Potential Forecast For Thunderstorm Based On Thermodynamic Instability Parameters In Nanjing

Unstable atmospheric stratification is an important factor to produce thunderstorms. Various kinds of convective parameters are used to represent the thunderstorm characterizations, which will help to understand the changes of thermodynamic and dynamic instability in this research. In order to improve the level of thunderstorm warning and forecasting, the forecasting methods are developed to predict the thunderstorm strength and possible occurrence regional.First, the data of three years lightning localization in Nanjing is used to classify the intensity of thunderstorm (ie: non-thunderstorms, normal thunderstorms, severity thunderstorm), and47convective parameters, which are selected from past research and forecasting, characterize the Nanjing of thunderstorm environment. Significant predictors are selected by relevance analysis to establish Bayesian classification method and Logistic regression method. Out of the two methods tested, it is found that logistic regression method gives better prediction performance with independent data sets.Second, using the lightning location data of Jiangsu Province (region from117°E-121°E,31°N--35°N) and the NCEP historical re-analysis data, the regional thunderstorm potential prediction model is built by Logistic regression method. A total of35convective predictors are calculated and11significant predictors are selected by relevance analysis. When more than four convective parameters are in an unstable state, indicated that the atmospheric stratification is unstable. Logistic regression equation can give thunderstorm occurrence probability in every grid. The possible thunderstorms occurrence range is forecasted by the probability distribution of thunderstorms in the region.The following conclusions about convective parameters are listed:(1) before thunderstorm occurrence, the environment in Nanjing is warm and moist air in low level, cold and dry air in mid-level, clockwise wind shear, and the unstable energy layer is deep. Most of thunderstorm doesn’t have inversion layer in low level. If the low level air is warmer and moister, mid-level air is colder and drier, the wind shear between the low and high level is stronger, that situation can lead to more strength thunderstorm.(2) Through the regression coefficient of each parameter in this two forecast models, Tmj and SWISS significantly affect single station prediction model forecast result, Tmj and I greatly impact of the regional thunderstorm forecast results.Both in single station prediction model and regional thunderstorm model, Tmj and SWISS are included, that indicate these two predictors can better reflect the different aspects of the atmospheric stratification. Tmj gives better forecasting skills in thunderstorm prediction. From the physical meaning of Tmj, it is found that the humidity (900and700hPa), and temperature of500hpa can obviously influence the thunderstorm development.(3) The more numbers of convective parameters is in unstable state, the greater probability of thunderstorm occurrence. Taking11convective parameters distribution and trend in to consideration, such as CAPE SSI, can better predict the possible thunderstorms strength.