A method for predicting vertical visibility based on aerosol and hydrometeor extinction contributions

Abstract

The application discloses a vertical visibility prediction method based on aerosol and water product extinction contribution, comprising the following steps: obtaining a prediction field output by a chemical weather numerical prediction model of a target area, performing aerosol activation parameterization based on aerosol grading mass concentration, calculating real-time cloud droplet number concentration, reading a mass extinction coefficient from a table to calculate aerosol vertical extinction coefficients of each model layer, calculating water product vertical extinction coefficients according to cloud droplet number concentration, cloud water content, ice crystal number concentration and cloud ice content of each model layer, calculating layer optical thickness according to the comprehensive vertical extinction coefficient and the thickness of the model layer, accumulating optical thickness layer by layer downward from the target height, and identifying vertical visibility based on the accumulated optical thickness. The method uses real-time cloud droplet number concentration to replace the fixed value in the cloud microphysical scheme, couples the extinction of aerosol and water product, improves the precision, applicability and timeliness of vertical visibility prediction under fog-haze and cloud-rain weather conditions, and has good interpretability.

Description

Technical Field

[0001] This invention relates to the fields of weather forecasting and atmospheric environment monitoring, and in particular to a method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous matter. Background Technology

[0002] Atmospheric visibility is a key meteorological parameter characterizing the transparency of the atmosphere. Its quantitative calculation is mainly based on the physical relationship between atmospheric extinction coefficient and visibility established by Koschmieder's law. Currently, atmospheric visibility is obtained mainly through two technical approaches: one is instrumental detection, which uses equipment such as horizontal visibility meters or lidar to invert the atmospheric extinction coefficient profile by emitting detection signals and receiving echoes, thereby estimating atmospheric visibility in the horizontal or vertical directions; the other is numerical model forecasting, which uses environmental meteorological numerical models to achieve large-scale and continuous forecasting. Visibility forecasting is crucial to compensate for the discontinuities in spatiotemporal coverage of instrument detection. In the existing operational forecasting system, the target products output by numerical models are mainly horizontal visibility, while quantitative calculation and operational forecasting of vertical visibility (i.e., the view from above) remain a gap. However, in application scenarios such as aviation flight safety assessment, UAV take-off and landing scheduling, and satellite remote sensing correction, vertical visibility at different altitudes is a key data support for ensuring flight safety, optimizing flight path planning, and improving the quality of remote sensing data. Therefore, the demand for operational forecasting of vertical visibility is becoming increasingly urgent.

[0003] Although instrumental detection can obtain vertical visibility information in local scenarios and scientific experiments, this type of method is essentially a diagnostic tool and cannot achieve operational forecasting of vertical visibility at future times. At the same time, most cloud microphysics schemes in existing numerical weather prediction systems use fixed cloud droplet number concentration parameterization schemes instead of obtaining dynamically activated aerosol number concentrations through the interaction mechanism between aerosols and clouds. This leads to significant deviations in the calculation of the vertical extinction coefficient under cloud and rain weather conditions. In addition, there is a lack of refined layered calculation capabilities for vertical extinction contributions, and the comprehensive extinction effect of aerosols and water molecules is not effectively coupled. It is difficult to achieve real-time forecasting of vertical visibility at any altitude within the framework of chemical weather models, and thus cannot meet the operational needs for three-dimensional visibility information. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous substances.

[0005] To achieve the above objectives, the present invention is implemented according to the following technical solution: This invention provides a method for predicting vertical visibility based on the extinction contributions of aerosols and aqueous matter, comprising: Obtain the forecast field output by the numerical weather prediction model for chemical weather in the target area. The forecast field includes aerosol mass concentration, cloud water content, cloud ice content, ice crystal number concentration and model layer thickness for each model layer. Aerosol activation parameters are parameterized based on aerosol mass concentration levels, and real-time cloud droplet number concentration is calculated. Based on the aerosol optical lookup table, the mass extinction coefficients of each aerosol component and each particle size range in each mode layer are read, and then weighted and accumulated with the corresponding aerosol mass concentration range to obtain the aerosol vertical extinction coefficient of each mode layer. Based on the cloud droplet number concentration, cloud water content, ice crystal number concentration, and cloud ice content of each model layer, the preset cloud droplet spectral distribution and ice crystal spectral distribution are integrated to obtain the effective radius of cloud droplets and the effective radius of ice crystals. The cloud water optical thickness and cloud ice optical thickness of each model layer are calculated, and the sum of the two is divided by the thickness of the corresponding model layer to obtain the vertical extinction coefficient of the aqueous material in each model layer. The vertical extinction coefficient of aerosols and the vertical extinction coefficient of aqueous substances in the same mode layer are added together to obtain the comprehensive vertical extinction coefficient. The product of the vertical extinction coefficient and the mode layer thickness is taken as the layer optical thickness. The optical thickness is accumulated layer by layer from the target height downwards. If the accumulated optical thickness meets the preset threshold, the corresponding accumulated path length is used as the vertical visibility at the target height. If the accumulated optical thickness does not meet the threshold at the ground, the target height is used as the vertical visibility.

[0006] Furthermore, the aerosol components include black carbon, organic carbon, mineral dust, sulfates, nitrates, sea salt, and ammonium salts; The hydrophilic aerosol components include sulfates, nitrates, ammonium salts, and organic carbon. Except for ammonium salts, each aerosol component includes 12 particle size ranges, with the particle size range being from 0.01 μm to 40.96 μm.

[0007] Furthermore, the method for parameterizing aerosol activation includes: Based on the aerosol mass concentration obtained from each model layer, the hygroscopic parameters of each aerosol component are obtained, and the supersaturation predicted by the model is obtained. Based on the aerosol mass concentration, hygroscopic parameters, and supersaturation, the number concentration of activatable aerosol particles in each model layer is calculated. The number concentration of activatable aerosol particles is used as the cloud droplet number concentration in the cloud microphysics scheme, replacing the preset fixed cloud droplet number concentration in the cloud microphysics scheme.

[0008] Further, the method for obtaining the supersaturation includes: The mass concentration of each aerosol component in each particle size range is converted into the number concentration of each range. The conversion formula is as follows: ; in For the first aerosol component number Number concentration of particle size range For the first aerosol components, the first Particle size range classification mass concentration; The volume fraction of each aerosol component in each particle size range is calculated based on its mass concentration and density. The hygroscopic parameters of each aerosol component are then weighted and summed based on these volume fractions to obtain the mixed hygroscopic parameter for each particle size range. The formula for calculating the mixed hygroscopic parameter is as follows: ; in For the first Hygroscopicity parameters of particle size range For the first Hygroscopic parameters of aerosol components, For the first The aerosol components in the first Volume fraction within particle size range; The critical supersaturation degree is calculated based on the geometric mean radius and mixed hygroscopicity parameters of each particle size range. The formula for calculating the critical supersaturation degree is as follows: ; ; in For the first Critical supersaturation for particle size range For the surface tension of water droplets, The molar mass of water, This is the universal gas constant. For the mode layer temperature, The density of liquid water; The maximum supersaturation of each model layer is determined based on the critical supersaturation and effective vertical velocity for each particle size range.

[0009] Furthermore, the method for obtaining the effective vertical velocity includes: Obtain the grid point vertical velocity and turbulent kinetic energy predicted by the model, and calculate the effective vertical velocity. The formula for the effective vertical velocity is: ; in For effective vertical velocity, The vertical velocity of the grid point. For turbulent kinetic energy, This is an empirical coefficient, with a value range of 0.5 to 1.5.

[0010] Furthermore, the method for obtaining the cloud droplet number concentration includes: The activation ratio of each particle size range is calculated based on the maximum supersaturation of each model layer and the critical supersaturation of each particle size range. The droplet number concentration of each particle size range is then multiplied by the corresponding activation ratio and summed to obtain the droplet number concentration of each model layer. The formula for calculating the droplet number concentration is as follows: ; in Cloud droplet number concentration, For the first The total concentration of aerosol components in the particle size range. For maximum supersaturation, Let be the error function. For the first The geometric standard deviation of the particle size ranges from 1.4 to 1.8. Physical constraints are applied to the cloud droplet number concentration, wherein the cloud droplet number concentration is less than or equal to the sum of the total concentrations of each particle size range, and greater than or equal to the lower limit of cloud droplet number concentration preset by the cloud microphysics scheme; The cloud droplet number concentration after physical constraints is used as the cloud droplet number concentration of the cloud microphysics scheme.

[0011] Further, the method for obtaining the mass extinction coefficient includes: Based on the aerosol components, the extinction efficiency factor at each particle size and relative humidity is pre-calculated using the Mie scattering theory. The corresponding mass extinction coefficient is then calculated based on the extinction efficiency factor. An aerosol optical lookup table is established using aerosol components, particle size, visible light wavelength, and relative humidity as indexes. For hydrophilic aerosol components, the particle size after hygroscopic growth at various relative humidities is calculated using the Köhler equation, and the corresponding extinction efficiency factor is calculated based on the particle size after hygroscopic growth. The formula for calculating the mass extinction coefficient is as follows: ; in For the first aerosol component number Mass extinction coefficient for particle size range For the first aerosol component number The extinction efficiency factor for each particle size range was pre-calculated based on Mie scattering theory. For the first The geometric mean of the effective radius of particles within the particle size range. For the first The density of the aerosol components.

[0012] Furthermore, the method for obtaining the vertical extinction coefficient of the aerosol includes: At each time step of the model integration, the mass extinction coefficients of each aerosol component and each particle size range are read from the aerosol optical lookup table based on the relative humidity predicted by the model. The read mass extinction coefficients are multiplied by the corresponding mass concentration of the aerosol range, and then accumulated for each aerosol component and each particle size range to obtain the aerosol vertical extinction coefficients of each model layer.

[0013] Furthermore, the method for obtaining the vertical extinction coefficient of the aqueous substance includes: The cloud droplet spectral distribution and ice crystal spectral distribution are obtained based on the Thompson cloud microphysics scheme, wherein the cloud droplet spectral distribution and ice crystal spectral distribution are gamma distributions; Based on the physically constrained cloud droplet number concentration, cloud water content, ice crystal number concentration, and cloud ice content, and using the gamma distribution spectrum assumption, the effective radius of cloud droplets and the effective radius of ice crystals are inverted using the spectral moment method. The formula for calculating the effective radius is as follows: ; ; in For the effective radius of the cloud droplet, The effective radius of the ice crystal, Cloud water content, Cloud ice content, Cloud droplet number concentration, Ice crystal number concentration, The shape parameters of the cloud droplet gamma spectrum. The shape parameters of the ice crystal gamma spectrum. For gamma-ray spectral moment ratio lookup table parameters; The optical thickness of cloud water and the optical thickness of cloud ice are calculated based on the effective radius of cloud droplets and the effective radius of ice crystals, respectively. The formula for calculating the optical thickness is as follows: ; ; in For cloud and water optical thickness, For the optical thickness of cloud ice, Cloud water content, Cloud ice content, , The parameters are used to fit the extinction coefficient of cloud water at different visible light wavelengths. , The extinction coefficient fitting parameters are for cloud ice, and the extinction coefficient fitting parameters are obtained based on Mie scattering theory. The vertical extinction coefficient of the aqueous phase in the same model layer is obtained by dividing the sum of the optical thickness of cloud water and the optical thickness of cloud ice in the same model layer by the thickness of the model layer.

[0014] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: This invention uses Koschmieder's law to accumulate the extinction coefficient layer by layer downwards along the target height and determine vertical visibility, providing vertical data support for scenarios such as aviation flight safety assessment and UAV take-off and landing scheduling. By introducing an aerosol activation parameterization method, cloud droplet number concentration is calculated in real time based on aerosol graded mass concentration, hygroscopic parameters, and supersaturation, replacing the preset fixed values ​​in traditional cloud microphysics schemes. This allows the hydrophyte extinction coefficient to dynamically link with the aerosol field and meteorological field, reducing the calculation deviation of the vertical extinction coefficient under cloud and rain weather. Through a dual-branch extinction contribution coupling calculation framework of aerosols and hydrophytes, the aerosol branch quickly reads the graded mass extinction coefficient by combining a pre-established Mie scattering optical lookup table with Köhler hygroscopic growth, while the hydrophyte branch calculates the optical thickness by the effective radius of cloud droplets and ice crystals. The two branches synthesize the comprehensive vertical extinction coefficient in the same mode layer, balancing computational efficiency and physical integrity. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the steps of a vertical visibility prediction method based on the extinction contribution of aerosols and aqueous substances in an embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] Reference Figure 1 As shown, this invention provides a method for predicting vertical visibility based on the extinction contributions of aerosols and aqueous matter, comprising: Obtain the forecast field output by the numerical weather prediction model for chemical weather in the target area. The forecast field includes aerosol mass concentration, cloud water content, cloud ice content, ice crystal number concentration and model layer thickness for each model layer. In practical assessments, based on Koschmieder's law, vertical visibility is defined as the distance downwards from the target's height. The fundamental equation for calculating atmospheric vertical visibility is constructed, and the formula for calculating vertical visibility is as follows: ; in The accumulated physical path length from the target height downwards, in meters. The optical thickness accumulated from the target height downwards is dimensionless. The vertical extinction coefficient of the current layer, in meters. -1 , H represents the current layer thickness, and H represents the target height. The preset threshold is a constant, usually 3.912, dimensionless. The preset threshold of 3.912 corresponds to the contrast threshold of 0.02 in Koschmieder's law. Vertical visibility at different altitudes was calculated based on the output of the WRF-Chem high-resolution chemical weather model. The WRF-Chem v4.4 model was used, with a horizontal resolution of 3 km and a 51-layer topographic-following coordinate system. The model top altitude was 50 hPa. A tiered approach was used for aerosol chemical mechanisms, and the Thompson aerosol sensing scheme was employed for cloud microphysical processes. physics =28, the forecast field output time interval is 1 hour, and vertical visibility diagnostic calculation is performed during model integration. The target height is selected as 1000m and 3000m. The forecast variables of each model layer in the target area are extracted from the WRF-Chem model output, including aerosol band mass concentration, in μg·m³. -3 It comprises seven components: black carbon, organic carbon, mineral dust, sulfate, nitrate, sea salt, and ammonium salt. Except for ammonium salt, it is divided into 12 particle size ranges from 0.01 to 40.96 μm, with particle diameters of 0.01-0.02 µm, 0.02-0.04 µm, 0.04-0.08 µm, 0.08-0.16 µm, 0.16-0.32 µm, 0.32-0.64 µm, 0.64-1.28 µm, 1.28-2.56 µm, 2.56-5.12 µm, 5.12-10.24 µm, 10.24-20.48 µm, and 20.48-40.96 µm. The particle size distribution can be adjusted according to the actual configuration of the coupled mode. This invention does not impose a unique limitation on the type of aerosol or the number of particle sizes. Cloud water content, unit: kg·m³. -3 Cloud ice content, unit kg·m -3 Ice crystal number concentration, unit m -3 Model layer thickness, in meters; relative humidity, in percentage; grid vertical velocity, in meters per second. -1 Turbulent kinetic energy TKE, unit m 2 ·s -2 At an altitude of approximately 1000m, corresponding to the 18th layer of the model, the typical forecast field shows a model layer thickness (characterized by the thickness of the pressure layer at each level) of 200m, cloud water content of 0.3%, cloud ice content of 0.05%, and ice crystal number concentration of 5.0 × 10⁻⁶. 4 Relative humidity 85%, turbulent kinetic energy 0.80; Aerosol activation parameters are parameterized based on aerosol mass concentration levels, and real-time cloud droplet number concentration is calculated. In the actual evaluation, the fifth particle size range in layer 18 is 0.32–0.64 μm, with a geometric mean radius r5 = 0.48 μm. After converting the mass concentration and number concentration of each component within the range, the mass concentration of sulfate in the range is 8.5 μg·m⁻¹. -3 The component density ρ is 1.76 g·m³. -3 The concentration for each grade is then 1.04 × 10⁻⁶. 7 m -3 The fractional mass concentration of nitrate was 6.2 μg·m³. -3 The component density ρ is 1.72 g·m³. -3 The concentration for each grade is 7.78 × 10⁻⁶. 6 m -3 The fractional mass concentration of organic carbon was 12.3 μg·m³. -3 The component density ρ is 1.20 g·m³. -3 The concentration for each grade is then 2.21 × 10⁻⁶. 7 m -3 The fractional mass concentration of black carbon was 2.5 μg·m³. -3 The component density ρ is 1.80 g·m³. -3 The concentration for each grade is 3.42 × 10⁻⁶. 6 m -3 The mass concentration of mineral dust was 15.0 μg·m³. -3 The component density ρ is 2.60 g·m³. -3 The concentration for each grade is 3.01 × 10⁻⁶. 6 m -3 The graded mass concentration of sea salt is 8.0 μg·m³. -3 The component density ρ is 2.20 g·m³. -3 The concentration for each grade is 5.84 × 10⁻⁶. 6 m -3 Then the total concentration N of the 5 levels total,5 =5.66×10 7 m -3 The weighted average hygroscopic parameter of the mixture, calculated based on the volume fraction of each component, is 0.342. Specifically, the hygroscopic parameter for sulfate is 0.61, for nitrate it is 0.67, for organic carbon it is 0.10, and for the hydrophobic components (black carbon and mineral dust) it is 0. The critical supersaturation is calculated based on the geometric mean radius of each particle size and the mixed hygroscopic parameter, where A = 1.08 × 10⁻⁶. −9 m, S c,5 =0.0072%, and the effective vertical velocity calculated based on the grid point vertical velocity and turbulent kinetic energy predicted by the model is 0.93 m·s. -1 Take c t =1.0, the maximum supersaturation S of the layer is calculated iteratively using the rising adiabatic parcel method based on the effective vertical velocity.max =0.35%. The activation ratio for each particle size range was calculated based on the maximum supersaturation of each model layer and the critical supersaturation of each particle size range. The droplet number concentration for each particle size range was multiplied by its corresponding activation ratio and then summed to obtain the droplet number concentration for each model layer. The geometric standard deviation was 1.6. After summing all ranges and applying physical constraints, the real-time droplet number concentration for layer 18 was obtained as Nc = 5.0 × 10⁻⁶. 7 m −3 This replaces the preset fixed cloud droplet number concentration of 1.0 × 10⁻⁶ in the Thompson scheme. 8 m −3 This enables the dynamic coupling of aerosol-cloud interactions; Based on the aerosol optical lookup table, the mass extinction coefficients of each aerosol component and each particle size range in each mode layer are read, and then weighted and accumulated with the corresponding aerosol mass concentration range to obtain the aerosol vertical extinction coefficient of each mode layer. In the actual evaluation, the extinction efficiency factor Q was calculated in advance based on Mie scattering theory in the 0.55μm visible light band for each aerosol component, each particle size range, and each relative humidity. ext Considering hydrophilic components such as sulfates, nitrates, ammonium salts, and organic carbon, a four-dimensional aerosol optical lookup table is established using the component-particle size-wavelength-relative humidity index. Based on this index, a hygroscopic growth effect according to the Köhler equation is applied to calculate the index. In this embodiment, 0.55 μm is used, but this can be extended to 0.44 μm, 0.67 μm, and other wavelengths most sensitive to the human eye. For each dry component (i,j,λ), the complex refractive index m of the corresponding component is... i =n i -k i i and the dry geometric mean radius r j,dry The extinction efficiency factor is calculated using the Bohren & Huffman algorithm. The formula for calculating the extinction efficiency factor of the dry component is as follows: ; in , is the scale parameter. , The Mie coefficient; Sulfate n=1.53, k≈0, level 5 r j,dry =0.48μm, Q is calculated ext,dry (SO4, 5, 0.55 μm) = 2.85. For hydrophilic components such as sulfates, nitrates, ammonium salts, and organic carbon, the particle size after hygroscopic growth needs to be calculated based on the relative humidity. According to the Köhler equation, the formula for calculating the particle hygroscopic growth factor f(RH) in supersaturated or high-humidity environments is: ; in Hygroscopic parameters of components , 7, 0, 0; Sulfate at f(85%) = 1.42, after moisture absorption, has a radius r. j,wet =r j,dry ×f(RH) = 0.48 × 1.42 = 0.68 μm. The Mie calculation is performed again using the wet radius to obtain the wet extinction efficiency factor Q. ext,wet =3.12, convert the extinction efficiency factor to the mass extinction coefficient. ;in The dry geometric mean radius is taken as the identification radius for each grade. Given the component density, the mass extinction coefficient K of the sulfate is... aero (SO4, 5, 0.55 μm, 85%) = 2.78 × 10 − 3 m 2 μg −1 Based on the combination of index traversal dimensions, a four-dimensional lookup table with 924 entries and a size of 7×12×1×11 is constructed. The table is stored in binary or NetCDF format and read in when the mode starts. In the integration process of chemical weather models, atmospheric conditions are updated every moment. In this embodiment, extinction calculation is directly embedded into the model's integration loop. Each time step, the model calculates new aerosol concentrations, cloud water content, and cloud droplet number concentrations, updates humidity and temperature, and reads the corresponding mass extinction coefficient from the aerosol optical lookup table based on the relative humidity of the current layer. These are then accumulated to obtain the aerosol extinction contribution of each layer. This contribution is then added to the hydrophyte extinction contribution given by the cloud microphysics scheme at the same moment to obtain the comprehensive extinction capacity of that layer at that moment. After each output cycle, these pre-calculated layered extinction coefficients are used for the final downward accumulation step. Starting from the target height, optical thickness is added layer by layer until it is thick enough that the human eye cannot see clearly. The accumulated distance is the vertical visibility. If the threshold is not reached even when adding to the ground, the vertical visibility is taken as the target height itself, meaning the ground is visible from the target height downwards. During each time step of model integration, the mass extinction coefficient K is read from the table based on the relative humidity forecast for each model layer. aero (i,j) are weighted and accumulated with the corresponding mass concentrations. For the 18th layer, RH = 85%. After referring to the table and accumulating, the vertical extinction coefficient of the aerosol in the 18th layer is 2.0 × 10⁻⁶. −3 m −1 ; Based on the cloud droplet number concentration, cloud water content, ice crystal number concentration, and cloud ice content of each model layer, the preset cloud droplet spectral distribution and ice crystal spectral distribution are integrated to obtain the effective radius of cloud droplets and the effective radius of ice crystals. The cloud water optical thickness and cloud ice optical thickness of each model layer are calculated, and the sum of the two is divided by the thickness of the corresponding model layer to obtain the vertical extinction coefficient of the aqueous material in each model layer. In practical assessments, based on the gamma distribution spectrum assumptions of the current Thompson scheme, the effective radius is inverted using the spectral moment method according to water content and number concentration, where the cloud droplet shape parameter index μ is used. c =INT(10 9 / N c )=2, g ratio The value range is 24, 60, 120, 210, 336, 504, 720, 990, 1320, 1716, 2184, 2730, 3360, 4080, 4896, with g corresponding to the 18th layer. ratio =60, ice crystal spectra are taken with fixed shape parameters, g ratio,i =6.0, substitute into the 18th layer parameter Q c =0.30g·m -3 Q i =0.05g·m -3 N c =5.0×10 7 m -3 N i =5.0×10 4 m -3 r e,c =7.9μm, r e,i =105.4μm, cloud water optical thickness and cloud ice optical thickness were calculated based on the effective radius of cloud droplets and the effective radius of ice crystals. COT cloud =CWP cloud ×(a w1 +a w2 / r e,c )=60×(−0.0166+1.85 / 7.9)=13.0, COT ice =CWP ice ×(a i1 +a i2 / r e,i ) = 10 × (0.000333 + 2.52 / 105.4) = 0.24, where a w and a i The extinction coefficient fitting parameters for cloud water and cloud ice at different wavelengths in the range of 0.7–10 μm are given by a. w1 The values ​​of a are -0.0101, -0.0166, and -0.0339. w2 The values ​​of a are 1.72, 1.85, and 2.16.i1 The values ​​of a are 0.000333, 0.000333, and 0.000333. i2 The value of CWP is 2.52, 2.52, 2.52. cloud =0.30g·m -3 ×200m=60g·m -2 CWP ice =10g·m -2 The vertical extinction coefficient K of the aqueous material was calculated based on the optical thickness of cloud water and cloud ice. vext_hydro =(COT cloud +COT ice ) / Δz=13.24 / 200=6.6×10 −2 m −1 Δz is the mode layer thickness; The vertical extinction coefficient of aerosols and the vertical extinction coefficient of aqueous substances in the same mode layer are added together to obtain the comprehensive vertical extinction coefficient. The product of the vertical extinction coefficient and the mode layer thickness is taken as the layer optical thickness. In the actual evaluation, the extinction contributions of aerosols and aqueous matter were added together to obtain the comprehensive vertical extinction coefficient of the 18th layer, K. vext =K vext_aero +K vext_hydro =2.0×10 −3 +6.6×10 −2 =6.8×10 −2 m −1 , layer optical thickness τ layer =K vext ×Δz=13.6, and the comprehensive vertical extinction coefficient and layer optical thickness of each mode layer below 1000m were calculated in sequence. When the layer optical thickness reached 200m, it dropped to 0.9. The optical thickness is accumulated layer by layer from the target height downwards. If the accumulated optical thickness meets the preset threshold, the corresponding accumulated path length is used as the vertical visibility at the target height. If the accumulated optical thickness does not meet the threshold at the ground, the target height is used as the vertical visibility.

[0018] In actual assessment, the optical thickness is accumulated layer by layer from 1000m downwards. Based on the vertical visibility formula, the optical thickness of the first layer (1000–800m) reaches 13.6, far exceeding the threshold of 3.912, indicating that the visual limit has been reached within the layer. The precise location within the layer, Δz, is calculated using a linear ratio. eff =τ c / K vext =3.912 / 0.068≈58m, indicating that in foggy and low-cloud weather, the drone cannot penetrate the dense cloud layer below at an altitude of 1000m, and the visible distance looking down is only about 58m, which should trigger the return-to-home or altitude adjustment command. In actual assessments, another embodiment targets an altitude of 3000m, with a relatively clean atmospheric K range between 3000 and 1000m. vext ≈3.0×10 -4 m -1 τ=0.6, accumulating from 3000m downwards, upper layer 3000–1000, layer optical thickness 0.6, cumulative optical thickness 0.6, cumulative path length 2000, since the threshold is reached within the 1000–800m layer, the required travel distance within the layer is approximately 49m, VIS v (3000m) = 2000 + 49 = 2049m. When looking down from a cruising altitude of 3000m, the vertical visibility is about 2049m, making it impossible to visually confirm the runway or ground references. In the actual assessment, the pattern forecast for Example 3 was a clean background, K vext ≈5.0×10 -5 m -1 Cloudless, accumulating from 1000m downwards, τ total =5.0×10 −5 ×1000=0.05, which is much smaller than 3.912. The cumulative value to the ground still does not reach the threshold. Therefore, the vertical visibility is taken as the target height itself. At a height of 1000m, the ground can be seen directly.

[0019] In this embodiment, the aerosol components include black carbon, organic carbon, mineral dust, sulfates, nitrates, sea salt, and ammonium salts; The hydrophilic aerosol components include sulfates, nitrates, ammonium salts, and organic carbon. Except for ammonium salts, each aerosol component includes 12 particle size ranges, with the particle size range being from 0.01 μm to 40.96 μm.

[0020] In this embodiment, the method for aerosol activation parameterization includes: Based on the aerosol mass concentration obtained from each model layer, the hygroscopic parameters of each aerosol component are obtained, and the supersaturation predicted by the model is obtained. Based on the aerosol mass concentration, hygroscopic parameters, and supersaturation, the number concentration of activatable aerosol particles in each model layer is calculated. The number concentration of activatable aerosol particles is used as the cloud droplet number concentration in the cloud microphysics scheme, replacing the preset fixed cloud droplet number concentration in the cloud microphysics scheme.

[0021] In this embodiment, the method for obtaining the supersaturation includes: The mass concentration of each aerosol component in each particle size range is converted into the number concentration of each range. The conversion formula is as follows: ; in For the first aerosol component number Number concentration of particle size range For the first aerosol components, the first Particle size range classification mass concentration; The volume fraction of each aerosol component in each particle size range is calculated based on its mass concentration and density. The hygroscopic parameters of each aerosol component are then weighted and summed based on these volume fractions to obtain the mixed hygroscopic parameter for each particle size range. The formula for calculating the mixed hygroscopic parameter is as follows: ; in For the first Hygroscopicity parameters of particle size range For the first Hygroscopic parameters of aerosol components, For the first The aerosol components in the first Volume fraction within particle size range; The critical supersaturation degree is calculated based on the geometric mean radius and mixed hygroscopicity parameters of each particle size range. The formula for calculating the critical supersaturation degree is as follows: ; ; in For the first Critical supersaturation for particle size range For the surface tension of water droplets, The molar mass of water, This is the universal gas constant. For the mode layer temperature, The density of liquid water; The maximum supersaturation of each model layer is determined based on the critical supersaturation and effective vertical velocity for each particle size range.

[0022] In this embodiment, the method for obtaining the effective vertical velocity includes: Obtain the grid point vertical velocity and turbulent kinetic energy predicted by the model, and calculate the effective vertical velocity. The formula for the effective vertical velocity is: ; in For effective vertical velocity, The vertical velocity of the grid point. For turbulent kinetic energy, This is an empirical coefficient, with a value range of 0.5 to 1.5.

[0023] In this embodiment, the method for obtaining the cloud droplet number concentration includes: The activation ratio of each particle size range is calculated based on the maximum supersaturation of each model layer and the critical supersaturation of each particle size range. The droplet number concentration of each particle size range is then multiplied by the corresponding activation ratio and summed to obtain the droplet number concentration of each model layer. The formula for calculating the droplet number concentration is as follows: ; in Cloud droplet number concentration, For the first The total concentration of aerosol components in the particle size range. For maximum supersaturation, Let be the error function. For the first The geometric standard deviation of the particle size ranges from 1.4 to 1.8. Physical constraints are applied to the cloud droplet number concentration, wherein the cloud droplet number concentration is less than or equal to the sum of the total concentrations of each particle size range, and greater than or equal to the lower limit of cloud droplet number concentration preset by the cloud microphysics scheme; The cloud droplet number concentration after physical constraints is used as the cloud droplet number concentration of the cloud microphysics scheme.

[0024] In this embodiment, the method for obtaining the mass extinction coefficient includes: Based on the aerosol components, the extinction efficiency factor at each particle size and relative humidity is pre-calculated using the Mie scattering theory. The corresponding mass extinction coefficient is then calculated based on the extinction efficiency factor. An aerosol optical lookup table is established using aerosol components, particle size, visible light wavelength, and relative humidity as indexes. For hydrophilic aerosol components, the particle size after hygroscopic growth at various relative humidities is calculated using the Köhler equation, and the corresponding extinction efficiency factor is calculated based on the particle size after hygroscopic growth. The formula for calculating the mass extinction coefficient is as follows: ; in For the first aerosol component number Mass extinction coefficient for particle size range For the first aerosol component number The extinction efficiency factor for each particle size range was pre-calculated based on Mie scattering theory. For the first The geometric mean of the effective radius of particles within the particle size range. For the first The density of the aerosol components.

[0025] In this embodiment, the method for obtaining the vertical extinction coefficient of the aerosol includes: At each time step of the model integration, the mass extinction coefficients of each aerosol component and each particle size range are read from the aerosol optical lookup table based on the relative humidity predicted by the model. The read mass extinction coefficients are multiplied by the corresponding mass concentration of the aerosol range, and then accumulated for each aerosol component and each particle size range to obtain the aerosol vertical extinction coefficients of each model layer.

[0026] In this embodiment, the method for obtaining the vertical extinction coefficient of the aqueous substance includes: The cloud droplet spectral distribution and ice crystal spectral distribution are obtained based on the Thompson cloud microphysics scheme, wherein the cloud droplet spectral distribution and ice crystal spectral distribution are gamma distributions; Based on the physically constrained cloud droplet number concentration, cloud water content, ice crystal number concentration, and cloud ice content, and using the gamma distribution spectrum assumption, the effective radius of cloud droplets and the effective radius of ice crystals are inverted using the spectral moment method. The formula for calculating the effective radius is as follows: ; ; in For the effective radius of the cloud droplet, The effective radius of the ice crystal, Cloud water content, Cloud ice content, Cloud droplet number concentration, Ice crystal number concentration, The shape parameters of the cloud droplet gamma spectrum. The shape parameters of the ice crystal gamma spectrum. For gamma-ray spectral moment ratio lookup table parameters; The optical thickness of cloud water and the optical thickness of cloud ice are calculated based on the effective radius of cloud droplets and the effective radius of ice crystals, respectively. The formula for calculating the optical thickness is as follows: ; ; in For cloud and water optical thickness, For the optical thickness of cloud ice, Cloud water content, Cloud ice content, , The parameters are used to fit the extinction coefficient of cloud water at different visible light wavelengths. , The extinction coefficient fitting parameters are for cloud ice, and the extinction coefficient fitting parameters are obtained based on Mie scattering theory. The vertical extinction coefficient of the aqueous phase in the same model layer is obtained by dividing the sum of the optical thickness of cloud water and the optical thickness of cloud ice in the same model layer by the thickness of the model layer.

[0027] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for predicting vertical visibility based on the extinction contributions of aerosols and aqueous substances, characterized in that, Includes the following steps: Obtain the forecast field output by the numerical weather prediction model for chemical weather in the target area. The forecast field includes aerosol mass concentration, cloud water content, cloud ice content, ice crystal number concentration and model layer thickness for each model layer. Aerosol activation parameters are parameterized based on aerosol mass concentration levels, and real-time cloud droplet number concentration is calculated. Based on the aerosol optical lookup table, the mass extinction coefficients of each aerosol component and each particle size range in each mode layer are read, and then weighted and accumulated with the corresponding aerosol mass concentration range to obtain the aerosol vertical extinction coefficient of each mode layer. Based on the cloud droplet number concentration, cloud water content, ice crystal number concentration, and cloud ice content of each model layer, the preset cloud droplet spectral distribution and ice crystal spectral distribution are integrated to obtain the effective radius of cloud droplets and the effective radius of ice crystals. The cloud water optical thickness and cloud ice optical thickness of each model layer are calculated, and the sum of the two is divided by the thickness of the corresponding model layer to obtain the vertical extinction coefficient of the aqueous material in each model layer. The vertical extinction coefficient of aerosols and the vertical extinction coefficient of aqueous substances in the same mode layer are added together to obtain the comprehensive vertical extinction coefficient. The product of the vertical extinction coefficient and the mode layer thickness is taken as the layer optical thickness. The optical thickness is accumulated layer by layer from the target height downwards. If the accumulated optical thickness meets the preset threshold, the corresponding accumulated path length is used as the vertical visibility at the target height. If the accumulated optical thickness does not meet the threshold at the ground, the target height is used as the vertical visibility.

2. The method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous matter according to claim 1, characterized in that, The aerosol components include black carbon, organic carbon, mineral dust, sulfates, nitrates, sea salt, and ammonium salts; The hydrophilic aerosol components include sulfates, nitrates, ammonium salts, and organic carbon. Except for the ammonium salts, each aerosol component includes 12 particle size ranges, with the particle size range being from 0.01 μm to 40.96 μm.

3. The method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous matter according to claim 1, characterized in that, The method for parameterizing aerosol activation includes: Based on the aerosol mass concentration obtained from each model layer, the hygroscopic parameters of each aerosol component are obtained, and the supersaturation predicted by the model is obtained. Based on the aerosol mass concentration, hygroscopic parameters, and supersaturation, the number concentration of activatable aerosol particles in each model layer is calculated. The number concentration of activatable aerosol particles is used as the cloud droplet number concentration in the cloud microphysics scheme, replacing the preset fixed cloud droplet number concentration in the cloud microphysics scheme.

4. The method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous matter according to claim 3, characterized in that, A method for obtaining the supersaturation includes: The mass concentration of each aerosol component in each particle size range is converted into the number concentration of each range. The conversion formula is as follows: ； in For the first aerosol component number Number concentration of particle size range For the first aerosol components, the first Particle size range classification mass concentration; The volume fraction of each aerosol component in each particle size range is calculated based on its mass concentration and density. The hygroscopic parameters of each aerosol component are then weighted and summed based on these volume fractions to obtain the mixed hygroscopic parameter for each particle size range. The formula for calculating the mixed hygroscopic parameter is as follows: ； in For the first Hygroscopicity parameters of particle size range For the first Hygroscopic parameters of aerosol components, For the first The aerosol components in the first Volume fraction within particle size range; The critical supersaturation degree is calculated based on the geometric mean radius and mixed hygroscopicity parameters of each particle size range. The formula for calculating the critical supersaturation degree is as follows: ； ； in For the first Critical supersaturation for particle size range, For the surface tension of water droplets, The molar mass of water, This is the universal gas constant. For the mode layer temperature, The density of liquid water; The maximum supersaturation of each model layer is determined based on the critical supersaturation and effective vertical velocity for each particle size range.

5. The vertical visibility prediction method based on the extinction contribution of aerosols and aqueous matter according to claim 4, characterized in that, The method for obtaining the effective vertical velocity includes: Obtain the grid point vertical velocity and turbulent kinetic energy predicted by the model, and calculate the effective vertical velocity. The formula for the effective vertical velocity is: ； in For effective vertical velocity, The vertical velocity of the grid point. For turbulent kinetic energy, This is an empirical coefficient, with a value range of 0.5 to 1.

5.

6. The method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous matter according to claim 3, characterized in that, A method for obtaining the cloud droplet number concentration includes: The activation ratio of each particle size range is calculated based on the maximum supersaturation of each mode layer and the critical supersaturation of each particle size range. The droplet number concentration of each particle size range is then multiplied by the corresponding activation ratio and summed to obtain the droplet number concentration of each mode layer. The formula for calculating the droplet number concentration is as follows: ； in Cloud droplet number concentration, For the first The total concentration of aerosol components in the particle size range. For maximum supersaturation, Let be the error function. For the first The geometric standard deviation of the particle size ranges from 1.4 to 1.

8. Physical constraints are applied to the cloud droplet number concentration, wherein the cloud droplet number concentration is less than or equal to the sum of the total concentrations of each particle size range, and greater than or equal to the lower limit of cloud droplet number concentration preset by the cloud microphysics scheme; The cloud droplet number concentration after physical constraints is used as the cloud droplet number concentration of the cloud microphysics scheme.

7. The method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous matter according to claim 1, characterized in that, A method for obtaining the mass extinction coefficient includes: Based on the aerosol components, the extinction efficiency factor at each particle size and relative humidity is pre-calculated using the Mie scattering theory. The corresponding mass extinction coefficient is then calculated based on the extinction efficiency factor. An aerosol optical lookup table is established using aerosol components, particle size, visible light wavelength, and relative humidity as indexes. For hydrophilic aerosol components, the particle size after hygroscopic growth at various relative humidities is calculated using the Köhler equation, and the corresponding extinction efficiency factor is calculated based on the particle size after hygroscopic growth. The formula for calculating the mass extinction coefficient is as follows: ； in For the first aerosol component number Mass extinction coefficient for particle size range For the first aerosol component number The extinction efficiency factor for each particle size range was pre-calculated based on Mie scattering theory. For the first The geometric mean of the effective radius of particles within the particle size range. For the first The density of the aerosol components.

8. The method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous matter according to claim 1, characterized in that, A method for obtaining the vertical extinction coefficient of the aerosol includes: At each time step of the model integration, the mass extinction coefficients of each aerosol component and each particle size range are read from the aerosol optical lookup table based on the relative humidity predicted by the model. The read mass extinction coefficients are multiplied by the corresponding mass concentration of the aerosol range, and then accumulated for each aerosol component and each particle size range to obtain the aerosol vertical extinction coefficients of each model layer.

9. The method for predicting vertical visibility based on the extinction contribution of aerosols and aqueous matter according to claim 1, characterized in that, A method for obtaining the vertical extinction coefficient of the aqueous substance includes: The cloud droplet spectral distribution and ice crystal spectral distribution are obtained based on the Thompson cloud microphysics scheme, and the cloud droplet spectral distribution and ice crystal spectral distribution are gamma distributions; Based on the physically constrained cloud droplet number concentration, cloud water content, ice crystal number concentration, and cloud ice content, and using the gamma distribution spectrum assumption, the effective radius of cloud droplets and the effective radius of ice crystals are inverted using the spectral moment method. The formula for calculating the effective radius is as follows: ； ； in For the effective radius of the cloud droplet, The effective radius of the ice crystal, Cloud water content, Cloud ice content, Cloud droplet number concentration, Ice crystal number concentration, The shape parameters of the cloud droplet gamma spectrum. The shape parameters of the ice crystal gamma spectrum. For gamma-ray spectral moment ratio lookup table parameters; The optical thickness of cloud water and the optical thickness of cloud ice are calculated based on the effective radius of cloud droplets and the effective radius of ice crystals, respectively. The formula for calculating the optical thickness is as follows: ； ； in For cloud and water optical thickness, For the optical thickness of cloud ice, Cloud water content, Cloud ice content, , The parameters are used to fit the extinction coefficient of cloud water at different visible light wavelengths. , The extinction coefficient fitting parameters are for cloud ice, and the extinction coefficient fitting parameters are obtained based on Mie scattering theory. The vertical extinction coefficient of the aqueous phase in the same model layer is obtained by dividing the sum of the optical thickness of cloud water and the optical thickness of cloud ice in the same model layer by the thickness of the model layer.

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