A method for constructing a three-dimensional coupled tide-circulation model in the South China Sea

Abstract

The invention discloses a method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea, comprising the following steps: S1 grid construction and water depth introduction; S2 initial condition setting; S3 lateral open boundary condition setting; S4 sea surface boundary condition setting: S4-1 sea surface momentum boundary condition, S4-2 sea surface heat flux boundary condition, S4-3 sea surface salinity boundary condition, and optimizing a method for determining solar shortwave radiation flux to obtain a high-resolution three-dimensional model, which can reflect the horizontal and vertical distribution laws of temperature and salinity in the South China Sea basin area to a certain extent, and can reproduce the distribution trend of the three-dimensional hydrodynamic process in the South China Sea.

Description

Technical Field

[0001] The present invention relates to the technical field of numerical simulation of tidal circulation in the South China Sea, and in particular to a method for constructing a three-dimensional coupled tidal circulation model in the South China Sea. Background Art

[0002] Tidal force refers to the effect of gravity on an object when the gravitational source exerts a force on the object. Since the distances from each point on the object to the gravitational source are different, the gravitational force is different, resulting in a gravitational difference, which causes a tearing effect on the object. This gravitational difference is the tidal force. Tidal force has a certain impact on the circulation and transport of materials on the continental shelf. In view of the fact that my country has a very wide coastline and the lack of understanding of the various complex mechanisms of tidal force, it is necessary to conduct in-depth research on the relationship between tidal force and circulation.

[0003] In recent years, the marine environment has been damaged, and the nutrient load near the coastline has increased, gradually affecting marine life and people's normal production activities. It is necessary to strengthen the study of tidal dynamics and ocean circulation to deepen the study of near-coastal material circulation. The three-dimensional hydrodynamic model is a marine numerical simulation model widely used in the world's oceans and regions. The construction of a three-dimensional tidal-circulation coupling model based on the three-dimensional hydrodynamic model can further explore the temporal and spatial distribution of the South China Sea ocean circulation and explore the influence mechanism of physical processes on marine ecological dynamic processes. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention provides a method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea.

[0005] The technical solution of the present invention is:

[0006] A method for constructing a three-dimensional coupled model of tides and circulations in the South China Sea comprises the following steps:

[0007] S1 Grid construction and water depth import: Based on the Princeton Ocean Model, an orthogonal curve grid is established. The grid along the shelf is roughly parallel to the coastline, and the grid across the shelf is perpendicular to the isobath. The vertical direction uses logarithmic sigma coordinates, and the water depth data is interpolated to the calculation grid of the South China Sea model through spline interpolation.

[0008] S2 Initial condition setting: the initial water level and flow velocity are both set to 0, and the initial temperature and salinity are interpolated from the winter average values ​​of the climate state to the calculation grid of the model;

[0009] S3 lateral open boundary condition setting:

[0010] S3-1 Water level boundary conditions: The water level adopts the non-gradient boundary conditions. The formula for assigning the inner area of ​​the water level value at the boundary during the calculation process of the model is:

[0011]

[0012] in, is the water level at the open boundary, is the water level value of the inner area adjacent to the boundary, - represents the east boundary and the north boundary, + represents the west boundary and the south boundary;

[0013] S3-2 Two-dimensional velocity boundary:

[0014]

[0015] Among them, η ext The water level at the open boundary provided for the exterior, is the two-dimensional flow velocity at the open boundary provided by the outside, g is the gravitational acceleration, and h is the water depth;

[0016] S3-3 Three-dimensional velocity boundary:

[0017] φ t +Cφ N =0

[0018] in: is the normal three-dimensional flow velocity at the open boundary, C is the disturbance propagation velocity, t represents time, N represents the normal direction of the open boundary, and the subscript represents the partial differential. When external forcing is not considered, the disturbance propagation velocity C can be expressed as:

[0019]

[0020] At this time, the three-dimensional velocity opening boundary can be expressed as:

[0021]

[0022] S3-4 Temperature-salinity boundary: The temperature-salinity boundary is provided by SODA data;

[0023] S4 sea surface boundary condition settings:

[0024] S4-1 Sea surface momentum boundary condition: Different wind field products are used to test the response of the South China Sea circulation model to different wind field data;

[0025] S4-2 Sea surface heat flux boundary condition: The sea surface heat flux boundary condition takes into account the net heat flux of the sea surface, including solar shortwave radiation, solar longwave radiation, sensible heat and latent heat flux, and the incident process of solar shortwave radiation in the water layer, plus a relaxed boundary condition. The specific formula is:

[0026]

[0027] Where T is the temperature value calculated by the model, T obsis the observed value of sea surface temperature, C is the relaxation coefficient, which is 0.7 m / day, z is the vertical coordinate, Q net is the net heat flux absorbed by the sea surface, including part of the solar shortwave radiation, all longwave radiation, sensible heat and latent heat flux, SW(z) is the solar shortwave radiation flux entering the water layer, ρ is the seawater density, C p is the specific heat of seawater;

[0028] S4-3 Sea surface salinity boundary condition: The sea surface salinity boundary condition adopts a relaxed boundary condition, and the specific formula is:

[0029]

[0030] Where: S is the sea surface salinity value calculated by the model, S obs is the actual observed sea surface salinity.

[0031] Furthermore, in the step S1, the number of grids in the horizontal direction is 400×160, and the calculation grid resolution is 2.5-3 km, which is a relatively high grid resolution.

[0032] Furthermore, in step S1, there are 31 sigma layers vertically, with higher resolution near the surface and bottom layers, so as to better simulate the boundary layer process of the ocean.

[0033] Furthermore, in step S1, the water depth is interpolated onto the model calculation grid using Etopo2v2 data by using a cubic spline interpolation method.

[0034] Furthermore, the temperature and salinity data in step S2 adopt the World Ocean Atlas 2001 data, which should reflect the dynamic exchange process of variables at the boundary as realistically as possible, and the global model provides open boundary conditions for the regional model.

[0035] Furthermore, the coefficient μ in step S3-3 is determined by the magnitude of the disturbance propagation speed:

[0036]

[0037] When C L ≤0, the velocity at the open boundary is given by the value at the open boundary calculated by the model in the previous time step. L When C is less than 1, the open boundary velocity is determined by the model calculation value and the disturbance propagation velocity. L When ≥1, the open boundary flow velocity is determined by the flow velocity of the inner area adjacent to the open boundary calculated by the current time step model, which improves the convergence efficiency of the model.

[0038] Furthermore, the wind field model in step S4-1 includes the HR wind field, the ERA-interim wind field, the NCEP wind field and the QSCAT / NCEP mixed wind field, and the response of the South China Sea circulation model to different wind field data is tested by using different wind field products.

[0039] Furthermore, the method for determining the solar shortwave radiation flux in step S4-2 is:

[0040] S4-2-1: Construct an atmospheric radiation transfer model and compare it with the solar shortwave radiation information table;

[0041] S4-2-2: Obtain atmospheric parameters in different intervals through AVHRR satellite radar information;

[0042] S4-2-3: Determine the solar shortwave radiation flux in the different intervals by searching the atmospheric parameters in the solar shortwave radiation information table.

[0043] Furthermore, the atmospheric parameters in step S4-2-2 include the solar zenith angle range, aerosol optical thickness, aerosol type, water vapor content, water cloud particle effective radius and water cloud optical thickness, wherein the solar zenith angle range is 0-90°, with an interval of 5°, the aerosol optical thickness is 0-3, the aerosol type is oceanic, and the water vapor content is 0-8g / cm 2 , interval 0.5, the effective radius of water cloud particles are 4μm, 8μm, 16μm, 32μm or 64μm, and the range of water cloud optical thickness is 1, 5, 10, 20, 30, 50, 100, 150, interval 1. By using satellite aerosol and cloud optical data and adopting neural network method, the ocean solar shortwave radiation results under clear sky and cloudy conditions can be calculated quickly and effectively.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The three-dimensional tidal-circulation coupling model construction method of the present invention limits the initial conditions, open boundary conditions and sea surface boundary conditions of the coupling model to obtain a high-resolution three-dimensional tidal-circulation coupling model, which can reflect the horizontal and vertical distribution laws of temperature and salinity in the South China Sea to a certain extent, reproduce the three-dimensional hydrodynamic and distribution trends of the South China Sea basin area, and can be further applied to the study of the influencing mechanism of the ecological dynamic process in the South China Sea.

[0046] (2) The method for constructing the three-dimensional tidal-circulation coupling model of the South China Sea of ​​the present invention optimizes the measurement of solar shortwave radiation flux, utilizes satellite aerosol and cloud optical data, and adopts a neural network method to quickly and effectively calculate the ocean solar shortwave radiation results under clear sky and cloudy conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a seasonal distribution diagram of surface wind stress in the experimental example of the present invention;

[0048] Figure 2 It is the distribution diagram of wind stress curl of four kinds of wind field data in winter on the sea surface in the experimental example of the present invention;

[0049] Figure 3 It is a distribution diagram of wind stress curl of four types of wind field data in the sea surface layer in summer in the experimental example of the present invention;

[0050] Figure 4 It is a Taylor relationship diagram between the sea surface height calculated by the model in the experimental example of the present invention and the TP satellite altimeter observation data, where a is winter and b is summer. DETAILED DESCRIPTION

[0051] Example 1

[0052] A method for constructing a three-dimensional coupled model of tides and circulations in the South China Sea comprises the following steps:

[0053] S1 grid construction and water depth import: Based on the Princeton Ocean Model, an orthogonal curve grid is established. The grid along the shelf is roughly parallel to the coastline, and the grid across the shelf is perpendicular to the isobath. The number of grids in the horizontal direction is 400×160, and the computational grid resolution is 2.5-3km. The vertical direction uses logarithmic sigma coordinates, which are divided into 31 sigma layers. The water depth data is interpolated to the computational grid of the South China Sea model through the spline interpolation method. The water depth uses Etopo2v2 data and is interpolated to the model computational grid through the cubic spline interpolation method.

[0054] S2 Initial condition setting: the initial water level and flow velocity are both set to 0, the initial temperature and salinity are interpolated from the winter average values ​​of the climate state to the calculation grid of the model, and the temperature and salinity data are from the World Ocean Atlas 2001;

[0055] S3 lateral open boundary condition setting:

[0056] S3-1 Water level boundary conditions: The water level adopts the non-gradient boundary conditions. The formula for assigning the inner area of ​​the water level value at the boundary during the calculation process of the model is:

[0057]

[0058] in, is the water level at the open boundary, is the water level value of the inner area adjacent to the boundary, - represents the east boundary and the north boundary, + represents the west boundary and the south boundary;

[0059] S3-2 Two-dimensional velocity boundary:

[0060]

[0061] Among them, η ext The water level at the open boundary provided for the exterior, is the two-dimensional flow velocity at the open boundary provided by the outside, g is the gravitational acceleration, and h is the water depth;

[0062] S3-3 Three-dimensional velocity boundary:

[0063] φ t +Cφ N =0

[0064] in: is the normal three-dimensional flow velocity at the open boundary, C is the disturbance propagation velocity, t represents time, N represents the normal direction of the open boundary, and the subscript represents the partial differential. When external forcing is not considered, the disturbance propagation velocity C can be expressed as:

[0065]

[0066] At this time, the three-dimensional velocity opening boundary can be expressed as:

[0067]

[0068] The coefficient μ is determined by the magnitude of the disturbance propagation speed:

[0069]

[0070] When C L ≤0, the velocity at the open boundary is given by the value at the open boundary calculated by the model in the previous time step. L When C is less than 1, the open boundary velocity is determined by the model calculation value and the disturbance propagation velocity. L When ≥1, the velocity at the open boundary is determined by the velocity of the inner area adjacent to the open boundary calculated by the model at the current time step;

[0071] S3-4 Temperature-salinity boundary: The temperature-salinity boundary is provided by SODA data;

[0072] S4 sea surface boundary condition settings:

[0073] S4-1 Sea surface momentum boundary condition: Different wind field products are used to test the response of the South China Sea circulation model to different wind field data. The wind field model is the HR wind field.

[0074] S4-2 Sea surface heat flux boundary condition: The sea surface heat flux boundary condition takes into account the net heat flux of the sea surface, including solar shortwave radiation, solar longwave radiation, sensible heat and latent heat flux, and the incident process of solar shortwave radiation in the water layer, plus a relaxed boundary condition. The specific formula is:

[0075]

[0076] Where T is the temperature value calculated by the model, T obs is the observed value of sea surface temperature, C is the relaxation coefficient, which is 0.7 m / day, z is the vertical coordinate, Q net is the net heat flux absorbed by the sea surface, including part of the solar shortwave radiation, all longwave radiation, sensible heat and latent heat flux, SW(z) is the solar shortwave radiation flux entering the water layer, ρ is the seawater density, C p is the specific heat of seawater;

[0077] S4-3 Sea surface salinity boundary condition: The sea surface salinity boundary condition adopts a relaxed boundary condition, and the specific formula is:

[0078]

[0079] Where: S is the sea surface salinity value calculated by the model, S obs is the actual observed sea surface salinity.

[0080] Example 2

[0081] This embodiment is basically the same as Embodiment 1, except that the sea surface momentum boundary condition is set differently.

[0082] S4-1 Sea surface momentum boundary condition: Different wind field products are used to test the response of the South China Sea circulation model to different wind field data. The wind field model is the ERA-interim wind field.

[0083] Example 3

[0084] This embodiment is basically the same as Embodiment 1, except that the sea surface momentum boundary condition is set differently.

[0085] S4-1 Sea surface momentum boundary condition: Different wind field products are used to test the response of the South China Sea circulation model to different wind field data. The wind field model is the NCEP wind field.

[0086] Example 4

[0087] This embodiment is basically the same as Embodiment 1, except that the sea surface momentum boundary condition is set differently.

[0088] S4-1 Sea surface momentum boundary condition: Different wind field products are used to test the response of the South China Sea circulation model to different wind field data. The wind field model is a QSCAT / NCEP hybrid wind field.

[0089] Example 5

[0090] This embodiment further defines the method for determining the solar shortwave radiation flux in step S4-2 based on embodiment 1.

[0091] The method for determining the solar shortwave radiation flux in step S4-2 is:

[0092] S4-2-1: Construct an atmospheric radiation transfer model and compare it with the solar shortwave radiation information table;

[0093] S4-2-2: Obtain atmospheric parameters in different ranges through AVHRR satellite radar information. The atmospheric parameters include solar zenith angle range, aerosol optical thickness, aerosol type, water vapor content, effective radius of water cloud particles and water cloud optical thickness. The solar zenith angle range is 0-90° with an interval of 5°, the aerosol optical thickness is 0-3, the aerosol type is oceanic, and the water vapor content is 0-8g / cm 2 , interval 0.5, the effective radius of water cloud particles is 4μm, 8μm, 16μm, 32μm or 64μm, and the optical thickness of water cloud ranges from 1, 5, 10, 20, 30, 50, 100, 150, interval 1;

[0094] S4-2-3: Determine the solar shortwave radiation flux in the different intervals by searching the atmospheric parameters in the solar shortwave radiation information table.

[0095] Experimental example

[0096] The tidal-circulation three-dimensional coupling model under different wind fields in Examples 1-4 was applied to a block in the northern South China Sea for testing, and the response of the calculation results of the South China Sea circulation model to different wind field data was tested to obtain the optimal wind field. The test results are as follows:

[0097] Each calculation example starts from a static state. The tidal-circulation three-dimensional coupled model first uses the monthly average forcing field for calculations for three years. After a three-year spin-up, the model uses the monthly average forcing field for another three years. The results of the last year are used for sensitivity comparison analysis of wind field data.

[0098] like Figure 1 , 2As shown in the figure, from the seasonal distribution of wind stress, the four wind field data are not much different, and all can reflect the seasonal evolution of the South China Sea monsoon: in winter, it is mainly controlled by the northeast monsoon, and the wind is relatively strong; in summer, it is controlled by the southwest monsoon, and the wind is relatively weak; spring and autumn are the monsoon transition seasons, and the wind direction and wind speed are not very stable; in winter, the northeast monsoon prevails in the South China Sea. Affected by the shape of the sea basin and the surrounding landforms, the northwest of the South China Sea is mainly controlled by negative wind stress curl, while the southeast is controlled by positive wind stress curl. The positive and negative wind stress curls are roughly bounded by the main axis of the South China Sea diamond basin.

[0099] like Figure 3 As shown, the summer monsoon in the South China Sea reverses, and the corresponding wind stress curl distribution also shows a distribution trend opposite to that in winter. The positive and negative wind stress curls are still bounded by the main axis of the South China Sea diamond basin. The northeastern part of the South China Sea is controlled by the positive wind stress curl, while the southwestern part is controlled by the negative wind stress curl.

[0100] The wind stress curl of the four wind field products can all show the above-mentioned seasonal evolution trend, but because the four wind field products have different sources and resolutions, their wind stress curl fields have great differences. In winter, the positive wind stress curl center in the northwest of the South China Sea is generally located in the waters near the northwest coast of Luzon Island, which is shown in the HR wind field, Qscat / NCEP mixed wind field and ERA-interim wind field, while in the NCEP wind field, the positive wind stress curl center is located in the middle of the northern basin of the South China Sea. In addition, due to the high resolution of the ERA-interm wind field and the Qscat / NCEP wind field, affected by the land topography of Luzon Island, positive and negative wind stress curls appear alternately. Figure 3 As shown in the figure, the distribution of wind stress curl field of the four wind field products in summer is slightly different. The positive and negative wind stress curls along the southwestern coast of Vietnam present a "dipole" distribution, but the magnitude of wind stress curl of different wind field products is slightly different.

[0101] like Figure 4 As shown in a, the root mean square errors of Examples 4 and 2 using Qscat / NCEP wind field and ERA-interim wind field forcing are relatively small, 0.53 and 0.54 respectively, and the root mean square error of Example 3 using NCEP wind field forcing is the largest (0.72). The correlation coefficient also has the same distribution law: the sea level height calculated by Examples 2 and 4 has the best correlation with TP data, with a correlation coefficient of about 0.85; while the calculated value of Example 3 has the worst correlation with TP observation results. For the standard deviation distribution, the standard deviation of Example 1 using HR wind field forcing is closest to 1, followed by Examples 2 and 4. Therefore, the calculation effect of the South China Sea model in winter is better when using Qscat / NCEP mixed wind field and ERA-interim wind field forcing, while the calculation effect of using only NCEP wind field forcing is the worst.

[0102] like Figure 4 As shown in Figure 2, the root mean square error of Example 4 is about 0.64, which is the smallest among the four examples. At the same time, the correlation coefficient between the calculation results of Example 4 and the TP data is the highest, reaching 0.81. However, the standard deviation of the calculation results of Example 4 relative to the TP observation data is not as good as the HR wind field forcing adopted in Example 1. As with the winter example, the worst calculation effect among the four examples is still Example 3 using NCEP wind field forcing. Generally speaking, the calculation effect of the South China Sea circulation model using the Qscat / NCEP mixed wind field of Example 4 is relatively good.

[0103] In summary, the South China Sea tidal-circulation coupled model can better reproduce the dynamic process of the South China Sea circulation when forced by the Qscat / NCEP mixed wind field, and the results calculated by the model are closest to the satellite altimeter data.

Claims

1. A method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea, characterized in that: The following steps are involved: S1 Grid construction and water depth import: Based on the Princeton Ocean Model, an orthogonal curve grid is established. The grid along the shelf is roughly parallel to the coastline, and the grid across the shelf is perpendicular to the isobath. The vertical direction uses logarithmic sigma coordinates, and the water depth data is interpolated to the calculation grid of the South China Sea model through spline interpolation. S2 Initial condition setting: the initial water level and flow velocity are both set to 0, and the initial temperature and salinity are interpolated from the winter average values ​​of the climate state to the calculation grid of the model; S3 lateral open boundary condition setting: S3-1 Water level boundary conditions: The water level adopts the non-gradient boundary conditions. The formula for assigning the inner area of ​​the water level value at the boundary during the calculation process of the model is: in, is the water level at the open boundary, is the water level value of the inner area adjacent to the boundary, - represents the east boundary and the north boundary, + represents the west boundary and the south boundary; S3-2 Two-dimensional velocity boundary: Among them, η ext The water level at the open boundary provided for the exterior, is the two-dimensional flow velocity at the open boundary provided by the outside, g is the gravitational acceleration, and h is the water depth; S3-3 Three-dimensional velocity boundary: φ t +Cφ N =0 in: is the normal three-dimensional flow velocity at the open boundary, C is the disturbance propagation velocity, t represents time, N represents the normal direction of the open boundary, and the subscript represents the partial differential. When external forcing is not considered, the disturbance propagation velocity C can be expressed as: At this time, the three-dimensional velocity opening boundary can be expressed as: S3-4 Temperature-salinity boundary: The temperature-salinity boundary is provided by SODA data; S4 sea surface boundary condition settings: S4-1 Sea surface momentum boundary condition: Different wind field products are used to test the response of the South China Sea circulation model to different wind field data; S4-2 Sea surface heat flux boundary condition: The sea surface heat flux boundary condition takes into account the net heat flux of the sea surface, including solar shortwave radiation, solar longwave radiation, sensible heat and latent heat flux, and the incident process of solar shortwave radiation in the water layer, plus a relaxed boundary condition. The specific formula is: Where T is the temperature value calculated by the model, T obs is the observed value of sea surface temperature, C is the relaxation coefficient, which is 0.7 m / day, z is the vertical coordinate, Q net is the net heat flux absorbed by the sea surface, including part of the solar shortwave radiation, all longwave radiation, sensible heat and latent heat flux, SW(z) is the solar shortwave radiation flux entering the water layer, ρ is the seawater density, C p is the specific heat of seawater; S4-3 Sea surface salinity boundary condition: The sea surface salinity boundary condition adopts a relaxed boundary condition, and the specific formula is: Where: S is the sea surface salinity value calculated by the model, S obs is the actual observed sea surface salinity.

2. The method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea according to claim 1, characterized in that: In the step S1, the number of horizontal grids is 400×160, and the calculation grid resolution is 2.5-3 km.

3. The method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea according to claim 1, characterized in that: In the step S1, there are 31 sigma layers vertically.

4. The method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea according to claim 1, characterized in that: In step S1, the water depth is interpolated onto the model calculation grid using Etopo2v2 data by using a cubic spline interpolation method.

5. The method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea according to claim 1, characterized in that: The temperature and salinity data in step S2 are from World Ocean Atlas 2001.

6. The method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea according to claim 1, characterized in that: The coefficient μ in step S3-3 is determined by the magnitude of the disturbance propagation speed: When C L ≤0, the velocity at the open boundary is given by the value at the open boundary calculated by the model in the previous time step. L When C is less than 1, the open boundary velocity is determined by the model calculation value and the disturbance propagation velocity. L When ≥1, the velocity at the open boundary is determined by the velocity of the inner area adjacent to the open boundary calculated by the model at the current time step.

7. The method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea according to claim 1, characterized in that: The wind farm models in step S4-1 include HR wind farm, ERA-interim wind farm, NCEP wind farm and QSCAT / NCEP mixed wind farm.

8. The method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea according to claim 1, characterized in that: The method for determining the solar shortwave radiation flux in step S4-2 is: S4-2-1: Construct an atmospheric radiation transfer model and compare it with the solar shortwave radiation information table; S4-2-2: Obtain atmospheric parameters in different intervals through AVHRR satellite radar information; S4-2-3: Determine the solar shortwave radiation flux in the different intervals by searching the atmospheric parameters in the solar shortwave radiation information table.

9. The method for constructing a three-dimensional coupled model of tide and circulation in the South China Sea according to claim 7, characterized in that: The atmospheric parameters in step S4-2-2 include the solar zenith angle range, aerosol optical thickness, aerosol type, water vapor content, water cloud particle effective radius and water cloud optical thickness, wherein the solar zenith angle range is 0-90°, with an interval of 5°, the aerosol optical thickness is 0-3, the aerosol type is oceanic, and the water vapor content is 0-8g / cm 2 , with an interval of 0.5, the effective radius of water cloud particles is 4μm, 8μm, 16μm, 32μm or 64μm, and the optical thickness of water cloud ranges from 1, 5, 10, 20, 30, 50, 100, 150, with an interval of 1.

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