Spatial Current Patterns Research Articles

Wintertime Variability of Currents in the Southwestern Taiwan Strait

AbstractA 57‐days record of surface currents observed from high‐frequency radars on the Chinese coast, along with wind records, are analyzed to investigate wintertime variability of surface currents in the southwestern Taiwan Strait. The M2 tide dominates tidal variability, and the semimajor axes of semidiurnal tidal current ellipses coincide well with bathymetry contours suggesting interactions with a propagating tidal wave. However, phase progressions suggest that this wave undergoes an angular reflection near the Taiwan Bank (TWB). Diurnal currents are less correlated to bathymetry perhaps because many different diurnal tide waves interact here. Surface currents are strongly related to winds at subtidal frequencies. Subtidal along‐strait currents have a correlation of 0.8 with along‐strait winds. However, three different spatial current patterns appear depending on the strength of along‐strait winter monsoon. Downwind currents occur when northeasterly wind is stronger than 10 m s−1. For medium winds, a gradual change in the pattern of currents is observed, including an offshore flow north of the TWB. In low winds conditions, when winds can be either northeasterly or (sometimes) southwesterly, the eastward flow along the northern edge of the TWB increases to 20 cm s−1; elsewhere flow is to the northeast. This forms a counter‐wind current when winds are from the northeast. By investigating the momentum balance, we find that in along‐strait direction wind stress and pressure gradient are important over the TWB, and a geostrophic balance dominates north of bank. In the cross‐strait direction, momentum is dominated by a geostrophic balance over the entire region.

The spatial current structure in the Indonesian Seas in November 2014, during The Expedition of Widya Nusantara (EWIN)

The spatial current patterns in the Indonesian seas were mapped based on a wide range of snapshot observations during the Expedition of Widya Nusantara (EWIN 2014) Leg 1 in November 2014. The current profiles were measured using the Shipboard Acoustic Doppler Current Profiler (SADCP) of the RV Baruna Jaya VIII. This study is aimed to reveal the current system in the Indonesian seas from observation. Remarkable current patterns of the Indonesian throughflow (ITF) were observed penetrating via the Mindanao Strait, southern Makassar Strait, and Lifamatola Passage, including its recirculation in the northern Maluku Sea and in the Sulawesi Sea. These results suggested that during the late Southeast Monsoon (SEM), the upper layer ITF is still significantly penetrating the Indonesian seas. The indication of anticyclonic and cyclonic circulations in the upper 50 m and lower 75 m, respectively, was also observed in the western Banda Sea

Electronic transport and spatial current patterns of 2D electronic system: A recursive Green’s function method study

Based on the scanned probe microscopes, the local current properties in a nanodevice can be clearly exposed. However, it is still a big challenge to experimentally observe the atomic scale varying current pattern. A numerical-aided method is therefore very important for getting the local current information in a microsystem. In this study, we show the nonequilibrium Green’s function method to calculate the transport properties of two-terminal devices. For applying this method to larger systems, a recursive procedure is present in detail. The correctness of this method is confirmed by calculating the transport properties of a clean 2DEG. The conductance steps in such a sample match the corresponding band structure very well. Then, we calculate the current patterns in quantum point contact under a saddle-point potential. Several current jets can be clearly spotted which correspond to transport channels in quantum point contact. Meanwhile, the interference streaks are spotted near the edges of the device due to the reflection of electrons at the edges.

Spatial current patterns, dephasing and current imaging in graphene nanoribbons

Using the non-equilibrium Keldysh Green's function formalism, we investigate the local, non-equilibrium charge transport in graphene nanoribbons (GNRs). In particular, we demonstrate that the spatial current patterns associated with discrete transmission resonances sensitively depend on the GNRs' geometry, size and aspect ratio, the location and number of leads and the presence of dephasing. We identify a relation between the spatial form of the current patterns, and the number of degenerate energy states participating in the charge transport. Furthermore, we demonstrate a principle of superposition for the conductance and spatial current patterns in multiple-lead configurations. We demonstrate that scanning tunneling microscopy can be employed to image spatial current paths in GNRs with atomic resolution, providing important insight into the form of local charge transport. Finally, we investigate the effects of dephasing on the spatial current patterns, and show that with decreasing dephasing time, the current patterns evolve smoothly from those of a ballistic quantum network to those of a classical resistor network.

Atomic Resolution Imaging of Currents in Nanoscopic Quantum Networks via Scanning Tunneling Microscopy

We propose a new method for atomic-scale imaging of spatial current patterns in nanoscopic quantum networks by using scanning tunneling microscopy (STM). By measuring the current flowing from the STM tip into one of the leads attached to the network as a function of tip position, one obtains an atomically resolved spatial image of "current riverbeds" whose spatial structure reflects the coherent flow of electrons out of equilibrium. We show that this method can be successfully applied in a variety of network topologies and is robust against dephasing effects.

静岡県馬込川河口域における非対称な流況場と堆砂特性

This paper investigates asymmetric current fields and resulting sedimentation characteristics observed around the Magome River mouth. Field survey was first conducted to obtain detailed bathymetry of the river mouth and to capture spatial current patterns by tracing wooden chips floated on the water surface. Image rectification technique was utilized to track the actual coordinates of wooden tracers. Time-varying water level and flow velocity near the bottom were also measured and, not only yielded time-varying tidal characteristics, did these data support the validity of estimated current patterns using wooden tracers. Circulation current patterns induced by broken waves were clearly observed in the area where the distance between two jetties was widened and local sedimentation was observed in the landward edge of this circulation current. This circulation current also caused asymmetric distributions of tidal current velocity across the narrow river mouth. Numerical analysis was finally conducted to investigate the influence of observed asymmetric current on the sand discharge rate at the river mouth.