A method for calculating the width of the western boundary flow

Abstract

This invention relates to the field of marine reanalysis data processing technology, specifically a method for calculating the width of western boundary currents. The steps are as follows: acquiring sea surface height field and current velocity field data, preprocessing them to obtain absolute velocity and an effectiveness mask; extracting contour lines from the height field, serializing the initial current axis point set, and obtaining the initial current axis through connectivity filtering and smoothing; calculating the tangential and normal directions of the current axis points, sampling absolute current velocity within a preset range of the normal direction, selecting the position of the maximum current velocity within a threshold to correct the current axis, and processing to obtain the final current axis; using the final current axis as a reference, constructing a width search profile along the normal direction, adjusting the sampling velocity according to the step size, and determining the boundary point when it is first below the threshold, invalid, out of bounds, or a land mask, calculating the half width or full width and outputting the coordinates; this method can output the width sequence along the current axis and the corresponding boundary point coordinates in batches, reducing the uncertainty caused by manual interaction and repeated parameter adjustments, avoiding current axis offset, and improving the consistency and repeatability of the results.

Description

Technical Field

[0001] This invention relates to the field of ocean observation and ocean reanalysis data processing technology, specifically a method for calculating the width of the western boundary current. Background Technology

[0002] For example, the width of western boundary currents such as the Kuroshio Current and the Gulf Stream is an important indicator characterizing changes in mainstream structure, energy, and transport, and is widely used for path change monitoring, dynamic mechanism analysis, and model evaluation. Current width calculations typically rely on criteria such as sea surface height contour lines, sea surface velocity thresholds, or half-width at half-height (WHM) profiles: one type of method approximates the flow axis by fixing contour lines or frontal positions and then determines the boundaries on both sides; another type of method searches for the velocity maxima on a pre-defined cross-section and determines the mainstream range using a fixed threshold. The above methods still have shortcomings in practical applications: First, the resolution and error structure of different data sources, such as satellite altimeter-derived geostrophic velocity and reanalysis velocity, vary significantly, resulting in poor comparability of the same threshold / contour line when comparing across datasets; Second, nearshore, island chain, and continental shelf topography, as well as missing measurements, can cause contour line breaks, flow axis jumps, or multi-peak profiles, making the width results sensitive to manual point selection, search window, and smoothing parameters, and difficult to automate; Third, most methods lack clear quality control and anomaly handling mechanisms, resulting in discontinuous or abnormal width values ​​in the spatiotemporal series, affecting statistical and physical interpretation.

[0003] Therefore, there is an urgent need for a method to calculate the width of the western boundary current that is applicable to multi-source sea surface data, has continuous flow axis constraints and boundary determination rules, and can output quality indicators. Summary of the Invention

[0004] The objective of this application is to provide a method for calculating the width of the western boundary flow to solve the problems mentioned in the background art, the steps of which are as follows: S1.1 Obtain sea surface height field data and sea surface velocity field data of the target sea area. The sea surface height field data includes either absolute dynamic height or sea surface height. The sea surface velocity field data includes sea surface geostrophic velocity and reanalysis near-surface velocity. S2.1 Preprocess the sea surface height field data and sea surface current field data to calculate the absolute velocity and the effective mask of the absolute velocity; S3.1. Based on the sea surface height field data, extract the preset contour lines and obtain the initial flow axis point set through serialized sampling. The serialized sampling is performed in the order of either longitude or latitude. S3.2 Perform connectivity filtering and smoothing on the point set of the initial flow axis to form the initial flow axis; S4.1 Calculate the local tangential direction and construct the normal direction for each flow axis point on the initial flow axis; S4.2. Discretely sample the absolute velocity of each flow axis point on the initial flow axis within a preset search range in the normal direction of each flow axis point. Select the position of the maximum absolute velocity that meets the velocity threshold as the corrected flow axis point, thereby obtaining the corrected flow axis. S4.3. Process the corrected flow axis to obtain the final flow axis; S5.1. Using the final flow axis as a reference, construct a width search profile at each final flow axis point along the normal direction of each final flow axis point, pointing uniformly in the specified direction. S5.2 Adjust the magnitude of the absolute velocity of the flow axis point of each final flow axis obtained by sampling with a preset step size. When the absolute velocity of the flow axis point of the final flow axis obtained by sampling is lower than the threshold for the first time, an invalid value appears, an out-of-bounds condition appears, or a land mask appears, determine the position corresponding to the sampling velocity as the boundary point. S5.3 Calculate the width of the target sea area and output the coordinates of the boundary points. The width result is either the half width or the full width. S6.1 Perform anomaly handling on the width result and output a sequence of values ​​along the final flow axis at different width positions and the corresponding coordinates of the final flow axis at different width positions.

[0005] Furthermore, the preprocessing in step S2.1 includes subdomain clipping, mesh unification, interpolation resampling, missing measurement processing, and necessary time averaging.

[0006] Furthermore, the absolute velocity in step S2.1 is calculated using the sea surface geostrophic current velocity as follows: ; in, Here, u represents the absolute velocity, v represents the zonal component of the geostrophic flow velocity, and v represents the meridional component of the geostrophic flow velocity.

[0007] Furthermore, the absolute velocity in step S2.1 is calculated using the reanalysis method for near-surface flow velocity as follows: ; in, To further analyze the zonal component of the near-surface flow velocity, To further analyze the meridional component of the near-surface flow velocity.

[0008] Furthermore, the preset contour lines in step S3.1 include contour lines for absolute dynamic altitude and contour lines for sea level altitude.

[0009] Furthermore, in step S4.3, the corrected flow axis is processed using an adaptive window smoothing and continuity constraint method.

[0010] Furthermore, the specified direction in step S5.1 is the direction pointing towards the land side.

[0011] Furthermore, in step 5.3, the half-width is the distance between the current axis point and the boundary point of the final current axis, while the full width is the distance between the boundary points on both sides of the target sea area along the width direction.

[0012] Furthermore, the method for handling the anomalies of the width result in step S6.1 is as follows: when the boundary point does not meet the validity condition, the boundary point is marked as an invalid point, and the invalid point is interpolated and completed along the direction of the final flow axis.

[0013] Furthermore, the validity conditions include either the velocity of the boundary point being lower than a threshold or the position of the boundary point exceeding the maximum search distance.

[0014] The above technical solution produces the following technical effects: 1) This method is based on sea surface height field data with preset contour line constraints and adaptive normal correction. Compared with the traditional approach that relies solely on manual point selection, fixed cross-sections, or subjective thresholds, this method corrects the normal of each flow axis point on the initial flow axis one by one to obtain the final flow axis. Finally, the boundary points are determined based on the absolute velocity of the flow axis points of the sampled final flow axis. This method can output the width sequence along the flow axis and the corresponding boundary point coordinates in batches, which significantly reduces the uncertainty caused by manual interaction and repeated parameter adjustment, avoids the problem of flow axis offset, improves the consistency and repeatability of the results, and facilitates long-term sequence monitoring and operational processing.

[0015] 2) This method incorporates invalid values ​​and boundary judgment, which can suppress abrupt changes in flow axis and abnormal width values ​​in scenarios such as nearshore, island chain, continental shelf topographic interference and local missing data, improve the stability of width diagnosis, and provide reliable basic indicators for the study of western boundary current structure changes, model evaluation and marine environmental monitoring. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method for calculating the western boundary flow width according to the present invention; Figure 2 A schematic diagram of the flow axis correction results based on AVISO contour line constraints; Figure 3 A schematic diagram of the flow axis correction results based on GLORYS contour line constraints; Figure 4 The relationship between the western half width of the Kuroshio Current and latitude; Figure 5 The relationship between the western half width of the Kuroshio Current and latitude. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0020] Please refer to Figure 1-5 This embodiment will describe in detail a method for calculating the width of the western boundary flow according to the present invention, and the specific steps are as follows: S1.1 Acquire sea surface height (ADT) and sea surface velocity (SSH) data for the target sea area. The sea surface height data includes either absolute dynamic height (ADT) or sea surface height (SSH). The sea surface velocity data includes geostrophic current velocity and reanalysis near-surface current velocity. In this embodiment, absolute dynamic height (ADT) and sea surface height (SSH) are collected using AVISO, along with geostrophic current velocity. The calculation area is then set to the Kuroshio sub-domain from 120°E to 150°E and from 20°N to 40°N. Furthermore, the AVISO data spans from 1993 to 2021, and GLORYS provides global ocean temperature, salinity, and current information, with a data spanning from 1993 to 2016. AVISO and GLORYS use multi-year average data, cropped according to latitude and longitude sub-domains, to generate the final dataset for subsequent calculations. It is important to note that the sea surface height variable in AVISO data is the absolute dynamic height field (ADT), which also provides the corresponding sea surface geostrophic velocity. In AVISO data processing, the determination of the initial current axis position and subsequent adjustments are based on the absolute dynamic height field (ADT). In GLORYS data, the sea surface height variable is the sea surface height (SSH), which also provides the reanalysis near-surface current velocity. Therefore, in GLORYS data processing, the determination of the initial current axis position and subsequent adjustments are based on the sea surface height (SSH) field.

[0021] S2.1. Preprocessing is performed on sea surface height and current field data to calculate absolute velocities and their validity masks, thereby eliminating interference from invalid data and ensuring the accuracy and reliability of processing results based on valid velocity data. Specifically, preprocessing includes subdomain clipping, grid unification, interpolation resampling, missing value handling, and necessary time averaging. Subdomain clipping selects data from a specific spatial range in the original dataset, focusing on the study area and excluding irrelevant information. Grid unification converts datasets from different sources, with different resolutions or coordinate systems, into a uniform spatial grid structure, ensuring data spatial consistency. Interpolation resampling estimates unknown point data using interpolation algorithms and adjusts the data spatial resolution by increasing or decreasing it to fit the target grid. Missing value handling addresses missing values ​​in the data by using methods such as interpolation imputation, mean substitution, and nearest-neighbor imputation to restore data integrity.

[0022] Necessary time averaging: Performing periodic averaging (such as daily, monthly, or yearly averaging) on ​​time series data eliminates short-term fluctuations and highlights long-term trends or periodic characteristics.

[0023] Furthermore, the absolute velocity is calculated using the sea surface geostrophic current velocity as follows: ; in, Here, u represents the absolute velocity, v represents the zonal component of the geostrophic flow velocity, and v represents the meridional component of the geostrophic flow velocity.

[0024] Furthermore, the absolute velocity is calculated using the reanalysis method for near-surface flow velocity as follows: ; in, To further analyze the zonal component of the near-surface flow velocity, To further analyze the meridional component of the near-surface flow velocity.

[0025] S3.1. Based on sea surface height field data, preset contour lines are extracted, and an initial set of current axis points is obtained through sequential sampling. The preset contour lines include contour lines of absolute dynamic height and sea surface height. Sequential sampling is performed in either longitude or latitude. Preferably, in this embodiment, the initial current axis points are based on the ADT=110cm contour line and the SSH=70cm contour line, which can stably reflect the core position of the current axis and is beneficial for current axis tracking and subsequent model calculations.

[0026] S3.2 Perform connectivity filtering and smoothing on the point set of the initial flow axis to form the initial flow axis.

[0027] S4.1 Calculate the local tangential direction for each flow axis point on the initial flow axis and construct the normal direction.

[0028] S4.2. For each flow axis point on the initial flow axis, the local tangential direction is calculated using adjacent flow axis points, and the normal direction is constructed. Within the preset search range of the normal direction, the absolute velocity of each flow axis point on the initial flow axis is discretely sampled. The position of the maximum absolute velocity that meets the velocity threshold is selected as the corrected flow axis point, thereby obtaining the corrected flow axis. Correcting the initial flow axis can improve the flow axis positioning accuracy, accurately capture the mainstream area, and enhance the stability of the flow axis.

[0029] S4.3. Adaptive window smoothing and continuity constraint methods are used to process the corrected flow axis to obtain the final flow axis. This step forces the flow axis to maintain physical consistency in the spatial or temporal dimensions, avoiding local breaks or abrupt changes in direction caused by data errors after correction. Moreover, the processed flow axis has both smoothness and structural integrity, providing a reliable foundation for subsequent applications such as watershed delineation, flow path simulation, and meteorological system analysis.

[0030] S5.1. Using the final flow axis as a reference, construct a width search profile at each final flow axis point along the normal direction of each final flow axis point, pointing uniformly in the specified direction. The specified direction is either the direction pointing towards the land side or a preset direction.

[0031] S5.2 Adjust the magnitude of the absolute velocity of each final flow axis point obtained from sampling using a preset step size. When the absolute velocity of the final flow axis point obtained from sampling first falls below the threshold, an invalid value appears, the value goes out of bounds, or a land mask appears, determine the position corresponding to the sampling velocity as the boundary point. To avoid calculation anomalies, set a maximum search distance, for example, 3°, and set a reasonable search step size, for example, 0.05°. Determine the boundary point coordinates of each flow axis point based on the calculated western half-width.

[0032] S5.3 Calculate the width of the target sea area and output the coordinates of the boundary points. The width result is either the half width or the full width. The half width is the distance between the current axis point and the boundary point of the final current axis, while the full width is the distance between the boundary points on both sides of the target sea area along the width direction.

[0033] S6.1 Perform anomaly handling on the width results and output a sequence of values ​​along the final flow axis at different width positions, along with the coordinates corresponding to those positions. When a boundary point does not meet the validity conditions—for example, if the boundary point's velocity is below a threshold, its position exceeds the maximum search distance, or the query point's velocity represents either land or a missing NaN—the boundary point is marked as invalid. Invalid points are then interpolated along the final flow axis. In this embodiment, the preset threshold for boundary points is 0.2 m / s. Furthermore, this embodiment sets the maximum search distance to 3° to avoid infinite searching caused by anomalies. In cases where a local tangential direction cannot be defined, such as when adjacent flow axis points completely overlap, the calculation result for that point will be marked as invalid NaN.

[0034] This method uses sea surface height contour lines as initial flow axis constraints and combines them with absolute velocity for point-by-point normal correction. This avoids the flow axis offset problem caused by relying solely on fixed sea surface height contour lines, resulting in a corrected flow axis that is closer to the core region of the high-speed current. Figure 2 It is evident that the flow axis continuity is better after normal correction and smoothing in AVISO data, which can better characterize the mainstream path of the Kuroshio Current.

[0035] Furthermore, this method does not rely on specific data products; it only requires inputting the sea surface height field and its corresponding current velocity field. For example, for AVISO data, the absolute dynamic height field (ADT) and its geostrophic velocity component can be used; for GLORYS data, the sea surface height (SSH) and its reanalysis surface current velocity component can be used. Please refer to further information. Figure 3 The method can also obtain continuous and stable flow axis identification results in GLORYS data, indicating that it has strong applicability to multi-source data.

[0036] Please refer to further information. Figure 4-5 The width identification results obtained from AVISO and GLORYS data can be compared and analyzed, demonstrating that this method has a consistent processing flow and comparable output results under different data source conditions. It can be used for monitoring changes in western boundary current structure, cross-validation of multi-source data, and ocean model assessment. The method's relatively simple process is suitable for batch processing of long-term series data, and it has good engineering application value.

[0037] It is noteworthy that those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0038] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0039] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0040] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

[0042] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for calculating the width of a western boundary flow, characterized in that, The steps are as follows: S1.1 Obtain sea surface height field data and sea surface velocity field data of the target sea area. The sea surface height field data includes either absolute dynamic height or sea surface height. The sea surface velocity field data includes sea surface geostrophic velocity and reanalysis near-surface velocity. S2.1 Preprocess the sea surface height field data and the sea surface current field data to calculate the absolute velocity and the effective mask of the absolute velocity; S3.

1. Based on the sea surface height field data, extract preset contour lines and obtain an initial set of current axis points through serialized sampling, wherein the serialized sampling is performed in the order of either longitude or latitude. S3.

2. Perform connectivity filtering and smoothing on the point set of the initial flow axis to form the initial flow axis; S4.1 Calculate the local tangential direction and construct the normal direction for each flow axis point on the initial flow axis; S4.

2. Discretely sample the absolute velocity of each flow axis point on the initial flow axis within a preset search range in the normal direction of each flow axis point on the initial flow axis, and select the position of the maximum absolute velocity that meets the velocity threshold as the corrected flow axis point, thereby obtaining the corrected flow axis. S4.

3. Process the corrected flow axis to obtain the final flow axis; S5.

1. Using the final flow axis as a reference, construct a width search profile at each flow axis point of the final flow axis, with the normal direction of each flow axis point uniformly pointing in a specified direction. S5.2 Adjust the magnitude of the absolute velocity of each final flow axis point obtained by sampling with a preset step size. When the absolute velocity of the final flow axis point obtained by sampling is lower than the threshold for the first time, an invalid value appears, an out-of-bounds condition occurs, or a land mask appears, determine the position corresponding to the flow axis point of the final flow axis as a boundary point. S5.3 Calculate the width of the target sea area and output the coordinates of the boundary point. The width result is either the half width or the full width. S6.1 Perform anomaly processing on the width result and output a sequence of values ​​along the final flow axis at different width positions and the coordinates corresponding to the final flow axis at different width positions.

2. The method for calculating the width of the western boundary flow according to claim 1, characterized in that, The preprocessing in step S2.1 includes subdomain clipping, mesh unification, interpolation resampling, missing measurement processing, and necessary time averaging.

3. The method for calculating the width of the western boundary flow according to claim 1, characterized in that, The absolute velocity mentioned in step S2.1 is calculated using the sea surface geostrophic current velocity method as follows: ； in, Let u be the absolute velocity, v be the latitudinal component of the sea surface geostrophic flow velocity, and v be the meridional component of the geostrophic flow velocity.

4. The method for calculating the width of the western boundary flow according to claim 1, characterized in that, According to claim 1, the method for calculating the width of the western boundary flow is characterized in that the absolute velocity in step S2.1 is calculated using the reanalysis near-surface flow velocity calculation method as follows: ； in, For the reanalysis of the zonal component of the near-surface flow velocity, The meridional component of the near-surface flow velocity in the reanalysis is given.

5. The method for calculating the width of the western boundary flow according to claim 1, characterized in that, The contour lines in step S3.1 include the contour lines of the absolute dynamic altitude and the contour lines of the sea surface altitude.

6. The method for calculating the width of the western boundary flow according to claim 1, characterized in that, In step S4.3, the corrected flow axis is processed using an adaptive window smoothing and continuity constraint method.

7. The method for calculating the width of the western boundary flow according to claim 1, characterized in that, The specified direction in step S5.1 is the direction pointing towards the land side.

8. The method for calculating the width of the western boundary flow according to claim 1, characterized in that, In step 5.3, the half-width is the distance between the flow axis point of the final flow axis and the boundary point, while the full width is the distance between the boundary points on both sides of the target sea area along the width direction.

9. The method for calculating the width of the western boundary flow according to claim 1, characterized in that, The method for handling the anomalies of the width result in step S6.1 is as follows: when the boundary point does not meet the validity condition, the boundary point is marked as an invalid point, and the invalid point is interpolated and completed along the direction of the final flow axis.

10. A method for calculating the width of a western boundary flow according to claim 9, characterized in that, The validity conditions include either the velocity of the boundary point being lower than the threshold, or the position of the boundary point exceeding the maximum search distance.

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