Current Circulation Research Articles

Subarctic-scale transport of 134Cs to ocean surface off northeastern Japan in 2020

We studied the spatiotemporal variations in 134Cs, 137Cs, and 228Ra concentrations at the sea surface off southeastern Hokkaido, Japan (off-Doto region) from 2018 to 2022 using low-background γ-spectrometry. The 134Cs concentrations in the off-Doto region, decay-corrected to the date of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, exhibited wide lateral variation each year (e.g., 0.7–1.1 mBq/L in 2020). By studying the 228Ra concentrations and salinity, this variation was explained based on the current mixing patterns. Furthermore, the 134Cs concentrations in the waters highly affected by the Oyashio Current (OYC) gradually increased from 2018 to 2020, and subsequently decreased in 2022. This implies that the water mass maximally contaminated with 134Cs was transported back to the side of the Japanese islands 10 years after the FDNPP accident along with counter-clockwise currents (e.g., the OYC) in the northern North Pacific Ocean. The 134Cs concentrations in the OYC-affected waters in the off-Doto region in 2020 were ~ 1/6 times those in the 134Cs-enriched core of waters off the western American Coast in 2015, which can be ascribed to dilution via spatial dispersion during subarctic current circulation. Overall, we elucidated the ocean-scale subarctic current systems in the northwestern North Pacific Ocean, including water circulation timespans.

Morphological change assessment of a coastal island in SE Bangladesh reveal high accumulation rates

It is essential to comprehend various morphological aspects, change dynamics, and stressors on the coastal environment in both contemporary and historical contexts. This study examines the potential for morphological changes in land use, erosion-sedimentation patterns, shoreline changes, and sediment accumulation on Sonadia Island in Southeast Bangladesh. To evaluate the extraordinarily high sediment accumulation phenomenon, the researchers used toposheets, historical maps, numerous satellite images, and field work observations. The investigation revealed that the shoreline of the island is subject to regular and rapid modifications. The island’s area coverage was 1.65 km2 in 1779, but it has grown 21 times to 36 km2 in 2021. From 1972 to 2021, the current study looks at land-use/land-cover changes on Sonadia Island, including mangrove (12.15 to 20.22 km2), tidal mudflats (6.69 to 4.63 km2), salt/shrimp fields (0 to 3.33 km2), dune (1.30 to 3.33 km2), beach sands (5.07 to 4.57 km2), and man-made forest (0 to 1.06 km2), as well as spatial changes in land. Between 1972 and 2021, erosion and sedimentation reached 1.35 km2 and 14.09 km2, respectively, resulting in a depositional rate of 0.29 km2 per year and an erosional rate of 0.03 km2 per year. The high accumulation rates are linked to shoreline activities such as mixing and reworking fluvial systems, longshore currents, tidal activity, strong waves, and seasonal current circulation patterns.

Quaternary sedimentary processes on the Bahamas: From platform to abyss

Understanding the interaction between sediment production on and export from shallow-water areas of platforms and slopes is primordial when assessing sedimentary processes on a carbonate-platform scale. In this manuscript we explore variations in facies, sediment export, sediment deposition and reorganisation, hydroacoustic- and small-scale sedimentary structures, but also assess the variability in current systems as observed during the Quaternary for the north-facing margin of Little Bahama Bank (LBB) and compare those characteristics with features observed on other slopes surrounding LBB and Great Bahama Bank (GBB).Over the past decade, the northern margin of LBB was explored during a series of oceanographic cruises of the CARAMBAR project, which included the collection of 24.270 km2 of bathymetry data, 6.398 km of very high-resolution seismic profiles, and 42 cores covering water depths ranging from 177 m to 4873 m. This study evaluates the results obtained from the analysis of sediment cores retrieved in the Great Abaco Canyon area (GAC), located between the lower northern LBB slope, which is connected to the abyssal plain. The analysis of the shallower parts of the LBB slope relies on earlier studies and are complementary to our data, and allow for a detailed analysis of the sedimentary processes acting along the entire LBB slope.The data reveal that Quaternary sediment distribution differs when moving from the north-eastern to the north-western LBB slope. The entire LBB slope is dissected by numerous canyons. Gravity processes enriched in coarse platform components occur infrequently and are concentrated within lobes in the east. Only coarse-grained rich bank facies can concentrate coarse grains on this margin. The western LBB slope is mostly influenced by fine-grained platform export and current circulation. The deeper GAC area is dominated by pelagic sediments that are supplied from the canyon sides and through tributaries. The sediment composition confirms that pelagic sediment production and current movements determine the sediment-deposition and redistribution processes at this site.The comparison with other Bahamian slopes demonstrates that a leeward position agrees with high sedimentation rates on the slopes resulting in specific morphologic structures, such as gullies and sediment waves, related to fine-grained sediment export, whereas platform-derived coarse-grained facies are deposited downstream in larger structures, such as canyons, that are not affected by the main wind direction. Slope angle could also have an impact on grain-size export, as it appears that coarse-grained deposits are frequent on steep slopes like those bordering the Exuma Sound basin.

A Virtual Vector Based DTC Scheme With Enhanced Resolution for Dual Inverter Fed Five-Phase IM Drives

A virtual voltage vector based direct torque control (DTC) scheme with enhanced resolution for five-phase induction motor (IM) drives with open-end stator windings, fed by two inverters, is proposed in this article. In the proposed scheme, the voltage space vector plane is divided into 20 sectors, by using 40 virtual voltage vectors produced as resultants of the virtual voltage vectors of the individual inverters thereby substantially increasing the sector resolution compared to the 10-sector based conventional five-phase DTC schemes. This DTC scheme incorporates a five-level hysteresis comparator for torque control and the required voltage vectors of different magnitudes are produced by appropriately combining the vectors of the two inverters. The increased sector resolution along with five-level hysteresis torque controller facilitates finer flux and torque control. As the effective common mode voltage in the motor windings is made zero in every switching period, both inverters can be connected to a common dc supply without causing circulation of zero sequence current. The proposed scheme is validated by performing experiment on a five-phase IM drive.

Mesoscale Circulation Controls Chlorophyll Concentrations in the East Australian Current Separation Zone

AbstractUnderstanding the distribution of chlorophyll on the continental shelves adjacent to western boundary currents is important, both from an ecosystem perspective, as well as for their role as a net sink of atmospheric CO2. However, in‐situ observations of chlorophyll in these dynamic regions are rare. Here, using more than a decade of underwater glider observations from 29 deployments in the East Australian Current (EAC) system, we examine the effect of the mesoscale western boundary current (WBC) circulation on chlorophyll distribution across the shelf. The extensive hydrographic dataset reveals that the mode of boundary current separation has a strong persistent spatial influence on both the stratification and chlorophyll distribution on the shelf between 31.5° and 34°S, a productive area adjacent to the EAC separation zone. We identify that subsurface chlorophyll maxima are common, and their depth and strength is dictated by the offshore mesoscale circulation associated with the WBC separation. The vertical chlorophyll distribution is modulated by the combination of the seasonal cycle and the sporadic influence of mesoscale eddies associated with WBC jet separation. Of the three dominant WBC separation scenarios, eddy dipoles result in shelf waters that are on average more stratified, have higher chlorophyll values, and a deeper chlorophyll maximum compared to other circulation modes. These results suggest that it is necessary to consider the influence of WBC dynamics on chlorophyll concentrations for accurate estimates of atmospheric CO2 uptake.

Characterizing the Variability of Boundary Currents and Ocean Heat Content Around New Zealand Using a Multi‐Decadal High‐Resolution Regional Ocean Model

AbstractNew Zealand is located in the southwest Pacific Ocean and is surrounded by a complex system of boundary currents that vary on a variety of time scales, with important impacts on weather, primary productivity, and fisheries. While various observational and modeling studies have shed light on many of the characteristics of New Zealand's ocean circulation, this study provides a comprehensive, quantitative, seamless, 3‐dimensional characterization of the region's boundary current circulation and ocean heat content. We use a 28 yr long hydrodynamic model simulation that accurately represents the mean and variability of the ocean circulation to characterize and quantify the temporal and spatial variability across the region. We show that low‐frequency variability in boundary current transport and upper ocean heat content are correlated over the entire New Zealand oceanic region. Oceanic eddies dominate heat content variability at intra‐annual scales in the northeast of the region, while on the west and southeast coasts heat content varies predominantly at interannual scales controlled by large‐scale changes in the subtropical and sub‐Antarctic fronts. The model shows a significant downstream strengthening and deepening of the boundary currents off northeast New Zealand which, if confirmed by observations, could suggest a significant new understanding of this Western Boundary Current system. This study presents a region‐wide characterization of the temporal and spatial variability of ocean currents and heat content, and their interconnections, providing a vital basis for understanding climate change impacts and the increasing occurrence of marine heatwaves.

Research on MMC Circulation Suppression Technology

Modular multilevel converters (MMCs) are extensively used in flexible high-voltage DC transmission systems. As an important part of them, it plays an important role in the normal use of MMCs. The main additional loss in the system is generated by the second harmonic in the circulating current. By summarizing and comparing current circulation control strategies. Based on the current research status of circulation suppression, we prospect the research direction of the MMC circulating current suppression.

Convective Density Current Circulations That Modulated Meso-γ Surface Winds near the Yarnell Hill Fire

On 30 June 2013, 19 Granite Mountain Hotshots firefighters were killed fighting a wildfire near Yarnell in the mountains of Central Arizona. They succumbed when the wildfire, driven by erratic winds, blocked their escape route and overran their location. A previous study is extended to simulate and analyze the downscale organization of convective circulations that redirected the wildfire, which started from the scale of the Rossby Wave Breaking over North America to a convective gust front that redirected the wildfire, trapping the firefighters. Five stages are found: Stage I, the initial deep prolonged gust front; Stage II, a front-to-rear jet and its ascending motions that organized high-based convection; Stage III, high-based dry microburst-induced downdrafts organized initially by ascending flow in Stage II that transported mass and entropy to the surface; Stage IV; multiple meso-γ-scale high centers and confluence zones formed that encompassed the firefighters’ location, which established a favorable environment leading to Stage V, canyon-scale circulations formed surrounding the fire. The atmosphere thus transitioned from supporting a deep and long-lived convective density current to elevated dry microbursts with mass and wind outflow into a canyon, redirecting the ongoing wildfire.

Vortex-bound solitons in topological superfluid 3He

The different superfluid phases of 3He are described by p-wave order parameters that include anisotropy axes both in the orbital and spin spaces. The anisotropy axes characterize the broken symmetries in these macroscopically coherent quantum many-body systems. The systems’ free energy has several degenerate minima for certain orientations of the anisotropy axes. As a result, spatial variation of the order parameter between two such regions, settled in different energy minima, forms a topological soliton. Such solitons can terminate in the bulk liquid, where the termination line forms a vortex with trapped circulation of mass and spin superfluid currents. Here we discuss possible soliton-vortex structures based on the symmetry and topology arguments and focus on the three structures observed in experiments: solitons bounded by spin-mass vortices in the B phase, solitons bounded by half-quantum vortices (HQVs) in the polar and polar-distorted A phases, and the composite defect formed by a half-quantum vortex, soliton and the Kibble-Lazarides-Shafi wall in the polar-distorted B phase. The observations are based on nuclear magnetic resonance (NMR) techniques and are of three types: first, solitons can form a potential well for trapped spin waves, observed as an extra peak in the NMR spectrum at shifted frequency; second, they can increase the relaxation rate of the NMR spin precession; lastly, the soliton can present the boundary conditions for the anisotropy axes in bulk, modifying the bulk NMR signal. Owing to solitons’ prominent NMR signatures and the ability to manipulate their structure with external magnetic field, solitons have become an important tool for probing and controlling the structure and dynamics of superfluid 3He, in particular HQVs with core-bound Majorana modes.

Spatiotemporal dynamics of chlorophyll-a in the Gorgan Bay and Miankaleh Peninsula biosphere reserve: Call for action

Gorgan Bay (GB) and Miankaleh Peninsula biosphere reserve has faced an endangering condition because of a significant water loss and quality degradation due to intensive eutrophication. However, a synoptic view of the spatiotemporal dynamic of eutrophication is missing. In this study, we first used MODIS data to trace the long-term trend of eutrophication in GB between 2003 and 2021. To investigate the intra-annual variability of Chl-a in GB at a much higher spatial resolution, we developed an Artificial Neural Network (ANN) algorithm that uses Sentinel-2 imagery to map monthly Chl-a in the water year 2020–2021. Finally, we explored the major physical controls on eutrophication in GB. Long-term status of trophic index in GB revealed that 4%, 18%, 15%, 24%, and 39% of the months between 2003 and 2021 were under the oligotrophic, intense oligotrophic, mesotrophic, eutrophic, and intense eutrophic condition, respectively. The results also showed a very good agreement between the observed Chl-a concentration and that estimated from ANN, as evidenced by R2 = 0.88 and RMSE = 1.51 mg/m3. We found that in eight months of the water year 2020–2021, there was a region of high Chl-a concentration in the southeast of GB near the outlet of the Qarasu River. We also observed that nutrient entrance to GB from the Qarasu River imposes a greater impact on Chl-a concentration in GB than that from the Gorganrud River. Our findings suggest that under the current GB's water circulation, the critical eutrophication status in GB has a slight impact on the pollution of the Caspian Sea, except along the southeastern shoreline.

A study of the wave effects on the current circulation in Galway Bay, using the numerical model COAWST

A model coupling waves and currents is set up for Galway Bay, Ireland, using COAWST. The impact of the coupling on the accuracy of the model is shown to be marginal on the overall statistics. The model is in good agreement with the available in-situ observations that are used for the validation. However a closer look at the data during storms shows a deterioration of the agreement, which is barely improved by the coupling. A special analysis of the different processes ruling the ocean circulation and wave propagation is conducted during Storm Hector (2018/06/14). It shows a strong wave-induced surge by 7cm in the back of Galway Bay, and a strong response in terms of currents along the coast of Clare of about 30cm/s. Most of the surge is attributed to the impact of the conservative wave-induced forcing terms, but the main process involved is not identified. The response in currents is partly attributed to the conservative wave-induced forcing terms, but mostly to the wave-enhanced surface roughness.

Formation of the Layered Circulation in South China Sea With the Mixing Stimulated Exchanging Current Through Luzon Strait

AbstractUsing the layered circulation in the South China Sea (SCS) as an example, a process‐oriented simulation was conducted to explore how the lateral exchanging current and basin circulation responded to the contrasting mixing in the marginal sea‐open ocean system and to the internal modulation over basin slope. Under conditions of intensified turbulent mixing () in the SCS, a crossing Luzon Strait density difference was generated and the net ageostrophic pressure gradient force drove the layered exchanging current with intensified westward deep intrusion into the SCS and an eastward middle outflow. The lateral exchanging current in turn developed a layered basin circulation in the semi‐enclosed middle and deep layers through directly providing external planetary vorticity flux, and releasing the internal potential energy indirectly. The vertical migration of the layered circulation structure over bottom slope owing to flow‐topography interaction is the major intrinsic response to the external exchanging current particularly in the semi‐enclosed deep basin. Although a small was adequate to maintain the basic layered circulation pattern, an intensified was required to extend the deep cyclonic circulation to the bottom. The intrusion of the western boundary current from open ocean not only maintained the strong upper cyclonic circulation but also intensified deep intrusion and modulated the deep layer circulation through vertical coupling. Both the deep density difference between the SCS and open ocean as well as associated vertical coupling should be considered to well understand the intensity of water exchange and the consequent layered circulation in the SCS.

The Loop Current Circulation Over the MIS 9 to MIS 5 Based on Planktonic Foraminifera Assemblages From the Gulf of Mexico

AbstractThe loop current (LC) in the Gulf of Mexico (GoM) is part of the western North Atlantic circulation. Recording its strength and slowdown variations can help us characterize the regional climate over the Late Pleistocene. To reconstruct the sea surface and the LC intensity in the eastern GoM, we study the distribution patterns of planktonic foraminifera in the core EN‐032‐18PC, spanning the end of Marine Isotope Stage (MIS) 9 to early MIS‐4. We reconstructed a sequence of paleoceanographic events based on stable isotopes (δ18O and δ13C) of the surface dweller Globigerinoides ruber and two faunal assemblages. The first assemblage explains most of the glacial and late interglacial periods, suggesting a subtropical environment with a deep thermocline and a reduced LC due to a moderate inflow of warm Caribbean waters. The second assemblage explains the warmest interglacial substages, dominated by tropical species, a shallow thermocline, and an extended LC, driven by summer insolation. Overall, surface ocean conditions led to more ecological successions and instability during the warmest interglacial substages than during glacial periods, as supported by the stable isotope records. Besides the GoM relationship to AMOC, as a regulator of heat transport to higher latitudes, we suggest that fluctuations in the LC rely on the migration of atmospheric circulation patterns and astronomical insolation forcing.

Effects of detached breakwaters on drowning due to rip and circulation currents

Effects of detached breakwaters on drowning due to rip and circulation currents

Topological visualization of the plasmonic resonance of a nano C-aperture.

The plasmonic response of a nano C-aperture is analyzed using the Vector Field Topology (VFT) visualization technique. The electrical currents that are induced on the metal surfaces when the C-aperture is excited by light is calculated for various wavelengths. The topology of this two-dimensional current density vector is analyzed using VFT. The plasmonic resonance condition is found to coincide with a distinct shift in the topology which leads to increased current circulation. A physical explanation of the phenomenon is discussed. Numerical results are presented to justify the claims. The analyses suggest that VFT can be a powerful tool for studying the physical mechanics of nano-photonic structures.

INTERPRETATION OF CURRENT AND TIDAL PATTERN AT SELANGOR RIVER, KUALA SELANGOR

Abstract. Tidal data has been used to determine long-term water level alterations. Tides are high-powered and notoriously hard to ascertain. Tidal analysis and prediction need substantial study with the requisite approaches, techniques, and tools in conjunction with weather parameters and natural calamities. TOtal TIde Solution (TOTIS) software, which is rooted in harmonic analysis, is one of the most often used software in Malaysia. This study aims to interpret the current circulation and tidal pattern at the Selangor River, Kuala Selangor, Selangor Darul Ehsan. A period of one-month data is retrieved via Valeport 740 Tide Gauge from tide gauge station, whereas the current data are retrieved via Valeport Current Meter 105, which are used to analysed. The latest updated data period for the tide gauge station utilised are based on the availability of data. Therefore, tides are predicted using 33 resolved constituents for two years, starting from January 2021 until December 2022. Tidal analysis generates tidal constituents, which are then used for tidal prediction. Root Mean Square Error (RMSE) and datum offset are used to evaluate software's output. It signifies that TOTIS software is trustworthy and reliable in terms of tidal analysis and prediction accuracy. The highest river current records with high speed occur during high tide phenomenon. The output data for magnitude of river current speed are derived satisfactorily with high precision. It aids in monitoring and analyse of an appropriate method to prevent or reduce additional river erosion.

Assessing the Projected Changes in European Air Stagnation due to Climate Change

Abstract Air pollution is a major environmental threat to human health. Pollutants can reach extreme levels in the lower atmosphere when weather conditions permit. As pollutant concentrations depend on scales and processes that are not fully represented in current global circulation models (GCMs), and it is often too computationally expensive to run models with atmospheric chemistry and aerosol processes, air stagnation is often used as a proxy for pollution events with particular success in Europe. However, the variables required to identify air stagnation can have biases in GCM output, which adds uncertainty to projected trends in air stagnation. Here, the representation of air stagnation in GCMs is assessed for Europe in the historical period and in end-of-century projections based on a high-emission scenario using three methods for identifying air stagnation. The monthly frequency of stagnation during summer and autumn is projected to increase with climate change when stagnation is identified by a well-established index. However, this increase is not present when air-stagnation frequency is estimated using a statistical model based on the synoptic- to large-scale atmospheric circulation. This implies that the projected increases in air stagnation are not driven by an increase in frequency or severity of large-scale circulation events that are conducive to stagnation. Indeed, projected changes to the atmospheric circulation in GCMs, in particular a reduction in atmospheric block frequency, would suggest a reduction in future air stagnation. Additional analyses indicate that the projected increases in stagnation frequency follow the trend toward more frequent dry days, which is apparently unrelated to the large-scale drivers of air stagnation.

A New Topology and Modulation Strategy to Suppress the Leakage Current in Transformerless Cascaded H-Bridge Inverters in PV Application

The use of transformerless inverters is common due to the lower cost, lighter weight, and higher efficiency. The lack of the transformer leads to the leakage current circulation through the parasitic capacitors, which increases the power losses, electromagnetic interferences, and safety issues. In this article, first, the proposed cascaded H-bridge (CHB) -based inverter’s equivalent common-mode (CM) model is determined. Then, a new multicarrier pulsewidth modulation strategy is proposed to suppress the leakage current. In the presented method, new redundancy states are provided due to the use of just one blocking switch. These extra redundancy states and the proposed modulation strategy help to keep the CM voltage (CMV) constant and suppress the leakage current. The validity of the proposed solution is verified by simulation in the MATLAB/Simulink environment. In addition, a universal prototype with a power rating of 600 W is built and tested, and the experimental results are presented to confirm the theoretical and simulation results. The experimental results show a maximum efficiency of 98.5% and a European efficiency of 98.3%. The proposed topology is also compared to the existing transformerless topologies to show its effectiveness.

Laboratory Study of Surfactant Film Compression and Boundary Transformation under the Action of Surface Waves

In this paper we present the results of a laboratory experiment simulating the mechanisms of a surfactant film localization under the action of periodic surface waves. It is shown that the film compressed by a surface wave, can be conditionally divided into three sections — the dense film region as the most distant from the wave source, the area of a diluted film and the region of relatively clean water. The paper is focused on the processes occurring in the diluted film region characterized by the transition from clean water to the dense film, where horizontal circulation currents are registered. The character of currents is varying depending on the wave amplitude so that the divergent circulation cells occur at small and large wave amplitudes, but at medium amplitudes the roller currents forming a convergence zone on the basin axis are observed. The experimentally obtained stationary distribution of surfactant concentration is compared with the previously developed model of film compression due to surface tension induced by waves. The comparison shows good agreement between the theory and the experimental results at small and large wave amplitudes. Their discrepancy at medium wave amplitudes in the diluted film region is presumably related to the presence of convergent cells which are not considered in the model.

Evaluation of the readership of the times of India newspaper and magazine in the hospitality segment in Madurai district

The study examines the factors that influence the readership of daily newspapers and magazines in guests staying at hotels. The study attempts to gain a granular understanding of the Times of India newspaper’s performance within the changing consumer behaviour trends observed in the hospitality market in Madurai District. The major factors which directly shift the satisfaction of the readers are determined, these factors are then assessed on their interactional nature with other decision variables to implement the best strategies to create increased readership. The tests are conceptualized to offer objective functions to improve the current circulation system of the Times of India daily newspaper. The linear relationship of the major factors was determined using the PLUM ordinal regression analysis. The results give clarity into the sales & marketing efforts needed to succeed in the hotel segment for the print media industry. The major criteria for enriching the target market characteristics of the hospitality segment by print media sales & marketing initiatives are studied in the results.