Global Ocean Reanalysis Research Articles

Sea Surface Salinity Inversion Model for Changjiang Estuary and Adjoining Sea Area with SMAP and MODIS Data Based on Machine Learning and Preliminary Application

Sea surface salinity (SSS) is one of the most important basic parameters for studying the oceanographic processes and is of great significance in identifying oceanic currents. However, for a long time, the salinity observation in the estuary and coastal waters has not been well resolved due to the technology limitation. In this study, the SSS inversion models for the Changjiang Estuary and the adjacent sea waters were established based on machine learning methods, using SMAP (Soil Moisture Active and Passive) salinity data combined with the specific bands and bands ratios of MODIS (Moderate Resolution Imaging Spectroradiometer). The performance of the three machine learning methods (Random Forest, Particle Swarm Optimization Support Vector Regression (PSO-SVR) and Automatic Machine Learning (TPOT)) are compared with accuracy verification by the in-situ measured SSS. Random Forest is proven to be effective for the SSS inversion in flood season, whereas TPOP performs the best for the dry season. The machine learning-based models effectively solve the problem of insufficient time span of SSS observation from salinity satellites. At the same time, an empirical algorithm was established for the SSS inversion for the sea areas with low salinity (<30 psu) where the machine learning based model fails with great errors. The average deviation of the complex SSS inversion models is −0.86 psu, validated with Copernicus Global Ocean Reanalysis Data. The long term series SSS dataset of March and August from 2003 to 2020 was then constructed to observe the salinity distribution characteristics of the flood season and the dry season, respectively. It is indicated that the distribution pattern of CDW can be divided into three categories: northeast-oriented expansion pattern, multi direction isotropic expansion pattern, and a turn pattern of which CDW shows changing direction, namely the northeast-southeast expansion pattern. The pattern of CDW expansion is indicated to be the comprehensive effect of the interaction of different currents. In addition, it is noteworthy that CDW shows increasing expansion with decreasing SSS in the front plume, especially in the flood season. This study not only gives a feasible solution for effective SSS observation, but also provides a dataset of basic oceanographic parameters for studying the coastal biogeochemical processes, evolution of land-sea interaction, and changing trend of material and energy transport by the CDW in the west Pacific boundary.

Study of storm-induced changes in circulation and temperature over the northern South China Sea during Typhoon Linfa

Hydrodynamic responses of the northern South China Sea (nSCS) to Typhoon Linfa in 2009 are examined using observations and model results. A shelf circulation model based on the Regional Ocean Modelling System (ROMS-nSCS) is used in quantifying the important physical processes affecting the storm-induced changes in circulation and hydrography in the upper ocean during Linfa. The ROMS-nSCS is forced by atmospheric forcing taken from the Climate Forecast System Reanalysis (CFSR). A parametric vortex is inserted into the CFSR atmospheric forcing to improve winds and sea-level air pressures associated with Linfa. The lateral open boundary condition of ROMS-nSCS is specified based on the global ocean circulation reanalysis produced by the Hybrid Coordinate Ocean Model (HYCOM). The simulated upper ocean circulation produced by ROMS-nSCS is characterized by strong wind-driven currents over the area affected directly by Linfa and intense near-inertial oscillations (NIOs) in the wake of Linfa. The simulated cooling in the wake of the storm is biased to the right of the storm track and agrees well with satellite-derived analysis data. The simulated NIOs also have significant rightward biases. The rotary spectral analysis of model currents demonstrates that the peak frequency fp of NIOs is about 9% greater than the local inertial frequency, which can be explained mostly by the vorticity of the background circulation. Analysis of model results also reveal that different dynamics are responsible for storm-induced cooling at different stages of Linfa. In the early development stage of Linfa, the cooling in the wake of the storm is affected mostly by the storm-induced advection in the vertical. In the mature stage of Linfa, the cooling in the wake of the storm is dominated by the joint effect of the storm-induced mixing and advection. Storm-induced warming occurs outside the wake of Linfa, due to downwelling generated by the storm.

Spatio-temporal analysis of east greenland polar front

The East Greenland Polar Front (EGPF) is an important front with strong salinity and temperature gradients in the Nordic Seas. It is formed by the interaction between Arctic-origin and Atlantic-origin water. The variations of EGPF are closely linked with sea ice melting and heat content transport associated with North Atlantic water recirculation. For a three-dimensional (3D) daily analysis, we use the global ocean eddy resolution reanalysis product (GLORYS12V1) from 1993 to 2018 to calculate the salinity and temperature horizontal gradient in the upper ocean and obtain the spatiotemporal distribution and intensity characteristics of EGPF. After assessment, the thresholds of the salinity and temperature fronts are set to 0.04 psu/km and 0.09°C/km, respectively. Compared with satellite observations of sea ice concentration, a significant spatial relationship is observed between the main position of EGPF and the ice edge before the sea ice shrinks to the continental shelf sea area. Affected by the freshening of the Arctic-origin water due to the melting of the sea ice, the intensity and area of EGPF show significant seasonal variations. Against the background of global warming, the sea ice area presents an obvious decreasing trend in the Greenland Sea. The melting of sea ice increased annually every summer from 1998 to 2018. The heat content transport of the Atlantic-origin water has also increased in recent years. The 3D characteristics (intensity and volume) of EGPF as salinity and temperature fronts exhibit increasing trends.

Dynamical Controls of the Eastward Transport of Overwintering Calanus finmarchicus From the Lofoten Basin to the Continental Slope

AbstractDiapausing populations of Calanus finmarchicus at depth in the Lofoten Basin (LB) return to the continental shelf and slope off the Lofoten‐Vesterålen Islands during the phytoplankton spring bloom to feed and spawn, forming surface swarms with a great abundance. To study how overwintering populations of C. finmarchicus move with the deep currents and return to the shelf, Lagrangian transport characteristics of particles in deep water between 2008 and 2019 were analyzed using Global Ocean Reanalysis and Simulation re‐analysis data and Lagrangian Coherent Structures (LCSs). Our analyses revealed that persistent eastward transport of diapausing C. finmarchicus between LB and continental slope occurred mainly between 600 and 1,100 m in the Arctic Intermediate Water. The consistency of the vertical distributions of C. finmarchicus abundance and salinity further suggests that physical factors control the horizontal distribution of the species. Hovmöller diagrams of kinetic energy indicate that there is an eastward advection of mean current at depth. The co‐occurrence between the eastward transport of LCSs and the eastward advection of the mean current provides direct evidence that the life history of C. finmarchicus is subjected to physical control in the Norwegian Sea.

Multiscale Energy Transfers and Conversions of Kuroshio in Luzon Strait and Its Adjacent Regions

Using the local multiscale energy and vorticity analysis (MS-EVA) and based on the global high-resolution ocean reanalysis product GLORYS12V1 for 20 years, this study investigates the energy transfers and conversions of Kuroshio in the Luzon Strait and its adjacent regions through three scales, namely, the climatological scale, the seasonal scale, and the eddy scale. The results show that the inverse cascades of kinetic energy dominate the energy transfer east of Luzon (at both the eddy and seasonal scales). Kuroshio transfers the climatological kinetic energy to the eddy scale through a forward energy cascade in Luzon Strait and east of Taiwan. Because the topography of Luzon Strait and Kuroshio jointly block and limit the westward propagation of non-local eddies, the eddy energy in the South China Sea west of Luzon Strait tends to depend on local forward potential energy cascades. In these subregions, potential energy drives the accumulation of kinetic energy under the action of buoyancy conversion: interannual (seasonal) potential energy as the source of multiscale energy in the Luzon Strait (the east of Taiwan).

Вклад мезомасштабных вихрей Лофотенской котловины в ее энергетику

A comparative assessment of the contribution of eddies and other dynamic structures to the energy of the Lofoten Basin is carried out. The basis of the study is the data of global ocean reanalysis GLORYS12V1 for 1993–2019. We estimate the total kinetic and potential energy as well as the corresponding contribution of eddy energy for a region bounded by an isobath of 3000 m. We use the method of automatic identification of vortices for the analysis which allows us to calculate the eddy kinetic and potential energy in the automatically selected areas of the eddies. We establish that the potential energy of both cyclones and anticyclones is on average 2–3 times higher than the kinetic
 energy values, and the energy values of kinetic and potential for anticyclones dominate relative to the energy of cyclones. We also consider the interannual variability and seasonal course of eddy kinetic and potential energy. The seasonal course revealed an increase in both types of energy in the winter months. It is established that the contribution of eddies to the total energy of the basin is small. The contribution of eddy kinetic energy to the total energy of the basin is 7.3%, and the contribution of eddy potential energy is 8.4%. This means that the main contribution to the energy of the basin is made not by mesoscale eddies, but by other dynamic structures i.e. filaments and background flow.

A global ensemble of ocean wave climate statistics from contemporary wave reanalysis and hindcasts

There are numerous global ocean wave reanalysis and hindcast products currently being distributed and used across different scientific fields. However, there is not a consistent dataset that can sample across all existing products based on a standardized framework. Here, we present and describe the first coordinated multi-product ensemble of present-day global wave fields available to date. This dataset, produced through the Coordinated Ocean Wave Climate Project (COWCLIP) phase 2, includes general and extreme statistics of significant wave height (Hs), mean wave period (Tm) and mean wave direction (θm) computed across 1980–2014, at different frequency resolutions (monthly, seasonally, and annually). This coordinated global ensemble has been derived from fourteen state-of-the-science global wave products obtained from different atmospheric reanalysis forcing and downscaling methods. This data set has been processed, under a specific framework for consistency and quality, following standard Data Reference Syntax, Directory Structures and Metadata specifications. This new comprehensive dataset provides support to future broad-scale analysis of historical wave climatology and variability as well as coastal risk and vulnerability assessments across offshore and coastal engineering applications.

The Irrawaddy River Jet in the Andaman Sea During the Summer Monsoon

The Irrawaddy (IR) is the largest river discharging into the Andaman Sea and plays an important role in the salinity distribution and the mixed layer physics of the Andaman Sea. This study presents the first report of the IR plume pathways in the Andaman Sea during the summer monsoon and the mechanisms behind them. An ocean circulation model is employed to conduct idealized experiments in which the freshwater forcing, due to rivers other than IR as well as precipitation, are ignored. Our simulations reveal that, during the summer monsoon, the discharge from Irrawaddy spreads as a freshwater jet oriented towards southeast and accumulates over the shelf at the eastern coast of the Andaman Sea. Climatology of Chlorophyll-a concentration measured by satellite and surface currents from global ocean model reanalysis indicates the presence of the Irrawaddy freshwater jet during the summer monsoon. The evolution of surface salinity and currents along the jet suggests that the IR freshwater traps momentum imparted by winds. The momentum balance in the Irrawaddy jet is between Coriolis and wind friction term, indicating that the freshwater jet is completely driven by winds during the summer monsoon. Surface distribution of wind friction term also shows that the northwest-southeast orientation of the Irrawaddy jet is due to the southwesterly orientation of the summer monsoon winds. Further experiments with three different wind forcing scenarios (no winds, winds over the equator only, and winds over the Bay of Bengal only) reveal that the flow of Irrawaddy jet during the summer monsoon is completely controlled by the local winds.

A northeast United States Atlantis marine ecosystem model with ocean reanalysis and ocean color forcing

The northeast United States Atlantis model (NEUSv2) is an end-to-end ecosystem model that can simulate biogeochemical, ecological, fishery, management, and socio-economic processes within marine ecosystems. As a major update to the original model, NEUSv2 includes changes to the model's functional group definitions and forcing data. NEUSv2 is the first Atlantis model to use a satellite-ocean-color-derived phytoplankton size class model that was tuned specifically for the region to force marine primary production. Additionally, physical ocean variables (currents, temperature, and salinity) were updated using a high-resolution global ocean reanalysis. Despite its coarse resolution, NEUSv2 was capable of reproducing the broad spatial patterns seen in the physical and biological forcing sources, with the exception of some circulation features. NEUSv2 produced plausible zooplankton and planktivore biomass, a stable lower trophic food web, and recent trends in zooplankton biomass. NEUSv2 meets calibration criteria for the persistence and long-term stability of functional group biomass. Given the success of this new Atlantis forcing approach, we detail the observations and challenges regarding spatial scale-related processes, data assimilation, and biological calibration. We also discuss possible tradeoffs with model scope, calibration, and the availability of feedback mechanisms. This NEUSv2 hindcast is well suited for exploring ecosystem-level sensitivity to lower trophic processes and for testing alternative biogeochemical forcing. Further developments will improve model performance for higher trophic levels.

Investigating of the two-core structure of the Atlantic North Equatorial Countercurrent with the GLORYS12V1 reanalysis

Twenty-six years of the high-resolution global ocean reanalysis GLORYS12V1 are used to investigate the temporal and spatial variability of the two-core structure of the North Equatorial Counter Current (NECC) in the western and central tropical Atlantic. The two cores of the NECC exhibit mean positions of 6.3°N±1.4° and 9.7°N±1°, and of 5.4°N±1.1° and 8.9°N±0.9° respectively in the area west of 32°W and in the area between 32°W and 22°W. Both areas witness a semi-annual cycle of the position of the southern core with northernmost positions respectively in May and July, and in March and July. The transport of the branch associated to the southern cores shows annual cycles with maxima occurring in August (>17 Sv) and July (>7 Sv) respectively in the western and central areas. The annual cycle in the West is influenced by the wind stress curl (WSC) strength. The central area might be influenced by a return flow of the northern branch of the South Equatorial Current over the central Atlantic. At the opposite, the transport associated with the NECC’s northern core shows the same annual cycles with maxima occurring in September in both areas. This transport of the NECC shows seasonal cycles leaded by the WSC strength with 1-month lag. 83% and 71% of the total transport between the first 150 m-depth is above the thermocline respectively in the western and central areas. In the West, the northern core transport shows year-to-year variations associated with the WSC strength, while the southern core position of the NECC in the central tropical Atlantic appears influenced by the InterTropical Convergence Zone migration.

An Intercomparison of Global Reanalysis Products for Southern Africa’s Major Oceanographic Features

A regional assessment of three global ocean reanalysis products is presented for southern Africa’s major oceanographic features. The reanalyses include Mercator Ocean’s Global Reanalysis (GLORYS), the Commonwealth Scientific and Industrial Research Organisation’s (CSIRO) Bluelink Reanalysis (BRAN) and the Fleet Numerical Meteorology and Oceanography Center’s (FNMOC) global Hybrid Coordinate Ocean Model (HYCOM) reanalysis. The aim is to provide modelers with sufficient information for selecting the appropriate product for use as boundary conditions to force their regional ocean models, as well as to provide marine industries, relevant government agencies and academics with insight into the optimal reanalysis product for their purposes. The reanalyses are compared to both assimilated and independent observational datasets spanning various regions within the southern African marine environment. While all reanalysis products reproduce the eastern and western boundary current systems surrounding southern Africa, limitations exist. BRAN outperforms the other reanalyses in its representation of the Mixed Layer Depth, contributing to its good representation of coastal SSTs in the Benguela upwelling system, whereas GLORYS and HYCOM’s misrepresented MLD result in significant warm biases in this region. The Angola-Benguela Frontal Zone and it’s variability is best reproduced by BRAN and HYCOM. The Agulhas Current system’s major components are well reproduced by both GLORYS and BRAN. HYCOM, however, simulates considerably more early retroflections than are observed which have resulted in its mean eastward location. While all the reanalyses overestimate the occurrence of Agulhas meanders, GLORYS and BRAN resolve the associated variability best. Agulhas Current transport is best resolved by GLORYS, unlike BRAN and HYCOM which largely overestimate the magnitude of its south-westward flow, linked to their misrepresentation of the Current’s vertical structure. The bay-scale and nearshore evaluations highlighted issues pertaining to the resolution of the reanalyses and their use at such a small scale. The reanalyses are limited by their resolution, as well as by their misrepresentation of submesoscale processes or lack thereof, prompting the need for the development of regional downscaled models in and around the southern African oceans based on the global ocean reanalysis products.

Topographically Trapped Waves Around South America With Periods Between 40 and 130 Days in a Global Ocean Reanalysis

AbstractThe South American continental slope hosts a variety of topographic waves. We use a 27‐year‐long global ocean reanalysis (1/12° Spatial resolution) to examine trapped waves (TWs) around South America at periods ranging from 40 to 130 days. The waves propagate from the Equatorial Pacific to the Tropical Atlantic (22°S) with phase velocities between 1.8 and 7 m/s according to the local background characteristics, such as stratification, slope steepness, latitude, mean flow and shelf width. The Madden‐Julian Oscillation (MJO) plays a key role in forcing the TWs in two ways (a) through an oceanic connection implying equatorial Kelvin waves reaching the western American Coast and (b) through an atmospheric teleconnection enhancing southerly winds in the south‐east Pacific. Furthermore, local winds, not necessarily linked with the MJO, modulate and trigger waves in specific locations, such as the Brazil‐Malvinas Confluence. Trapped waves impact the along‐shore currents: during the positive phase of the waves the near‐surface flow is enhanced by about 0.1 m/s.

Intraseasonal variability of the Indonesian throughflow associated with the Madden-Julian Oscillation

Intraseasonal variability (20–90 days) of the Indonesian Throughflow (ITF), which is primarily forced by the Madden-Julian Oscillation (MJO), is investigated using a high-resolution global ocean reanalysis and satellite altimeter data. Previous studies show that during the MJO active phase, downwelling Kelvin waves generated in the central equatorial Indian Ocean propagate along the coast of Sumatra and Java islands, affecting the ITF transport at exit passages in the Indonesian Seas and Makassar Strait. However, the intraseasonal variation of the ITF transport through these straits over the MJO life cycle, especially during the suppressed phase, has not been quantified. To quantify the ITF transport associated with the MJO, composites of ITF transport through major straits in the Indonesian Seas are constructed using a 0.08° global HYbrid Coordinate Ocean Model (HYCOM) reanalysis. A prominent reduction of ITF transport through major straits is found during the MJO active phase, and a transport enhancement comparable to the reduction is evident during the suppressed phase. As a result, the net effect of the MJO on the mean ITF transport is very small due to the cancellation of the enhancement and reduction. The magnitude of the MJO-associated ITF transport variation through all ITF exit passages is about 6 Sv, which is about 50% of the total transport. While the propagation of coastal Kelvin waves during the MJO active phase and their impact on ITF transport is clearly evident in the composite, such Kelvin wave influence on ITF transport is not clearly detected during the suppressed phase. This suggests that anomalous winds over the Maritime Continent (MC) area are mostly responsible for the ITF variation during the suppressed phase in many MJO events. Yet, during some MJO events, remotely-forced upwelling Kelvin waves and their significant impact on the ITF transport are evident during the MJO suppressed phase.

Interannual Variability of the Latitude of Separation of the Brazil Current: Teleconnections and Oceanic Rossby Waves Propagation

AbstractThe latitude of separation of the Brazil Current (LSBC) variability is analyzed with a view to unveiling the physical mechanisms that modulate the turning point of the Brazil Current at low frequencies. The global ocean reanalysis ORAP5.0 spanning the period 1979–2013 is employed for this purpose. Three characteristic periodicities of the LSBC variability are found on the basis of a Singular Spectrum Analysis: 2, 4 and 10 years. Lagged sea surface height (SSH) correlation maps relate these modulations to Rossby wave propagation. According to these maps, the biennial signal might be triggered by the Atlantic Niño and the Indian Ocean Dipole. In the last case, SSH anomalies propagate around the southern tip of Africa, connecting the Indian and Atlantic oceans. Correlation maps suggest that the 4‐year signal is triggered by both the Atlantic Niño and the ENSO in the equatorial Pacific Ocean. The ENSO‐related anomalies travel through the Indonesian Throughflow along the western Australian coast, where Rossby waves are excited. These anomalies propagate to the eastern coast of Madagascar and feed into the Agulhas Current, eventually leaking into the Atlantic basin. Finally, the decadal signal is associated to the leading mode of decadal variability of the South Pacific Ocean. SSH propagating patterns derived from ORAP5.0 data are also obtained with satellite altimetry during the overlapping period (1993–2013), which strengthens confidence in our results. The association of the LSCB modulations to characteristic climate variability modes suggests that the position of the LSCB could be predicted.

The Copernicus Global 1/12° Oceanic and Sea Ice GLORYS12 Reanalysis

GLORYS12 is a global eddy-resolving physical ocean and sea ice reanalysis at 1/12° horizontal resolution covering the 1993-present altimetry period, designed and implemented in the framework of the Copernicus Marine Environment Monitoring Service (CMEMS). The model component is the NEMO platform driven at the surface by atmospheric conditions from the ECMWF ERA-Interim reanalysis. Ocean observations are assimilated by means of a reduced-order Kalman filter. Along track altimeter sea level anomaly, satellite sea surface temperature and sea ice concentration, as well as in situ temperature and salinity vertical profiles are jointly assimilated. A 3D-VAR scheme provides an additional correction for the slowly-evolving large-scale biases in temperature and salinity. The performance of the reanalysis shows a clear dependency on the time-dependent in situ observation system. The general assessment of GLORYS12 highlights a level of performance at the state-of-the-art and the capacity of the system to capture the main expected climatic interannual variability signals for ocean and sea ice, the general circulation and the inter-basins exchanges. In terms of trends, GLORYS12 shows a higher than observed warming trend together with a slightly lower than observed global mean sea level rise. Comparisons made with an experiment carried out on the same platform without assimilation show the benefit of data assimilation in controlling water mass properties and sea ice cover and their low frequency variability. Moreover, GLORYS12 represents particularly well the small-scale variability of surface dynamics and compares well with independent (non-assimilated) data. Comparisons made with a twin experiment carried out at 1/4° resolution allows characterizing and quantifying the strengthened contribution of the 1/12° resolution onto the downscaled dynamics. GLORYS12 provides a reliable physical ocean state for climate variability and supports applications such as seasonal forecasts. In addition, this reanalysis has strong assets to serve regional applications and provide relevant physical conditions for applications such as marine biogeochemistry. In the near future, GLORYS12 will be maintained to be as close as possible to real time and could therefore provide relevant and continuous reference past ocean states for many operational applications.

Assessing Eddying (1/12°) Ocean Reanalysis GLORYS12 Using the 14‐yr Instrumental Record From 59.5°N Section in the Atlantic

AbstractThe eddy‐resolving (1/12°) global ocean reanalysis GLORYS12 is assessed against 14 years (2002–2015) of independent hydrographic observations collected at 59.5°N in the North Atlantic. Two multi‐observations statistical analyses, ISAS‐15 and ARMOR‐3D, and an eddy‐permitting (1/4°) reanalysis, GLORYS025, also contribute to this comparison. The mean thermohaline structure along the 59.5°N section revealed by the observations is well‐reproduced by GLORYS12, except for the overflow waters. A good agreement with observations is found for linear trends over the whole period, exhibiting a dipole‐like pattern with a cooling/freshening in the main thermocline and a warming/salinization below. However, localized discrepancies with observations suggest the need for improvement in the reanalysis system (especially in the overflows representation and the consistency between the forcing and data assimilation system) and the deep observational array. The reanalysis reliably represents the ocean heat content in the upper 700‐m layer but shows significant differences with observations between 700 and 2,000 m. The meridional volume and heat transports across the 59.5°N section are compared for years when ADCP observations were available. The reanalysis does not reproduce the variability observed in the western boundary current but agrees well with observed transports in the other parts of the section. The reanalysis reproduces the major mesoscale eddy features that contribute to the meridional transport and provides the large‐scale context of their location. The analysis of time correlation at all measurement points demonstrated that GLORYS12 is the most accurate among the analyzed datasets used in this study to represent and explain the observed ocean characteristics and variability along that section.

Global implications of surface current modulation of the wind-wave field

The influence of ocean surface currents on the global wind-wave field is revisited. State-of-the-art numerical spectral wave model simulations with and without surface currents taken from an eddy resolving global ocean reanalysis were compared. As a global average, simulations forced with currents display significantly better agreement with altimeter derived wave heights. The bias and root mean square error in significant wave heights are mostly reduced when including current forcing, especially in the Southern Ocean. An overall improvement in wave periods and wave direction is also seen when comparing model outputs with the Australian and United States buoy network observations. Including surface ocean current forcing in wave simulations reduces the simulated wave heights in most areas of the world, due to a decreased relative wind given by co-flowing winds and currents. Current-induced refraction generates important changes in wave direction in western boundary current and tropical regions. Furthermore, large and broad changes in friction velocity, atmosphere-to-ocean energy flux, whitecap cover and Stokes drift velocities are observed in equatorial regions. Finally, the importance of the wave model resolution for representing wave–current interactions was tested by comparing results from eddy-permitting (lower resolution) and eddy-resolving (higher resolution) configurations. We conclude that the main patterns of current-induced refraction are well represented in both cases, albeit that the higher resolution simulation represents these in a more detailed manner. Finally, the implications that the observed wave–current interactions have on several ocean processes are discussed.

Evaluation of global high-resolution reanalysis products based on the Chinese global oceanography forecasting system: 基于中国全球海洋预报系统(CGOFS)的全球高分辨率再分析产品评估

The global high-resolution marine reanalysis products that were independently developed by the National Marine Environmental Forecasting Center based on the Chinese Global Oceanography Forecasting System (CGOFS), are evaluated by comparing their climatologies with internationally recognized data from WOA (Word Ocean Atlas), SODA (Simple Ocean Data Assimilation), AVISO (Archiving, Validation, and Interpretation of Satellite Oceanographic Data), and C-GLORS (Global Ocean Reanalysis System). The results show that the SST RMSEs of CGOFS and SODA against WOA are 0.51 °C and 0.43 °C respectively; and in the North Pacific, the SST of CGOGS is closer to that of WOA than SODA. The SSS RMSEs of CGOFS and SODA compared with WOA are 0.48 PSU and 0.40 PSU, respectively. CGOFS can reproduce the main large-scale ocean circulation globally, and obtain a similar vertical structure of the Equatorial Undercurrent as SODA. The RMSE of the CGOFS global sea-level anomaly against AVISO is 0.018 m. The monthly averaged sea-ice extents are between those of SODA and C-GLORS in each month; the growth and ablation characteristics of the ice volume are consistent with SODA and C-GLORS; but the ice volume of CGOFS is greater than that of SODA and C-GLORS. In general, the climatology of the CGOFS global high-resolution reanalysis products are basically consistent with similar international products, and can thus provide reliable data for the improvement of marine science and technology in China.摘要通过同化系统将观测资料与海洋数值模式融合得到的海洋再分析产品为海洋科学研究提供了重要的资料基础.本文采用WOA,SODA,AVISO和GLORS四种数据资料与我国自主研发的中国全球海洋预报系统(CGOFS)的气候态结果进行了对比, 结果表明:CGOFS和SODA的全球海表面温度与WOA的均方根误差分别为0.51 和 0.43°C.CGOFS和SODA的海表面盐度与WOA的均方根误差分别为0.48和0.40 PSU;海流方面, CGOFS能较好的刻画主要大洋环流分布及赤道潜流的垂向结构;CGOFS的全球海表面高度异常与AVISO的均方根误差为0.018m;多年月平均海冰外缘线覆盖面积介于SODA 和 GLORS之间, 海冰体积的生消规律与SODA 和 GLORS一致.总体来看, CGOFS全球高分辨率海洋再分析产品的气候态结果与国际同类产品基本一致, 可为提升我国海洋综合科技实力提供可靠的资料保障.

SAM-driven variability of the southwestern Atlantic shelf sea circulation

The objective of the present study is to analyze the interannual variability of the Southwestern Atlantic Continental Shelf (SWACS) circulation and its thermohaline structure. To accomplish it we employed the global ocean reanalysis ORAP5.0, which spans the 35-years period 1979–2013. ORAP5.0 satisfactorily reproduces the most distinctive features of the SWACS circulation and its variability on different timescales, including the interannual scale. The first mode of a joint empirical orthogonal function (EOF) analysis of sea surface temperature (SST), sea surface salinity (SSS), and vertically averaged horizontal velocities is significantly correlated with the first mode of interannual variability of the atmosphere in the Southern Hemisphere, the Southern Annular Mode (SAM). Remarkably, the shelf sea response has been found to be statistically significant not only in the Patagonian Shelf (south of 40 °S), as discussed in the literature, but also in the Northern Shelf (north of 40°S). During the active phases of the leading mode, current anomalies develop as a result of the sea surface height adjustment to Ekman transport at the coastline induced by alongshore wind anomalies. Modification of the advection terms in the salinity and heat budgets due to changes in the circulation and heat surface fluxes generate SST and SSS anomalies along the SWACS. It is suggested that these anomalies drive changes in the mixed layer depth and that these changes can modulate the interannual variability of the chlorophyll-a concentration during austral spring in the frontal zones.

The Río de la Plata plume dynamics over the Southwestern Atlantic Continental Shelf and its link with the large scale atmospheric variability on interannual timescales

The interannual variability of the Río de la Plata plume over the Southwestern Atlantic Continental Shelf is analyzed based on the global ocean reanalysis ORAP5.0 and the global atmospheric reanalysis Era-Interim for the 35-years period 1979–2013. A regional validation of the dataset is performed to evaluate the ocean reanalysis ability to solve the main features associated with the plume dynamics. Following the satisfactory evaluation, an Empirical Orthogonal Function analysis is performed to extract characteristic modes of variability of the sea surface salinity. Three leading modes explain 35%, 30% and 15% of the total variance and are associated with large scale atmospheric variability patterns characteristic of the Southern Hemisphere circulation. Mode 1 is characterized by marked salinity anomalies to the south and north of the RdlP Estuary mouth. Its particular imprint is associated with an organized alongshelf wind structure modulated by the Southern Annular Mode (SAM). Mode 2 presents salinity anomalies that extend from the RdlP Estuary to the Uruguayan and southern Brazilian coasts and is related to interannual variability of the RdlP discharge and to regional wind forcing over the plume. Both the river outflow and the atmospheric forcing over the shelf are strongly associated with the Pacific South American pattern (PSA1). Finally, mode 3 presents large salinity anomalies at 38°S, south of the mouth of the RdlP Estuary and is associated with displacements of the freshwater plume due to local wind stress anomalies over the estuary, which are modulated by the PSA2.