Coastal upwelling events along the southern coast of Java during the 2008 positive Indian Ocean Dipole

To understand the coastal upwelling system along the southern coast of Java, we investigated ocean temperature and salinity obtained from an Argo float. In 2008, a positive Indian Ocean Dipole (IOD) event began to develop in early May and anomalously cool SST developed around south of Java from May to September. During the peak of the IOD, an Argo float successfully observed vertical structure of temperature and salinity within 90 km from Java. The float observed two intraseasonal-scale temperature cooling events in July and August, with significant upward movements of the thermocline more than 90 m. Concurrent with the signals, anomalous southeasterly alongshore winds, lowering of local SST and sea level, and upward expansion of high-salinity water were also observed. During the event in August, vertical velocity estimated by the anomalous wind stress agreed well with the observations. These results indicate that the Argo float observed the coastal upwelling, which was enhanced by the 2008 positive IOD, along the southern coast of Java.     

基于神经网络的全球三维温盐场重构技术研究

文章利用果蝇优化广义回归神经网络算法FOAGRNN (fruit fly optimization algorithm, FOA; generalized regression neural network, GRNN)对SODA (simple ocean data assimilation)再分析数据进行训练, 构建海表温度、盐度、海面高度与次表层温盐场之间的投影关系模型, 并在全球范围使用SODA和卫星遥感数据评估了模型的应用性能。首先, 利用独立的2016年SODA海表数据作为模型输入进行理想重构试验, 结果显示全球重构温、盐平均均方根误差(MRMSE)分别为0.36℃和0.08‰, 与世界海洋图集WOA13资料相比减小约50%和60%。然后, 利用卫星观测的海表信息作为模型输入进行实际应用试验, 并与Argo观测剖面进行比较评估。试验结果表明, 重构模型能有效表征海水温、盐特征, 其中重构温、盐MRMSE分别为0.79℃和0.16‰, 相比WOA气候态减小27%和11%。误差的垂向分布显示, 重构温度RMSE从海表向下迅速增大, 至100m达到峰值1.35℃, 而后又迅速回落,至250m处为0.81℃, 跃层往下不断减小; 重构盐度RMSE基本随深度增大而减小, 误差峰值位于25m附近, 约为0.25‰。此外, Argo浮标跟踪分析和区域水团统计结果也表明模型能够较好地刻画海洋三维温盐场的内部结构特征。     

Argo时代东南印度洋上层盐度变化对海平面年代际演变的影响

In the past nearly two decades, the Argo Program has created an unprecedented global observing array with continuous in situ salinity observations, providing opportunities to extend our knowledge on the variability and effects of ocean salinity. In this study, we utilize the Argo data during 2004–2017, together with the satellite observations and a newly released version of ECCO ocean reanalysis, to explore the decadal salinity variability in the Southeast Indian Ocean(SEIO) and its impacts on the regional sea level changes. Both the observations and ECCO reanalysis show that during the Argo era, sea level in the SEIO and the tropical western Pacific experienced a rapid rise in 2005–2013 and a subsequent decline in 2013–2017. Such a decadal phase reversal in sea level could be explained, to a large extent, by the steric sea level variability in the upper 300 m. Argo data further show that, in the SEIO, both the temperature and salinity changes have significant positive contributions to the decadal sea level variations. This is different from much of the Indo-Pacific region, where the halosteric component often has minor or negative contributions to the regional sea level pattern on decadal timescale. The salinity budget analyses based on the ECCO reanalysis indicate that the decadal salinity change in the upper 300 m of SEIO is mainly caused by the horizontal ocean advection. More detailed decomposition reveals that in the SEIO, there exists a strong meridional salinity front between the tropical low-salinity and subtropical high salinity waters. The meridional component of decadal circulation changes will induce strong cross-front salinity exchange and thus the significant regional salinity variations.     

全球海洋Argo网格数据集制作与可靠性验证

利用改进的 Barnes 逐步订正法,结合一个混合层模型,构建完成了一个新版(2004-2017 年) 全球海洋(79. 5°S~79. 5°N,180°W~180°E)Argo 三维网格温、盐度资料集及衍生数据产品。 与旧版网格数据集相比,新版数据集采用一阶近似(表层温、盐度通过混合层内温、盐度线性拟合得出)的混合层模型,改善了资料集在表层的准确性;与 WOA13 资料集、同类 Argo 资料集和锚碇浮标观测资料的可靠性检验结果表明,新版全球海洋 Argo 网格数据集提供的资料是可信的,其质量也是有充分保证的。     

The Global Distribution of Diapycnal Mixing and Mixing Coefficient Tensor in the Upper 2000m Ocean from Argo Observations

Diapycnal Mixing (DM) within the upper 2000m of the global ocean is calculated by a fine-scale parameterization using the multiyear-mean density gridded product that created by employing all the Argo float observations to date through the recently published equation of seawater TEOS-10. The geographic distribution of Argo-derived DM derived in this study is spatial-dependent and varies with latitude and depth. The magnitude and pattern of DM is favorably validated by comparisons with previous studies. Furthermore, the mixing coefficient tensor K is calculated and analyzed. Components of the tensor fitting for the geopotential coordinate models are also presented. It is found that the tensor components in horizontal direction, K_xx and K_yy, have similar magnitude and distribution pattern. In the vertical, K_zz is enhanced over regions with rough topography and strong wind (e.g., Westerly region), suggesting agreement with previous estimates. This work presents a scheme to estimate the DM and mixing coefficient tensor using Argo observations, and offers a useful Argo-based mixing product for the purpose of promoting the study and modeling of ocean circulation and other processes.     

Upper Ocean Four-Dimensional Variational Data Assimilation in the Arabian Sea and Bay of Bengal

A regional ocean circulation model with four-dimensional variational data assimilation scheme is configured to study the ocean state of the Indian Ocean region (65°E–95°E; 5°N–20°N) covering the Arabian Sea (AS) and Bay of Bengal (BoB). The state estimation setup uses 10 km horizontal resolution and 5 m vertical resolution in the upper ocean. The in-situ temperature and salinity, satellite-derived observations of sea surface height, and blended (in-situ and satellite-derived) observations of sea surface temperature alongwith their associated uncertainties are used for data assimilation with the regionally configured ocean model. The ocean state estimation is carried out for 61 days (1 June to 31 July 2013). The assimilated fields are closer to observations compared to other global state estimates. The mixed layer depth (MLD) of the region shows deepening during the period of assimilation with AS showing higher MLD compared to the BoB. An empirical forecast equation is derived for the prediction of MLD using the air–sea forcing variables as predictors. The surface and sub-surface (50 m) heat and salt budget tendencies of the region are also investigated. It is found that at the sub-surface, only the advection and diffusion temperature and salt tendencies are important.     

Differential diffusion: an oceanographic primer

Even where mean gradients of temperature T and salinity S are both stabilizing, it is possible for the larger molecular diffusivity of T to result in differential diffusion, the preferential transfer of T relative to S. The present note reviews existing evidence of differential diffusion as provided by laboratory experiments, numerical simulations, and oceanic observations. Given potentially serious implications for proper interpretation of estimates of diapycnal density diffusivity from both ocean microscale measurements and ocean tracer release experiments, as well as the sensitivity of predictive global ocean models to this diffusive parameter, it is essential that this process be better understood in the oceanographic context.     

国际Argo计划执行现状剖析

国际Argo计划自2000年实施以来,世界上25个国家和团体已经在全球海洋中布放了5000余个Argo浮标,其中在海上正常工作的浮标已经超过3000个。这标志着全球Argo实时海洋观测网已经全面建成。文中将系统介绍国际Argo计划主要成员国在浮标布放、回收和Argo资料管理等方面所作出的贡献,以帮助读者对这21世纪的重大国际海洋观测计划有一较全面、深入的了解。     

Twenty years of ocean observations with China Argo

The international Argo program, a global observational array of nearly 4 000 autonomous profiling floats initiated in the late 1990s, which measures the water temperature and salinity of the upper 2 000 m of the global ocean, has revolutionized oceanography. It has been recognized one of the most successful ocean observation systems in the world. Today, the proposed decade action “OneArgo” for building an integrated global, full-depth, and multidisciplinary ocean observing array for beyond 2020 ...     

HM2000型剖面浮标的主要特征及其应用

HM2000 型剖面浮标是一种新颖的国产海洋观测仪器,可以长期在海上自由漂移并连续测量 0~2 000 m 水深内的海水温、盐度剖面数据,已被国际 Argo 组织用于全球 Argo 实时海洋观测网建设和维护。 详细介绍了该型浮标的工作原理、结构、功能和主要技术指标等,并与 APEX 型浮标进行了比较分析, 表明了 HM2000 型剖面浮标具有明显的功能优势,且测量的温、盐度质量是有足够保证的,完全可以替代国外浮标用来主导建设我国的 Argo 区域海洋观测网。     

Significant salinity increase in subsurface waters of the South China Sea during 2016–2017

The South China Sea(SCS) is the largest semi-enclosed marginal sea in the North Pacific. Salinity changes in the SCS play an important role in regional and global ocean circulation and the hydrological cycle. However, there are few studies on salinity changes over the SCS due to lack of high-quality and long-term observations. In the past decade, the deployment of floats from the Argo program in the SCS and their accumulated temperature and salinity profiles have made it possible for us to examine salinity changes over the entire basin. In this study,salinity changes were investigated with Argo and underwater glider temperature and salinity observations and gridded temperature–salinity objective analyses(UK Met Office Hadley Centre EN4.2.1 objective analysis and China Argo Real-time Data Center BOA_Argo). The results indicated that the subsurface water in the entire SCS became significantly saltier during 2016–2017. The most significant salinity increase was found during 2016 in the northeastern SCS. The subsurface water in the northeastern SCS exhibited a salinity maximum above 35, which was recorded by three Argo floats during 2015–2016. Such high salinity water was rarely observed and reported prior to the Argo era. Average salinity of 2016–2017 along the 25.5σ_θ–23.5σ_θ isopycnal surfaces in the whole SCS is 0.014-0.130 higher than the climatology. Increases in subsurface salinity started from the northeastern SCS and extended southwestward gradually. Moreover, the subsurface salinity changes, especially in the northern SCS,exhibited a semiannual lead behind the subsurface Luzon Strait transport. Further analysis indicated that the predominance of advection, driven by subsurface Luzon Strait transport, led to salinification along the western boundary of the SCS. In other parts of the SCS, negative wind stress curl trends tended to preserve the high salinity characteristics of the subsurface water.     

基于微波遥感技术海面盐度反演方法

海面盐度(sea surface salinity,SSS)是研究海洋变化及其气候效应重要的物理量,对海洋生态环境、海洋可持续发展至关重要.为了提高海面盐度反演精度,本文通过对SMAP卫星L波段微波辐射计测量的亮温数据进行海面盐度反演研究,考虑风、浪等影响海面粗糙度的环境因子对Klein-Shift模型(简称K-S模型...     

Using satellite altimetry to correct mean temperature and salinity fields derived from Argo floats in the ocean regions around Australia

We present results from a suite of methods using in situ temperature and salinity data, and satellite altimetric observations to obtain an enhanced set of mean fields of temperature, salinity (down to 2000-m depth) and steric height (0/2000 m) for a time-specific period (1992–2007). Firstly, the improved global sampling resulting from the introduction of the Argo program, enables a representative determination of the large-scale mean oceanic structure. However, shortcomings in the coverage remain. High variability western boundary current eddy fields, continental slope and shelf boundaries may all be below their optimal sampling requirements. We describe a simple method to supplement and improve standard spatial interpolation schemes and apply them to the available data within the waters surrounding Australia (100°E–180°W; 50°S–10°N). This region includes a major current system, the East Australian Current (EAC), complex topography, unique boundary currents such as the Leeuwin Current, and large ENSO related interannual variability in the southwest Pacific. We use satellite altimetry sea level anomalies (SLA) to directly correct sampling errors in in situ derived mean surface steric height and subsurface temperature and salinity fields. The surface correction is projected through the water column (using an empirical model) to modify the mean subsurface temperature and salinity fields. The errors inherent in all these calculations are examined. The spatial distribution of the barotropic–baroclinic balance is obtained for the region and a ‘baroclinic factor’ to convert the altimetry SLA into an equivalent in situ height is determined. The mean fields in the EAC region are compared with independent estimates on repeated XBT sections, a mooring array and full-depth CTD transects.     

Statistical structure of spatial variability of the ocean thermohaline fields from argo profiling data, 2005–2007

The means, variances, and three-dimensional spatial covariances of the ocean temperature and salinity anomalies in the upper 1400 m layer have been estimated using data of the Argo profiling floats from 2005 to 2007. The results of data processing suggest the continuation of general warming of the ocean waters noted in a number of papers based on earlier data. A pronounced geographical and vertical nonuniformity characterizes this warming but, as a whole, it is mostly distinct in the upper 100 m layer both in the tropics and midlatitudes. For the first time, the unique characteristics of the Argo observing system allowed us to obtain previously unfeasible estimates of the spatial statistics for salinity field. In particular, it has been demonstrated that the spatial structure of salinity anomalies is similar to those of temperature, excluding the case of the near-surface layer.     

Argo-type profiling float observations under the Arctic multiyear ice

To monitor and better understand temperature and salinity conditions in the Arctic Ocean interior, we developed a new Argo-type ocean profiling system for the polar oceans. This Polar Ocean Profiling System (POPS) consists mainly of an ice platform and an Argo-type subsurface CTD profiler. The ice platform includes a system controller that manages all data acquisition, processing, formatting, and messaging. Iridium satellite communication technology sends the observation data and also allows remote commands to be sent from the laboratory to the buoy. The profiler is mounted on an oceanographic cable interfaced to the platform; the profiler moves along the cable between depths of 10 and 1000 m. The inductive modem system provides data transfer between the ice platform and the profiler. In April 2005, field tests of the POPS were conducted in the Arctic Ocean near the North Pole. Later on, commands were sent via Iridium from the laboratory to the buoy to change the data sampling acquisition frequency, allowing us to obtain 14 temperature and salinity profiles during the first 22 days. We confirmed that POPS could measure temperature and salinity with conservative accuracies better than 0.01 °C for temperature and 0.01 for salinity. Following this test, we initiated the observation of the Arctic Ocean from 10 m down to 1000 m depths in April 2006 using POPS, and we also started sending the data to the global telecommunication system (GTS) in real time. These data are the first Argo data sent from the Arctic Ocean. Not only Arctic oceanographers but also everyone who is interested in Arctic oceanographic conditions can easily access these data from the Argo data server.     

Importance of Reference Dataset Improvements for Argo Delayed-Mode Quality Control

For the Argo Project, monitoring the global upper ocean by a large number of profiling floats, maintaining the quality of salinity data is critical; the goal for measurement accuracy is ±0.01. Experiments using the method of Wong et al. (2003), the standard delayed-mode quality control (dQC) for the Project, show that its performance depends critically on the reference datasets used. This study concludes that the method is useful for Argo and has sufficient potential to achieve the goal for salinity measurement in the North Pacific, when suitable reference datasets are prepared. Considering the Wong et al. (2003) algorithms, we suggest that reference datasets with the following characteristics will be most suitable for Argo dQC: They should be basically derived from the most extensive datasets, such as the latest World Ocean Database; in regions with denser observations, datasets with carefully quality controls should be used; in the regions with subsurface temperature inversions, such as the subarctic North Pacific, the profiles used for the reference must extend below the deepest temperature maximum to prepare proper salinities for the deep layer reference.     

Determination of water component age in ocean models: application to the fate of North Atlantic Deep Water

A method allowing the calculation of both concentration and age of an individual water component is used to examine the penetration and fate of North Atlantic Deep Water (NADW) in a global ocean model. The method is consistent with the recent theory of water component age by Delhez et al. Its application in ocean models is straightforward and involves specification of two ideal tracers, and its efficacy is verified here via comparison with water component ages obtained by a second method, involving the time history of a single ideal tracer, and whose application is rather more restricted. Age estimates by the two methods are compared in the case of an interior ocean source region (suitable for marking the model's NADW, and forming the main focus of the study) and in the case of a ocean surface source region (featuring high density surface water in the far Northern Atlantic). The concentration and age of NADW are determined for two versions of the model, differing only in the inclusion or exclusion of isoneutral diffusion. The age and, especially, the concentration of NADW in the deep Southern, Indian and Pacific Oceans are significantly lower in the version with isoneutral diffusion. Both versions indicate that most of the NADW ultimately reaches the surface in the model Southern Ocean.     

Improvement of short-termforecasting in the northwest Pacific through assimilating Argo data into initial fields

The impact of assimilating Argo data into an initial field on the short-term forecasting accuracy of temper- ature and salinity is quantitatively estimated by using a forecasting system of the western North Pacific, on the base of the Princeton ocean model with a generalized coordinate system （POMgcs）. This system uses a sequential multigrid three-dimensional variational （3DVAR） analysis scheme to assimilate observation da- ta. Two numerical experiments were conducted with and without Argo temperature and salinity profile data besides conventional temperature and salinity profile data and sea surface height anomaly （SSHa） and sea surface temperature （SST） in the process of assimilating data into the initial fields. The forecast errors are estimated by using independent temperature and salinity profiles during the forecasting period, including the vertical distributions of the horizontally averaged root mean square errors （H-RMSEs） and the horizontal distributions of the vertically averaged mean errors （MEs） and the temporal variation of spatially averaged root mean square errors （S-RMSEs）. Comparison between the two experiments shows that the assimila- tion of Argo data significantly improves the forecast accuracy, with 24% reduction of H-RMSE maximum for the temperature, and the salinity forecasts are improved more obviously, averagely dropping of 50% for H-RMSEs in depth shallower than 300 m. Such improvement is caused by relatively uniform sampling of both temperature and salinity from the Argo drifters in time and space.     

Using Argo data to investigate the Meridional Overturning Circulation in the North Atlantic

Using a variety of oceanographic data, including direct volume transports in the Florida Strait, and Argo float profiles and drift velocities at 24°N and 36°N in the North Atlantic, inverse calculations are presented in which the net meridional transport, down to a depth of approximately 1600 m, is estimated at both latitudes for a 5-year period 2003–2007. The upper ocean is divided into seven layers using neutral density, and mass conservation constraints have been applied to a closed box bounded by these latitudes, including the Florida Strait. Ekman layer transports have been included in the top-most layer, and the inverse calculation has solved for changes from the initial reference velocities, Ekman and Florida Strait transports, given a priori estimates on the accuracy of each of these quantities. Solutions with and without transformations due to Mediterranean Water (MW) formation are made. Our results indicate that (1) time-averaged transport estimates derived from Argo have significant less eddy noise than individual hydrographic sections, (2) Argo drift velocities provide information to the inverse solution for the ocean interior, and (3) comparison of the total integrated interior mass transports in the thermocline waters for the period 2003–2007 with the previous estimates based on trans-ocean hydrographic sections shows that, within the errors of our estimation, the upper limb of the Atlantic Meridional Overturning Circulation has not significantly changed since 1957.