Search

A third-generation wave model is driven by the synthetic wind field combined with the revised Holland wind and surface wind product from the National Centers for Environmental Prediction (NCEP). The temporal and spatial characteristics of the wind waves and swell during the typhoon are studied, as well as the responses of their wave energy spectra to the source terms. The results show that the typhoon waves have a more complicated asymmetric structure than the wind field, and the maximum significant wave height is always located on the right side of the direction along which the typhoon is moving, where wind waves are dominant, due to the extended fetch. The nonlinear wave–wave interaction helps to redistribute the energy of the wind seas at a high frequency to the remotely generated swells at a low frequency, ensuring that the typhoon wave's energy spectrum remains unimodal. This process occurs in regions without extended fetch, and a similar continued downshift in frequency as the wave–wave interaction occurs for the wind input as well when the waves outrun the typhoon, due to the nonlinear coupling between the wind and growing swells. [ABSTRACT FROM AUTHOR]

Marginal seas are usually fulfilled with strongly varying mesoscale eddies (MEs), which evolutions plays vital roles in regulating global oceanic energy equilibrium, triggering subemesoscale processes with strong vertical velocity, and inducing high biogeochemistry transport. But the temporal evolutions of MEs and submesoscale processes with several kilometers' resolutions are difficult to be measured by traditional observations with passive working mode. The automatic underwater gliders (AUGs) and vehicles (AUVs) positively observe oceanic motion, and could provide us spatiotemporal synchronization information for strongly varying MEs. Here, we present a 9-year high dense dataset of AUVs/AUGs observations in 2014–2022 in the South China Sea (SCS) can be downloaded from https://doi.org/10.57760/sciencedb.11996 (Qiu et al., 2024b). Totally, 9 AUG and 2 AUV cruise experiments were conducted, and 83 AUGs (2 AUVs) equipment were deployed with zonal and temporal resolutions of < 7 km and <6 hour. It covers the area of eddy's birth, propagation, and dissipation, presenting us the most complete data to investigate the evolution of MEs at different life stages. 40 % of them reach resolutions < 1 km and < 1 hour, which provides us the dynamic characteristics of submesoscale instabilities across and along front at the eddy edge. This dataset has potential in improving the forecast accuracy in physical and biogeochemistry numerical model. Much more aggressive field investigation programs will be promoted by the NSFC in future. [ABSTRACT FROM AUTHOR]

Sonic layer depth (SLD) is crucial in ocean acoustics research and profoundly influences sound propagation and Sonar detection. Carrying 90% of oceanic kinetic energy, mesoscale eddies significantly impact the propagation of acoustic energy in the ocean. Recent studies classified mesoscale eddies into normal eddies (warm anticyclonic and cold cyclonic eddies) and abnormal eddies (cold anticyclonic and warm cyclonic eddies). However, the influence of mesoscale eddies, especially abnormal eddies, on SLD remains unclear. Based on satellite altimeter and reanalysis data, we explored the influence of mesoscale eddies on seasonal variations in SLD in the South China Sea. We found that the vertical structures of temperature anomalies within the eddies had a significant impact on the sound speed field. A positive correlation between sonic layer depth anomaly (SLDA) and eddy intensity (absolute value of relative vorticity) was investigated. The SLDA showed significant seasonal variations: during summer (winter), the proportion of negative (positive) SLDA increased. Normal eddies (abnormal eddies) had a more pronounced effect during summer and autumn (spring and winter). Based on mixed-layer heat budget analysis, it was found that the seasonal variation in SLD was primarily induced by air–sea heat fluxes. However, for abnormal eddies, the horizontal advection and vertical convective terms modulated the variations in the SLDA. This study provides additional theoretical support for mesoscale eddy–acoustic coupling models and advances our understanding of the impact of mesoscale eddies on sound propagation. [ABSTRACT FROM AUTHOR]

Submesoscale process is an important part in the kinetic energy cascade from large‐scale circulation to turbulent dissipation, and a key component of the global heat budget. Its dynamic response to weather event is an important process in forecasting marine bio‐chemical matter transport. So how will submesoscale instabilities response to tropical cyclones (TCs) is worth studying. Based on underwater glider observations and 1‐km high resolution numerical modeling, we investigated two TCs (Roke and Haitang)‐induced submesoscale baroclinic instabilities and their dynamic mechanisms in the Northern South China Sea. The TC Haitang induced significant surface cooling, mixed layer deepening, front sharpening, and enhanced the mixed layer baroclinic and symmetric instabilities. The submesoscale kinetic energy also enhanced sharply after TC Haitang, which was higher correlated with increased mesoscale strain rates. The submesoscale energetics analysis revealed that the enhanced frontal submesoscale kinetic energy after TC Haitang was mainly from potential energy release via baroclinic energy conversion. Four groups of sensitivity numerical experiments revealed that the turbulent heat buoyancy flux and the Ekman buoyancy flux contributed equally to the positive baroclinic energy conversion during the TC Haitang. This study helps us to understand the multiscale oceanic energy transfers and submesoscale air‐sea interaction processes. Plain Language Summary: The oceanic submesoscale process has scale ranges with 0.1–10 km in the horizontal, 0.01–1 km in the vertical, and hours‐days in time. The submesoscale process is a key component of the global energy balance and the heat budget, and can be generated by the atmosphere forcing, for example, cold weather, tropical cyclones (TCs). Based on 2‐km high resolution underwater glider and our set‐up 1‐km numerical modeling data, we found TC Haitang could trigger submesoscale symmetric instability and mixed layer baroclinic instabilities. The former instability gains kinetic energy from geostrophic currents, and the latter draw energy from the mesoscale flow potential energy in the northern South China Sea. The frontal submesoscale kinetic energies (KEs) enhanced sharply after TC Haitang. Based on the submesoscale kinetic energy budget analysis, we suggested that the enhanced frontal KEs after TC Haitang was transferred from potential energy via mixed layer baroclinic energy conversion. After conducting four groups of sensitivity numerical experiments, we found that the turbulent heat buoyancy flux and the Ekman buoyancy flux contributed to the strong vertical buoyancy fluxes during the TC Haitang. This study improves our understanding in submesoscale air‐sea interaction. Key Points: Both the submesoscale frontogenetic function and kinetic energy got enhanced after tropical cyclone (TC) HaitangThe enhanced submesoscale kinetic energy after TC Haitang was primarily dominated by the mixed layer baroclinic instabilityThe vertical buoyancy fluxes were mainly induced by turbulent heat and Ekman buoyancy fluxes during TC Haitang [ABSTRACT FROM AUTHOR]

As a key component of meridional overturning circulation, mid-deep circulation plays a crucial role in the vertical and meridional distribution of heat. However, due to a lack of observation data, current knowledge of the dynamics of mid-deep circulation currents moving through basin boundaries and complicated seabed topographies is severely limited. In this study, we combined oceanic observation data, bathymetric data, and numerical modeling of the northwest continental margin of the South China Sea to investigate (i) the main features of mid-deep circulation currents traveling through the central depression belt and (ii) how atmospheric-forcing (winds) mesoscale oceanic processes such as eddies and current–topography interactions modulate the mid-deep circulation patterns. Comprehensive results suggest that the convergence of different water masses and current–topography interactions take primary responsibility for the generation of instability and enhanced mixing within the central depression belt. By contrast, winds and mesoscale eddies have limited influence on the development of local circulation patterns at mid-deep depths (>400 m). This study emphasizes that the intensification and bifurcation of mid-deep circulation; specifically, those induced by a large depression belt morphology determine the local material cycle (temperature, salinity, etc.) and energy distribution. These findings provide insights for a better understanding of mid-deep circulation structures on the western boundary of ocean basins such as the South China Sea. [ABSTRACT FROM AUTHOR]