Ocean Structure Research Articles

Upper ocean structure determines the contrasting typhoon-induced chlorophyll-a responses in the northwest Pacific

Upper ocean structure determines the contrasting typhoon-induced chlorophyll-a responses in the northwest Pacific

Vibrational characteristic simulations regarding connecting two different semi-spheroidal shells and a full-spheroidal shell with a conical shell categorized in underwater structures

Recently, the related structures of marine, underwater, and ocean structures, covering, ice-breaking devices, riser pipes, ballast water gears, gliders, and underwear noise migrations, can be counted by Connected Shells (CSs). Accordingly, for the first time, the investigation related to vibration outputs associated with connecting two different semi-spheroidal shells and a full-spheroidal shell with a conical shell, namely Connected Spheroidal-Conical Shell Assembly (CSCSA) organized in three assembly groups is examined here. In detail, General Shell Hypothesis (GSH) and the First Shear Deformation Theory (FSDT) are connected to find the main formulations of the CSCSAs' shell elements. Addedly, the Motion Governing Differential Equations (MGDEs) associated with each shell element related to the CSCSAs are identified as implementing Hamilton's principle. Addedly, the MGDEs associated with the CSCSA components are discretized, realizing the Generalized Differential Quadrature Method (GDQM). Thereafter, the Natural Frequency Factors (NFFs) of the CSCSAs are determined by implementing the eigenvalue determination. Also, the NFFs measured by the suggested context are linked to the NFFs determined using classical FEM-constructed commercial software to validate the provided approach since previous research has not been conducted on these structures in the literature (except one type related to the CSCSAs). More importantly, the largest observed inaccuracy is less than 1%. Consistent with this, the responses of this investigation may be operated as the benchmark. Finally, the impacts of the geometrical parameters connected to the CSCSAs on the NFFs of the structure are identified via the design and solution of original cases.

Study on vertical line source Green's function for hydrodynamic calculations of ocean structures in water with ice cover

The numerical calculation of panel integrals associated with the Green's function satisfying water surface condition with ice cover is the basis for the boundary element method (BEM) to solve hydrodynamic problems of ocean structures in ice regions. In order to simplify the calculation process and reduce the time consuming, the vertical line source representing the analytical integral of ice-covered Green's function over vertical line segment is firstly derived in this paper. Then a semi-analytical quadrature, which accumulates a series of vertical line sources distributing along the horizontal direction, can be derived for the panel integral. In the numerical implementation, the asymptotic analysis method is employed to eliminate the singularity at zero point of the denominator, variable substitution is performed to treat the integral at infinite and approximate polynomials are introduced to evaluate the Bessel functions. Through the calculations of vertical line and panel integrals of Green's function and its derivatives, the analytical expression of vertical line source is proved to be accurate and more efficient than the normal numerical quadrature. Based on this, a BEM program is developed and applied in the hydrodynamic calculations of submerged structures with ice cover. The computed results are found to be in excellent agreement those of the validated BEM based on point source, which further verifies the reliability and practicability of utilization of vertical line source.

Thermal response to sequential tropical cyclone passages: Statistic analysis and idealized experiments

The cold wake caused by a tropical cyclone (TC) extends for hundreds of kilometers and persists for several weeks, thus influencing the surface response for any subsequent TCs that might pass over it. It is commonly accepted that sea-surface temperature (SST) cooling, as produced by a single TC, occurs primarily through vertical mixing. However, when there are sequential TCs, the earlier TC can dramatically change the thermal structure of the upper ocean, which may influence the subsequent development of a latter-occurring TC (LTC). Therefore, the contribution of horizontal advection and vertical mixing to SST-cooling during the passage of LTCs is of great interest. Using a 19-year-long observational dataset and the heat budget analysis of an idealized numerical simulation, the SST change during the passage of sequential TCs is investigated. The results demonstrate that, on average, the SST cooling caused by the LTC shows an overall decreasing trend with enhanced lingering wakes. Budget analysis of the model simulations suggests that an earlier TC can suppress the vertical mixing induced by an LTC mainly through an alteration of dynamics within the deepened mixed layer and that the contribution of vertical mixing to the SST cooling is weaker due to the intensification of the earlier TC. The weakened vertical mixing dominates the decreased SST cooling induced by an LTC. In contrast, the cold wake generated by an earlier TC can produce more cold water on the right side of the TC’s track, which contributes to stronger horizontal advection upon the arrival of the LTC. In general, the effects of the earlier TC can suppress the sea-surface thermal response to an LTC. If the contribution of the horizontal advection to SST cooling is neglected, the SST cooling induced by an LTC could be reduced by about 40%. As for the response of the sub-surface water to the passage of an LTC, the weakened warm anomaly induced by vertical mixing and the enhanced cooling anomaly caused by the vertical advection explain the reduced tendency for the mixed layer to deepen. As a result, the tendency for the mixed layer depth (MLD) to increase is suppressed during the passage of an LTC. These results highlight the importance of optimally depicting cold wakes in numerical simulations to improve the prediction of the upper ocean’s response to sequential TCs.

Chromosome-level genome of the three-spot damselfish, Dascyllus trimaculatus.

Damselfishes (Family: Pomacentridae) are a group of ecologically important, primarily coral reef fishes that include over 400 species. Damselfishes have been used as model organisms to study recruitment (anemonefishes), the effects of ocean acidification (spiny damselfish), population structure, and speciation (Dascyllus). The genus Dascyllus includes a group of small-bodied species, and a complex of relatively larger bodied species, the Dascyllus trimaculatus species complex that is comprised of several species including D. trimaculatus itself. The three-spot damselfish, D. trimaculatus, is a widespread and common coral reef fish species found across the tropical Indo-Pacific. Here, we present the first-genome assembly of this species. This assembly contains 910 Mb, 90% of the bases are in 24 chromosome-scale scaffolds, and the Benchmarking Universal Single-Copy Orthologs score of the assembly is 97.9%. Our findings confirm previous reports of a karyotype of 2n = 47 in D. trimaculatus in which one parent contributes 24 chromosomes and the other 23. We find evidence that this karyotype is the result of a heterozygous Robertsonian fusion. We also find that the D. trimaculatus chromosomes are each homologous with single chromosomes of the closely related clownfish species, Amphiprion percula. This assembly will be a valuable resource in the population genomics and conservation of Damselfishes, and continued studies of the karyotypic diversity in this clade.

Crevasse refreezing and signatures of retreat observed at Kamb Ice Stream grounding zone

Ice streams flowing into Ross Ice Shelf are presently responsible for around 10% of the mass flux from West Antarctica, with the noteworthy exception of Kamb Ice Stream, which stagnated in the late 1800s. The subsequent reduction in ice supply led to grounding-line retreat at the coastal margin where Kamb transitions into the floating Ross Ice Shelf. Grounding-line migration is linked to broader changes in ice-sheet mass balance and sea level, but our understanding of related ice, ocean and seafloor interactions is limited by the difficulty in accessing these remote regions. Here we report in situ observations from an underwater vehicle deployed at Kamb that show how fine-scale variability in ice and ocean structure combine to influence a diversity of ice–ocean interactions. We found a stratified water column within a tenth of a degree of freezing at the ice base and mapped basal crevasses with supercooled water and active marine ice formation. At the seafloor, we interpret parallel ridges as crevasse impressions left as the ice lifted off during grounding-line retreat. These observations from a recently ungrounded sub-shelf environment illuminate both the geomorphological signatures of past grounding-line retreat and the fine-scale sensitivity of ongoing ice–ocean interactions to ice topography.

Profiles of Two JOMAE Associate Editors (The Fifth in a Continuing Series)

Profiles of Two JOMAE Associate Editors (The Fifth in a Continuing Series)

Tectonic control on travertine and silica sinter deposition in oceanic transform-fault setting: the case of the Lýsuskarð volcano-geothermal area, Snæfellsnes Peninsula, Iceland

ABSTRACT Deposition of terrestrial carbonate (i.e. travertine) and silica sinter in geothermal areas is always closely linked to the presence of relevant crustal structures which enhance the permeability in the upper crust favouring the upflow of fluids to the surface. Most travertine deposits are originated by geothermal fluids stored within carbonate reservoirs in continental crust, and their morphology and areal distribution provide useful information on geometry, kinematics, and age of faults which control the fluid flow. In this paper, we focus on the tectonic control on a travertine depositional system, associated with silica sinter, developing in oceanic crust, in the Lýsuskarð volcano-geothermal area on the Snæfellsnes Peninsula, West Iceland. The presence of HCO3 and Ca in the geothermal fluids is related to chemical-physical processes linked to fluid–rock interaction that occurs in the geothermal reservoir made up of tholeiitic basalt, by fluids enriched in CO2 of deep origin (i.e. magmatic). Travertine deposits consist of mounds and slopes, which are still in formation and overlie the silica sinter deposits. Both sinter and travertine deposits derive from thermal springs aligned according to two trends: NNE-SSW and WNW-ESE. This evidence suggests the occurrence of buried, permeable, and thus active faults, which control the circulation of fluids containing HCO3 and Ca. Faults are near parallel to those which define the rift systems and transform zones in Iceland, and probably comprise the still active sector of the abandoned transform zone that, starting with the Snæfellsnes Peninsula, interrupts eastward the northern continuation of the western and eastern rift-zones in the south-central Iceland. In this setting, we refer, for the first time, travertine and silica sinter deposition to an oceanic active crustal structure.

Ocean turbulent boundary-layer influence on ice crystal behaviour beneath fast ice in an Antarctic ice shelf water plume: The “dirty ice”

The oceanic connection between ice shelf cavities and sea ice influences sea ice development and persistence. One unique feature in regions near ice shelves is the potential for sea ice growth due to crystal accretion on its underside. Here we present observations of ocean boundary-layer processes and ice crystal behaviour in an Ice Shelf Water outflow region from the Ross/McMurdo Ice Shelves. From a fast ice field camp during the Spring of 2015, we captured the kinematics of free-floating relatively large (in some cases 10s of mm in scale) ice crystals that were advecting and then settling upwards in a depositional layer on the sea ice underside (SIPL, sub-ice platelet layer). Simultaneously, we measured the background oceanic temperature, salinity, currents and turbulence structure. At the camp location the total water depth was 536 m, with the uppermost 50 m of the water column being in-situ super-cooled. Tidal flow speeds had an amplitude of around 0.1 m s-1 with dissipation rates in the under-ice boundary layer measured to be up to ε=10-6 W kg-1. Acoustic sampling (200 kHz) identified backscatter from large, individually identifiable suspended crystals associated with crystal sizes larger than normally described as frazil. Measurement of crystals in the SIPL found dimensions of the range 5-200 mm with an average of 93-101 mm depending on the year. The existence and settlement of crystals has implications for understanding SIPL evolution, the structure of sea ice, as well as the fate of Ice Shelf Water.

Using the two-way nesting technique AGRIF with MARS3D V11.2 to improve hydrodynamics and estimate environmental indicators

Abstract. In the ocean, mesoscale or submesoscale structures and coastal processes are associated with fine scales. The simulation of such features thus requires the hydrodynamic equations to be solved at high-resolution (from a few hundred meters down to a few tens of meters). Therefore, local mesh refinement is a primary issue for regional and coastal modeling. The AGRIF (adaptive grid refinement in Fortran) library is committed to tackling such a challenge for structured grids. It has been implemented in MARS3D (Model for Application at Regional Scale), a semi-implicit, free-surface numerical model developed by Ifremer (the French Research Institute for Exploitation of the Sea) for coastal environmental research and studies. As its time scheme uses an alternating-direction implicit (ADI) algorithm, the two-way nesting implementation differs from the one in explicit models. The present paper describes the specifics of the AGRIF introduction and how the nesting preserves some essential properties (mass, momentum and tracer conservations) along with the induced constraints (bathymetric coherence between grids and increase in computation cost). The use and the performance of this new tool are detailed over two configurations that illustrate the wide range of scales and resolutions typically targeted by coastal applications. The first one is based on multiple high-resolution (500 m) grids that pave the coastal ocean over thousands of kilometers, allowing a continuum between the regional and coastal scales. The second application is more local and has a finer resolution (50 m). It targets a recurrent question for semi-enclosed bays, i.e., the renewal time indicator. Throughout these configurations, the paper intends to compare the two-way nesting method with the traditional one-way approach. It highlights how the MARS3D-AGRIF tool proves to be an efficient way to both improve the physical hydrodynamics and unravel ecological challenges.

Chloride Ion Corrosion Resistance of Innovative Self-Healing SMA Fiber-Reinforced Engineering Cementitious Composites under Dry-Wet Cycles for Ocean Structures

To evaluate the chloride ion corrosion resistance of proposed innovative self-healing concrete based on shape memory alloys (SMA) and engineering cementitious composites (ECC), a total of 2 kinds of 22 specimens were prepared. Chloride ion corrosion tests of self-healing SMA-ECC concrete under dry-wet cycles were carried out. It was found that the chloride ion erosion depths of SMA-ECC were significantly smaller than that of MC, and the growth rate of erosion depth of SMA-ECC was obviously smaller than that of MC after 15 dry-wet (dry and wet) corrosion cycles. The chloride ion content of SMA-ECC vanished at the erosion depth more than 10 mm, which was consistent with the test result of AgNO3 solution color-rendering test. Test results indicate that, compared to marine concrete (MC), SMA-ECC has a better chloride ion corrosion resistance behavior. Moreover, the chloride ion concentration of SMA-ECC at a chloride ion erosion depth of less than 10 mm decreased more significantly than that of MC, indicating that almost all chloride salt solution reacted in the outer layer of SMA-ECC, which is consistent with the conclusions of 4.1 and 4.2. Finally, based on the erosion distribution of chloride ions and Fick’s second law, a calculation model describing the relationship between the apparent chloride ion diffusion coefficient and the boundary condition of the chloride ion content was proposed.

Potential determinants affecting the growth of China’s ocean economy: An input-output structural decomposition analysis

Developing the ocean economy has become an important strategy for economic transformation in major coastal countries. A clear understanding of what has driven ocean industrial growth is crucial for the growth of China’s ocean economy to fulfill UN’s Sustainable Developing Goals 14 (SDG 14). In this study, we first compiled and developed high-resolution, long-term coverage and comparable list of China’s Ocean Economic Input-Output Tables (OEIOTs) for years 2007, 2012, and 2017. Subsequently, we creatively employed an SDA model to quantify ocean industrial structure linkages from an intra- and intersectoral perspective, and then examined the potential determinants of ocean industrial growth. Our results show that the intersectoral spillover effect has become the most critical driver for ocean economic development, and the average intersectoral feedback effect and spillover effect of marine industry have been stronger than those of the land industry. Notably, the continuous decline in the average intersectoral spillover has caused the loss of the total ocean economic growth. We also find that the contribution of the dynamic multiplier effect to the primary ocean industrial growth has decreased and its positive effect needs to be stimulated. The key driver of the intersectoral linkage mechanism to the secondary ocean industrial growth has expanded significantly, whereas its contribution to the tertiary ocean industrial growth has been relatively insufficient. Our findings yield clear policy recommendations for strengthen the linkage effects of different ocean industrial sectors to enhance their growth potential and upgrade the ocean economic structure for better fulfilling SDG 14.

Dependence of ocean surface filaments on wind speed: An observational study of North Atlantic right whale habitat

Coherent filaments at the ocean surface often appear to be transient watermass boundaries, where currents converge, surfactants accumulate, and frontal structure at depth can possibly delineate enhanced biological activity in the upper water column. Spaceborne synthetic aperture radar (SAR) permits filaments to be observed at O[1-km] resolution, but extensive coherent structures are more apparent in weaker winds. A wind speed adjustment is proposed for filaments (i.e., contiguous SAR contrasts) of at least 10 km in length. Measures of dependence (distance correlation and the linear and nonlinear components of Pearson correlation) are examined to identify a broad peak in the relationship between filament contrast and weak or moderate values of surface wind speed, where a variable wind speed exponent is employed to maximize these measures.Three locations of recent North Atlantic right whale (Eubalaena glacialis) sightings in the Gulf of St. Lawrence are sampled between 2008 and 2020 by 324 Radarsat-2 SAR scenes and 10-m wind speed from the ERA5 reanalysis. The inverse relationship between SAR contrast magnitude and wind speed is quantified, and a reduced correlation is obtained for all three domains when SAR contrast is weighted by wind speed to the power of 0.8. A more uniform emphasis on ocean surface structure within a SAR scene, or across multiple scenes, can thus be considered in the search for prey aggregations of the North Atlantic right whale.

Modulation of Upper Ocean Vertical Temperature Structure and Heat Content by a Fast-Moving Tropical Cyclone

Abstract The ocean temperature response to tropical cyclones (TCs) is important for TC development, local air–sea interactions, and the global air–sea heat budget and transport. The modulation of the upper ocean vertical temperature structure after a fast-moving TC was studied at the observation stations in the northern South China Sea, including TCs Kalmaegi (2014), Rammasun (2014), Sarika (2016), and Haima (2016). The upper ocean temperature and heat response to the TCs mainly depended on the combined effect of mixing and vertical advection. Mixing cooled the sea surface and warmed the subsurface, while upwelling (downwelling) reduced (increased) the subsurface warm anomaly and cooled (warmed) the deeper ocean. An ideal parameterization that depends on only the nondimensional mixing depth (HE), nondimensional transition layer thickness (HT), and nondimensional upwelling depth (HU) was able to roughly reproduce sea surface temperature (SST) and upper ocean heat change. After TCs, the subsurface heat anomalies moved into the deeper ocean. The air–sea surface heat flux contributed little to the upper ocean temperature anomaly during the TC forcing stage and did not recover the surface ocean back to pre-TC conditions more than one and a half months after the TC. This work shows how upper ocean temperature and heat content varies by a TC, indicating that TC-induced mixing modulates the warm surface water into the subsurface, and TC-induced advection further modulates the warm water into the deeper ocean and influences the ocean heat budget. Significance Statement Tropical cyclones can cause a strong ocean response that modulates the upper ocean temperature structure and contributes to the local heat budget and transport. This manuscript shows how mixing and vertical advection modulate upper ocean temperature after four fast-moving tropical cyclones, and then gives a parameterization of how sea surface temperature and upper ocean heat change depend on the two mechanisms. The temperature anomalies can propagate into deeper ocean after the tropical cyclones, and sea surface heat flux is not important for upper ocean temperature response during a tropical cyclone. These results show how the upper ocean temperature responses to a tropical cyclone, and influences the local heat budget.

Hydrodynamic Analysis of Rigid-Flexible Composite Structure of Large Aquaculture Platform Subjected to Waves

Deep-sea aquaculture cages have an important role in the marine fishery development process. With the increase of the sea depth, the sea conditions will be worse, as waves ups and downs, the stability performance of the cages decreases obviously. As the deep sea water is far away from the land, the environment is complex and changeable and the poor mobility of the system, all these factors can bring great economic losses to the aquaculture practitioners. Compared to the traditional cage system, the large aquaculture platform is more prominent. The aquaculture platform is composed of flexible bodies and slender rigid components. As the flexible bodies and the slender rigid components are coupled with each other, the response of the whole system is very complicated. For such a complex ocean system structure, the numerical simulation in the initial design stage can greatly speed up the design process and save many experimental resources. The aquaculture platform has been discretized into a lumped mass model based on the unique properties of a particular sea state and an aquaculture platform, and OrcaFlex has developed a dynamic simulation approach based on those parameters. With the change of the wave direction, the real-time response of the 6.8 thousand tons aquaculture platform under different wave directions has been realized. The dynamic response of the mooring system under different wave directions is obtained. The findings offer a theoretical foundation for the optimal aquaculture platform design.

Structure and morphology of the Red Sea, from the mid-ocean ridge to the ocean-continent boundary

The diversity and complexity of existing models on the structure of the Red Sea is the result of a mobile sedimentary cover that not only hides most of the basement and oceanic structures but also hamper the geophysical signals. In this study, we combined published with new unpublished geophysical data to propose a revised interpretation of the structure of the lithosphere between the Hanish Islands (ca. 13.5°N) and the Dead Sea Fracture Zone (ca. 27.5°N). The recognition of allochthonous salt and overburden allows to propose a structural model with simple geometries that are consistent with the present-day kinematic constraints (GPS velocities and Euler Poles) and with the rules of plate's motion on a sphere (Euler Theorem).We mapped a continuous Mid Ocean Ridge segment parallel to the main rift orientation in the southern Red Sea that becomes highly discontinuous and more oblique towards the north as it gets closer to the Euler Pole. These segments all point towards the Euler pole and are consistently offset to the right by transform faults in the central and northern Red Sea cumulating an offset of 400 km. The transform faults are accommodating seafloor spreading in the Red Sea and cluster in three main fracture zones: (1) the Ikwan Fracture Zone near the Ikwan (or Brother) Islands, (2) the Zabargad Fracture Zone in the vicinity of the Zabargad Island and (3) the Jeddah Fracture Zone offshore the Jeddah/Port Sudan area (central Red Sea). Based on a new seismic reflection dataset and published data we propose an interpretation of the Ocean Continent Transition (OCT) in the Red Sea. We bring new evidence (magnetic lineaments, distance of the OCT to the ridge, basin stratigraphy) to support a Middle Miocene (ca. 14 Ma) age for the initiation of seafloor spreading throughout the Red Sea, and we discuss this event with the initiation of strike-slip motion in the Aqaba-Dead Sea transform zone. Finally, compiling all available data and literature, we propose a regionally coherent geodynamic reconstruction using two different poles of rotation for the rifting and seafloor spreading phases.

Behaviour and confinement-based direct design of concrete-filled cold-formed stiffened steel tubular short columns

The advantages of concrete-filled square steel tubular columns are currently being widely utilised in various applications, especially in marine and ocean structures. However, the use of slender cross-sectional tubes significantly reduces the concrete core confining effect due to the local buckling (LB) phenomenon of these tubes. Accordingly, welded stiffeners have been proposed to generate stiffened steel tubes to reduce the effect of LB. But due to welding, residual stress causes significant initial imperfections in the columns. This has resulted in the emergence of the concrete-filled cold-formed stiffened steel tubular (CFSST) columns that consist of cold-formed longitudinal stiffeners embedded in the concrete core. The literature shows that studies into the response of these columns are relatively limited. Accordingly, finite element (FE) modelling of CFSST columns with cold-formed steel tubes is used herein to increase the data bank of these columns. First, available test results on such columns using carbon steels were used to validate the FE models. Then, parametric studies were generated to suggest an innovative lateral confining pressure. These studies were also used to explore the effect of the depth-to-thickness ratio of the outer steel tube, concrete cylindrical strength and stiffener depth on the resistance and behaviour of the square CFSST columns with cold-formed steel tubes. It was found that increasing the cylindrical concrete strength is the most effective way to increase the ultimate strength of the columns, although it decreases the ductility of the columns. In addition, the strengths of CFSST short columns with cold-formed steel tubes were compared with the Japanese, British, European and Chinese codified strengths, which were found to provide conservative predictions. Finally, a new strength was provided for the CFSST short columns with cold-formed steel tubes based on a proposed linear law formula for the lateral confining pressure caused by the stiffened cold-formed tubes.

How does 4DVar data assimilation affect the vertical representation of mesoscale eddies? A case study with observing system simulation experiments (OSSEs) using ROMS v3.9

Abstract. Accurate estimates and forecasts of ocean eddies in key regions such as western boundary currents are important for weather and climate, biology, navigation, and search and rescue. The dynamic nature of mesoscale eddies requires data assimilation to produce accurate eddy timings and locations in ocean model simulations. However, data assimilating models are rarely assessed below the surface due to a paucity of observations; hence it is not clear how data assimilation impacts the subsurface eddy structure. Here, we use a suite of observing system simulation experiments to show how the subsurface representation of eddies is changed within data assimilating simulations even when assimilating nearby observations. We examine in detail two possible manifestations of how the data assimilation process impacts three-dimensional eddy structure, namely, by producing overly active baroclinic instability and through inaccurate vertical mode structure. Therefore, in DA simulations, subsurface temperature structures can be too deep and too warm, particularly in dynamic eddy features. Our analyses demonstrate the need for further basic research in ocean data assimilation methodologies to improve the representation of the subsurface ocean structure.

Composite Analysis-Based Machine Learning for Prediction of Tropical Cyclone-Induced Sea Surface Height Anomaly

Sea surface height anomaly (SSHA) induced by tropical cyclones (TCs) is closely associated with oscillations and is a crucial proxy for thermocline structure and ocean heat content in the upper ocean. The prediction of TC-induced SSHA, however, has been rarely investigated. This study presents a new composite analysis-based random forest (RF) approach to predict daily TC-induced SSHA. The proposed method utilizes TC's characteristics and pre-storm upper oceanic parameters as input features to predict TC-induced SSHA up to 30 days after TC passage. Simulation results suggest that the proposed method is skillful at inferring both the amplitude and temporal evolution of SSHA induced by TCs of different intensity groups. Using a TC-centered 5°×5° box, the proposed method achieves highly accurate prediction of TC-induced SSHA over the Western North Pacific with root mean square error of 0.024m, outperforming alternative machine learning methods and the numerical model. Moreover, the proposed method also demonstrated good prediction performance in different geographical regions, i.e., the South China Sea and the Western North Pacific subtropical ocean. The study provides insight into the application of machine learning in improving the prediction of SSHA influenced by extreme weather conditions. Accurate prediction of TC-induced SSHA allows for better preparedness and response, reducing the impact of extreme events (e.g., storm surge) on people and property.

Significant Diurnal Warming Events Observed by Saildrone at High Latitudes

AbstractThe sea surface temperature (SST) is one of the essential parameters needed to understand the climate change in the Arctic. Saildrone, an advanced autonomous surface vehicle, has proven to be a useful tool for providing accurate SST data at high latitudes. Here, data from two Saildrones, deployed in the Arctic in the summer of 2019, are used to investigate the diurnal variability of upper ocean thermal structure. An empirical cool skin effect model with dependence on the wind speed with new coefficients was generated. Several local large diurnal warming events were observed, the amplitudes of warming in the skin layer >5 K, rarely reported in previous studies. Furthermore, the warming signals could persist beyond 1 day. For those cases, it was found surface warm air suppressed the surface turbulent heat loss to maintain the persistence of diurnal warming under low wind conditions. Salinity also plays an important role in the formation of upper ocean density stratification during diurnal warming at high latitudes. A less salty and hence less dense surface layer was likely created by precipitation or melting sea ice, providing favorable conditions for the formation of upper ocean stratification. Comparisons with two prognostic diurnal warming models showed the simulations match reasonably well with Saildrone measurements for moderate wind speeds but exhibit large differences at low winds. Both schemes show significant negative biases in the early morning and late afternoon. It is necessary to improve the model schemes when applied at high latitudes.