A method for calculating cross-shelf water flux at a shelf break of the East China Sea

Abstract

This invention relates to the field of ocean current velocity inversion technology, specifically to a method for calculating trans-shelf water flux at a shelf break in the East China Sea. The method includes: obtaining long-term series observation data; establishing a regional coordinate system: establishing a moving coordinate system that changes with the continental slope topography, a coordinate system (n) across the 200-meter isobath, a coordinate system (l) along the 200-meter isobath, and a coordinate system (z) perpendicular to the sea surface; and constructing a dynamic equation: constructing the trans-shelf water flux q, which is the trans-shelf water flux in the horizontal direction, by vertical integration along the 200-meter isobath. This method is primarily based on satellite altimeter data and historical field observation data, using a reasonable dynamic model to calculate the trans-shelf water flux. It avoids the need for extensive field ocean current observation equipment and numerical calculation methods that require significant computational resources, offering advantages such as better economy, increased safety, reliable measurement accuracy, and greater convenience.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ocean current velocity inversion, and particularly relates to a dynamic calculation method based on multi-source observation data, and especially relates to a cross-shelf water flux calculation method at the shelf break of the East China Sea. BACKGROUND

[0002] The cross-shelf water exchange at the shelf break of the East China Sea is a dynamic phenomenon commonly existing in the edge of large-scale circulation, which can promote the exchange of materials such as nutrients, heat, carbon particles, etc. between the deep sea and the near-shore shelf area, and significantly affect the ecology and climate system of the near-shore area. Therefore, it is necessary to master the variation characteristics of the cross-shelf water flux of the East China Sea, which has very important scientific significance and practical value for a series of problems such as climate change, marine environmental protection, carbon particle transport, etc. in the near-shore area of China.

[0003] Although the research on cross-shelf water exchange has been carried out for a long time, due to the large spatial span (about 1000 km) and steep topography (the ratio of horizontal distance to vertical distance is about 1:10) of the East China Sea shelf, it is difficult and expensive to deploy field observation equipment, and the calculation of water flux across the entire East China Sea shelf is mainly based on numerical simulation, satellite altimeter data and box model. Although numerical simulation can provide rich three-dimensional data to study the water exchange along the entire shelf, the accuracy of the model driving field, the accuracy of the topography and the different selection schemes of the equation discretization method may lead to certain inaccuracy of the simulation results. Satellite altimeter data can provide relatively accurate horizontal spatial distribution along the entire East China Sea slope and long time series variation, but it is limited to the surface layer and lacks information of the current below the water surface. The calculation of the current based on the box model also needs long-term observation of the flow rate of the other two closed sections, which also has the defects of high cost and lack of local three-dimensional flow field information.

[0004] Although the inventor's previous research paper "Temporal and spatial variation of cross-shelf water exchange and nutrient exchange in the East China Sea based on satellite and in-situ observation data" gives a method for calculating the cross-shelf water flux at the shelf break of the East China Sea, the final calculation results of this scheme have certain differences with the conclusions of previous scholars' research, therefore, considering the economic cost and practicality, an economic, more accurate, complete spatial coverage and longer time length calculation method of the cross-shelf water flux at the shelf break of the East China Sea is needed. SUMMARY

[0005] To solve at least one of the technical problems in the foregoing background art, the present application aims to provide an East China shelf slope break cross-shelf water flux calculation method, which is mainly based on satellite altimeter data and historical field observation data, and uses a reasonable dynamic model to calculate the cross-shelf water flux, avoiding the method of using a large number of field current observation equipment and the numerical calculation method using a large amount of computing resources, and having the characteristics of good economy, more safety, reliable measurement accuracy and more convenient.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions.

[0007] An East China shelf slope break cross-shelf water flux calculation method comprises:

[0008] Obtaining long time series observation data:

[0009] Establishing a regional coordinate system: a moving coordinate system that changes with the land slope topography, a coordinate system (n) in the direction of the 200-meter isobath, a coordinate system (l) in the direction of the 200-meter isobath, and a coordinate system (z) in the vertical direction from the sea bottom to the sea surface;

[0010] Building a dynamic equation: building a cross-shelf water flux q on the 200m isobath vertical integral, that is, the space-time change of the cross-shelf water flux in the horizontal direction,

[0011] (8)

[0012] Wherein, v is the cross-shelf flow rate; v g is the geostrophic flow rate; τ w and τ b are the surface and bottom friction stresses along the l direction; ρ is the seawater density; p is the seawater pressure; ρ a is the air density; C D is the friction drag coefficient that changes with the wind speed; U is the wind speed at the sea surface 10 meters along the land slope direction; kb is the bottom friction coefficient (k b =0.0025); u gb is the bottom geostrophic flow rate along the land slope direction; and

[0013]

[0014] Wherein, φ is the dimension.

[0015] In some embodiments, the long time series observation data includes multi-source fusion observation temperature and salinity data provided by the European data center (COPERNICUS), satellite altimeter surface flow field data of AVISO, and sea surface wind field data of NCDC. The horizontal spatial resolutions of the three kinds of data are all 1 / 4°*1 / 4°, the time resolutions are all processed into monthly, the time lengths are all 26 years, and the spans are all from 1993 to 2018.

[0016] In some embodiments, the dynamic equation is constructed by using the hydrostatic assumption, the baroclinic assumption and the geostrophic approximation.

[0017] In some embodiments, the dynamic equation ignores the friction stress in the cross-shelf direction because the flow velocity in the cross-shelf direction is one order of magnitude smaller than the flow velocity along the continental slope.

[0018] In some embodiments, q is at least calibrated with the actual water flux in terms of the bottom and sea level flux.

[0019] In some embodiments, at least two water flux measuring instruments are arranged from the bottom to the sea level to measure the water flux of the water flow including at least the bottom and the sea surface, and q is calibrated with the measurement results; by arranging multiple water flux measuring instruments to obtain accurate water flux values, the accuracy of q is improved, thereby improving the accuracy of the total cross-shelf water flux Q.

[0020] In some embodiments, q is integrated along the entire length of the 200-meter isobath l The total cross-shelf water flux Q of the vertical cross-sectional area integral of the entire 200-meter isobath is obtained by integrating from the northeast of Taiwan Province of China to the southwest of Kyushu, that is, the total cross-shelf water flux changes with time:

[0021] (9).

[0022] A computer device includes a memory, a processor, and computer instructions stored on the memory and running on the processor, when the computer instructions are run by the processor, the foregoing method is completed.

[0023] A machine-readable storage medium is used to store computer instructions, when the computer instructions are executed by a processor, the foregoing method is completed.

[0024] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined with each other to obtain specific embodiments.

[0025] The beneficial effects of the present application are:

[0026] 1. No need to place the sea current observation equipment on site, saving manpower and financial resources, and the sea current calculation accuracy also has certain reliability;

[0027] 2. Compared to satellite remote sensing observation, this method can also provide underwater ocean current information;

[0028] 3. Compared to numerical models that consume a lot of computing resources on supercomputers, this method can run on local computers, which is more efficient in terms of computing resources, more convenient, and saves time.

[0029] 4. This invention has a simple structure, is flexible in operation, and is easily accepted by relevant units such as marine operational surveys and forecasting, and has high commercial promotion and application value.

[0030] The present invention adopts the above-mentioned technical solution to achieve the above objectives, which makes up for the shortcomings of the prior art, is reasonably designed, and is easy to operate. Detailed Implementation

[0031] COPERNICUS is the European Data Center.

[0032] AVISO stands for Archive Validation and Interpretation of Satellite Oceanography, and it is the data center for satellite oceanography archives at the French National Centre for Space Research.

[0033] NCDC stands for National Climate Data Center.

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1:

[0036] This paper presents a method for calculating trans-shelf water flux at shelf break points in the East China Sea, specifically using the 200-meter isobath. First, it collects and integrates spatially complete long-term observational data: multi-source fused temperature and salinity data from the European Data Center (COPERNICUS), surface flow field data from AVISO satellite altimeters, and sea surface wind field data from NCDC. All three datasets have a horizontal spatial resolution of 1 / 4° × 1 / 4°, a temporal resolution of monthly, and a time span of 26 years, from 1993 to 2018.

[0037] The calculation of the cross-shelf flow velocity at the shelf break (200-meter isobath) of the East China Sea requires the establishment of a coordinate system and dynamic equation suitable for the region. On the one hand, due to the terrain of the East China land slope not being north-south, it is not possible to define the cross-shelf direction according to the traditional Cartesian coordinate system, and a moving coordinate system needs to be established that changes with the terrain of the land slope. Therefore, a local right-handed coordinate system at the 200-meter isobath of the East China Sea is first established, defining the coordinate system n in the direction of the 200-meter isobath, the coordinate system l in the direction along the 200-meter isobath, and the coordinate system z in the vertical direction from the sea bottom to the sea surface. According to the definition of the moving coordinate system, the normal direction of each coordinate point on the 200-meter isobath will change with the terrain.

[0038] Embodiment 2:

[0039] Based on the foregoing embodiments, considering the existence of nonlinear terms, it is difficult to directly solve the cross-shelf flow velocity through the original equation, and it is necessary to refer to domestic and foreign theories to establish a dynamic equation suitable for the study of cross-shelf heat exchange in the East China Sea. The static hypothesis, the Bousinessq hypothesis, and the geostrophic approximation are adopted, and the previous research results show that the frictional stress of the surface layer and the bottom layer has an impact on the cross-shelf exchange, so the dynamic equation needs to retain the frictional stress of the surface layer and the bottom layer along the land slope direction, and since the cross-shelf flow velocity is one order of magnitude smaller than the flow velocity along the land slope direction, the equation can ignore the frictional stress in the cross-shelf direction.

[0040] The kinematic equation at the 200-meter isobath is constructed as follows:

[0041] (1)

[0042] wherein f is the Coriolis parameter; v is the flow velocity in the cross-shelf direction; u is the flow velocity along the land slope direction; g is the gravitational acceleration; p is the sea water density; p is the sea water pressure; t is the frictional stress along the land slope direction; c1=(5.92+5.25sin 2 φ)×10 -3 (mdb -1 ), c2=2.21×10 -6 (mdb -2 ), and p is the dimension. The kinematic equation of the 200-meter isobath constructed in the application comprehensively considers the flow velocity in the cross-shelf direction, the flow velocity along the land slope direction, and the relationship between the sea water depth and the pressure and density, which is beneficial to obtaining a more accurate total cross-shelf water flux Q, so that the cross-shelf water flux result obtained by the application is close to the cross-shelf water flux result obtained by the previous scholars through field observation, without the need to go to the site for measurement, thereby saving a large amount of manpower and financial resources while obtaining a reliable and accurate sea current calculation precision, which has high commercial promotion and application value.

[0043] The cross-shelf flow velocity v is obtained through formula (1):

[0044] (2)

[0045] Among them, the geostrophic flow velocity v g Defined as:

[0046] (3)

[0047] For v g By taking the vertical derivative and applying the static assumption to formula (3), we obtain the relationship between the vertical gradient of the geostrophic velocity and the horizontal density gradient:

[0048] (4)

[0049] Integrating equation (4) from z to the sea surface (z=0m) yields the trans-shelf geostrophic velocity v. g :

[0050] (5)

[0051] At the surface, the trans-shelf surface geostrophic flow velocity v0 (i.e., v) of AVISO g (0) is used as the reference velocity, and the vertical distribution of the trans-shelf geostrophic velocity is obtained:

[0052] (6)

[0053] Among them, the geostrophic flow velocity u along the continental slope direction g for:

[0054] (7)

[0055] Where u0 is the surface geostrophic velocity of AVISO along the slope direction.

[0056] Integrating equation (2) along the depth from the seabed (z=-200 m) to the sea surface (z=0 m), we obtain the trans-shelf water flux q, which is the spatial and temporal variation of the trans-shelf water flux in the horizontal direction, at the 200-meter isobath.

[0057] (8)

[0058] Where, τ w and τ b For the surface and subsurface frictional stresses along the l direction, ρ a C is the density of air. D Let U be the friction drag coefficient as a function of wind speed, U be the wind speed at 10 meters above the sea surface along the continental slope, and kb be the bottom friction coefficient (k b =0.0025), u gbThe bottom geostrophic flow velocity along the land slope direction is q, and in particular, q is at least matched with the actual water flux in terms of the sea bottom and sea level flow, and a total of five water flux measuring instruments are arranged at 0 m, 50 m, 100 m, 150 m and 200 m above the sea bottom to the sea level to measure the water flux including the sea bottom and the sea surface, and accurate water flux values are obtained by arranging a plurality of water flux measuring instruments, which helps to improve the accuracy of q, thereby improving the accuracy of the total cross-shelf water flux Q.

[0059] The total cross-shelf water flux Q of the entire 200-meter isobath vertical area integral is obtained by integrating q along the entire 200-meter isobath length l from the northeast of Taiwan Province to the southwest of Kyushu, i.e., the total cross-shelf water flux changes with time:

[0060] (9)

[0061] The water fluxes of the four sections of the Taiwan Strait, the Tsushima Strait, the east of Taiwan Province and the Tsugaru Strait have been basically understood through field observation data, and the water fluxes of the four sections are also calculated in this paper to verify the accuracy of the water flux obtained by the method of this paper. The calculation results are shown in Table 1.

[0062] Table 1-Comparison of water fluxes of main sections of the East China Sea calculated by the method of this application and historical results

[0063]

[0064] As can be seen from Table 1, the multi-year average water flux data of the Taiwan Strait, the Tsushima Strait, the 200-meter isobath, the east of Taiwan Province and the Tsugaru Strait calculated by the method of this application are consistent with the results of the prior research, indicating that the accuracy of the calculation of the cross-shelf water flux of this application is high; compared with the prior art, this application comprehensively considers the flow velocity in the cross-shelf direction, the flow velocity along the land slope direction, and the relationship between the depth and pressure and density of seawater, which is beneficial to improve the calculation accuracy of the sea current, and when calculating the cross-shelf water flux q of the 200-meter isobath by vertical integration, q is at least matched with the actual water flux in terms of the sea bottom and sea level flow, and a plurality of water flux measuring instruments are arranged at the sea bottom to the sea level to measure the water flux including the sea bottom and the sea surface, and accurate water flux values are obtained by arranging a plurality of water flux measuring instruments, which helps to improve the accuracy of q, thereby further improving the accuracy of the total cross-shelf water flux Q.

[0065] The cross-continental shelf water flux calculation method of the East China Sea provided in the application comprehensively considers the flow velocity in the cross-continental shelf direction, the flow velocity along the continental slope direction, and the relationship between the water depth and the pressure and density, and is matched with the vertical integral cross-continental shelf water flux q on the 200-meter isobath by using the water flux data obtained by a water flux measuring instrument, including the water flux data at the sea bottom and the sea level, so as to improve the accuracy of q and obtain more accurate total cross-continental shelf water flux Q, so that the cross-continental shelf water flux result obtained by calculation is close to the cross-continental shelf water flux result obtained by the prior scholars through field observation, without the need of going to the site for measurement, while saving a large amount of manpower and financial resources, the sea current calculation accuracy with good reliability and accuracy can also be obtained, and the application value is high in commercial promotion and application.

[0066] The conventional techniques in the above embodiments are the prior art known by those skilled in the art, and thus are not described in detail herein.

[0067] The details of the application are known.

Claims

1. A method for calculating cross-shelf water flux at the shelf break of the East China Sea, characterized in that The application relates to a method for calculating a long-time series of cross-shelf water flux. Obtaining long-time series of observation data; Establishing a regional coordinate system: a moving coordinate system changing with the land-slope topography, a coordinate system n in the direction of the 200-meter isobath, a coordinate system l in the direction of the 200-meter isobath and a coordinate system z in the vertical direction from the sea bottom to the sea surface; Constructing a dynamic equation: constructing a cross-shelf water flux q vertically integrated on the 200-meter isobath, that is, the spatio-temporal variation of the cross-shelf water flux in the horizontal direction, (8) where v is the cross-shelf flow velocity; v g is the geostrophic velocity; τ w and τ b are the surface and bottom friction stresses along the l direction, respectively; p is the seawater density; p is the seawater pressure; p a is the air density; C D is the frictional drag coefficient as a function of wind speed; U is the wind speed at 10 meters above the sea surface along the continental slope direction; k b is the bottom friction coefficient, k b = 0.0025; u gb is the bottom geostrophic velocity along the continental slope direction; and Wherein, phi is the dimension.

2. The method of claim 1, wherein: The long-time series of observation data comprises multi-source fusion observation temperature-salinity data provided by the European data center COPERNICUS, satellite altimeter surface flow field data of AVISO and sea surface wind field data of NCDC.

3. The method of claim 1, wherein: When the dynamic equation is constructed, q is at least registered with the actual water flux in terms of the sea bottom and sea surface flow.

4. The method of claim 1, wherein: When the dynamic equation is constructed, at least two water flux measuring instruments are arranged on the sea bottom to the sea surface to measure the water flow water flux of at least the sea bottom and the sea surface, and q is registered with the measurement results.

5. The method according to any one of claims 1 to 4, characterized in that: The construction of the dynamic equation specifically comprises: The constructed kinematic equation at the 200-meter isobath is: (1) Where f is the Coriolis parameter; v is the flow velocity along the trans-shelf direction; u is the flow velocity along the continental slope direction; g is the gravitational acceleration; ρ is the seawater density; p is the seawater pressure; τ is the frictional stress along the continental slope direction; c1=(5.92+5.25sin 2 φ)×10 -3 (mdb -1 c2 = 2.21 × 10 -6 (mdb -2 ), where φ is the dimension; The cross-shelf flow velocity v is obtained through formula (1): (2) where the geostrophic current velocity v g is defined as: (3) For v g Taking the vertical derivative and applying the hydrostatic assumption to equation (3), we obtain the relation between the vertical gradient of the geostrophic velocity and the horizontal density gradient: (4) Integrating equation (4) from z to the sea surface z = 0 m gives the cross-shelf geostrophic velocity v g : (5) At the surface, the cross-shelf geostrophic velocity v0 from AVISO is taken as the reference velocity, v0 = v g (0), and the vertical distribution of the cross-shelf geostrophic velocity is obtained as (6) where the geostrophic current velocity u along the land slope direction g is: (7) Wherein, u0 is the surface geostrophic flow velocity in the land-slope direction of AVISO; The equation (2) is integrated along the depth from the sea bottom z=-200m to the sea surface z=0m, and the cross-shelf water flux q vertically integrated on the 200-meter isobath is obtained, that is, the spatio-temporal variation of the cross-shelf water flux in the horizontal direction: (8) where τ w and τ b are the surface and bottom friction stresses along the l direction, p a is the air density, C D is the friction drag coefficient as a function of wind speed, U is the wind speed at 10 meters above the sea surface along the l direction, kb is the bottom friction coefficient, k b = 0.0025, and u gb is the bottom geostrophic current speed along the l direction.

6. The method according to any one of claims 1 to 4, characterized in that: q is the cross-shelf water transport along the entire 200-m isobath l The total cross-shelf water transport Q across the 200-m isobath, i.e., the total cross-shelf water transport as a function of time, is obtained by integrating from the northeastern part of Taiwan Province to the southwestern part of Kyushu, Japan: (9)。 7. A computer device comprising a memory, a processor and computer instructions stored on the memory and running on the processor, when the computer instructions are run by the processor, the method of any one of claims 1-6 is completed.

8. A machine-readable storage medium for storing computer instructions, when the computer instructions are executed by the processor, the method of any one of claims 1-6 is completed.

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