Ocean Dynamics最新文献

In this paper, a fusion model based on convolution and self-attention with multi-subimage input model (CNN-SA-MS) is proposed to estimate significant wave height (SWH) from shipborne X-band radar images. The model takes multiple radar subimages as input simultaneously, which not only improves the accuracy of SWH inversion by including more information, but also avoids the restriction of selecting a single subimage in the upwind direction and dependence on external devices for wind data provision. Based on the characteristics of radar images and computational efficiency considerations, this paper selects three radar subimages as the input for the model. The comparison data from buoys and ECMWF are used for training and testing. After averaging the results of 64 radar images, the root mean square error (RMSE) and correlation coefficient (CC) of the CNN-SA-MS model are 0.197 m and 0.903, respectively. The results show that the CNN-SA-MS model improves the accuracy and stability of SWH estimation compared to single-subimage CNN regression model. For the two time periods with significant discrepancies between radar data and ECMWF predictions, we introduce satellite altimeter information as a source of reference for evaluation. The resulting analysis indicates that the significant wave height estimates generated by CNN-SA-MS model are more reliable.

Ocean waves are generally a mix of wind sea and swell. Given the significant disparities in their impact on engineering, the separation of wind sea and swell is of great significance for marine research and engineering applications. This work focuses on studying the methods for separating wind sea and swell from directional wave spectra in finite-depth waters (i.e., the south coast of Sri Lanka). The error caused by deep-water dispersion relationship in the identification of wind sea using wave age (WA) criterion in finite-depth waters is revealed. The magnitude of error increases with decreasing water depth and higher wind speeds. Subsequently, the impact of WA thresholds on the partitioned results of wind sea and swell is examined, followed by a summary on the procedure determining an appropriate WA threshold. Finally, effort is devoted to studying the overshoot phenomenon (OP) criterion, which does not rely on wind data. Overall, the OP criterion performs consistently with the WA criterion. However, the generation and dissipation of OP require some time. Therefore, the OP criterion exhibits a lag in capturing the growing wind sea as well as the transition of the wind sea to a young swell. Misclassification of wind sea by the OP criterion further contaminates the bulk parameters of swell. Moreover, when the wind direction changes slowly, the delays of OP-based wind sea become negligible, leading to improved identification of wind sea and swell.

Abstract

This study examines the seasonal and intraseasonal modulation of near-inertial wind power associated with fluctuations in unidirectional wind speed in the Bay of Bengal (BoB). For that purpose, we use concurrent measurements of high-resolution in situ near-surface current and wind speed from six moorings in the BoB. It is found that the annual mean of near-inertial wind power in the BoB shows roughly similar magnitude (0.25–0.35 mW m⁻²) at all the mooring locations. However, in response to the seasonal evolution of monsoonal wind forcing, near-inertial wind power shows significant annual variability, with a maximum during summer (~ 0.4–0.5 mW m⁻²) and fall (~ 0.3–0.4 mW m⁻²) and a minimum during winter (~ 0.1 mW m⁻²) and spring (~ 0.2 mW m⁻²). In addition, it is also found that modulation of near-inertial wind power due to summer monsoon intraseasonal oscillation (MISO), such as its magnitude, reaches as large as ~ 1 mW m⁻² at the mooring in the northern BoB during phases 3–4 of MISO. Using a high vertical resolution of current profile data, the near-inertial kinetic energy (NIKE) budget in the mixed layer in the northern BoB shows good temporal correspondence with the magnitude of the rate of change of NIKE and near-inertial wind power, with a maximum magnitude of the rate of change of NIKE lags the wind power by 24 hr. The NIKE budget also indicates that a significant portion of near-inertial wind power dissipates in the mixed layer and rarely energises the depth regime underneath the mixed layer.

The primary aim of this research is to investigate how the presence of toxicity, stemming from phytoplankton, impacts fishing activities, catch levels, and financial returns. It is hypothesized that this toxicity arises when zooplankton accumulates harmful substances while consuming phytoplankton. To achieve this objective, we analyze a model resembling a prey-predator relationship involving phytoplankton. We examine the stable conditions in our model by utilizing eigenvalue analysis and calculate the optimal fishing effort that maximizes profitability for fishermen, employing the concept of generalized Nash equilibrium. Additionally, we explore the most effective harvesting strategy by applying Pontryagin’s maximum principle. In our numerical simulations, we identify the key variables that influence all economic aspects of the model, including fishing effort, catch levels, and benefits. Furthermore, we compare our results with findings from previous research.

Decadal variability in the ocean is an important indicator of climate system shifts and has considerable influences on marine ecosystems. We investigate the responses of decadal variability over the global ocean regions using nine CMIP6 models (BCC-CSM2-MR, CESM2-WACCM, CMCC-ESM2, EC-Earth3-Veg-LR, FGOAL-f3-L, INM-CM5-0, MIROC6, MPI-ESM1-2-LR, and NorESM2-MM). Our results show that climate models can capture the Pacific Decadal Oscillation, Tropical Pacific Decadal Variability, South Pacific Decadal Oscillation, and Atlantic Multidecadal Variability under present-day conditions. The ocean decadal variabilities are becoming weaker and their periods are decreasing, especially under the strong global warming scenario. However, there is a discrepancy between the Tropical Pacific Decadal Variability and the other three modes of climate variability. This might be caused by the nearly unchanged atmospheric forcing in the equatorial region, which is decreasing in the higher latitude regions.

Mass loss from the Antarctic Ice Sheet is dominated by basal melting–induced warm ocean water. Ice-sheet mass loss and thinning of buttressing ice shelves occur primarily in the Amundsen and Bellingshausen Seas. Here, we show that in a global ocean simulation using the 0.25° Nucleus for European Modeling of Ocean (NEMO) model driven by the JRA55 reanalysis from 1982 to 2017, the Amundsen sector of the Antarctic continental shelf acts as a gateway, regulating the on-shelf access of warm Circumpolar Deep Water (CDW) from the deep ocean and its westward transfer to other sectors up to ca. 90° E, particularly the Ross Sea. As a result, anomalies in Antarctic-shelf-averaged temperature mainly originate in the Amundsen sector. These changes are primarily governed by shifts in the Amundsen Sea Low associated with tropical climate variability, modulating the on-shelf transport of CDW via wind-driven perturbations to ocean currents. The ensuing temperature anomalies progress westward from the Amundsen Sea via three distinct routes: a slow, convoluted westward pathway on the shelf via the Antarctic Coastal Current; a faster westward pathway along the shelf break via the Antarctic Slope Current and then onto the shelf along topographic troughs; and a third, eastward route toward the Bellingshausen sector, whereby temperature anomalies are transported into a region of local wind-generated changes farther north. These results emphasize the importance of the Amundsen sector for climate variability over the Antarctic shelves.

A three-layer quasi-geostrophic model was developed to examine the topographic eddies generated around the Eratosthenes Seamount in the southeastern Levantine basin, particularly the dipolar vortex structure, consisting of the anticyclonic Cyprus Eddy and a smaller-scale cyclone. The numerical experiments were carried out using the Contour Dynamics Method, imposing an eastward flow with different inclinations and intensities along the western boundary of the model domain to imitate the Mid-Mediterranean Jet. The dual nature of topographic eddies was previously reported to be generated frequently in a homogeneous ocean approximation, but in the current study, the consideration of baroclinicity primarily simulated a single vortex attributed to the Cyprus Eddy with the small-scale cyclone to be generated occasionally. Also, it was demonstrated that the direction and intensity of the imposed eastward flow along the western boundary of the model domain are the main factors in the formation of the cyclonic vortex. The modeling results showed a qualitative agreement with the geostrophic patterns derived from in-situ observations in the wider sea area of the Eratosthenes Seamount.