Ocean Products Research Articles

Improving Water Leaving Reflectance Retrievals from ABI and AHI Data Acquired Over Case 2 Waters from Present Geostationary Weather Satellite Platforms

The current generation of geostationary weather satellite instruments, such as the Advanced Baseline Imagers (ABIs) on board the US NOAA GOES 16 and 17 satellites and the Advanced Himawari Imagers (AHIs) on board the Japanese Himawari-8/9 satellites, have six channels located in the visible to shortwave IR (SWIR) spectral range. These instruments can acquire images over both land and water surfaces at spatial resolutions between 0.5 and 2 km and with a repeating cycle between 5 and 30 min depending on the mode of operation. The imaging data from these instruments have clearly demonstrated the capability in detecting sediment movements over coastal waters and major chlorophyll blooms over deeper oceans. At present, no operational ocean color data products have been produced from ABI data. Ocean color data products have been operationally generated from AHI data at the Japan Space Agency, but the spatial coverage of the products over very turbid coastal waters are sometimes lacking. In this article, we describe atmospheric correction algorithms for retrieving water leaving reflectances from ABI and AHI data using spectrum-matching techniques. In order to estimate aerosol models and optical depths, we match simultaneously the satellite-measured top of atmosphere (TOA) reflectances on the pixel by pixel basis for three channels centered near 0.86, 1.61, and 2.25 μm (or any combinations of two channels among the three channels) with theoretically simulated TOA reflectances. We demonstrate that water leaving reflectance retrievals can be made from ABI and AHI data with our algorithms over turbid case two waters. Our spectrum-matching algorithms, if implemented onto operational computing facilities, can be complimentary to present operational ocean versions of atmospheric correction algorithms that are mostly developed based on the SeaWiFS type of two-band ratio algorithm.

Importance of Boundary Processes for Heat Uptake in the Subpolar North Atlantic

AbstractThe decadal to multidecadal temperature variability of the intermediate (700–2,000 m) North Atlantic Subpolar Gyre (SPG) significantly imprints the global pattern of ocean heat uptake. Here, the origins and dominant pathways of this variability are investigated with an ocean analysis product (EN4), an ocean state estimate (ECCOv4), and idealized modeling approaches. Sustained increases and decreases of intermediate temperature in the SPG correlate with long‐lasting warm and cold states of the upper ocean with the largest anomalous vertical heat exchanges confined to the vicinity of continental boundaries and strong ocean currents. In particular, vertical diffusive processes along the boundaries of the Labrador, Irminger, and Newfoundland basins are important drivers of the recent intermediate depth warming trend observed during 1996–2014. The overall effect of those processes is captured by a one‐dimensional diffusive model with appropriate boundary‐like parametrization and demonstrated through the boundary‐focused downward propagation of a passive tracer in a 3‐D numerical simulation. Our results imply that the slow and quasi‐periodic ventilation of intermediate thermohaline properties and associated heat uptake in the SPG are not strictly driven by convection‐restratification events in the open seas but also receives a key contribution from boundary sinking and mixing. Increased skill for modeling and predicting intermediate‐depth ocean properties in the North Atlantic will hence require the appropriate representation of surface‐deep dynamical connections within the boundary currents encircling Greenland and Newfoundland.

On Removal of Sea State Contribution to Sentinel‐1 Doppler Shift for Retrieving Reliable Ocean Surface Current

AbstractThe Doppler frequency shift acquired by Synthetic Aperture Radar (SAR) contains information about ocean surface motion induced by waves and the underlying ocean currents in the radar range direction. An accurate estimate of the wave‐induced contribution is therefore required to derive a reliable estimation of the ocean surface current. In this study, we developed an empirical model for estimating the wave‐induced Doppler shift based on Sentinel‐1B Wave Mode (WV) Level 2 Ocean products acquired from December 2017 to January 2018 collocated with wind field from ECMWF and wavefield from WAVEWATCH III. We found that the relationship between the wind field at 10 m height and the Doppler shift from Sentinel‐1 is in agreement with previous findings based on ASAR observations. Retraining of the conventional CDOP model for the Sentinel‐1 observations (CDOP‐S) yields distinct improvements. We speculate that the improvement is due to different sensor properties and hence biases in the data. Moreover, combing wave and wind information into the model yield considerable improvements especially for the Southern Ocean and the North Pacific. Given accurate wave bias correction, the ocean surface radial velocity maps based on 2 months of Sentinel‐1 acquisitions agree with ocean surface current climatology derived from multiyear drifter observations. This suggests that Sentinel‐1 Doppler shift observations can be used to study ocean surface currents with 20 km spatial resolutions at a monthly time scale.

Inconsistent Atmosphere‐Ocean Dynamics and Multidecadal Zonal SST Gradient Trends Across the Equatorial Pacific Ocean in Reanalysis Products

AbstractOcean reanalysis products are routinely employed as reality checks in model evaluations and for process studies. This is especially so for critical regions such as the equatorial cold tongue (ECT) in the eastern equatorial Pacific where models suffer a chronic cold bias. ECT is a major player in the Pacific equatorial zonal sea surface temperature (SST) gradient (ΔEWSST) that has a significant impact on oceanic heat uptake and thus global climate. Hence, we investigate the reliability of three ocean reanalysis products for surface flux and ocean dynamic controls on ΔEWSST and Niño3.4 SST trends. We infer that while Niño3.4 SST trends are positive in all products, the signs of ΔEWSST trends do not agree with each other because initial conditions likely play a big role in their evolution. However, for ΔEWSST trends, the effect of initial conditions gets canceled out to some extent. Mixed layer heat budget and trends in ocean dynamic features such as tropical and subtropical cells, equatorial undercurrent, and subsurface temperatures are also diagnosed. We show that two reanalysis products that show a strengthening of ΔEWSST have contradicting trends in their surface heat flux and ocean dynamic contributions. This suggests that without accurate surface heat and momentum fluxes, data assimilation techniques may produce an east–west trend that is inconsistent among each other. Reanalysis products must address these issues considering the importance of this gradient.

ANN-Based Estimation of Low-Latitude Monthly Ocean Latent Heat Flux by Ensemble Satellite and Reanalysis Products.

Ocean latent heat flux (LHF) is an essential variable for air–sea interactions, which establishes the link between energy balance, water and carbon cycle. The low-latitude ocean is the main heat source of the global ocean and has a great influence on global climate change and energy transmission. Thus, an accuracy estimation of high-resolution ocean LHF over low-latitude area is vital to the understanding of energy and water cycle, and it remains a challenge. To reduce the uncertainties of individual LHF products over low-latitude areas, four machine learning (ML) methods (Artificial Neutral Network (ANN), Random forest (RF), Bayesian Ridge regression and Random Sample Consensus (RANSAC) regression) were applied to estimate low-latitude monthly ocean LHF by using two satellite products (JOFURO-3 and GSSTF-3) and two reanalysis products (MERRA-2 and ERA-I). We validated the estimated ocean LHF using 115 widely distributed buoy sites from three buoy site arrays (TAO, PIRATA and RAMA). The validation results demonstrate that the performance of LHF estimations derived from the ML methods (including ANN, RF, BR and RANSAC) were significantly better than individual LHF products, indicated by R2 increasing by 3.7–46.4%. Among them, the LHF estimation using the ANN method increased the R2 of the four-individual ocean LHF products (ranging from 0.56 to 0.79) to 0.88 and decreased the RMSE (ranging from 19.1 to 37.5) to 11 W m−2. Compared to three other ML methods (RF, BR and RANSAC), ANN method exhibited the best performance according to the validation results. The results of relative uncertainty analysis using the triangle cornered hat (TCH) method show that the ensemble LHF product using ML methods has lower relative uncertainty than individual LHF product in most area. The ANN was employed to implement the mapping of annual average ocean LHF over low-latitude at a spatial resolution of 0.25° during 2003–2007. The ocean LHF fusion products estimated from ANN methods were 10–30 W m−2 lower than those of the four original ocean products (MERRA-2, JOFURO-3, ERA-I and GSSTF-3) and were more similar to observations.

Validation of Sentinel-1 offshore winds and average wind power estimation around Ireland

Abstract. In this paper, surface wind speed and average wind power derived from Sentinel-1 Synthetic Aperture Radar Level 2 Ocean (OCN) product were validated against four weather buoys and three coastal weather stations around Ireland. A total of 1544 match-up points was obtained over a 2-year period running from May 2017 to May 2019. The match-up comparison showed that the satellite data underestimated the wind speed compared to in situ devices, with an average bias of 0.4 m s−1, which decreased linearly as a function of average wind speed. Long-term statistics using all the available data, while assuming a Weibull law for the wind speed, were also produced and resulted in a significant reduction of the bias. Additionally, the average wind power was found to be consistent with in situ data, resulting in an error of 10 % and 5 % for weather buoys and coastal stations, respectively. These results show that the Sentinel-1 Level 2 OCN product can be used to estimate the wind resource distribution, even in coastal areas. Maps of the average and seasonal wind speed and wind power illustrated that the error was spatially dependent, which should be taken into consideration when working with Sentinel-1 Synthetic Aperture Radar data.

Evaluation of remotely sensed prediction and forecast models for Vibrio parahaemolyticus in the Chesapeake Bay

Over the last decade, an increase of gastrointestinal illness due to Vibrio parahaemolyticus in the consumption of raw shellfish has been reported in multiple regions around the United States. Studies mainly attribute this increase to rising sea surface temperatures and prolonged warm seasons in the mid-latitudes. Historically, temperature has been the main environmental determinant used to predict V. parahaemolyticus concentrations in shellfish and surface water. However, studies using in situ sampling campaigns have shown that additional water quality parameters can be useful in predicting the bacterium. While the time and cost of obtaining in situ samples throughout the Chesapeake Bay at regular time intervals can exceed available resources, satellite remote sensing has the potential to provide predictions at higher temporal and spatial resolutions. This study uses satellite ocean color remote sensing and sea surface temperature (SST) from the Moderate Resolution Imaging Spectroradiometer (MODIS) to investigate the utility of remotely sensed information for Vibrio parahaemolyticus predictions in the Chesapeake Bay and whether additional remotely sensed information can improve predictions over conventional SST-based models. We find that the addition of remotely sensed salinity, total suspended solids, and chlorophyll-a generally improves presence and abundance predictions compared to SST-only models. Models using remote sensing reflectances and SST also show potential for V. parahaemolyticus predictions, which could bypass the intermediary step of deriving water quality products from reflectances. Remotely sensed ocean color products and SST from one week prior to in situ V. parahaemolyticus measurements are evaluated and shown to be useful in bacterium predictions, which could provide lead-time for management decisions. The forecast models using ocean color products in addition to SST showed improvement over SST-only forecast models. The results of this study suggest that remote sensing can be a valuable tool to aid in higher resolution V. parahaemolyticus predictions and forecasts in the Chesapeake Bay, particularly when multiple environmental predictors are employed. However, the complexities of using remotely sensed data for ecological modeling applications and evaluating model performance also highlight the need for more research in this area.

Nonlinear effects of marine economic growth and technological innovation on marine pollution: Panel threshold analysis for China's 11 coastal regions

Conventional wisdom has it that marine economic growth and technological innovation help to reduce pollution of the oceans. Few studies, however, have examined whether the relationship is nonlinear and to what extent the effects have been realized. To fill this gap, this study takes 11 coastal regions of China during the period 2000–2016 and, using the panel threshold model, examines the nonlinear effects of per capita gross ocean product (GOP) and marine patents on marine pollution as represented by the quantity of industrial wastewater discharged directly into the sea. The results reveal that the increase in per capita GOP strongly promotes marine pollution across the three phases of panel threshold model, but the degree of influence is gradually declining, implying that China is still located in the first half of the Environment Kuznets Curve (EKC), before the peak. Thus, a negative correlation of the GOP–pollution nexus can be expected if current trends continue, which suggests that the development of the marine economy may alleviate ocean environmental pressures. As for marine patents, no significant correlations in the low- and mid-level phases were found, but a strong impact by marine patents on pollution is shown in the high-level phase, indicating that the accumulation of technological innovation related to the marine economy is playing an increasingly important role in reducing marine pollution. Finally, the numbers of provinces/municipalities in the three phases have been identified. Several important policy implications for development of the marine economy are highlighted.

Interannual Variability of Lower Equatorial Intermediate Current Response to ENSO in the Western Pacific

AbstractThe ocean currents of the tropical Pacific Ocean vary with El Niño‐Southern Oscillation (ENSO) cycles. A mooring time series obtained during 2014–2018 in the western Pacific reveal that interannual variability extends to Lower Equatorial Intermediate Current (LEIC). The LEIC velocity anomalies are significantly correlated with the Niño‐3.4 index at an 11‐month lag. Monthly velocity data from the global ocean physical reanalysis product and from a linear continuously stratified ocean model during 1993–2018 capture the 2015–2016 signal and are used to identify the underlying mechanism. During El Niño (La Niña) events, the direct wind forcing in the central tropical Pacific and the reflection of Kelvin waves in the eastern Pacific during the first autumn‐winter period contribute comparably to an eastward (westward) current anomaly in the western Pacific during the second autumn‐winter period. This process is achieved mainly through the generation of the second baroclinic mode and off‐equatorial westward‐propagating downwelling (upwelling) Rossby waves.

Improving low-quality satellite remote sensing reflectance at blue bands over coastal and inland waters

The satellite remote sensing reflectance (Rrs(λ)) at two short blue bands (410 or 412 nm and 443 nm) are prone to large uncertainties in coastal and inland waters, prohibiting algorithms from generating reliable ocean color products associated with these bands. In this study, we developed an algorithm to estimate Rrs(41×) and Rrs(443) when the satellite Rrs(λ) in blue bands suffer from large uncertainties. The algorithm first determines the Rrs(λ) spectral shape from the satellite-measured Rrs(λ) values at three wavelengths of 48× (486, 488, or 490), 55× (547, 551, or 555), and 67× (667, 670, or 671) nm. The algorithm then derives Rrs(41×) and Rrs(443) from the estimated Rrs(λ) spectral shape with algebraic formulations. We assessed the algorithm performance with satellite (SeaWiFS, MODISA, and VIIRS-SNPP) and in situ Rrs(λ) matchups from global waters. It is shown that the uncertainties of estimated Rrs(41×) and Rrs(443) are substantially smaller than the original satellite products when applicable. Besides, implementation of the algorithm contributes to a significant increase in the number of utilizable Rrs(41×) and Rrs(443) values. The algorithm is relatively stable and is best applicable to the satellite Rrs(λ) spectra for which the Rrs(48×) and Rrs(55×) measurements are subject to small uncertainties. The demonstrations support the application of the blue-band estimation algorithm to a wide range of coastal waters.

Oceanic Processes in Ocean Temperature Products Key to a Realistic Presentation of Positive Indian Ocean Dipole Nonlinearity

AbstractA positive Indian Ocean Dipole (pIOD) refers to a sea surface temperature anomaly pattern with cold anomalies in the equatorial eastern Indian Ocean and warm anomalies in the west, leading to floods in the eastern African countries and droughts and bushfires in Indonesia and Australia. The pIOD displays strong inter‐event differences, ranging from an extreme event dominated by westward‐extended strong cold anomalies along the equator, to a moderate event with weakened cooling confined to region off Sumatra‐Java. Representation of the extreme pIOD varies vastly across ocean temperature products. Here we show that products generated in a system explicitly involving subsurface oceanic processes capture the nonlinear dynamics of the extreme pIOD, i.e., the equatorial nonlinear zonal and vertical advection, and systematically produce a more realistic extreme pIOD. Thus, our study identifies ocean temperature products that are more suitable for studying extreme pIOD and its climatic impacts.

Estimation of High-Resolution Global Monthly Ocean Latent Heat Flux from MODIS SST Product and AMSR-E Data

Accurate estimation of satellite-derived ocean latent heat flux (LHF) at high spatial resolution remains a major challenge. Here, we estimate monthly ocean LHF at 4 km spatial resolution over 5 years using bulk algorithm COARE 3.0, driven by satellite data and meteorological variables from reanalysis. We validated the estimated ocean LHF by multiyear observations and by comparison with seven ocean LHF products. Validation results from monthly observations at 96 widely distributed buoy sites from three buoy site arrays (TAO, PIRATA, and RAMA) indicated a bias of less than 7 W/m2 with R2 of more than 0.80 (p<0.01) and with a King–Gupta efficiency (KGE) of over 0.84. Our estimated ocean LHF also performs well in simulating annual variability and predicting between-site variability, as indicated by a bias of lower than 6 W/m2 and an R2 of more than 0.84 (p<0.01). Overall, the average KGE for estimated ocean LHF increased by 18%–23% compared to other LHF products, indicating robust LHF estimation performance. Importantly, our estimated annual ocean LHF has similar global spatial distribution compared to other LHF products, although there are general differences in LHF values due to the difference in the models and the spatial resolution.

An Evaluation of the Chinese HY-2B Satellite’s Microwave Scatterometer Instrument

The HY-2B scatterometer (HSCAT-B) has now completed a one-year orbit. The instrument was declared operational after six months of in-orbit testing. The ocean wind field products are routinely being made available to the global science community. The HY-2B will work with the HY-2A to provide the Ku-band sea surface observations on a long-term scale, and this collaboration is expected to be important for disaster prevention and mitigation, as well as globally focused climate change research. However, to obtain reasonable evaluations of the system’s functional, performance, and instrument stability results, the temperature, internal calibration parameters, attitude angles, and normalized radar cross section (NRCS) of the instrument were rigorously analyzed during the in-orbit tests. This study provided an overview of the six-month in-orbit testing process results. The temperature levels of some important parts of the scatterometer were found to meet the design requirements. The internal calibration and noise power had shown similar trends and were both within the normal range. The attitude angles, which mainly included the roll and pitch, had displayed variations within a very small scope. The evaluation results of the Amazon rainforest observations indicated that the scatterometer instrument had met all the design requirements and had established a good database for geophysical processing.

Inversion of multiangular polarimetric measurements from the ACEPOL campaign: an application of improving aerosol property and hyperspectral ocean color retrievals

Abstract. NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, scheduled for launch in the time frame of late 2022 to early 2023, will carry the Ocean Color Instrument (OCI), a hyperspectral scanning radiometer, and two multiangle polarimeters (MAPs), the UMBC Hyper-Angular Rainbow Polarimeter 2 (HARP2) and the SRON Spectro-Polarimeter for Planetary EXploration one (SPEXone). One purpose of the PACE MAPs is to better characterize aerosol properties, which can then be used to improve atmospheric correction for the retrieval of ocean color in coastal waters. Though this is theoretically promising, the use of MAP data in the atmospheric correction of colocated hyperspectral ocean color measurements have not yet been well demonstrated. In this work, we performed aerosol retrievals using the MAP measurements from the Research Scanning Polarimeter (RSP) and demonstrate its application to the atmospheric correction of hyperspectral radiometric measurements from SPEX airborne. Both measurements were collected on the same aircraft from the Aerosol Characterization from Polarimeter and Lidar (ACEPOL) field campaign in 2017. Two cases over ocean with small aerosol loading (aerosol optical depth ∼0.04) are identified including colocated RSP and SPEX airborne measurements and Aerosol Robotic Network (AERONET) ground-based observations. The aerosol retrievals are performed and compared with two options: one uses reflectance measurement only and the other uses both reflectance and polarization. It is demonstrated that polarization information helps reduce the uncertainties of aerosol microphysical and optical properties. The retrieved aerosol properties are then used to compute the contribution of atmosphere and ocean surface for atmospheric correction over the discrete bands from RSP measurements and the hyperspectral SPEX airborne measurements. The water-leaving signals determined this way are compared with both AERONET and Moderate Resolution Imaging Spectroradiometer (MODIS) ocean color products for performance analysis. The results and lessons learned from this work will provide a basis to fully exploit the information from the unique combination of sensors on PACE for aerosol characterization and ocean ecosystem research.

Interannual variations in spring lightning activity and convective rainfall over South China during the TRMM era

The interannual variability of spring lightning activity over South China (SC) and its driving mechanism are examined using the Tropical Rainfall Measuring Mission (TRMM) satellite-estimated convective rain rate and merged lightning flash rate datasets together with atmospheric and oceanic reanalysis products over the TRMM period (1998–2014). SC is climatologically characterized by high lightning flash densities, strong convective rainfall, and large convective available potential energy (CAPE) during spring. The spring SC lightning activity (SCLA) has a strong year-to-year variability, and the standard deviation of flash rates shows a spatially coherent annular distribution centered over the Pearl River Delta. The interannual variations of spring SCLA are not only highly correlated with those of convective rainfall and CAPE, but also significantly correlated with El Nino–Southern Oscillation (ENSO). The anomalously frequent SCLA tends to follow El Nino events, while infrequent SCLA preferentially follows La Nina events. Composite analyses demonstrate that during spring for the more frequent SCLA cases, the upper tropospheric atmospheric response to El Nino-related sea surface temperature anomaly (SSTA) patterns leads to strong southwesterlies over SC in conjunction with tropical westerlies over the tropical Indian Ocean, forming a divergent environment over SC. The upper-level divergence is coupled with low-level moisture convergence, generating strong mid-tropospheric updrafts to lift more air parcels to reach their level of free convection, thereby producing stronger convection with frequent SCLA. In contrast, the anomalous circulation forced by La Nina-related SSTA patterns is conducive to suppressed convection over SC and infrequent SCLA.

Injection of Oxygenated Persian Gulf Water Into the Southern Bay of Bengal

AbstractPersian Gulf Water (PGW) is an oxygenated, high‐salinity water mass that has recently been detected in the Bay of Bengal (BoB). However, little is known about the transport pathways of PGW into the BoB. Ocean glider observations presented here demonstrate the presence of PGW in the southwestern BoB. Output from an ocean reanalysis product shows that this PGW signal is associated with a northward‐flowing filament of high‐salinity water. Particle tracking experiments reveal two pathways: one in the eastern Arabian Sea that takes a minimum of 2 years and another in the western Arabian Sea that takes a minimum of 3 years. The western pathway connects to the BoB via equatorial currents. The greatest influx of PGW occurs between 82° and 87°E during the southwest monsoon. We propose that injection of PGW to the BoB oxygen minimum zone (OMZ) contributes to keeping oxygen concentrations in the BoB above the level at which denitrification occurs.

A Grey Theory-Based Economic Prediction Method of Port and Ocean Engineering

Liu, J., 2020. A grey theory-based economic prediction method of port and ocean engineering. In: Gong, D.; Zhang, M., and Liu, R. (eds.), Advances in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 106, pp. 197–200. Coconut Creek (Florida), ISSN 0749-0208.With the rapid development of science and technology, economic prediction has been applied to many fields of economic events, mainly to predict the development of law and future situations. Through scientific prediction, we can provide a rigorous scientific basis for economic activities. There are a variety of prediction methods and theories, such as grey theory, fuzzy prediction method, time series method, compound interest method, etc. With the rapid growth of China's economy, China's port and marine engineering has made great achievements and has become an indispensable economic growth point in China's national economy. Therefore, on the basis of the grey theory, this paper makes a grey model first-order one variable (GM [1,1]) model prediction of port and marine engineering economy, which mainly includes three aspects: gross ocean product, port cargo throughput, and container throughput in coastal areas. Through the GM (1,1) model, we can correctly understand and predict the throughput of the port. Finally, this paper puts forward some suggestions that can better carry out the economic development of port and marine engineering.

Observations for Model Intercomparison Project (Obs4MIPs): status for CMIP6

Abstract. The Observations for Model Intercomparison Project (Obs4MIPs) was initiated in 2010 to facilitate the use of observations in climate model evaluation and research, with a particular target being the Coupled Model Intercomparison Project (CMIP), a major initiative of the World Climate Research Programme (WCRP). To this end, Obs4MIPs (1) targets observed variables that can be compared to CMIP model variables; (2) utilizes dataset formatting specifications and metadata requirements closely aligned with CMIP model output; (3) provides brief technical documentation for each dataset, designed for nonexperts and tailored towards relevance for model evaluation, including information on uncertainty, dataset merits, and limitations; and (4) disseminates the data through the Earth System Grid Federation (ESGF) platforms, making the observations searchable and accessible via the same portals as the model output. Taken together, these characteristics of the organization and structure of obs4MIPs should entice a more diverse community of researchers to engage in the comparison of model output with observations and to contribute to a more comprehensive evaluation of the climate models. At present, the number of obs4MIPs datasets has grown to about 80; many are undergoing updates, with another 20 or so in preparation, and more than 100 are proposed and under consideration. A partial list of current global satellite-based datasets includes humidity and temperature profiles; a wide range of cloud and aerosol observations; ocean surface wind, temperature, height, and sea ice fraction; surface and top-of-atmosphere longwave and shortwave radiation; and ozone (O3), methane (CH4), and carbon dioxide (CO2) products. A partial list of proposed products expected to be useful in analyzing CMIP6 results includes the following: alternative products for the above quantities, additional products for ocean surface flux and chlorophyll products, a number of vegetation products (e.g., FAPAR, LAI, burned area fraction), ice sheet mass and height, carbon monoxide (CO), and nitrogen dioxide (NO2). While most existing obs4MIPs datasets consist of monthly-mean gridded data over the global domain, products with higher time resolution (e.g., daily) and/or regional products are now receiving more attention. Along with an increasing number of datasets, obs4MIPs has implemented a number of capability upgrades including (1) an updated obs4MIPs data specifications document that provides additional search facets and generally improves congruence with CMIP6 specifications for model datasets, (2) a set of six easily understood indicators that help guide users as to a dataset's maturity and suitability for application, and (3) an option to supply supplemental information about a dataset beyond what can be found in the standard metadata. With the maturation of the obs4MIPs framework, the dataset inclusion process, and the dataset formatting guidelines and resources, the scope of the observations being considered is expected to grow to include gridded in situ datasets as well as datasets with a regional focus, and the ultimate intent is to judiciously expand this scope to any observation dataset that has applicability for evaluation of the types of Earth system models used in CMIP.

Evaluation on the Capability of Revealing Ocean Swells from Sentinel-1A Wave Spectra Measurements

AbstractWave measurements retrieved bySentinel-1Alevel-2 ocean (OCN) products are sensitive to swells other than wind seas, and are considered to provide a finer resolution of ocean swells. To assess the capability of swell retrieval globally, OCN products are validated against WAVEWATCH III (WW3) wave spectra for two available incidence angles [“wave mode” (WV); WV1: 23°; WV2: 36°], focused on the integral wave parameters and most energetic wave system ofSentinel-1A. The wave parameter difference betweenSentinel-1Aand WW3 along antenna look angles for WV1 demonstrates the obvious impact of the nonlinearity influence in the azimuth direction, resulting in an unrealistically high wave height at the low wave frequency, and the spurious split of wave systems in the range direction, due to the vanishing of velocity bunching modulation. WV2 is less pronounced in these two aspects, but tends to shift wave energy to a higher wave frequency in the range direction. The inside discrepancy of wave energy has two noticeable features: the difference in peak wavelengths in the wave spectrum is positively clustered in the azimuth direction and negatively clustered in the range direction; some of the most energetic partitions derived fromSentinel-1Aare difficult to assign to any wave systems in WW3. This phenomenon could be related to wind-wave coupling as the azimuth cutoff/WW3 peak wavelength is confined to a ratio below 0.5 for the negative difference betweenSentinel-1Aand WW3 peak wavelengths and the spectral distance of most energetic wave system inSentinel-1Ahighly resembles “swell pools.”

Detection of the Oyashio and Kuroshio fronts under the projected climate change in the 21st century

We evaluate the Oyashio and Kuroshio fronts latitudinal transition under the projected climate change scenarios using eddy resolving regional ocean climate projection products from 1981 to 2100. The regional ocean climate projections are produced based on dynamical downscaling of four CMIP5 models and two RCP experiments RCP2.6 and RCP8.5. Two approaches of the fronts detection methods are compared. One is conventional approach based on subsurface specific isotherm and another is newly proposed approach based on the Oyashio and Kuroshio water temperature and salinity (TS) profiles that may change as the global warming progresses. It is found that the Oyashio TS profile rapidly shift to be high both in temperature and salinity in RCP8.5 cases while the Kuroshio TS profile shows small change toward the end of the twenty-first century in all cases. Northward shift of the Oyashio and Kuroshio fronts reaches 2° northward by the late twenty-first century in extreme case of RCP8.5 cases from the temperature-based definition. On the other hand, the northward shifts of fronts are less than 1° when we use the TS-based definition. The comparison of both fronts positions with the surface velocity distributions suggest that the TS-based definition captures transitions of the fronts better than the temperature-based definition.