatorial) and mid latitude regions. Based on this dynamical trait, a reduced-dynamics adjoint technique is developed and implemented with a three-dimensional model using vertical normal mode decomposition. To reduce the complexity of the variational data assimilation problem, the adjoint equations are based on a one-active-layer reduced-gravity model, which approximates the first baroclinic mode, as opposed to the full three-dimensional model equations. The reduced dimensionality of the adjoint model leads to lower computational cost than a traditional variational data assimilation algorithm. The technique is applicable to regions of the ocean where the SSH variability is dominated by the first baroclinic mode. The adjustment of the first baroclinic mode model fields dynamically transfers the SSH information to the deep ocean layers. The technique is developed in a modular fashion that can be readily implemented with many three-dimensional ocean models. For this study, the method is tested with the Navy Coastal Ocean Model (NCOM) configured to simulate the Gulf of Mexico.     

基于 MODWT航行数据滤波方法变换的海洋重力观测

厄特弗斯效应是动态海洋重力测量的主要误差来源,厄特弗斯改正精度与航速和航向角精度密切相关。本文从最大重叠离散小波变换系数的分布特性入手,利用改进的定量化 Lipschitz 条件来确定观测曲线的正则性,提出了一种海洋重力观测中含噪航行数据的滤波方法,该方法在抑制噪声干扰的同时能够很好地保留测量信号的局部特征。本文提供了两组海洋重力测量中航速和航向角数据的处理结果,充分验证了本文方法的可靠性与有效性。     

基于卫星海面高度资料的太平洋海区涡旋能谱分析

在空间均匀和各向同性的假定下,地转湍流理论认为涡旋动能随尺度分布遵循k–n定律(k为波数)。但实际海洋受边界、地形、层结等,具有明显的非均匀、各向异性特征。鉴于此,我们基于近30a卫星高度计资料,分别计算了热带、副热带、中高纬度等海洋涡旋强度不同区域的海面高度异常(SSHA)波数谱,进而利用线性回归拟合方法估算出中尺度波段上SSHA波数谱的斜率,并与地转湍流理论预测进行了对比。研究结果显示:SSHA波数谱从赤道到中高纬度逐渐变陡,其斜率由–4减到–5,基本符合赤道线性波动理论和准地转湍流理论的预测。SSHA波数谱斜率存在纬向与经向差异,例如在赤道地区,纬向谱比相应的经向谱陡;而在南极绕极流区域,经向谱斜率大于纬向谱斜率。SSHA波数谱斜率的各向异性表明海洋中尺度运动受β效应影响,具有明显的经向和纬向差异。以上结果表明,海洋中尺度运动介于准二维和三维之间,不能用一个全球普适的湍流理论模型来描述。     

海洋环流模式中卫星遥感资料同化的应用进展

物理海洋研究长久以来一直受到观测资料不足的制约,然而这一状况随着现代观测技术的迅猛发展得到了很大的改善。卫星遥感技术的发展提供了覆盖全球的、连续、实时的卫星观测数据,这是其他任何资料都无法比拟的。这些数据大部分难以直接运用来改善气候预测或数值模拟分析,然而资料同化技术的出现和发展改善了这一情况。     

Effects of the deep ocean circulation on the reservoir characteristics of the ocean

To examine the effects of the deep ocean circulation on the characteristics of the ocean as a reservoir, age distributions of the material whose source and sink are at the ocean surface are calculated using an idealized vertical two-dimensional model of the ocean. The results show that the large-scale vertical circulation of the deep water accelerates the renewal of deep water and reduces the average age of the material. It is also shown that the multi-layered structures of the deep circulation are more realistic than the one-layered structure and promote the renewal of the deep water.     

基于遥感数据的温度剖面预报研究

为了提高温度剖面的预报精度,提出了一种基于遥感数据的温度剖面预报方法.文中使用27个实测温度剖面和遥感SST、SSHA数据实现了对温度剖面的预报,并用该点的ARGO数据进行了检验.实验结果表明,将遥感数据同化到温度剖面的预报中是可行的,并能有效的提高温度剖面的预报精度.     

卫星高度计资料揭示的冬季南海吕宋冷涡的双涡结构

吕宋冷涡是南海海洋环流系中最重要的涡旋之一。利用卫星高度计资料时空较高分辨率的优势,发现冬季吕宋冷涡有可能是由2个气旋式涡旋所组成的,一个气旋式涡旋位于吕宋岛的西侧(LCE1),另一个位于吕宋岛的西北(LCE2)。利用相关分析、功率谱分析等,估计了局地风应力和黑潮在形成吕宋冷涡过程中各自的贡献。研究结果表明,LCE1只存在于冬季,与吕宋岛西侧局地的风应力旋度有关;LCE2位于进入吕宋海峡的黑潮的西侧,全年存在,可能是由黑潮所诱生的气旋式涡旋,其变化主要周期为季节内振荡。     

Accuracy assessment of global ocean tide models in the South China Sea using satellite altimeter and tide gauge data

In this study, to meet the need for accurate tidal prediction, the accuracy of global ocean tide models was assessed in the South China Sea(0°–26°N, 99°–121°E). Seven tide models, namely, DTU10, EOT11 a, FES2014, GOT4.8,HAMTIDE12, OSU12 and TPXO8, were considered. The accuracy of eight major tidal constituents(i.e., Q₁, O₁, P₁,K₁, N₂, M₂, S₂ and K₂) were assessed for the shallow water and coastal areas based ...     

孟加拉湾上层地转环流周年变化的遥感研究

应用1993～2003年TOPEX/Poseidon卫星测高数据结合历史水文资料,反演了孟加拉湾海面动力地形的平均周年变化,探讨了孟加拉湾上层环流季节特征和演变规律.结果显示,虽然孟加拉湾的大气环流受季风支配年周期波动显著,但表层环流形态的周年演变却呈3个不同的阶段.1～4月间(东北季风后期)湾内受一个海盆尺度的强大反气旋式环流的支配,湾口为西向流;5月西南季风骤起,印度季风漂流越过印度半岛南端出现在湾口,湾内反气旋环流弱化,在其南北两侧各出现一气旋式涡,构成5～9月间南北相间的三涡结构;10月东北季风再起,湾口漂流再次转向,10～12月间湾内则为海盆尺度的弱气旋式环流.受上述环流格局影响,位于西边界的印度沿岸流亦呈相应的3个阶段变化.分析表明,孟加拉湾风应力旋度的变化是造成湾内环流3个阶段演变的主要原因.本地风场和来自赤道海域的外强迫的共同驱动形成了孟加拉湾环流周年演变的独特规律.