Method and system for forecasting and testing asymmetric precipitation of tropical cyclones

Abstract

The invention relates to the field of meteorological research, in particular to a forecasting test method and system for asymmetric rainfall of a tropical cyclone. The method comprises the following steps: step 1, obtaining observed and forecasted tropical cyclone data, and calculating an average observed and forecasted tropical cyclone position; step 2, extracting tropical cyclone rainfall in the observation and forecast rainfall field; 3, calculating relative asymmetric rainfall of observation rainfall and forecast rainfall; step 4, calculating rainfall asymmetry indexes of observation and forecast rainfall; 5, calculating the radius and azimuth angle of the observation and forecast rainfall gravity center; 6, converting the relative asymmetric precipitation field to a target direction coordinate system; and 7, calculating a forecast error. According to the method, the asymmetric rainfall forecast of the tropical cyclones can be qualitatively and quantitatively checked, the difference of the asymmetric rainfall forecast capabilities of the tropical cyclones in different modes, different forecast time periods and the like can be reflected, and a support is provided for improving the rainfall forecast of the tropical cyclones.

Description

Technical Field

[0001] The invention relates to the field of meteorological research, and in particular to a forecast verification method and system for asymmetric precipitation in a tropical cyclone. Background Art

[0002] Tropical cyclones are low-pressure vortices that occur over tropical or subtropical oceans. They are one of the most destructive natural disasters in the world. Precipitation is one of the most important hazard factors for tropical cyclones, which may cause extremely destructive disasters. Accurately predicting where heavy precipitation will occur is of great significance for disaster prevention and mitigation. At present, the accuracy and refinement of tropical cyclone precipitation forecasts are far from meeting actual needs, and the forecast level needs to be improved urgently. Testing the forecast to clearly understand whether the forecast can better reflect the observed precipitation distribution characteristics and what are the shortcomings is a prerequisite for using and improving the forecast.

[0003] In observations, tropical cyclone precipitation is not distributed symmetrically around the central axis, but has a certain degree of asymmetry. Previous studies have shown that the intensity of asymmetry in tropical cyclone precipitation varies under different circumstances. For example, when the intensity of tropical cyclones is stronger, the asymmetry of tropical cyclone precipitation is weaker. Some studies have explored the influencing factors of asymmetric tropical cyclone precipitation, indicating that environmental vertical wind shear is an important factor affecting the asymmetric distribution of tropical cyclone precipitation. In the Northern Hemisphere, tropical cyclone precipitation is often concentrated in front of or to the left of the downwind shear of environmental vertical wind shear. The asymmetry of tropical cyclone precipitation poses a considerable challenge to forecasting. In the past, due to the limitations of the level of tropical cyclone precipitation forecasting, the examination of the fine structure of these precipitations has not received enough attention. With the improvement of the forecasting level, whether the forecast can better predict the strength of asymmetry of tropical cyclone precipitation and the distribution of asymmetric precipitation is becoming increasingly important.

[0004] At present, there are few methods for forecasting and verifying asymmetric precipitation in tropical cyclones. In the prior art, there is a method of comparing the observed and predicted composite distribution of precipitation relative to the vertical wind shear of the environment for verification. However, due to the great influence of the intensity of tropical cyclones, the precipitation cannot well reflect the asymmetric distribution characteristics of precipitation. In addition, this method is a qualitative test and lacks quantitative testing. In order to better evaluate the forecasting ability of tropical cyclone asymmetric precipitation, it is necessary to develop new methods and use new indicators to verify asymmetric precipitation forecasts. Summary of the invention

[0005] The purpose of the present invention is to provide a forecast verification method and system for asymmetric precipitation in tropical cyclones, which can perform qualitative and quantitative verification on asymmetric precipitation in tropical cyclones. For qualitative verification, the present invention proposes relative asymmetric precipitation to characterize asymmetric precipitation, which can reduce the influence of precipitation intensity, so as to better compare the spatial distribution of observed and predicted asymmetric precipitation. For quantitative verification, the present invention uses the position of the center of gravity of tropical cyclone precipitation to verify the spatial distribution of asymmetric precipitation, and proposes a precipitation asymmetry index to verify the intensity of precipitation asymmetry.

[0006] In a first aspect, the present invention provides a method for predicting and verifying asymmetric precipitation in a tropical cyclone, comprising the following steps:

[0007] Step 1: Obtain observed and forecast tropical cyclone data and calculate the average observed and forecast tropical cyclone positions;

[0008] Step 2: Extract tropical cyclone precipitation from observed and forecast precipitation fields;

[0009] Step 3: Calculate the relative asymmetric precipitation of observed and forecast precipitation;

[0010] Step 4: Calculate the precipitation asymmetry index of observed and forecast precipitation;

[0011] Step 5: Calculate the radius and azimuth of the observed and predicted precipitation gravity center;

[0012] Step 6: Convert the relatively asymmetric precipitation field to the target direction coordinate system;

[0013] Step 7: Calculate the forecast error.

[0014] In a second aspect, the present invention provides a tropical cyclone asymmetric precipitation forecast verification system, comprising:

[0015] Tropical cyclone position calculation module, used to calculate the average observed and predicted tropical cyclone positions;

[0016] Tropical cyclone precipitation extraction module, used to extract tropical cyclone precipitation from observed and forecast precipitation fields;

[0017] Relative asymmetric precipitation calculation module, used to calculate the relative asymmetric precipitation of observed and forecast precipitation;

[0018] A precipitation asymmetry index calculation module is used to calculate the precipitation asymmetry index of observed and forecast precipitation;

[0019] The precipitation gravity center calculation module is used to calculate the radius and azimuth of the observed and predicted precipitation gravity center;

[0020] A conversion module, used to convert the relatively asymmetric precipitation field into a target direction coordinate system;

[0021] The forecast error calculation module is used to calculate the forecast error.

[0022] In a third aspect, the present invention provides an electronic device comprising: a memory and a processor; the memory is used to store a computer program; the processor executes the computer program in the memory to implement the forecast verification method for asymmetric precipitation in a tropical cyclone as described in any one of claims 1-8.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention uses relatively asymmetric precipitation to reflect asymmetric precipitation in tropical cyclones. Compared with the precipitation used in the past, the influence of tropical cyclone intensity is significantly reduced, and the asymmetric distribution characteristics of precipitation can be better reflected.

[0025] 2. Compared with the previous qualitative test, the present invention adds a quantitative test of tropical cyclone asymmetric precipitation. The present invention uses the position of the tropical cyclone precipitation center of gravity to quantitatively characterize the spatial distribution of asymmetric precipitation, and uses the precipitation asymmetry index to quantitatively characterize the intensity of precipitation asymmetry, so that the error can be quantified.

[0026] 3. Through the method of the present invention, the forecast deviation of the model forecast for asymmetric precipitation of tropical cyclones can be discovered. By comparing the error indicators, the differences in forecast capabilities of different models and different forecast time periods can be reflected, which can provide strong support for improving the tropical cyclone precipitation forecast.

[0027] 4. The tropical cyclone asymmetric precipitation characterization method of the present invention is not limited to forecast verification, but can also be used to study the changing laws of tropical cyclone asymmetric precipitation and its influencing factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic flow chart of a tropical cyclone asymmetric precipitation forecast verification method proposed by the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific implementation examples.

[0030] like Figure 1 As shown, in one embodiment of the present invention, a method for forecasting and verifying asymmetric precipitation in a tropical cyclone is provided, and the method comprises the following steps:

[0031] Step 1: Obtain observed and forecast tropical cyclone data and calculate the average observed and forecast tropical cyclone positions;

[0032] Step 2: Extract tropical cyclone precipitation from observed and forecast precipitation fields;

[0033] Step 3: Calculate the relative asymmetric precipitation of observed and forecast precipitation;

[0034] Step 4: Calculate the precipitation asymmetry index of observed and forecast precipitation;

[0035] Step 5: Calculate the radius and azimuth of the observed and predicted precipitation gravity center;

[0036] Step 6: Convert the relatively asymmetric precipitation field to the target direction coordinate system;

[0037] Step 7: Calculate the forecast error.

[0038] Specifically, in step 1, the time period to be tested can be selected as 3 hours; the method for obtaining the observed and forecasted tropical cyclone data within the time period to be tested includes: the data includes the observed and forecasted tropical cyclone position and the 3-hour cumulative precipitation data of the grid point; wherein

[0039] The observed tropical cyclone positions can be obtained from the tropical cyclone best track data IBTrACS (International BestTrack Archive for Climate Stewardship), with a time resolution of 3 hours. The website is https: / / climatedataguide.ucar.edu / climate-data / ibtracs-tropical-cyclone-best-track-data;

[0040] Observation grid precipitation data can be obtained from the Global Precipitation Measurement (GPM); its time resolution is 30 minutes, and the website is https: / / giovanni.gsfc.nasa.gov / giovanni / . The accumulated precipitation data for a given time period can be directly output from this website;

[0041] The predicted tropical cyclone positions can be obtained by processing the model forecast results using the vortex tracking program GFDL Vortex Tracker, the website of which is

[0042] https: / / dtcenter.org / community-code / gfdl-vortex-tracker;

[0043] The forecast grid precipitation data is the 3-hour cumulative precipitation forecast in the model forecast to be tested;

[0044] Furthermore, in step one, the method for calculating the average observed and predicted tropical cyclone position includes: averaging the tropical cyclone positions at the start and end times of a 3-hour cumulative precipitation period, and using the average tropical cyclone position as the tropical cyclone center of the period.

[0045] In step 2, the method for extracting tropical cyclone precipitation from the observed and forecast precipitation fields includes:

[0046] A circular area with a radius of 500 km is selected to separate the tropical cyclone precipitation; of course, in other embodiments, other radii can be selected or other tropical cyclone precipitation separation methods can be used for precipitation separation according to needs; in this embodiment, a radius of 500 km is used as the preset radius, and circles are made with the observed and predicted tropical cyclone centers as the center and 500 km as the radius. If the distance between the grid point and the tropical cyclone center does not exceed a radius of 500 km, the precipitation on the grid point is retained, otherwise it is set to a missing value.

[0047] In step 3, the method for calculating the relative asymmetric precipitation of observed and forecast precipitation includes:

[0048] A 10km wide ring is constructed for the observed and predicted precipitation fields respectively, which is 500km away from the center of the tropical cyclone and surrounds the center; of course, in other embodiments, the preset width may also be other sizes;

[0049] For each grid point, the precipitation R i , which can be regarded as axisymmetric precipitation and the superposition of asymmetric precipitation Ra, namely:

[0050]

[0051] Among them, axisymmetric precipitation is the average precipitation of all grid points within the circle where the grid point is located; defines the relative asymmetric precipitation R at the grid point r is the asymmetric precipitation Ra and the axisymmetric precipitation ratio.

[0052] In step 4, the method for calculating the precipitation asymmetry index of observed and forecast precipitation includes:

[0053] The precipitation asymmetry A of a ring is defined as:

[0054]

[0055] Where n is the number of grid points in the ring;

[0056] The asymmetry index A_index of the entire precipitation field is the average value of the asymmetry A of all circular rings. The higher the A_index value, the more asymmetric the precipitation.

[0057] In step 5, the method for calculating the radius and azimuth of the observed and predicted precipitation gravity center includes:

[0058] First, find the longitude and latitude of the precipitation center of gravity. The calculation method is:

[0059]

[0060] where lat i ,lon i and R i denote the latitude, longitude and precipitation of grid point i respectively;

[0061] Calculate the distance from the center of gravity of precipitation to the center of tropical cyclone, that is, the radius of the center of gravity; here, the longitude and latitude of the center of gravity of precipitation and the longitude and latitude of the center of tropical cyclone are used to calculate the great circle distance between the two points, in km. Preferably, existing programs in languages ​​such as NCL or MATLAB can be used for calculation;

[0062] The coordinate azimuth of the precipitation gravity center with the target direction (such as the north direction, the tropical cyclone movement direction and the environmental vertical wind shear direction, etc.) as the main axis is calculated, that is, the azimuth of the gravity center; wherein the azimuth is the tropical cyclone center as the origin, the target direction as the coordinate main axis, and the angle between the straight line passing through the grid point where the gravity center is located and the center of the tropical cyclone and the main axis in a clockwise direction from the coordinate main axis, and the angle range is [0°, 360°); the longitude and latitude of the precipitation gravity center and the longitude and latitude of the tropical cyclone center are used here to calculate the angle, and preferably, existing programs in languages ​​such as NCL or MATLAB can be used for calculation.

[0063] Since the target directions may be different between different samples, such as the movement direction of tropical cyclones and the direction of environmental vertical wind shear, the relatively asymmetric precipitation field needs to be converted to the target direction coordinate system.

[0064] In step six, the method of converting the relatively asymmetric precipitation field into the target direction coordinate system specifically includes:

[0065] Taking the center of the tropical cyclone as the origin and the target direction as the main coordinate axis, a grid with a resolution of 10km×10km is established within 500km of the origin, and the nearest neighbor interpolation method is used to interpolate the relatively asymmetric precipitation onto the grid. In this way, when the relatively asymmetric precipitation distribution map is output for comparison, the target directions all point to the same direction, which is convenient for subjective qualitative analysis. Of course, in other embodiments, the preset radius size and grid resolution can also be other sizes.

[0066] In step seven, the method for calculating the forecast error includes one or more of the following methods:

[0067] Calculate the relative asymmetric precipitation error: In the target direction coordinate system, subtract the forecast from the observed relative asymmetric precipitation at each grid point to obtain the relative asymmetric precipitation error at the grid point;

[0068] Calculate the relative asymmetric precipitation error index: The relative asymmetric precipitation error index is the average of the absolute values ​​of the relative asymmetric precipitation errors of all grid points in the precipitation field;

[0069] Calculate the distance error of the precipitation center of gravity: The distance error of the precipitation center of gravity is the difference between the radius of the predicted and observed precipitation center of gravity. If the predicted position is closer to the center of the tropical cyclone, the distance error is negative.

[0070] Calculate the angular error of the precipitation gravity center: the angle between the origin and the predicted and observed precipitation gravity center position vectors is the angular error of the gravity center. If the predicted position is on the left hand side of the observed position, add a negative sign before the angle.

[0071] Calculate the asymmetry error: The asymmetry error is the difference between the predicted and observed asymmetry index A_index.

[0072] Based on the above embodiments, an embodiment of the present application provides a forecast verification system for asymmetric precipitation in tropical cyclones, including:

[0073] Tropical cyclone position calculation module, used to calculate the average observed and predicted tropical cyclone positions;

[0074] Tropical cyclone precipitation extraction module, used to extract tropical cyclone precipitation from observed and forecast precipitation fields;

[0075] Relative asymmetric precipitation calculation module, used to calculate the relative asymmetric precipitation of observed and forecast precipitation;

[0076] A precipitation asymmetry index calculation module is used to calculate the precipitation asymmetry index of observed and forecast precipitation;

[0077] The precipitation gravity center calculation module is used to calculate the radius and azimuth of the observed and predicted precipitation gravity center;

[0078] A conversion module, used to convert the relatively asymmetric precipitation field into a target direction coordinate system;

[0079] The forecast error calculation module is used to calculate the forecast error.

[0080] In this embodiment, the working method of each module refers to the above embodiment and will not be described again.

[0081] Based on the above embodiments, an embodiment of the present application provides an electronic device, comprising: a memory and a processor; the memory is used to store a computer program; the processor executes the computer program in the memory to implement the forecast verification method for asymmetric precipitation in tropical cyclones as described above.

Claims

1. A prediction verification method for asymmetric precipitation in tropical cyclones. It is characterized in that The following steps are involved: Step 1: Obtain observed and forecast tropical cyclone data and calculate the average observed and forecast tropical cyclone positions; Step 2: Extract tropical cyclone precipitation from observed and forecast precipitation fields; Step 3: Calculate the relative asymmetric precipitation of observed and forecast precipitation; Step 4: Calculate the precipitation asymmetry index of observed and forecast precipitation; Step 5: Calculate the radius and azimuth of the observed and predicted precipitation gravity center; Step 6: Convert the relatively asymmetric precipitation field to the target direction coordinate system; Step 7: Calculate the forecast error.

2. The tropical cyclone asymmetric precipitation forecast verification method according to claim 1, It is characterized in that In the step 1, the tropical cyclone data include the observed and predicted tropical cyclone positions and the accumulated precipitation data of the grid points during the time period to be tested; The method for calculating the average observed and predicted tropical cyclone position includes: averaging the tropical cyclone positions at the start and end times of the cumulative precipitation period in the time period to be tested, and taking the average tropical cyclone position as the tropical cyclone center of the period.

3. The tropical cyclone asymmetric precipitation forecast verification method according to claim 2, It is characterized in that In step 2, the method for extracting tropical cyclone precipitation in the observed and forecasted precipitation field includes: A circular area with a preset radius is selected to separate the tropical cyclone precipitation. A circle is drawn with the observed and predicted tropical cyclone center as the center and the preset radius as the radius. If the distance between the grid point and the tropical cyclone center does not exceed the preset radius, the precipitation on the grid point is retained, otherwise it is set as a missing value.

4. The tropical cyclone asymmetric precipitation forecast verification method according to claim 3, It is characterized in that In step 3, the method for calculating the relative asymmetric precipitation of the observed and predicted precipitation includes: For the observed and predicted precipitation fields, a ring with a preset radius and a preset width around the center is constructed respectively; for each grid point, the precipitation R i , which can be regarded as axisymmetric precipitation and the superposition of asymmetric precipitation Ra, namely: The axisymmetric precipitation R is the average precipitation of all grid points in the circle where the grid point is located; the relative asymmetric precipitation R on the grid point is defined as r is the asymmetric precipitation Ra and the axisymmetric precipitation ratio.

5. The tropical cyclone asymmetric precipitation forecast verification method according to claim 4, It is characterized in that In step 4, the method for calculating the precipitation asymmetry index of observed and predicted precipitation includes: The precipitation asymmetry A of a ring is defined as: Where n is the number of grid points in the ring; the asymmetry index A_index of the entire precipitation field is the average value of the asymmetry A of all rings. The higher the A_index value, the more asymmetric the precipitation.

6. The tropical cyclone asymmetric precipitation forecast verification method according to claim 5, It is characterized in that In step 5, the method for calculating the radius and azimuth of the observed and predicted precipitation gravity center includes: Calculate the centroid of precipitation: Among them, lat i ,lon i and R i denote the latitude, longitude and precipitation of grid point i respectively; Calculate the distance from the center of gravity of precipitation to the center of the tropical cyclone, which is the radius of the center of gravity; Calculate the coordinate azimuth of the precipitation center of gravity with the target direction as the main axis, that is, the azimuth of the center of gravity; the azimuth is the angle between the main axis and the straight line passing through the grid point where the center of gravity is located and the center of the tropical cyclone in a clockwise direction with the target direction as the main axis of the coordinate, and the angle range is [0°, 360°).

7. The tropical cyclone asymmetric precipitation forecast verification method according to claim 6, It is characterized in that In step 6, the method of converting the relatively asymmetric precipitation field to the target direction coordinate system includes: Taking the center of the tropical cyclone as the origin and the target direction as the main coordinate axis, a grid with a resolution of αkm×αkm within the preset radius of the origin is established, and the relatively asymmetric precipitation is interpolated onto the grid using the nearest neighbor interpolation method.

8. The tropical cyclone asymmetric precipitation forecast verification method according to claim 7, It is characterized in that In step 7, the method for calculating the forecast error includes one or more of the following methods: Calculate the relative asymmetric precipitation error: In the target direction coordinate system, subtract the forecast from the observed relative asymmetric precipitation at each grid point to obtain the relative asymmetric precipitation error at the grid point; Calculate the relative asymmetric precipitation error index: The relative asymmetric precipitation error index is the average of the absolute values ​​of the relative asymmetric precipitation errors of all grid points in the precipitation field; Calculate the distance error of the precipitation center of gravity: The distance error of the precipitation center of gravity is the difference between the radius of the predicted and observed precipitation center of gravity. If the predicted position is closer to the center of the tropical cyclone, the distance error is negative. Calculate the angular error of the precipitation gravity center: the angle between the origin and the predicted and observed precipitation gravity center position vectors is the angular error of the gravity center. If the predicted position is on the left hand side of the observed position, add a negative sign before the angle. Calculate the asymmetry error: The asymmetry error is the difference between the predicted and observed asymmetry index A_index.

9. A forecast verification system for asymmetric precipitation in tropical cyclones. It is characterized in that include: Tropical cyclone position calculation module, used to calculate the average observed and predicted tropical cyclone positions; Tropical cyclone precipitation extraction module, used to extract tropical cyclone precipitation from observed and forecast precipitation fields; Relative asymmetric precipitation calculation module, used to calculate the relative asymmetric precipitation of observed and forecast precipitation; A precipitation asymmetry index calculation module is used to calculate the precipitation asymmetry index of observed and forecast precipitation; The precipitation gravity center calculation module is used to calculate the radius and azimuth of the observed and predicted precipitation gravity center; A conversion module, used to convert the relatively asymmetric precipitation field into a target direction coordinate system; The forecast error calculation module is used to calculate the forecast error.

10. An electronic device, It is characterized in that include: Memory and processor; The memory is used to store computer programs; The processor executes the computer program in the memory to implement the tropical cyclone asymmetric precipitation forecast verification method as described in any one of claims 1-8.

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