scholarly journals Reconstruction of Ocean Front Model Based on Sound Speed Clustering and Its Effectiveness in Ocean Acoustic Forecasting

2021 ◽  
Vol 11 (18) ◽  
pp. 8461
Author(s):  
Yuyao Liu ◽  
Wei Chen ◽  
Wen Chen ◽  
Yu Chen ◽  
Lina Ma ◽  
...  
Keyword(s):  
Sound Speed ◽  
Frontal Zone ◽  
Transmission Loss ◽  
Structural Characteristics ◽  
Kuroshio Extension ◽  
Reanalysis Data ◽  
Reconstruction Method ◽  
Ocean Front ◽  
Sea Area ◽  
The Kuroshio

As a mesoscale phenomenon of the ocean, the ocean front can directly affect the structural characteristics of sound speed profiles and further affect the acoustic propagation characteristics of the sea area. In this paper, we use the fuzzy C-means (FCM) algorithm to cluster the surface sound speed in the sea area of the Kuroshio Extension (KE) and detect the frontal zone of Kuroshio Extension (KEF). At the same time, the sound speed profile (SSP) is used instead of the temperature profile to establish the model of the sound speed field in the front area of the Kuroshio Extension and to improve the theoretical model of the ocean front. Compared with the actual ocean front calculated by reanalysis data, the root means square error (RSME) of the transmission loss (TL) calculated by the model is controlled below 6 dB, which proves the validity of the model. Finally, we propose the melt function in the model to forecast the depth change of the acoustic convergence area. Compared with the actual calculation result based on reanalysis data, the root means square error (RSME) of the depth forecasting after the frontal zone is 43.3 m. This reconstruction method does not rely on the high spatial resolution data of the whole sea depth and can be of referential significance to acoustic detection in the ocean front environment.

scholarly journals Ocean Front Reconstruction Method Based on K-Means Algorithm Iterative Hierarchical Clustering Sound Speed Profile

2021 ◽  
Vol 9 (11) ◽  
pp. 1233
Author(s):  
Yuyao Liu ◽  
Wei Chen ◽  
Yu Chen ◽  
Wen Chen ◽  
Lina Ma ◽  
...  
Keyword(s):  
Hierarchical Clustering ◽  
Gulf Stream ◽  
Sound Speed ◽  
Frontal Zone ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Reconstruction Method ◽  
Speed Profile ◽  
Sound Speed Profile ◽  
Ocean Front

As one of the most common mesoscale phenomena in the ocean, the ocean front is defined as a narrow transition zone between two water masses with obviously different properties. In this study, we proposed an ocean front reconstruction method based on the K-means algorithm iterative hierarchical clustering sound speed profile (SSP). This method constructed the frontal zone from the perspective of SSP. Meanwhile, considering that acoustic ray tracing is a very sensitive tool for detecting the location of ocean fronts because of the strong dependence of the transmission loss (TL) on SSP structure, this paper verified the feasibility of the method from the perspective of the TL calculation. Compared with other existing methods, this method has the key step of iterative hierarchical clustering according to the accuracy of clustering results. The results of iterative hierarchical clustering of the SSP can reconstruct the ocean front. Using this method, we reconstructed the ocean front in the Gulf Stream-related sea area and obtained the three-dimensional structure of the Gulf Stream front (GSF). The three-dimensional structure was divided into seven layers in the depth range of 0–1000 m. Iterative hierarchical clustering SSP by K-means algorithm provides a new method for judging the frontal zone and reconstructing the geometric model of the ocean front in different depth ranges.

scholarly journals Mesoscale SST Dynamics in the Kuroshio–Oyashio Extension Region

2019 ◽  
Vol 49 (5) ◽  
pp. 1339-1352 ◽  
Author(s):  
Zhao Jing ◽  
Ping Chang ◽  
Xuan Shan ◽  
Shengpeng Wang ◽  
Lixin Wu ◽  
...  
Keyword(s):  
Kuroshio Extension ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Reanalysis Data ◽  
Sea Surface ◽  
Height Anomaly ◽  
Theoretical Expression ◽  
Surface Salinity ◽  
Density Anomaly ◽  
The Kuroshio

Abstract Mesoscale eddies have been extensively studied based on the sea surface height anomaly (SSHA). However, it is the sea surface temperature anomaly (SSTA) that is vital to the mesoscale eddy–atmosphere interactions. In this study, we analyze the amplitude relationship between SSHA and SSTA (referred to as the H-T amplitude relationship) in the Kuroshio–Oyashio extension (KOE) region using both observational and reanalysis data. It is found that the spatial distribution of mesoscale SSHA variance is not coincident with mesoscale SSTA variance. The former peaks in the Kuroshio extension around 35°N whereas the latter is strongest in the Oyashio extension around 40°N. Regression analyses indicate that the rate of SSTA change per SSHA change is 1.8°C m−1 in the Kuroshio extension (145°–160°E, 34°–36°N) but increases drastically by a factor of 3–4 to 6.2°C m−1 in the Oyashio extension (145°–160°E, 39°–41°N). A theoretical expression for the H-T amplitude relationship is derived. Analyzing this expression suggests that the stronger H-T amplitude relationship in the Oyashio extension than the Kuroshio extension is mainly attributed to 1) the smaller thermal expansion coefficient due to the colder background SST, 2) the stronger salinity compensation effect that works against the contribution of SSTA change to sea surface density anomaly (SSDA) change, and 3) the shallower vertical structure of mesoscale eddies. The second factor is ascribed to the strong surface salinity front in the Oyashio extension, while the third factor is found to be qualitatively consistent with the shallower baroclinically unstable modes due to the shallower density front there.

Cold air outbreak over the Kuroshio extension region

OCEANS 2009 ◽  
2009 ◽  
Author(s):  
T. G. Jensen ◽  
T. Campbell ◽  
T. A. Smith ◽  
R. J. Small ◽  
R. Allard
Keyword(s):  
Kuroshio Extension ◽  
Cold Air ◽  
Cold Air Outbreak ◽  
The Kuroshio ◽  
Kuroshio Extension Region

scholarly journals Variability of the nutrient stream near Kuroshio's origin

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chen-Tung Arthur Chen ◽  
Ting-Hsuan Huang ◽  
Chi-Hsuan Wu ◽  
Haiyan Yang ◽  
Xinyu Guo
Keyword(s):  
Pacific Ocean ◽  
Continental Shelf ◽  
East China Sea ◽  
Kuroshio Extension ◽  
Subsurface Water ◽  
East China ◽  
The East China Sea ◽  
High Productivity ◽  
China Sea ◽  
The Kuroshio

AbstractThe Kuroshio—literally “the Black Stream”—is the most substantial current in the Pacific Ocean. It was called the Black Stream because this oligotrophic current is so nutrient-poor in its euphotic zone that the water appears black without the influence of phytoplankton and the associated, often colored dissolved organic matter. Yet, below the euphotic layer, nutrient concentrations increase with depth while current speed declines. Consequently, a core of maximum nutrient flux, the so-called nutrient stream, develops at a depth of roughly between 200 and 800 m. This poorly studied nutrient stream transports nutrients to and supports high productivity and fisheries on the East China Sea continental shelf; it also transports nutrients to and promotes increased productivity and fisheries in the Kuroshio Extension and the subarctic Pacific Ocean. Three modes of the Kuroshio nutrient stream are detected off SE Taiwan for the first time: one has a single-core; one has two cores that are apparently separated by the ridge at 120.6–122° E, and one has two cores that are separated by a southward flow above the ridge. More importantly, northward nutrient transports seem to have been increasing since 2015 as a result of a 30% increase in subsurface water transport, which began in 2013. Such a nutrient stream supports the Kuroshio's high productivity, such as on the East China Sea continental shelf and in the Kuroshio Extension SE of Japan.

A Positive Feedback Process Related to the Rapid Development of an Extratropical Cyclone over the Kuroshio/Kuroshio Extension

2018 ◽  
Vol 146 (2) ◽  
pp. 417-433 ◽  
Author(s):  
Hidetaka Hirata ◽  
Ryuichi Kawamura ◽  
Masaya Kato ◽  
Taro Shinoda
Keyword(s):  
Water Vapor ◽  
Positive Feedback ◽  
Heat Supply ◽  
Rapid Development ◽  
Kuroshio Extension ◽  
Heat Fluxes ◽  
Latent Heating ◽  
Sensible Heat ◽  
Feedback Process ◽  
The Kuroshio

Abstract The active roles of sensible heat supply from the Kuroshio/Kuroshio Extension in the rapid development of an extratropical cyclone, which occurred in the middle of January 2013, were examined by using a regional cloud-resolving model. In this study, a control experiment and three sensitivity experiments without sensible and latent heat fluxes from the warm currents were conducted. When the cyclone intensified, sensible heat fluxes from these currents become prominent around the cold conveyor belt (CCB) in the control run. Comparisons among the four runs revealed that the sensible heat supply facilitates deepening of the cyclone’s central pressure, CCB development, and enhanced latent heating over the bent-back front. The sensible heat supply enhances convectively unstable conditions within the atmospheric boundary layer along the CCB. The increased convective instability is released by the forced ascent associated with frontogenesis around the bent-back front, eventually promoting updraft and resultant latent heating. Additionally, the sensible heating leads to an increase in the water vapor content of the saturated air related to the CCB through an increase in the saturation mixing ratio. This increased water vapor content reinforces the moisture flux convergence at the bent-back front, contributing to the activation of latent heating. Previous research has proposed a positive feedback process between the CCB and latent heating over the bent-back front in terms of moisture supply from warm currents. Considering the above two effects of the sensible heat supply, this study revises the positive feedback process.

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