Hasil untuk "Oceanography"

J. Haberman, A. Jaani, A. Kangur

Shiqiu Peng, Hua Zhang, Jiawen Liao et al.

Abstract Ocean circulations are essential for global climate, redistributing heat and water across ocean basins. The Andaman Sea (AS), a key semi‐enclosed sea connecting to the Bay of Bengal, has lacked sufficient observational data to understand its intermediate circulation. Based on advanced reanalysis data sets, for the first time, we here report a very interesting natural phenomenon, that is, the basin‐wide intermediate circulation of the AS changes its direction twice yearly between cyclonic and anticyclonic, somewhat like a YOYO being played by a kid. A further insightful analysis based on numerical experiments demonstrates that it is the Kelvin waves propagating from the equatorial Indian Ocean that drive basin‐wide intermediate circulation with a semi‐annual cycle under the constraint law of the potential vorticity conservation. This finding highlights the critical role of equatorial Kelvin waves in driving the AS intermediate circulation, advancing our understanding of circulation dynamics in a marginal sea like the AS.

Marius Manolache, Alexandra Ionelia Manolache, Gabriel Andrei

Excessive reliance on traditional energy sources such as coal, petroleum, and gas leads to a decrease in natural resources and contributes to global warming. Consequently, the adoption of renewable energy sources in power systems is experiencing swift expansion worldwide, especially in offshore areas. Floating solar photovoltaic (FPV) technology is gaining recognition as an innovative renewable energy option, presenting benefits like minimized land requirements, improved cooling effects, and possible collaborations with hydropower. This study aims to assess the levelized cost of electricity (LCOE) associated with floating solar initiatives in offshore and onshore environments. Furthermore, the LCOE is assessed for initiatives that utilize floating solar PV modules within aquaculture farms, as well as for the integration of various renewable energy sources, including wind, wave, and hydropower. The LCOE for FPV technology exhibits considerable variation, ranging from 28.47 EUR/MWh to 1737 EUR/MWh, depending on the technologies utilized within the farm as well as its geographical setting. The implementation of FPV technology in aquaculture farms revealed a notable increase in the LCOE, ranging from 138.74 EUR/MWh to 2306 EUR/MWh. Implementation involving additional renewable energy sources results in a reduction in the LCOE, ranging from 3.6 EUR/MWh to 315.33 EUR/MWh. The integration of floating photovoltaic (FPV) systems into green hydrogen production represents an emerging direction that is relatively little explored but has high potential in reducing costs. The conversion of this energy into hydrogen involves high final costs, with the LCOH ranging from 1.06 EUR/kg to over 26.79 EUR/kg depending on the complexity of the system.

YAO Weimin, ZHENG Yungu, LIU Bo et al.

The control of Spartina alterniflora has become a significant issue for coastal and island nations worldwide. The choice of chemical control and herbicides has a direct impact on the health of wetland ecosystems, and thus possesses significant scientific research value. To better understand the research progress in chemical control and herbicides for Spartina alterniflora, this study utilized bibliometric methods and VOSviewer software to visualize literature data retrieved from the Web of Science. Preliminary screening using “Spartina alterniflora herbicides” as keywords primarily resulted in three themes: invasive plant management, wetland weeding and preservation, and the working principles of those herbicides. The overlay visualization of co-occurrence analysis showed that research foci had gradually shifted towards the exploration and application of environmentally friendly novel herbicides. Based on this foundation, this study conducted further literature retrieves on chemical control of Spartina alterniflora and its novel herbicides, with the following results: during the period from 2000 to 2024, the number of publications and citation frequency in this research field showed a similar upward trend, characterized by “an initial slow increase followed by a rapid rise”. The disciplines involved in this research field were primarily plant science, agriculture, and environmental science. Correspondingly, the main journals publishing in this area also focused more on weed management technology and invasive plant management. The main contributing countries were concentrated in coastal and island nations, with the United States, Brazil, and China demonstrating the strongest research capacity in this research field. The main hotspots included the mechanism of action and the resistance of herbicides, the analysis and degradation of herbicides, and management and ecological restoration of herbicides. Synthesizing the above analysis, this study provided a prospective outlook on the research of chemical control of Spartina alterniflora and its novel herbicides. Future research may further explore the mechanisms of environmental biological adaptive responses, the scientific management and sustainable development, as well as interdisciplinary research and technological innovation.

Nicolas Weidberg, Wayne Goschen, Jennifer M. Jackson et al.

Vertical migrations of zooplankters have been widely described, but their active movements through shallow, highly dynamic water columns within the inner shelf may be more complex and difficult to characterize. In this study, invertebrate larvae, currents, and hydrographic variables were sampled at different depths during and after the presence of fronts on three different cruises off the southern coast of South Africa. Internal wave dynamics were observed in the hydrographic data set but also through satellite imagery, although strong surface convergent currents were absent and thermal stratification was weak. During the first two cruises, fronts were more conspicuous and they preceded strong onshore currents at depth which developed with the rising tide. Vertical distributions of larvae changed accordingly, with higher abundances at these deep layers once the front disappeared. The third cruise was carried out during slack tides, the front was not conspicuous, deep strong onshore currents did not occur afterward and larval distributions did not change consistently through time. Overall, the vertical distributions of many larval taxa matched the vertical profiles of shoreward currents and multivariate analyses revealed that these flows structured the larval community, which was neither influenced by temperature nor chlorophyll. Thus, the ability to regulate active vertical positioning may enhance shoreward advection and determine nearshore larval distributions.

Hans van Haren

Growing evidence is found in observations and numerical modelling of the importance of steep seafloor topography for turbulent diapycnal mixing leading to redistribution of suspended matter and nutrients, especially in waters with abundant internal tides. One of the remaining questions is the extent of turbulent mixing away from and above nearly flat topography, which is addressed in this paper. Evaluated are observations from an opportunistic, week-long mooring of high-resolution temperature sensors above a small seafloor slope in about 1200 m water depth of the Eastern Mediterranean. The environment has weak tides, so that near-inertial motions and -shear dominate internal waves. Vertical displacement shapes suggest instabilities to represent locally generated turbulent overturns, rather than partial salinity-compensated intrusions dispersed isopycnally from turbulence near the slope. This conclusion is supported by the duration of instabilities, as all individual overturns last shorter than the mean buoyancy period and sequences of overturns last shorter than the local inertial period. The displacement shapes are more erratic than observed in stronger stratified waters in which shear drives turbulence, and better correspond with predominantly buoyancy-driven convection-turbulence. This convection-turbulence is confirmed from spectral information, generally occurring dominant close to the seafloor and only in weakly stratified layers well above it. Mean turbulence values are 10-100 times smaller than found above steep ocean topography, but 10 times larger than found in the open-ocean interior.

Qian Wu, Jing Meng, Xu Chen et al.

Internal tides serve as essential intermediate steps in the cascading of oceanic energy, playing a crucial role in oceanic mixing. M2 internal tides are the dominant tidal constituent in many oceanic regions, significantly influencing ocean dynamics. The Madagascar–Mascarene Region has high-energy internal tides, but due to a lack of observational studies, their propagation remains underexplored and warrants further investigation. In this study, we used satellite altimetry data to capture the sea surface manifestation of the first-mode M2 internal tides in the region. The results show that the Mascarene Plateau plays a key role in shaping the region’s uneven internal tide distribution. The Mascarene Strait is the most intense generation area, with an east-west energy flux of 1.42 GW. Using the internal tidal energy concentration index, we decomposed the internal tidal beams, finding the primary beam oriented at 148°. These beams propagate outward for over 800 km, with a maximum distance exceeding 1000 km. Geostrophic currents intensify the northward refraction of westward-propagating internal tides in the Mascarene Basin, particularly between 15°S and 20°S.

Hans van Haren

Above steep deep-sea topography internal tidal waves may break vigorously. The associated turbulent mixing is important for resuspending matter, bringing it tens of meters away from the seafloor for redistribution. While intense turbulence-generation occurs around a primary (frontal) bore during each transition from warming downslope to cooling upslope phase of the internal (tidal) carrier wave, a secondary bore can appear about half a wave-period later before the turn to the warming phase. As will be demonstrated from a 100-day mooring array consisting of 200 high-resolution temperature sensors between h = 6-404 m above a steep slope of a large North-Atlantic seamount and a low-resolution acoustic Doppler current profiler sampling between 50 and 450 m, secondary bores show about the same turbulence intensity as around primary bores but they generally show larger overturns that always reach the seafloor. The secondary bores associate with a sudden drop in along-isobath flow speed, a (renewed) increase in upslope flow of up to |0.2| m s-1, and with first-harmonic quarter-diurnal periodicity which provides a spectral peak for turbulence dissipation rate. While each bore is different in appearance, varying from curved like a primary bore to almost straight upward with a ragged bore, secondary bores are in a first approximation forward breaking in contrast with backward breaking primary bores.

Ágnes Baran, Sándor Baran

Although by now the ensemble-based probabilistic forecasting is the most advanced approach to weather prediction, ensemble forecasts still might suffer from lack of calibration and/or display systematic bias, thus require some post-processing to improve their forecast skill. Here we focus on visibility, which quantity plays a crucial role e.g. in aviation and road safety or in ship navigation, and propose a parametric model where the predictive distribution is a mixture of a gamma and a truncated normal distribution, both right censored at the maximal reported visibility value. The new model is evaluated in two case studies based on visibility ensemble forecasts of the European Centre for Medium-Range Weather Forecasts covering two distinct domains in Central and Western Europe and two different time periods. The results of the case studies indicate that post-processed forecasts are substantially superior to the raw ensemble; moreover, the proposed mixture model consistently outperforms the Bayesian model averaging approach used as reference post-processing technique.

Michael Tsyrulnikov, Elena Astakhova, Dmitry Gayfulin

Imperfections and uncertainties in forecast models are often represented in ensemble prediction systems by stochastic perturbations of model equations. In this article, we present a new technique to generate model perturbations. The technique is termed Additive Model-uncertainty perturbations scaled by Physical Tendencies (AMPT). The generated perturbations are independent between different model variables and scaled by the local-area-averaged modulus of physical tendency. The previously developed Stochastic Pattern Generator is used to generate space and time-correlated pseudo-random fields. AMPT attempts to address some weak points of the popular model perturbation scheme known as Stochastically Perturbed Parametrization Tendencies (SPPT). Specifically, AMPT can produce non-zero perturbations even at grid points where the physical tendency is zero and avoids perfect correlations in the perturbation fields in the vertical and between different variables. Due to a non-local link from physical tendency to the local perturbation magnitude, AMPT can generate significantly greater perturbations than SPPT without causing instabilities. Relationships between biases and spreads caused by AMPT and SPPT were studied in an ensemble of forecasts. The non-hydrostatic, convection-permitting forecast model COSMO was used. In ensemble prediction experiments, AMPT perturbations led to statistically significant improvements (compared to SPPT) in probabilistic performance scores such as spread-skill relationship, CRPS, Brier Score, and ROC area for near-surface temperature. AMPT had similar but weaker effects on near-surface wind speed and mixed effects on precipitation.

Pengwei Hu, Ying Cui, Chenyu Zhao et al.

Due to the interference between the main hull and the outrigger of the pentamaran, resistance is greatly affected. Therefore, research on the pentamaran front outrigger inclination angle has further practical significance for reducing resistance. In this study, the pentamaran front outrigger inclination angle was analyzed by CFD method, the ship motion in waves was simulated by overlapping grid technology, and the resistance of the pentamaran in static water and waves was predicted by using the unsteady RANS equation. First, a series of validation studies were carried out for the numerical methods used in the study. Then, the influence of the front outrigger inclination angle on the pentamaran resistance performance under different working conditions is calculated and discussed. In order to analyze the influence of the change of the front outrigger inclination angle on the resistance, free surface wave-making and hull pressure are further discussed. The results show that the influence of the front outrigger inclination angle change on the resistance of the pentamaran has a certain rule, and the resistance of the pentamaran can be reduced by adjusting the front outrigger inclination angle.

Tao Jiang, Yize Sun, Hai Huang et al.

Autonomous underwater manipulation is very important for the robotic and intelligence operations of oceanic engineering. However, a small target often involves limited features and results in inaccurate visual matching. In order to improve visual measurement accuracy, this paper has proposed an improved unsharp masking algorithm to further enhance the weak texture region of blurred and low contrast images. Moreover, an improved ORB feature-matching method with adaptive threshold, non-maximum suppression and improved random sample consensus has also been proposed. To overcome unknown underwater disturbances and uncertain system parameters in the underwater robotic manipulations, an adaptive non-singular terminal sliding mode controller has been proposed with a quasi-barrier function to suppress the chattering problem and improve grasp accuracy for small target. Oceanic experiments have been conducted to prove the performance of the proposed method.

Yuzhi Zhang, Shumin Zhang, Yang Wang et al.

Accurate channel estimation is the fundamental requirement for recovering underwater acoustic orthogonal time–frequency space (OTFS) modulation signals. As the Doppler effect in the underwater acoustic channel is much more severe than that in the radio channel, the channel information usually cannot strictly meet the compressed sensing sparsity assumption in the orthogonal matching pursuit channel estimation algorithm. This deviation ultimately leads to a degradation in system performance. This paper proposes a novel approach for OTFS channel estimation in underwater acoustic communications, utilizing a model-driven deep learning technique. Our method incorporates a residual neural network into the OTFS channel estimation process. Specifically, the orthogonal matching pursuit algorithm and denoising convolutional neural network (DnCNN) collaborate to perform channel estimation. The cascaded DnCNN denoises the preliminary channel estimation results generated by the orthogonal matching pursuit algorithm for more accurate OTFS channel estimation results. The use of a lightweight DnCNN network with a single residual block reduces computational complexity while still preserving the accuracy of the neural network. Through extensive evaluations conducted on simulated and experimental underwater acoustic channels, the outcomes demonstrate that our proposed method outperforms traditional threshold-based and orthogonal matching pursuit channel estimation techniques, achieves superior accuracy in channel estimation, and significantly reduces the system’s bit error rate.

Fabio Quezada-Perez, Sebastián Mena, Cindy Fernández-García et al.

In the past decades, one of the most widely reported phenomena on Caribbean reefs is the general fall in coral cover and rise in macroalgae. Reefs with low coral cover and high macroalgal abundances are often presumed to provide poorer ecosystem functions and services. In this study, we assessed the condition of coral reefs on the Caribbean Coast of Costa Rica and determined how eight key ecosystem metrics varied in response to different coral and fleshy macroalgae covers. Most reefs surveyed had high fleshy macroalgae and low live coral covers, with an average (±SD) of 31 ± 28% and 14 ± 13% per site. The value of many of the ecosystem metrics estimated for coral reefs of the region appears to be lower than what has been reported for other areas in the Caribbean. We found that the rugosity, urchin density, fish richness, total fish biomass, large fish density, and the potential fishery value of the reef were higher in sites with low fleshy macroalgae covers (<10%). Our results concur with the prevailing paradigm that an increase in macroalgae abundance could reduce the ecosystem services provided by coral reefs.

Arnida L. Latifah, Henokh Lugo Hariyanto, Durra Handri et al.

This paper investigates the wind wave deformations above two isolated shallow seamounts using a phase-resolved wave model simulation using the HAWASSI-AB software. The first seamount is located some 8 km from the south coast of Jawa, Indonesia, near Glagah, with its top area about 2 m from the water level, while the second is the Socotra Rock, in the East China Sea, which has a top 4.6 m under the sea surface. The simulations found that isolated shallow bathymetry may generate a crossing sea region endangering ships. In both domains, short-crested wave simulations of second order show strong refraction and diffraction effects when waves run towards and downstream of the top of the seamount. Waves near the summit embrace the seamount and form a focal area with larger waves downstream. After crossing the Socotra Rock, the interaction waves lead to a crossing sea in the deep water. On the other hand, having passed the Glagah, waves further downstream are partly absent over a substantial stretch of the coast. For both cases, the phase-resolved wave simulation results determine detailed wind wave conditions and wave spectra over the whole area, compensating for a lack of experimental data.

J. Carcione, F. Mainardi, J. Ba et al.

The important consequence of the Kramers-Kronig relations (KKrs) is that dissipative behavior in material media inevitably implies the existence of dispersion, i.e., a frequency dependence in the constitutive equations. Basically, the relations are the frequency-domain expression of causality and correspond mathematically to pairs of Hilbert transforms. The relations have many forms and can be obtained with diverse mathematical tools. Here, two different demonstrations are given in the electromagnetic case, illustrating the eclectic mathematical apparatus available for this purpose. Then, we apply the acoustic (mechanical)-electromagnetic analogy to obtain the elastic versions. Finally, we discuss the concepts of stability and passivity and provide a novel algorithm to compute the relations numerically by using the fast Fourier transform.

Luna Hiron, Philippe Miron, Lynn K. Shay et al.

Loop Current Frontal Eddies (LCFEs) are known to intensify and assist in the Loop Current (LC) eddy shedding. These eddies can also modify the circulation in the eastern Gulf of Mexico (GoM) by attracting water and passive tracers such as chlorophyll and pollutants to the LC-LCFE front. During the 2010 Deepwater Horizon oil spill, part of the oil was entrained not only in the LC-LCFE front but also inside an LCFE, where it remained for weeks. This study assesses the ability of the LCFEs to transport water and passive tracers without exchange with the exterior (i.e., Lagrangian coherence) using altimetry and a high-resolution model. The following open questions are answered: (1) How long can the LCFEs remain Lagrangian coherent at and below the surface? (2) What is the source of water for the formation of LCFEs? (3) Can the formation of LCFEs attract shelf water? The results show that LCFEs are composed of waters originating from the outer band of the LC front, the region north of the LC, and the shelf, and potentially drive cross-shelf exchange of particles, water properties, and nutrients. At depth (~180 m), most LCFE water comes from the outer band of the LC front in the form of smaller frontal eddies. Once formed, LCFEs can transport water and passive tracers in their interior without exchange with the exterior for weeks: these eddies remained Lagrangian coherent for up to 25 days in the altimetry dataset and 18 days at the surface and 29 days at depth (~180 m) in the simulation. LCFE can remain Lagrangian coherent up to a depth of ~560 m. Additional analyses confirm that the LCFE involved in the oil spill formed from water near the oil rig location. Temperature-salinity diagrams show that LCFEs are composed of GoM water as opposed to LC water. Thus, LCFE formation modify the surrounding circulation and the transport of oil and other passive tracers in the eastern GoM.

Shaopeng Wei, Yan Dai, Qiang Zhang

Detecting high-speed and maneuvering targets is challenging in early warning radar applications. Modern early warning radar has many functions such as detection, tracking, imaging, and recognition which need a high signal-to-noise ratio (SNR). Thus, long-time coherent integration is a necessary method to realize high SNR requirements. However, high-speed and maneuverable motion cause range and Doppler migration, which brings about serious coherent integration loss. Traditional integration methods usually have the drawbacks of model mismatching and high computational complexity. This paper establishes a novel long coherent processing interval (CPI) integration algorithm that detects maneuvering and weak targets which have a low reflection cross-section (RCS) and low echo SNR. The range and Doppler migration problems are solved via a layer integration by blending the association in a tracking-before-detection (TBD) technique. Compact SNR gain is achieved with a target information transmission mechanism and an updated constant false alarm ratio (CFAR) threshold. The algorithm is applicable in multiple target scenarios by considering different velocity ambiguities and maneuvers. A simulation and real-measured experiments confirm the effectiveness of the algorithm.

Sunyong Kim, Jae-Heung Park, Jong-Seong Kug

Abstract The East Asian countries have experienced heavy rainfalls in boreal summer 2020. Here, we investigate the dynamical processes driving the rainfall extremes in East Asia during July and August. The Indian Ocean basin warming in June can be responsible for the anticyclonic anomalies in the western North Pacific (WNP), which modulate the zonally-elongated rainfalls in East Asia during July through an atmospheric Rossby wave train. In August, the East Asian rainfall increase is also related to the anticyclonic anomalies in the subtropical WNP, although it is located further north. The north tropical Atlantic warming in June partly contributes to the subtropical WNP rainfall decrease in August through a subtropical teleconnection. Then the subtropical WNP rainfall decrease drives the local anticyclonic anomalies that cause the rainfall increase in East Asia during August. The tropical Indian Ocean anomalously warmed in June and the subtropical WNP rainfall decreased in August 2020, which played a role in modulating the WNP anticyclonic anomalies. Therefore, the record-breaking rainfall extremes in East Asia that occurred during summer 2020 can be explained by the teleconnections associated with the tropical origins among the Indian, Pacific, and Atlantic Oceans and their interbasin interactions.

Chrisna Adhi Suryono, Agus Indarjo, Baskoro Rochaddi et al.

Chlorpyrifos from agricultural activities eventually will flow to marine waters through rivers. This research was conducted to determine the resistance of bacteria from seawater of 100ppm Chlorpyrifos.  Three of the five bacterial strains was isolated from seawater from Brebes and Pati, Central Java were selected because they were resistant to the pesticide chlorpyrifos. Analysis of 16S rRNA gene sequences showed that the isolates belonged to the genus Virgibacillus spp. (2 strains) and Bacillus sp (1 strains). This bacterial strain has great potential ability to bioremediation of coastal waters of Brebes and Pati, Central Java from chlorpyrifos pesticide residues.     Khlorpifos dari hasil kegiatan pertanian lama kelamaan akan menuju ke perairan laut melalui aliran sungai.  Penelitian dilakukan untuk mengetahui resistensi baktrei dari air laut yang tahan terhadap 100ppm Khlorpirifos.  Tiga dari lima strain bakteri yang diisolasi dari air laut dari Brebes dan Pati Jawa Tengah dipilih karena resisten terhadap pestisida khlorpirifos.  Analisis sekuens gen 16S rRNA menunjukkan bahwa isolat termasuk dalam genus Virgibacillus sp. (2 strain) dan Bacillus sp (1 strain). Strain bakteri ini memiliki potensi penggunaan yang besar untuk bioremediasi perairan pesisir Brebes dan Pati Jawa Tengah dari residu pestisida klorpirifos.