CN115793099A - Method for identifying attenuation of intensity of cyclone in login tropical zone and evaluating influence of attenuation on rainfall - Google Patents
Method for identifying attenuation of intensity of cyclone in login tropical zone and evaluating influence of attenuation on rainfall Download PDFInfo
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Abstract
The invention discloses a method for identifying the strength attenuation of a tropical cyclone during landing and evaluating the influence of the tropical cyclone on rainfall. According to the method, kaplan-DeMaria exponential decay fitting is carried out on the intensity within 24 hours after the tropical cyclone logs in to obtain the intensity decay time scale of the tropical cyclone, time change characteristic analysis is carried out on the intensity decay time scale of the tropical cyclone logging in, factors influencing the intensity decay of the tropical cyclone logging in are explored, the relative contribution of the influencing factors to the intensity decay of the tropical cyclone logging in is quantitatively evaluated, and the influence of the intensity decay change of the tropical cyclone logging in the tropical cyclone is finally discussed by combining three aspects of sea surface temperature rise, tropical cyclone path transfer and large-scale environmental characteristics to clarify the physical mechanism of the intensity decay change of the tropical cyclone logging in the tropical cyclone. The invention has the beneficial effects that: further improving the weather service guarantee capability of city safety and providing scientific basis for disaster prevention and reduction, tropical cyclone disaster resistance and government decision.
Description
Technical Field
The invention relates to the technical field of atmospheric science, in particular to a method for identifying the attenuation of the strength of a tropical cyclone landing and evaluating the influence of the attenuation on rainfall.
Background
Tropical cyclones are cyclonic vortices that occur on tropical and subtropical ocean surfaces. The pacific northwest is an area where tropical cyclones occur most frequently in the world, and 30 tropical cyclones are generated on average each year, which accounts for about 33% of the total number of tropical cyclones generated in the world. China is located in the west of the northwest pacific ocean, and nearly half of the territories (northern Liaoning, south to Hainan, and west to 100 degrees E in the southwest) can be affected by tropical cyclones. The average number of tropical cyclones logging in China every year is 7, and the occurrence time is usually 5-10 months. The tropical cyclone landing is often accompanied by disastrous weather such as storm, storm and storm, wherein the storm and subsequent flood caused by the tropical cyclone often cause huge socio-economic loss and casualties to affected areas.
Due to the reasons of land obstruction, friction energy consumption, far away from a water vapor source and the like, the tropical cyclone quickly attenuates after landing. The Li and Chakraborty studies found that the intensity declined more slowly than 75% to 50% one day after tropical cyclone landing in the north atlantic ocean before 50 years. Zhu et al and Song et al found that the decay of tropical cyclonic landings on the continental united states and asian continental lands was slowing down over the past several decades. Some studies have demonstrated a power-law relationship between tropical cyclonic landing strength and economic losses, so that slowing down the decay of strength after tropical cyclonic landing may increase potential disasters in inland regions. However, current research on how the intensity attenuation changes of landing tropical cyclones affect the rainfall of tropical cyclones is still deficient. Based on the method, the research on the change of the attenuation time scale (tau) of the intensity of the tropical cyclone in the land has important significance on the prediction and destructive potential estimation of the tropical cyclone rainfall, the weather service guarantee capability of city safety can be further improved, and scientific basis is provided for disaster prevention and reduction, tropical cyclone disaster resistance and government decision making.
Disclosure of Invention
The method aims to provide a method for identifying the attenuation of the intensity of landing tropical cyclone and evaluating the influence of the attenuation on rainfall on the tropical cyclone aiming at the defect of a research method for the influence of the attenuation of the intensity of landing tropical cyclone on the rainfall of the tropical cyclone.
The invention discloses a method for identifying the attenuation of the strength of a tropical cyclone landing and evaluating the influence of the tropical cyclone landing on rainfall, which comprises the following steps of:
step S1: collecting data; collecting actually measured optimal path data of the tropical cyclone, global precipitation data and meteorological reanalysis data;
step S2: screening a tropical cyclone; screening all login tropical cyclones according to the optimal tropical cyclone path data obtained in the step S1, and selecting login tropical cyclones meeting the principle according to the login tropical cyclone screening principle;
and step S3: identifying the intensity attenuation time scale of the tropical cyclone when landing; combining the login tropical cyclones meeting the principle obtained in the step S2, carrying out Kaplan-DeMaria exponential decay fitting on the intensity of each tropical cyclone within 24 hours after login to identify the corresponding login tropical cyclone intensity decay time scale tau, and excluding login tropical cyclone events with the standard deviation being 2 times larger than the mean value of tau;
and step S4: identifying the characteristic of attenuation change of the intensity of the tropical cyclone during landing; combining the values of the tau of the login tropical cyclones obtained in the step S3, counting time sequences of the values of the tau of the login tropical cyclones, analyzing probability density curves of the values of the tau of the login tropical cyclones in two stages before and after a research period, and identifying time variation characteristics of the values of the tau of the login tropical cyclones;
step S5: identifying influence factors of the attenuation change of the intensity of the landing tropical cyclone; performing correlation analysis between factors possibly influencing the attenuation of the landing tropical cyclone and the time sequence by combining the time sequence of the tau value of the landing tropical cyclone obtained in the step S4, and identifying all factors influencing the attenuation change of the intensity of the landing tropical cyclone;
step S6: quantifying the relative contribution of the influence factors of the attenuation change of the cyclone strength of the landing tropical; combining all the factors influencing the attenuation change of the intensity of the login tropical cyclone obtained in the step S5, and quantifying the relative contribution of each factor to the attenuation change of the intensity of the login tropical cyclone according to a relative contribution calculation method;
step S7: analyzing a physical mechanism of the attenuation change of the intensity of the landing tropical cyclone; combining the characteristic of the attenuation change of the intensity of the login tropical cyclone obtained in the step S4 with all factors influencing the attenuation change of the intensity of the login tropical cyclone obtained in the step S5, and clarifying a physical mechanism of the attenuation change of the intensity of the login tropical cyclone from two aspects of tropical cyclone path transfer and large-scale environmental characteristics;
step S8: identifying tropical cyclone rainfall and quantitative indexes thereof; and (3) identifying the login tropical cyclone rainfall field based on an objective weather map analysis method by combining the login tropical cyclone obtained in the step (S2), and further identifying the login tropical cyclone rainfall index.
Step S9: analyzing the influence of the attenuation change of the intensity of the landing tropical cyclone on the rainfall of the tropical cyclone; and (4) combining the tau value of the login tropical cyclone obtained in the step (S3) and the login tropical cyclone rainfall index obtained in the step (S8), counting the change condition of the tropical cyclone rainfall index, performing correlation analysis of the tropical cyclone rainfall index and the tau value of the login tropical cyclone, and further analyzing to obtain the influence of the attenuation change of the login tropical cyclone strength on the tropical cyclone rainfall.
The beneficial effects provided by the invention are as follows:
(1) The invention provides a method for identifying the intensity attenuation speed condition of a landing tropical cyclone, which identifies the long-term variation trend of the intensity attenuation speed of the landing tropical cyclone and analyzes the physical mechanism of the intensity attenuation speed variation of the landing tropical cyclone, and has important significance for estimating the destructive potential of the landing tropical cyclone.
(2) According to the method, the influence of the attenuation change of the intensity of the login tropical cyclone on the time-space process of rainfall is analyzed through the difference of the tropical cyclone rainfall in different attenuation areas of the intensity of the login tropical cyclone, and the amplification effect of the attenuation reduction of the intensity of the login tropical cyclone on the tropical cyclone rainfall is clarified.
Drawings
FIG. 1 is a flow chart of an implementation of a method for identifying the attenuation of the intensity of a landing tropical cyclone and evaluating its impact on rainfall;
FIG. 2 is a graph of tropical cyclone landing intensity decay rate characteristics and correlation analysis of the sea surface temperature of the Pacific ocean northwest and landing tropical cyclone intensity decay time scale (τ) for landing in China in 1967-2018;
FIG. 3 is longitude of landing center, latitude of landing center, moving speed within 24 hours after landing, moving speed of vertical coastline within 24 hours after landing, landing intensity and their relation with τ of 143 tropical cyclones in 1967-2018;
FIG. 4 is a graph of the variation of the generation position of the tropical cyclone landing versus the landing position in 1967-2018;
FIG. 5 is a large scale environmental difference analysis of the development of tropical cyclones in the east and south China landing areas from 1967 to 2018;
FIG. 6 is a large scale environmental variable difference spatial profile of maximum 10 years and minimum 10 years of longitude for a landing tropical cyclone center;
fig. 7 is 8/3/18 in 1989: month 00-8, day 5 18:00 space-time evolution of rainfall caused by tropical cyclones Ken and variation curves of rainfall indexes (Pmean and Pmax) of tropical cyclones caused within 48 hours;
FIG. 8 is a boxplot analysis of the change rate of index of rainfall for tropical cyclone caused by landing tropical cyclone in 1979-2018 as the corresponding τ quantile of landing tropical cyclone;
FIG. 9 is time variation of index of tropical cyclone rainfall in unlimited rainfall range caused by logging in tropical cyclone in 1979-2018 and its response analysis with corresponding year tau mean;
FIG. 10 is the time variation of index of tropical cyclone rainfall in the limited rainfall range caused by logging in tropical cyclone in 1979-2018 and its response analysis with corresponding year tau mean value.
Detailed Description
To make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be further described with reference to the accompanying drawings.
The invention first explains the relevant basic concepts and the core points of the application as follows, and then elaborates the technical scheme of the invention.
Referring to FIG. 1, FIG. 1 is a schematic flow chart of a method of the present invention; an enhanced hybrid differential evolution method for interplanetary exploration orbit design comprises the following steps:
step S1: collecting data; collecting actually measured optimal path data of the tropical cyclone, global precipitation data and meteorological reanalysis data;
step S2: screening a tropical cyclone; combining the optimal path data of the tropical cyclone obtained in the step S1, firstly screening all login tropical cyclones, and further selecting proper login tropical cyclones according to a login tropical cyclone screening principle;
and step S3: identifying the intensity attenuation time scale of the tropical cyclone when landing; combining the login tropical cyclones obtained in the step S2, carrying out Kaplan-DeMaria exponential decay fitting on the intensity of each tropical cyclone within 24 hours after login to identify a corresponding login tropical cyclone intensity decay time scale (tau), and further excluding the phenomenon that the standard deviation is more than 2 times of the mean value of the tau;
and step S4: identifying the attenuation change characteristics of the intensity of the landing tropical cyclone; combining the values of the tau of the login tropical cyclones obtained in the step S3, counting time sequences of the values of the tau of the login tropical cyclones, analyzing probability density curves of the values of the tau of the login tropical cyclones in two stages before and after a research period, and identifying time variation characteristics of the values of the tau of the login tropical cyclones;
step S5: identifying influence factors of the attenuation change of the strength of the tropical cyclone during landing; performing correlation analysis between factors possibly influencing the attenuation of the landing tropical cyclone and the time sequence by combining the time sequence of the tau value of the landing tropical cyclone obtained in the step S4, and identifying all factors influencing the attenuation change of the intensity of the landing tropical cyclone;
step S6: quantification of relative contribution of influence factors of the attenuation change of the strength of the cyclone of the landing tropical; combining all the factors influencing the attenuation change of the intensity of the login tropical cyclone obtained in the step S5, and quantifying the relative contribution of each factor to the attenuation change of the intensity of the login tropical cyclone according to a relative contribution calculation method;
step S7: analyzing a physical mechanism of the attenuation change of the intensity of the landing tropical cyclone; combining the characteristic of the attenuation change of the intensity of the login tropical cyclone obtained in the step S4 and all the factors influencing the attenuation change of the intensity of the login tropical cyclone obtained in the step S5, and clearly distinguishing a physical mechanism of the attenuation change of the intensity of the login tropical cyclone from two aspects of tropical cyclone path transfer and large-scale environmental characteristics;
step S8: identifying tropical cyclone rainfall and quantitative indexes thereof; and (3) identifying the login tropical cyclone rainfall field based on an objective weather map analysis method by combining the login tropical cyclone obtained in the step (S2), and further identifying the login tropical cyclone rainfall index.
Step S9: analyzing the influence of the attenuation change of the intensity of the landing tropical cyclone on the rainfall of the tropical cyclone; and (4) combining the tau value of the login tropical cyclone obtained in the step (S3) and the login tropical cyclone rainfall index obtained in the step (S8), counting the change condition of the tropical cyclone rainfall index, performing correlation analysis of the tropical cyclone rainfall index and the tau value of the login tropical cyclone, and further analyzing to obtain the influence of the attenuation change of the login tropical cyclone strength on the tropical cyclone rainfall.
In the method of the present invention, in step S1, the optimal path data of the tropical cyclone includes a cyclone center position of the tropical cyclone every 6 hours, a near-center maximum wind speed; the global precipitation data is lattice precipitation data with high space-time resolution, the time resolution is 3 hours, and the spatial resolution is 0.1 degree multiplied by 0.1 degree; the weather reanalysis data comprises warp wind, weft wind, relative vorticity, vertical speed, relative humidity, specific humidity, whole layer of water vapor, warp water vapor flux, weft water vapor flux, soil humidity and sea surface temperature.
In step S2, the logging-in tropical cyclone screening principle includes four steps: (1) the intensity of the tropical cyclone at the position before landing is required to reach the strong tropical storm level and above (the intensity is more than or equal to 24.5 m/s); (2) the tropical cyclone stays on land for at least 24 hours, namely the tropical cyclone is recorded on land at least for 4 continuous 6-hour positions; (3) the strength of the tropical cyclone after landing cannot be increased; (4) the tropical cyclone can not generate the conditions of temperate degeneration and temperate transition at one position before landing and four positions after landing.
In the step S3, the formula that the intensity within 24 hours after the tropical cyclone lands is attenuated by a Kaplan-DeMaria exponential expression is as follows:
in the formula, V (t) is the intensity of the tropical cyclone landing, and t is the time within 24 hours after the tropical cyclone landing (t = t since the tropical cyclone is resolved into 6 hours by time, t = t) 1 ，t 2 ，t 3 ，t 4 ，V(t 1 ) τ is the intensity decay time scale for the intensity of the first location of the landing tropical cyclone. Therefore, 4-position ln (V (t)/V (t) 1 ) The slope of the fitted line is-1/tau. The larger the value of tau, the slower the intensity decay of the cyclone in the landing tropical zone.
In the step S4, the time variation characteristic of the landing tropical cyclone intensity decay time scale is a variation trend calculated by a least square method, and a slope obtained by fitting a time sequence of a study variable by the least square method is the variation trend. The least squares fit equation for the slope is as follows:
wherein b is the slope, n is the total years of the study period, x i For the ith year of the study period,
mean value of years of study period, y i To investigate the i-th year value of a variable in a study period,
mean values of study variables over the study period.
In the step S5, the factors which may influence the attenuation of the landing tropical cyclone include the landing center position of the tropical cyclone (including longitude and latitude of the landing center), the landing intensity, the moving speed within 24 hours after landing and the offshore sea surface temperature, then the correlation between the factors and the time series of the tau value of the landing tropical cyclone is analyzed by using a sperman correlation coefficient, the significance of the correlation obtained by using a t test is verified, and finally all the factors which influence the attenuation of the landing tropical cyclone are screened according to the magnitude of the correlation and the significance thereof.
In step S6, the relative contribution calculating method includes three steps:
(1) dividing the research period into two periods, counting the mean value of the intensity tau of the landed tropical cyclone in the two periods, and calculating the increment N of the mean value of the intensity tau of the landed tropical cyclone in the later period relative to the earlier period a (this increment is the increment under the influence of all factors together); (2) in calculating the relative contribution of a certain factor, assuming that other factors do not change in the later period, namely only considering the influence of the factor on the attenuation of the landing tropical cyclone in the later period, calculating the average value of the landing tropical cyclone tau in the later period, and subtracting the average value from the average value obtained in the previous period to obtain the increment N of the average value of the landing tropical cyclone tau under the influence of the factor alone 1 (ii) a (3) Percentage of increase in mean value of landing tropical cyclone τ under influence of a factor alone divided by the increase under influence of all factors together (N) 1 /N a 100%) is the relative contribution of this factor to the attenuation effect of the intensity of the landing tropical cyclone.
In the step S7, the tropical cyclone path transfer is obtained by studying a long-term variation trend of a generation location and a landing location of the tropical cyclone, and then dividing the landing location of the tropical cyclone into two regions, and performing a difference analysis between the generation development and a large-scale environment of the two regions, wherein the study variables include the generation location (generation longitude and latitude) of the landing tropical cyclone, duration at sea, landing strength, moving speed within 24 hours after landing, and specific humidity of a landing point 500 hPa. In addition, the physical mechanism of the attenuation change of the tropical cyclone strength needs to be clarified by combining the spatial difference distribution of large-scale environment variables.
In the step S8, six tropical cyclone rainfall indexes are logged in: (1) the mean value of the lattice point rainfall, namely the mean value of the rainfall of each lattice point at unit time in the rainfall range caused by the cyclone of the heat belt; (2) the maximum value of the grid point rainfall, namely the maximum value of the grid point rainfall at unit time in the rainfall range caused by the cyclone of the heat zone; (3) the mean value of the total rainfall amount of the lattice points in the rainfall range is not limited, namely the mean value of the total rainfall amount of all the lattice points which do not limit rainfall in the rainfall range in a fixed time period after the thermal zone cyclone landing; (4) the maximum value of the total amount of lattice point rainfall in the rainfall range is not limited, namely the maximum value of the total amount of all lattice point rainfall in which rainfall occurs in the rainfall range is not limited in a fixed time period after the thermal zone cyclone landing; (5) limiting the mean value of the total rainfall amount of the lattice points in the rainfall range, namely limiting the mean value of the total rainfall amount of all the lattice points subjected to rainfall in the rainfall range in a fixed period after the thermal zone cyclone landing; (6) and limiting the maximum value of the total amount of lattice point rainfall in the rainfall range, namely limiting the maximum value of the total amount of all lattice point rainfall in which rainfall occurs in the rainfall range in a fixed period after the thermal zone is logged in a cyclone manner.
It should be noted that the term "not limiting the rainfall range" means that the tropical cyclone is logged in a range formed by all the grid points where rainfall occurs within a certain period, that is, the grid points are not limited by the fact that rainfall must exist at any time in the period. In contrast, the limited rainfall range means a range formed by all the lattice points where rainfall exists at each unit time in a certain period of the tropical cyclone landing, that is, the lattice points have rainfall at each unit time in the period. Therefore, the number of rainfall cells in the unlimited range is large, and the number of rainfall cells in the limited range is small.
In step S9, the change of the index of tropical cyclone rainfall includes: (1) the change conditions of mean values of the lattice rainfall and the interval mean values of the maximum rate of change of the lattice rainfall in a fixed time period in an interval (0-10 th, 10-20th, 8230; 90-100 th) of 10 quantiles are averaged from small to large in the tau value of all the login tropical cyclones; (2) obtaining the average value of the lattice point rainfall total amount and the long-term variation trend of the maximum value of the lattice point rainfall total amount through a least square method; the analysis of the correlation between the index of the tropical cyclone rainfall and the value of the landing tropical cyclone τ in the step S9 is to analyze the correlation between the mean value of the numerical value distribution of the landing tropical cyclone τ and the mean value of the rainfall change rate in the corresponding section, the correlation between the time series of the mean value of the total amount of rainfall at the grid points (the maximum value of the total amount of rainfall at the grid points) and the time series of the value of the landing tropical cyclone τ by using a sperman correlation coefficient, and to test the significance of the correlation obtained by using a t test.
The embodiment takes Tropical Cyclone (TC) landing in china in 1967-2018 as an example, and further describes the technical scheme of the method for identifying the intensity attenuation of the landing tropical cyclone and evaluating the influence of the identification on rainfall. The examples are intended to illustrate the invention, but are not intended to limit the scope of the invention, as the invention is equally applicable to different regions or time periods.
An implementation flow chart of the method for identifying the attenuation of the intensity of the cyclone of the landing tropical and evaluating the influence of the cyclone on rainfall is shown in fig. 1, and comprises the following specific steps:
(1) Acquiring basic data;
in the present embodiment, a tropical cyclone optimal path data set of IBTrACS version 4 (International Best Track architecture for simulation stepardshift version 4) is collected, including cyclone center position every 3 hours of the tropical cyclone, near center maximum wind speed, and data set time covering 1967-2018. It should be noted that when the attenuation change of the intensity of the landing tropical cyclone is analyzed, the 6-hour-by-6-hour path data in the IBTrACS data set from 1967 to 2018 is selected for research, and when the rainfall of the tropical cyclone is analyzed, the 3-hour-by-3-hour path data in the IBTrACS data set from 1979 to 2018 is selected for establishing the relationship between the tropical cyclone and the rainfall; rainfall variables in ground meteorological element driving data sets in China are collected, the time sequence is 1979-2018, the time resolution is 3 hours, and the horizontal spatial resolution is 0.1 degrees multiplied by 0.1 degrees; ERA5 reanalysis data in the European middle-term weather forecast center (ECMWF) are collected, and the reanalysis data of the weather comprise the warp wind, the weft wind, the relative vorticity, the vertical speed, the relative humidity, the specific humidity, the whole layer of water vapor, the warp water vapor flux, the weft water vapor flux, the soil humidity and the sea surface temperature. Table 1 shows selected data information:
TABLE 1 Main data information
(2) Screening the tropical cyclone;
in the embodiment, the tropical cyclone that lands in China in 1967-2018 is screened by using the optimal path data of the tropical cyclone of IBTrACS version 4, and the specific screening principle of the landing tropical cyclone comprises four steps: (1) the intensity of the tropical cyclone at the position before landing is required to reach the strong tropical storm level and above (the intensity is more than or equal to 24.5 m/s); (2) the tropical cyclone stays on land for at least 24 hours, namely the tropical cyclone is recorded on land at least for 4 continuous 6-hour positions; (3) the strength of the tropical cyclone after landing cannot be increased; (4) the tropical cyclone can not generate the conditions of temperature zone degeneration and temperature zone transition at one position before landing and four positions after landing. According to the four conditions, 150 fields of tropical cyclones are selected and obtained.
(3) Identifying the intensity attenuation time scale of the tropical cyclone when landing;
in this example, based on 150 tropical cyclones obtained in example (2) and landing in 1967-2018 in china, kaplan-dematia exponential fitting is performed on the intensity of each tropical cyclone within 24 hours after landing, and the Kaplan-dematia exponential decay formula is as follows:
in the formula, V (t) is the intensity of the tropical cyclone landing, and t is the time within 24 hours after the tropical cyclone landing (t = t since the tropical cyclone is resolved into 6 hours by time, t = t) 1 ，t 2 ，t 3 ，t 4 )，V(t 1 ) τ is the intensity of the first place of landing tropical cyclone, and τ is the decay time scale of the intensity of landing tropical cyclone. Therefore, the slope of the fitted line for 4 positions is-1/τ. The larger the value of tau, the slower the intensity decay of the cyclone in the landing tropical zone.
Next, events with an unusually large 7-field decay time scale (τ) were excluded in 150-field tropical cyclones (i.e., events greater than 2 times the standard deviation of the τ mean were excluded). Finally, there are 143 tropical cyclone landing events as subjects of research on the influence of the intensity attenuation of the landing tropical cyclone on rainfall.
(4) Identifying the attenuation change characteristics of the intensity of the landing tropical cyclone;
in this example, based on the τ values of 143 field tropical cyclones obtained in example (3) in 1967-2018 for landing in china, the study period 1967-2018 is divided into two equal-length periods (1967-1992 and 1993-2018) with 1992 as a boundary, and 143 tropical cyclone paths screened in the two periods are shown in fig. 2a. In 1967-1992 and 1993-2018, the coverage area of the landing tropical cyclone intensity decay time scale (i.e. τ) was larger, indicating that the difference in the intensity decay of each landing tropical cyclone was larger, suggesting that there are multiple factors that have an effect on the decay of a single tropical cyclone (fig. 2 b). Compared with the tau value probability density curve in 1967-2018 and 1993-2018, the tau high value is obviously shifted to the right, the probability of occurrence of the tau high value in the period is larger, and the slow decay speed of the intensity of the tropical cyclone of landing is shown.
Furthermore, the time sequence of the tau value of the tropical cyclone landing is counted, and the change trend of the tau value is calculated according to a least square method, wherein the change trend is the change characteristic of the 143-field tropical cyclone landing in China in 1967-2018. As shown in FIG. 2c, from the change of the sliding average tau value in 1967-2018, the tau value showed a significant rising trend (p < 0.01) at a rate of 1.8h/decade in the past 1967-2018, increasing from 22h to 32h with a rising amplitude of 45%.
(5) Identifying influence factors of the attenuation change of the intensity of the landing tropical cyclone;
in the embodiment, based on the time series of tau values of tropical cyclones landing in China in 1967-2018 obtained in the embodiment (4), the positions of the landing centers of the tropical cyclones (including the longitude of the landing centers and the latitude of the landing centers), the landing strength, the moving speed within 24 hours after landing and the long-term change trend of sea surface temperature are analyzed, the correlation between the factors and the time series of tau values of the landing tropical cyclones is analyzed by adopting a sperman correlation coefficient, the significance of the correlation obtained by adopting a t test is verified, and finally all factors influencing the attenuation of the landing tropical cyclones are screened according to the correlation and the significance thereof.
The results show that the longitude of the landing center of tropical cyclone shows a significant trend of increasing (p < 0.05) at a rate of 0.23degrees/decade within 1967-2018, with a significant positive correlation with τ (r =0.34,p is less than 0.05; FIGS. 3 a-b); the central latitude of landing presents a weak polar movement trend with 0.07degrees/decade and a weak positive correlation with tau (r =0.19, p =0.18; fig. 3 c-d); the tropical cyclone landing strength shows a remarkable increasing trend (p) at a rate of 0.40 (m/s)/decade<0.05 And exhibits a significant positive correlation with τ (r =0.27,p)<0.10; FIGS. 3 i-j); moving speed within 24 hours after landing and moving speed (V) of vertical shoreline t And V t sin ℃. Varies) showed a weak positive correlation with τ (all correlation coefficients r were low and did not pass significance tests (FIGS. 3 e-h); the sea surface temperature showed a significant trend of increase (p < 0.01) at a rate of 0.11K/decade over the last 52 years, with a significant positive correlation with the τ value (r =0.49, p < 0.01; FIGS. 2d, f). In conclusion, the strength and weakness of the influence factors of the strength attenuation of the tropical cyclone landing are sequentially the sea surface temperature, the position of the center of the tropical cyclone landing and the landing strength, and the influence of the moving speed of the tropical cyclone within 24 hours after the tropical cyclone landing on the strength attenuation of the tropical cyclone landing is weak.
(6) Quantification of relative contribution of influence factors of the attenuation change of the strength of the cyclone of the landing tropical;
in this embodiment, the influence factors of the attenuation of the intensity of the tropical cyclone landing obtained in embodiment (5) are sequentially sea surface temperature, tropical cyclone landing center position, and landing intensity. Then, the relative contribution of each factor to the attenuation change of the cyclone intensity of the landing tropical cyclone is quantified according to a relative contribution calculation method, and considering that the correlation of the tau change in the research with the sea surface temperature and the landing position (longitude and latitude of landing), the relative contribution of the sea surface temperature increase and the landing position change to the tau is firstly calculated by referring to the calculation methods of Li and Chakraborty, and the specific process is as follows (the following numerical values are shown in a table 2):
(1) in 1967-1992, the east China (south China) region τ mean was 33.29 (25.53) h and the proportion of landing tropical cyclone events was 46.15% (53.85%), whereas in 1993-2018, the east China (south China) region τ mean was 34.58 (26.27) h and the proportion of landing tropical cyclone events was 53.95% (46.05%), with both regions τ mean increasing. In 1967-1992 (1993-2018), the tau mean of the tropical cyclone event in China landing is 29.11 (30.76) h, and the tau value increased in the two previous and later periods is 1.65h.
(2) If the proportion of the event of landing tropical cyclone is kept unchanged (the sea surface temperature is increased as a control variable at the moment), it can be obtained that in 1993-2018, the mean value of tau of the event of landing tropical cyclone in China is 30.11h (46.15% × 34.58+53.85% × 26.27= 30.11), the increment of tau caused by the increase of the sea surface temperature is 1h (30.11-29.11 = 1h), so that the relative contribution of the sea surface temperature to tau is 60.6% (1/1.65 = 60.6%).
(3) If the sea surface temperature does not change between 1967-1992 and 1993-2018 (when the landing tropical cyclone position changes as a control variable), it can be obtained that in 1993-2018, the mean value of τ of the chinese landing tropical cyclone event is 29.72h (53.95% × 33.29+46.05% × 25.53= 29.72), the increment of τ caused by the landing tropical cyclone position change is 0.61h (29.72-29.11 = 0.61), so the relative contribution of the landing tropical cyclone position change to τ is 37.0% (0.61/1.65 = 37.0%). At the same time, the relative contribution of the increase in intensity of the landing tropical cyclone to τ was 2.4% (100% -60.6% -37.0% = 2.4%).
In summary, the relative contributions of the sea surface temperature increase, landing location change and landing tropical cyclone intensity increase to τ in this example are 60.6%, 37.0% and 2.4%, respectively.
TABLE 2 comparison of tropical cyclone intensity decay time scales (τ) in east and south China
(7) Analyzing a physical mechanism of the attenuation change of the intensity of the landing tropical cyclone;
in this embodiment, based on the characteristic of the variation in the intensity attenuation of the landing tropical cyclone obtained in example (4) and all the factors affecting the variation in the intensity attenuation of the landing tropical cyclone obtained in example (5), the physical mechanism of the variation in the intensity attenuation of the landing tropical cyclone is clear from both aspects of transfer of the tropical cyclone path and large-scale environmental characteristics.
First, the tropical cyclone path transfer was obtained by studying the long-term variation tendency of the tropical cyclone generation position and landing position, and fig. 4 shows that the landing longitude and landing latitude of the tropical cyclone show a significant increase tendency at rates of 0.23 and 0.15 deg/decade (p <0.05 and p < 0.10), respectively, in 1967-2018; the generation longitude of tropical cyclones shows a significantly increasing trend (p < 0.05) at a rate of 0.60degrees/decade, and the generation latitude shows a decreasing trend at a rate of-0.14 degrees/decade. In the embodiment, the landing position of the tropical cyclone is further east and north, and the generation position is further east.
Subsequently, the tropical cyclone landing position is divided into two areas, namely east China and south China, and the two areas are subjected to generation development and large-scale environment difference analysis, wherein the research variables comprise the generation position (generation longitude and latitude) of the tropical cyclone landing, the duration of the sea, the landing strength, the moving speed within 24 hours after landing and the specific humidity of a landing point 500 hPa. Fig. 5 shows that, from the generation positions of the tropical cyclones in the areas landing on east and south of china and the duration of the sea (fig. 5 a-c), the generation longitudes, the generation latitudes and the duration of the tropical cyclones in the sea in the area landing on east of china are all significantly higher than those in south of china, indicating that the generation positions of the tropical cyclones in the area landing on east of china are more eastern and northern than those in south of china. This makes the tropical cyclone movement path more tortuous and results in an increased duration of the tropical cyclone on the sea, suggesting that tropical cyclones landing in the east China area last longer on the sea than in the south China area. The tropical cyclone lasts longer at sea and more water vapor may be carried inside the storm. From the difference in the specific humidity mean values of the layers in the regions of east and south china 6 hours before and after the landing point of the tropical cyclone (fig. 5 f), the specific humidity content of 500hPa of the tropical cyclone at the landing of east china is significantly higher than that of south china, indicating that the increase in the duration of the tropical cyclone at sea potentially increases the moisture content carried by the landing tropical cyclone. The water vapor amount in the tropical cyclone is an important reason for influencing the change of tau, and the more the tropical cyclone carries when landing, the slower the intensity attenuation speed of the landing tropical cyclone is.
Then, a physical mechanism of the attenuation change of the intensity of the tropical cyclone landing is clarified by combining spatial difference distribution of large-scale environment variables, the difference of environment variables of 10 years with the largest longitude of a landing center of the tropical cyclone and 10 years with the smallest longitude of the landing center is synthetically researched, and in the 10 years with the largest longitude of the landing center, the lower-layer relative vorticity of the east China area which is abnormal and the airflow which is above the east China area and rotates anticlockwise are obtained through analysis, so that the TC can maintain the strong cyclone which rotates anticlockwise after landing (fig. 6a and d); the negative anomaly of mid-level vertical velocity (increase in upward motion) facilitates maintenance of central updraft after tropical cyclone landing (figure 6 b); higher mid-low relative humidity and significantly increased overall steam can promote steam condensation releasing latent heat, maintaining tropical cyclone warm-core structure (fig. 6c, f); the exceptionally weak vertical wind shear also facilitates the maintenance of the tropical cyclonic warm core structure (fig. 6 d); the abnormally high soil humidity in the east China area is beneficial to improving the thermal conductivity to generate more lasting latent heat flux and is beneficial to maintaining the tropical cyclone on land after landing (figure 6 h). However, none of the south China areas have the favorable environmental conditions described above.
(8) Logging in tropical cyclone rainfall and identification of quantitative indexes of the tropical cyclone rainfall;
in this embodiment, based on the login tropical cyclone obtained in the embodiment (2), a rainfall field of the login tropical cyclone is identified based on an objective weather map analysis method, and then rainfall indexes of the login tropical cyclone are identified, in order to research the influence of the attenuation of the intensity of the login tropical cyclone on the rainfall of the tropical cyclone, six evaluation indexes are adopted: (1) the mean value of the lattice point rainfall (Pmean), namely the mean value of the rainfall of each lattice point in the rainfall range caused by the cyclone of the heat band for three hours; (2) the maximum lattice point rainfall (Pmax), namely the maximum value of lattice point rainfall in a rainfall range caused by three hours of thermal zone cyclone; (3) the average value PTmean24 (PTmean 48) of the lattice rainfall total amount within 24 (48) hours after logging in, namely the average value of the rainfall total amount of each lattice point within an unlimited rainfall range (a range formed by all the lattice points subjected to rainfall within a corresponding research period after logging in a tropical cyclone) within 24 (48) hours after logging in TC; (4) the maximum value PTmax24 (PTmax 48) of the lattice rainfall total amount within 24 (48) hours after logging in, namely the maximum value of the rainfall total amount of each lattice point within the rainfall range which is not limited within 24 (48) hours after the thermal zone cyclone logging in; (5) the average value re-PTmean24 of the lattice rainfall total amount within 24 hours after logging, namely the average value of the rainfall total amount of each lattice point within a limited rainfall range (a range formed by all the lattice points with rainfall at each unit time within a corresponding research period after logging on by the tropical cyclone) within 24 hours after logging on by the tropical cyclone; (6) and the maximum value re-PTmax24 of the grid point rainfall within 24 hours after the landing, namely the maximum value of the rainfall of each grid point within the rainfall limiting range within 24 hours after the thermal zone cyclone landing.
The tropical cyclone Ken logged in china in 1989 and the induced rainfall thereof are selected to exemplify the above six indexes, and the spatial distribution of rainfall caused by each unit time of the tropical cyclone Ken within 48 hours and the time-dependent change curve thereof are shown in fig. 7. In fig. 7a-q, since the average value and the maximum value of the rainfall at all the grid points in the spatial distribution map at each unit time are Pmean and Pmax, the change curves of Pmean and Pmax at each unit time within 48 hours by Ken are shown in fig. 7 r. Ken is re-PTmean24 and re-PTmax24 calculated in the limited range, namely the average value and the maximum value of the total rainfall amount of all grid points in the black point area in the graph 7a-i within 0-24 h. PTmean24 (PTmean 48) and PTmax24 (PTmax 48) in an unlimited range by Ken are the average and maximum values of the total rainfall at each grid point within 0 to 24 (0 to 48) hours.
(9) Analyzing the influence of the attenuation change of the intensity of the landing tropical cyclone on the rainfall of the tropical cyclone;
in this embodiment, based on the τ value of the landing tropical cyclone obtained in example (3) and the six landing tropical cyclone rainfall indexes obtained in example (8), the change situation of the change rate of the tropical cyclone rainfall along with a more detailed τ interval is firstly known, τ is divided into 10 quantiles (0-10 th, 10-20th, \8230;, and 90-100 th) from small to large, the change rate of the tropical cyclone rainfall in the 10 τ quantile intervals is counted, a box-shaped graph is drawn, and a linear regression model of the box-shaped graph and τ is constructed. From the linear correlation relationship between the τ quantile interval and the tropical cyclone rainfall change rate sequence (fig. 8), the change rates of Pmean24, pmax24, pmean48 and Pmax48 increase with the increase of the τ quantile interval. Wherein, the change rates of Pmean48 and Pmax48 and the tau quantile interval are in a positive correlation (r is 0.30 and 0.36 respectively; fig. 8 c-d) which is obvious (p is less than 0.01), which shows that the increase of the change rate of the rainfall rate within 48 hours after the reduction of the landing TC intensity attenuation is more obvious, which means that the TC rainfall within 48 hours after the landing is enhanced by the reduction of the landing TC intensity attenuation.
Subsequently, the long-term variation tendency of each tropical cyclonic rainfall index was calculated by the least square method, and the results showed that in 1979 to 2018, PTmean24, PTmax24, PTmean48, PTmax48, re-PTmean24 and re-PTmax24 all exhibited significant increase trends (p <0.01 or p < 0.05) of 2.0 mm/decade, 23.0mm/decade, 1.9mm/decade, 24.2mm/decade, 13.1mm/decade and 16.7mm/decade, respectively (see fig. 9a, c, e, g and fig. 10a, c). Further, correlation analysis of each tropical cyclonic rainfall index and the time series of landing tropical cyclone τ values was performed, and the results showed that PTmean24, PTmax24, PTmean48, PTmax48, re-PTmean24, and re-PTmax24 all showed a significant (p < 0.01) highly positive correlation with τ (r is 0.64, 0.76, 0.67, and 0.70, respectively; fig. 9b, d, f, h and fig. 10b, d). This shows that the time scale τ of the decay of the intensity of the landing tropical cyclone is the main influence factor of PTmean24, PTmax24, PTmean48 and PTmax48, and the slower the decay speed of the intensity of the landing tropical cyclone is, the higher the mean and maximum values of the total TC rainfall induced at each grid point of 24 hours and 48 hours after landing are correspondingly.
The beneficial effects of the invention are:
(1) The invention provides a method for identifying the intensity attenuation speed condition of a landing tropical cyclone, which identifies the long-term variation trend of the intensity attenuation speed of the landing tropical cyclone and analyzes the physical mechanism of the intensity attenuation speed variation of the landing tropical cyclone, and has important significance for estimating the destructive potential of the landing tropical cyclone.
(2) According to the method, the influence of the attenuation change of the intensity of the landing tropical cyclone on the time-space process of rainfall is analyzed through the difference of the rainfall of the tropical cyclone under different landing tropical cyclone intensity attenuation intervals, and the amplification effect of the attenuation of the intensity of the landing tropical cyclone on the rainfall is clarified.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. A method for identifying the strength attenuation of a tropical cyclone during landing and evaluating the influence of the tropical cyclone on rainfall is characterized by comprising the following steps: the method comprises the following steps:
step S1: collecting data; collecting actually measured tropical cyclone optimal path data, global precipitation data and meteorological reanalysis data;
step S2: screening the tropical cyclone; screening all login tropical cyclones according to the optimal tropical cyclone path data obtained in the step S1, and selecting login tropical cyclones meeting the principle according to the login tropical cyclone screening principle;
and step S3: identifying the intensity attenuation time scale of the tropical cyclone when landing; combining the login tropical cyclones meeting the principle obtained in the step S2, carrying out Kaplan-DeMaria exponential decay fitting on the intensity of each tropical cyclone within 24 hours after login to identify the corresponding login tropical cyclone intensity decay time scale tau, and excluding login tropical cyclone events with the standard deviation being 2 times larger than the mean value of tau;
and step S4: identifying the characteristic of attenuation change of the intensity of the tropical cyclone during landing; combining the values tau of the login tropical cyclones obtained in the step S3, counting time sequences of the values tau of the login tropical cyclones, analyzing probability density curves of the values tau of the login tropical cyclones in two stages before and after a research period, and identifying time variation characteristics of the values tau of the login tropical cyclones;
step S5: identifying influence factors of the attenuation change of the strength of the tropical cyclone during landing; performing correlation analysis between factors possibly influencing the attenuation of the landing tropical cyclone and the time sequence by combining the time sequence of the tau value of the landing tropical cyclone obtained in the step S4, and identifying all factors influencing the attenuation change of the intensity of the landing tropical cyclone;
step S6: quantifying the relative contribution of the influence factors of the attenuation change of the cyclone strength of the landing tropical; combining all the factors influencing the attenuation change of the intensity of the login tropical cyclone obtained in the step S5, and quantifying the relative contribution of each factor to the attenuation change of the intensity of the login tropical cyclone according to a relative contribution calculation method;
step S7: analyzing a physical mechanism of the attenuation change of the intensity of the landed tropical cyclone; combining the characteristic of the attenuation change of the intensity of the login tropical cyclone obtained in the step S4 with all factors influencing the attenuation change of the intensity of the login tropical cyclone obtained in the step S5, and clarifying a physical mechanism of the attenuation change of the intensity of the login tropical cyclone from two aspects of tropical cyclone path transfer and large-scale environmental characteristics;
step S8: logging in tropical cyclone rainfall and identification of quantitative indexes of the tropical cyclone rainfall; and (3) identifying the login tropical cyclone rainfall field based on an objective weather map analysis method by combining the login tropical cyclone obtained in the step (S2), and further identifying the login tropical cyclone rainfall index.
Step S9: analyzing the influence of the attenuation change of the intensity of the landing tropical cyclone on the rainfall of the tropical cyclone; and (4) combining the tau value of the login tropical cyclone obtained in the step (S3) with the rainfall index of the login tropical cyclone obtained in the step (S8), counting the change condition of the rainfall index of the tropical cyclone, analyzing the correlation between the rainfall index of the tropical cyclone and the tau value of the login tropical cyclone, and further analyzing to obtain the influence of the attenuation change of the strength of the login tropical cyclone on the rainfall of the tropical cyclone.
2. The method for identifying the attenuation of the intensity of landing tropical cyclone and evaluating the influence of landing tropical cyclone on rainfall as claimed in claim 1, wherein: in step S1, the optimal path data of the tropical cyclone includes a cyclone center position and a near-center maximum wind speed of the tropical cyclone every 6 hours;
the global precipitation data are lattice precipitation data with high space-time resolution, the time resolution is 3 hours, and the space resolution is 0.1 degree multiplied by 0.1 degree;
the meteorological reanalysis data comprises warp wind, weft wind, relative vorticity, vertical speed, relative humidity, specific humidity, whole layer water vapor, warp water vapor flux, weft water vapor flux, soil humidity and sea surface temperature.
3. The method for identifying the attenuation of the intensity of landing tropical cyclone and evaluating the influence of landing tropical cyclone on rainfall as claimed in claim 1, wherein: in step S2, the logging-in tropical cyclone screening principle includes four steps:
step 1: the intensity of the hot belt cyclone at the position before landing reaches the storm level of the strong hot belt and above;
step 2: the tropical cyclone stays on land for at least N hours; n is a preset value;
and step 3: the strength of the tropical cyclone after landing does not increase continuously;
and 4, step 4: the tropical cyclone does not have the conditions of temperature zone degeneration and temperature zone transition at one position before landing and four positions after landing.
4. A method of assessing the attenuation of tropical cyclone intensity landing and its impact on rainfall as claimed in claim 3, wherein: in step S3, the formula that the intensity within 24 hours after the tropical cyclone landing is in Kaplan-DeMaria exponential attenuation is as follows:
wherein V (t) is the intensity of the tropical cyclone landing, t is the time within 24 hours after the tropical cyclone landing, the time resolution of the tropical cyclone is 6 hours, and t = t 1 ，t 2 ，t 3 ，t 4 ，V(t 1 ) τ is the intensity decay time scale for the intensity of the first location of the landing tropical cyclone.
5. The method for identifying the attenuation of the intensity of landing tropical cyclone and evaluating the influence of landing tropical cyclone on rainfall as claimed in claim 1, wherein: in the step S4, the time change characteristic of the attenuation time scale of the tropical cyclone intensity is logged in to obtain a change trend calculated by a least square method, the least square method is used for fitting and researching a time sequence of variables, so that the obtained slope is the change trend, and the least square fitting formula of the slope is as follows:
wherein b is the slope, n is the total years of the study period, x i For the ith year of the study period,
mean value of years of study period, y i To investigate the year i value of a variable over the study period,
mean values of study variables over the study period.
6. A method of identifying and assessing the effect of landing tropical cyclone intensity decay on rainfall as claimed in claim 1 in which: in the step S5, factors which may influence the attenuation of the tropical cyclone landing include the landing center position of the tropical cyclone, the landing intensity, the moving speed within 24 hours after landing and the sea surface temperature;
analyzing the correlation between factors capable of influencing the attenuation of the landing tropical cyclone and a time sequence of a tau value of the landing tropical cyclone by adopting a spearman correlation coefficient;
and (4) checking the significance of the obtained correlation by adopting a t test, and screening all factors influencing the attenuation of the landing tropical cyclone according to the magnitude of the correlation and the significance thereof.
7. A method of identifying and assessing the effect of landing tropical cyclone intensity decay on rainfall as claimed in claim 1 in which: in step S6, the relative contribution calculating method includes three steps:
step 1: dividing the research period into a front period and a rear period, counting the mean value of the landing tropical cyclone tau in the two periods, and calculating the increment N of the mean value of the landing tropical cyclone strength tau in the rear period relative to the previous period a ；
And 2, step: when calculating the relative contribution of any factor, only considering the influence of the factor on the attenuation of the landing tropical cyclone in the later period, calculating the average value of the landing tropical cyclone tau in the later period, and obtaining the average value of the previous period in the step 1Making a difference to obtain the increment N of the mean value of the logging tropical cyclone tau under the single influence of the factor 1 ；
And step 3: dividing the increment of the mean value of the logging tropical cyclone tau under the influence of a certain factor by the increment under the influence of all factors to obtain the percentage N 1 /N a 100%, where the percentage is the relative contribution of this factor to the impact of landing tropical cyclone strength attenuation.
8. A method of identifying and assessing the effect of landing tropical cyclone intensity decay on rainfall as claimed in claim 1 in which: the total number of the tropical cyclone rainfall indexes logged in the step S8 is six: the average value of the lattice point rainfall, the maximum value of the lattice point rainfall, the average value of the lattice point rainfall total amount in the rainfall unlimited range, the maximum value of the lattice point rainfall total amount in the rainfall unlimited range, the average value of the lattice point rainfall total amount in the rainfall limited range and the maximum value of the lattice point rainfall total amount in the rainfall limited range.
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