Surface Current Patterns Research Articles

Assimilation of Surface Geostrophic Currents in the East Sea Using the Ensemble Kalman Filter

The conventional ocean data assimilation process typically involves assimilating hydrographic data, such as temperature and salinity measurements, obtained from both satellites and in-situ observations. This study introduces a novel approach to enhance ocean circulation modeling by assimilating surface geostrophic currents derived from satellite altimetry data using the ensemble Kalman filter. To match the time scales for the variability in the observed surface geostrophic currents and the model currents, the current velocities from the model were low-pass filtered. The optimal cut-off period for the low-pass filter was determined to be 31 days in the East Sea. Eight sensitivity experiments were then conducted to examine the effects of observation error and low-pass filtering during the assimilation of surface geostrophic current data. Assimilation experiments with surface geostrophic current data improved surface currents but had minor negative impacts on the temperature and salinity when compared with assimilation experiments without surface geostrophic current data. Notably, the experiment with an observation error of 10 cm/s for the geostrophic current outperformed the other experiments. Surface geostrophic current assimilation improved the sea surface temperature during winter and effectively modified surface current patterns during autumn in the East Sea. Assimilating satellite-derived surface geostrophic currents in the ocean circulation model thus enhanced the accuracy of surface circulation simulation. This improvement in ocean analysis data offers significant benefits for understanding ocean climate change and for developing marine management strategies.

Inset-fed quad-port hexagonal-shaped MIMO T-shaped slots on patch with slots on ground plane antenna for IoT and X-band applications

A compact and novel inset-fed hexagonal-shaped multiple input multiple output patch (IHMP) antenna with T-shaped slot is designed for IoT and X-band applications. The IHMP antenna comprises with four identical hexagonal-shaped radiating elements. In order to achieve better diversity performance and low mutual coupling, radiating elements P1, P4 are positioned side by side with ideal distance and P2, P3 are positioned opposite to P1, P4. The proposed hexagonal-shaped MIMO antenna is prototyped on low-cost Fr-4 substrate with the dimensions of 28 × 28 × 1.6 mm3. It achieves dual bandwidths (S11 < −10 dB) of 1.37 GHz (2.12–3.49 GHz) and 1.69 GHz (8.07–9.76 GHz) at 2.5 and 8.7 GHz resonating frequencies. The IHMP antenna having gain of 5.68dBi, and 5.51dBi at 2.5 and 8.7 GHz, respectively. At operating frequencies, surface current distribution and radiation patterns are examined. To calculate the diversity performance of the IHMP antenna, MIMO parameters envelope correlation coefficient < 0.05 within the band, diversity gain > 9.9 within the band, total active reflection coefficient, channel capacity loss < 0.2 bits/sec/Hz, and mean effective gain −3 dB < MEG < −6 dB are also investigated. The simulated and experimentally obtained results are presented and they are in fine agreement.

Asymmetric transmission for linearly polarized terahertz waves without polarization conversion

In this study, a novel metamaterial (MM) architecture is presented, which comprises cut wires and split-ring resonators (SRRs) and demonstrates asymmetric transmission characteristics. Unlike previously reported multi-layer chiral structures, spatial asymmetry is introduced by aligning the cut wires and SRRs with the propagation direction of electromagnetic waves. This innovative alignment effectively disrupts time-reversal symmetry, enabling asymmetric transmission. A thorough analysis of the electromagnetic field distribution and surface current patterns offers insights into the fundamental mechanisms underlying this asymmetric transmission. Notably, the ability of this MM design to maintain the polarization state of transmitted waves positions it as a promising candidate for terahertz systems applications.

Pasang Surut dan Arus di Muara Sungai Kapuas Sepok Pangkalan, Teluk Bengkolan, Kalimantan Barat

Tides and currents influence the dynamics and biochemical circulation in a bay or estuary. This research aims to conduct an initial study of tides and currents in Bengkolan Bay, which is home to the mangrove ecosystem in West Kalimantan Province. Elevation and current measurements were carried out for 15 days at the mouth of the Kapuas River Sepok Pangkalan (north side of Bengkolan Bay) using tidal palms and drifters. The measurement results show that the pattern of water surface movement and currents at the research location is very dependent on ocean tidal patterns. Diurnal tides play a very large role (10 times) compared to semidiurnal tides. This big role causes the type of tides in Bengkolan Bay to be diurnal. Although semidiurnal tides have a small contribution, shallow water tidal constituent are actually caused by semidiurnal tidal energy dissipation.

Miniaturization of antenna using metamaterial loaded with CSRR for wireless applications

This paper proposes a compact decagon antenna for wireless applications based on inspired metamaterial (MTM) loaded with a modified complementary split ring resonator (CSRR). A MTM loaded with CSRR is used to achieve a size reduction of 50% when compared to a traditional antenna. The suggested decagon antenna's ground plane has been loaded with CSRR. The antenna was made on an FR4 substrate with a thickness of 1.6 mm and εr=4.4 and has a very small dimension of 0.288 λ_0x0.272 λ_0x0.013 λ_0 (where λ_0 represent center frequency at 2.4 GHz). The given antenna has a 90 MHz bandwidth (2.40-2.50 GHz) with a peak gain of 2.36 dB. The presented design is validated by showing simulated results of the S parameter, VSWR, gain, surface current, and radiation pattern. The proposed antenna is well suited for wireless applications.

A Multiband and Multifunctional Metasurface for Linear and Circular Polarization Conversion in Reflection Modes

Multifunctional integrated meta-devices are the demand of modern communication systems and are given a lot of attention nowadays. Most of the research has focused on either cross-polarization conversion (CPC) or linear-to-circular (LP–CP) conversion. However, simultaneously realizing multiple bands with good conversion efficiency remains crucial. This paper proposes a multiband and multifunctional dual reflective polarization converter surface capable of converting a linearly polarized (LP) wave into a circularly polarized (CP) wave, in frequency bands of 12.29–12.63 GHz, 16.08–24.16 GHz, 27.82–32.21 GHz, 33.75–38.74 GHz, and 39.70–39.79 GHz, with 3 dB axial ratio bandwidths of 2.7%, 40.15%, 14.6%, 13.76%, and 0.2%, respectively. Moreover, the converter is capable of achieving CPC with a polarization conversion ratio (PCR) that exceeds 95%, within the frequency ranges of 13.10–14.72 GHz, 25.43–26.00, 32.46–32.56 GHz, and 39.14–39.59 GHz. In addition, to identify the fundamental cause of the CPC and LP–CP conversion, a comprehensive theoretical investigation is provided. Furthermore, the surface current distribution patterns at different frequencies are investigated to analyze the conversion phenomena. A sample prototype consisting of 20 × 20 unit cells was fabricated and measured, verifying our design and the simulated results. The proposed structure has potential applications in satellite communications, radar, stealth technologies, and reflector antennas.

Enriched Regions of 228Ra Along the U.S. GEOTRACES Pacific Meridional Transect (GP15)

AbstractThe half‐life of 228Ra (5.7 years) aligns well with near‐surface and near‐bottom ocean mixing timescales. Because 228Ra is sourced from sediments, regions of enhanced activity represent water that has recently interacted with sediments on the continental margin or seabed. The GP15 meridional transect from Alaska to Tahiti along152°W encountered several regions in the upper ocean where 228Ra was enriched. These enrichments follow surface and subsurface ocean current patterns and pair with earlier measurements of 228Ra and transient radionuclides to reveal the origins of these enriched regions. An enriched region at Alaska margin stations 1–3 was sourced locally but did not extend to the Alaskan trench at station 4. A large shallow region between 47° and 32°N. was sourced from the west by the North Pacific Current; another shallow enriched region between 11° and 5° N was also sourced from the west by the North Equatorial Countercurrent. Subsurface enrichments (100–400 m) between 18 and 47°N were associated with Central Mode Water and North Pacific Intermediate Water. The 228Ra activities in the upper Pacific were six times lower than activities in the Atlantic. In deep waters the primary enrichment was 27°–47°N. Two stations (32° and 37°N) were especially enriched, having near‐bottom inventories several times greater than other stations. With these two exceptions the remaining Pacific stations exhibited averaged inventories lower than those in the Atlantic. There was one region of enriched 223Ra (half‐life = 11 days) above the Puna Ridge near Hawaii.

TRIPLE-BAND CIRCULAR PATCH MICROSTRIP ANTENNA FOR WIRELESS COMMUNICATION

In this article, a triple-band patch antenna using a circular patch microstrip antenna is constructed with a low-profile patch antenna using a 1.5 mm thick FR4 substrate (εr= 4.3). As mobile devices like smartphones and laptops become more common, the usage of tiny, triple-band antennas has also become more common. The objective of this research is to design a circular patch antenna with a 3–11 GHz dipole-like radiation pattern, which may be used for industrial, scientific, and medical reasons. For the suggested triple-band antenna design, the slotted radiator with six arches and the reduction of the ground plane are among the components. In addition, the standard 50 Ω RF transmission line stimulates the patch antenna; this transmission line is attached to the microstrip line by an impedance-compliant SMA connection. Data from the experiments are obtained, evaluated, and compared; to the patch's surface current distributions, gain, and radiation patterns. According to the measurements, S11 has an impedance bandwidth in the 5.5 GHz band of less than -10 dB, 6.6 GHz band, and 10.4 GHz band at all frequencies. The superb radiation pattern performance, relatively consistent gain throughout the bands, and practical bandwidths of this antenna make it a good choice for C-band and dual X-band applications.

Study of Driving Force and Surface Current Patterns in Labuan Bajo from High Frequency Radar data from October to December 2018

Surface ocean current data in Labuan Bajo from October to December 2018 for determine the characteristics of the surface current and identify the influence of wind and tides in generating surface current. The current data set is derived from measurements of high frequency (HF) radar, which operates on the electromagnetic wave spectrum at high frequency or short wave. Method of data analysis by processing surface current velocity and direction of the zonal and meridional into spatial and temporal graphs. The result showed the average current speed in October was 0.13 m/s, the average current speed in November was 0.12 m/s, and the average current speed in December was 0.09 m/s. The empirical orthogonal function (EOF) Mode 1 has a variance of 56.2% because of the tides, Mode 2 has a variance of 26.6% because of bi-weekly variability, and Mode 3 has a variance of 17.2% because of the intra-seasonal period. This shows that tides have a greater influence on the study region than any other driving force. These results are intended to be useful to the public, particularly in terms of sustainable coastal marine management in Labuan Bajo. Especially in terms of preventing boat accidents caused by ocean currents.

Performance analysis of global HYCOM flow field using Argo profiles

ABSTRACT Flow field data generated by ocean models are important for simulating ocean currents and circulation patterns, which are essential components in digital Earth construction. To evaluate the accuracy of model-simulated flow fields, Array for Real-time Geostrophic Oceanography (Argo) float observations can be considered benchmarks. In this study, a novel method for comparing Argo profiles with 3-dimensional trajectories obtained by simulating Argo floats in Hybrid Coordinate Ocean Model (HYCOM)-provided flow fields was proposed. Surface and subsurface trajectories were calculated, and their spatial matching characteristics were analyzed. The results demonstrated that (1) the HYCOM surface and subsurface flow fields generally conform to the basic characteristics and trends of ocean currents; (2) the HYCOM sea surface current field error pattern exhibits a symmetrical distribution centered on the equator in the Northern and Southern Hemispheres and increases with increasing latitude; and (3) the HYCOM subsurface flow field exhibits regional differences, with the largest differences in the Gulf Stream, North Atlantic Warm Current, and Westerly Wind Drift region. Through analysis of the disparities between HYCOM and Argo data, the effectiveness of using model simulation data can be enhanced, and the accuracy and dependability of ocean models can be improved.

On the variability of ocean surface current in the Bay of Bengal using self-organizing map (SOM)

The self-organizing map (SOM) is implemented to explore various ocean surface current patterns in the Bay of Bengal (BoB) from 1993 – 2015 based on a satellite sensor-derived current product estimated by combining geostrophic, wind-driven, and temperature-driven current components. Four major patterns/groups corresponding to some of the primary current systems in the BoB are obtained (G1, G2, G3, and G4). The start and end of all the patterns drastically varied year to year and are primarily related to positive and negative Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) years. The correlation of ENSO and the following year's transition date from WBC to SMC is 0.70, while -0.76 for IOD and transition date from EICC to WMC. Through temporal analysis and monthly frequency of occurrence measurements, this study reveals that the first significant dominant pattern is observed during the summer monsoon season when the southwest monsoon current (SMC) is visible near the south of Sri Lanka (pattern G1). The following major pattern is the winter monsoon current (WMC) in the south of Sri Lanka (pattern G4), whose formation is contributed by the northeast monsoon and westward propagating Rossby wave. The other two dominating patterns are East India Coastal Current (EICC, G2) and Western Boundary Current (WBC, G3). SOM analysis is then performed on WBC with 9 nodes (3×3,namedP1toP9), which captures the meandering nature (P3), and meandering in the presence of SMC (P2), the straight nature (P7) and in the presence of SMC (P4). The spatial and temporal analysis of nine SOM patterns (P1 – P9) suggests that the non-meandering nature of WBC (P4) occurs more frequently than meandering WBC (P2).

Identification of Surface Current Patterns in Small Pelagic Fishing Areas in the Western Season of the Spermonde Islands, Indonesia

Monsoonal wind commonly affects Indonesian waters, blowing in an adversative direction by turns in one year. These are well-known as west and east monsoonal winds. Spermonde Archipelago waters, located on the west coast of the southern part of South Sulawesi, is a water region comprising various islands with relatively shallow waters and situated in Makassar Strait. The study aimed to identify the pattern of current surface movement in each monsoon period, especially on the west monsoon on Small Pelagic Fish Catches Area. Data used in this study consisted of primary and secondary data. Primary data were obtained in the field for three months (April to Jun, second monsoonal transition monsoon into east monsoon). In December, the wind pattern was dominated from the northwest with a maximum speed of 8 knots. The surface current pattern offshore was from the south (0.16 m/s) to the north with decreasing speed (0.03 m/s). Meanwhile, in low tide, the current surface pattern offshore was from the north (speed may reach up to 0.04 m/s) to the south with an increasing speed of 0.20 m/s. The peak of the west monsoon occurs in January to February with high rainfall, and wind speed is dominated from south-west and west directions. Current pattern occurred in the offshore, either at high or low tide, showed similar pattern, which was divided into east and south directions.

Generalized magnetostatic target field method for shielded magnetic field coils in a separable coordinate system.

A theoretical method is described to analytically calculate a pair of surface current densities, which produce a desired static magnetic field in one region of the space and zero magnetic field in another. The analysis is based on the known relationship between a surface current density and a stream function, the equivalence of stream functions and surface magnetic dipole density, and the scalar potential representation of the associated magnetic field in free space. From these relations, we formulate the magnetostatic problem, which is often treated as a vector field problem, as a scalar field problem in which a two-dimensional scalar field (stream function) is related to a three-dimensional one (magnetic scalar potential) via the differentiation of the electrostatic Green's function 1/|r-rs|. It is shown that, in a coordinate system in which a separated form of the Green's function exists (separable coordinate system), there exists a simple relationship between a harmonic component of a stream function and a harmonic component of the magnetic scalar potential. The method is applied to calculate idealized surface current patterns for actively shielded, linear gradient field coils in the Cartesian, cylindrical, and spherical coordinates.

Hydrodynamic Characteristics and Sediment Distribution Patterns in Wulan Delta Estuary, Demak, Indonesia

The Wulan Delta, located in Wedung, Demak, was formed due to the sedimentation process of the Wulan and Serang rivers. Sediment transport starts from rivers to the sea; the process carries nutrients and various chemicals derived from agricultural, industrial, or household activities. This study aims to analyze the characteristics of hydrodynamics, suspended sediment, and bottom sediments in the Wulan Delta waters, Demak. Field data were collected in transitional season two (October) 2022. The obtained data were then analyzed in the laboratory at the Faculty of Fisheries and Marine Science. Results showed that the speed of the surface current in the study area ranged from 0 to 0.1 m/s in spring tide conditions with a surface current pattern coming from the direction of Semarang toward Jepara and 0–0.18 m/s in neap tide conditions with a current pattern coming from the direction of Jepara toward Semarang. The Wulan Delta has a sedimentary characteristic dominated by fine silt, which is as much as 82%–98%, with a deposition characteristic dominated by wave energy that causes successful sediment sorting with a sorting index of −2.25 to 2 and strongly asymmetrical to a small size with a skewness curve value of two.

DESAIN ANTENA MICROSTRIP RECTANGULAR ARRAY 1x4 PADA FREKWENSI 2.2 UNTUK RADAR KAPAL

This study aims to analyze antennas' characteristics at a frequency of 2.2 GHz, including the value of return loss, VSWR, gain, bandwidth, surface current, and radiation pattern. The antenna characteristics have been designed using simulations made with FR-4 substrates with a dielectric constant ε_r= 4.3 and substrate thickness (h) = 1.6 mm and copper patches with a patch thickness of 0.035 mm. Single antennas are made first to get the desired parameters, then continue to make 1x2 and 1x4 antenna arrays. The feeding antenna array is arranged using the Wilkinson power divider technique on the side of the patch. Antenna array planning aims to increase the antenna gain value as well as the antenna directivity value. From the simulation results, successive values were obtained starting from a single antenna, a 1x2 antenna array, and a 1x4 antenna array which included return loss of -22 dB, 25.9 dB, and -15.3 dB. Swr values are 1.1,1.1,1,1.4 each. The gain values are 3.38 dB, 5.52 dB, 7.84 dB, respectively. Antenna bandwidth is obtained by 100 MHz, 400 MHz, and 200MHz. The angular width obtained is 99.40, 92.20, and 80.20.

Hydrodynamic model approach to study the pattern of sea surface currents around the Tanjungpinang City reclamation site

This study aims to study the pattern of sea surface currents at the research site using a hydrodynamic modelling approach. Hydrodynamic models are approaches used to study large-scale and long-term patterns of sea surface currents (past, present, and future projections). Study on the sea surface currents at the research site was conducted by constructing the 2D hydrodynamics model which was simulated for 30 days to describe the pattern of sea surface current at the research site. Finite differences methods were used in solving the equation of the 2D hydrodynamic model. Validation result showed that the model has a good performance and it was relevance to in-situ measurement. The simulation results showed a significant difference in current velocity during high and low tides. Current velocity is higher at high tide (0.15-0.18 m/s) than at low tide (0.06-0.10 m/s). At high tide, current direction is dominant towards the southeast and southwest. At low tide, current direction is dominant to the north and northwest. The sea surface currents at the research site are strongly influenced by tidal conditions. At high tide, sea surface current will move towards the coast and at low tide the sea surface current will move away from the coast.

Seasonal spreading and age of Citarum River water in the Jakarta Bay

Citarum River is considered one of the most polluted rivers in the world, which could contribute to Jakarta Bay’s environmental quality. The purpose of this study is to predict the impact of the Citarum River on Jakarta Bay’s pollution by understanding the river’s seasonal spreading and water age. This study uses numerical ocean modeling for the largest river flowing to Jakarta Bay in 2016. The constituent-oriented age and residence time theory (CART), which supports a solution to the environmental problems in this bay, was employed to comprehend long-term river water movement. The CART’s water age calculation module is embedded in a numerical hydrodynamic model to generate the temporal variation and spatial distribution of Citarum River water. Hydrographic observations were used to validate the model in February, May, and November this year. Surface current distribution patterns, which were controlled by surface wind stress and river discharge, determined the seasonal spread of the Citarum River water distribution. Meanwhile, the average age of Citarum River water in Jakarta Bay was a few days.

Effects of Closed-Loop Devices on Omnidirectional Beam Patterns Radiated from WAVE Monopole Antennas

This study investigates the influence of closed-loop devices on omnidirectional beam patterns radiated from a Wireless Access for Vehicle Environment (WAVE) monopole antenna for facilitating communication stability in Vehicle-to-Vehicle and Vehicle-to-Everything technology. Single, dual, and quadruple closed-loop devices were introduced into the monopole antenna, and their surface current density and radiation beam patterns were analyzed by using the high-frequency structure simulator (HFSS) and computer simulation technology (CST) programs. As the closed-loop devices reflected the signal radiated from the antenna, the distribution of the surface current was concentrated around the monopole due to the creation of a closed-loop surface current path, which increased the gain value. The average gain was considerably increased by introducing closed-loop devices. The proposed antenna has an average gain of 1.57 dBi and a peak gain of 6.29 dBi at the operating frequency. Furthermore, omnidirectional beam patterns with a beam width of 359° were obtained by introducing four closed-loop devices into the monopole antenna, which eliminated nearly all null points in the frequency range of 5.85–5.925 GHz.

Mangroves in the “Plasticene”: High exposure of coastal mangroves to anthropogenic litter pollution along the Central-West coast of India

Anthropogenic litter is a ubiquitous stressor in the global ocean, and poses ominous threats to oceanic biodiversity and ecosystem functioning. At the terrestrial-ocean interface, tropical mangrove forests are subject to substantial exposure to mismanaged litter from inland and marine sources. While the effects of litter in different marine ecosystems are well-documented, research on the ecological consequences of litter pollution on mangroves remain nascent stage. Here, we investigated anthropogenic litter concentration, composition, probable sources, and impact on coastal mangroves along the Central West coast of India. The mean concentration of trapped litter was measured 8.5 ± 1.9 items/m2 (ranged 1.4 ̶ 26.9 items/m2), and 10.6 ± 0.5 items/tree (ranged 0 ̶ 85 items/tree) on the mangrove floor and mangrove canopy, respectively. Plastic dominated 83.02 % of all litter deposited on the mangrove forest floor and 93.4 % of all entangled litter on mangrove canopy. Most litter comprised single-use plastic products across all surveyed locations. Mangrove floor cleanliness was assessed using several indices, such as Clean Coast Index, General Index, Hazardous Items Index, and Pollution Load Index, reiterating an inferior cleanliness status. The pollution load index indicates “Hazard level I" plastic pollution risk across the mangroves. Litter concentration differed markedly across all sites. However, a significantly higher concentration of stranded litter was detected in the densely populated urban agglomeration and rural areas with inadequate solid waste management. Probable sources of litter indicate land-based (local) and sea-originated (fishing). Supportive information on the transport and accumulation of marine litter is examined based on the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) model version 2 reanalysis of surface wind and current pattern across the Arabian Sea followed by MIKE simulated tide-induced coastal current. Mangrove pneumatophores and branches were found to be damaged by entangled plastics. Hence, determining litter quantum and their probable input source is pivotal in mitigating anthropogenic litter impact on mangrove ecosystems and fostering mangrove conservation. Overall, results envisage that stringent enforcement, implementation of an integrated solid waste management framework, and general behavioral change of the public are crucial to mitigate litter/plastic pollution.

Cavity-Backed Slot V2X Antenna for Automotive Applications

In this work, a cavity-backed slot antenna has been designed to cover vehicle-to-everything (V2X) frequencies (5.85−5.9255.85-5.925 GHz). The antenna is made to be easily integrated in a vehicle windshield or rear mirror. The cavity-backed slot antenna does not require a ground plane to sit on which makes it an ideal model for below horizon performance. Antenna simulation has been done using high-frequency structure simulator (HFSS) and then on-foam and on vehicle’s windshield measurements have been carried out inside an anechoic chamber. The proposed antenna achieved a linear average gain (LAG) above 2.5 dBi in the targeted V2X elevation and azimuth angles with better than 15 dB return loss. The antenna performance has been reported in terms of reflection coefficient, surface current density, radiation pattern, LAG, and efficiency.