Study On Optimization And Simulation Of Wire Icing Parameterization Scheme

Based on the hourly standard ice thickness model,by using the surface observation data,the sounding data and the observation records from the wire icing event,we simulate and verify various modules from this model,and analyze the cause of the simulation errors.Based on the mechanism of freezing rain and rime occurrence and meteorological conditions in China,we improve this model,simulate and discussed a large-scale wire icing accident occurred in South China in early January to February on 2008.The main conclusions are as follows:(1)In original icing model,The freezing rain forecast scheme can predict the freezing rain to some extent,but some misses forecast events still exist.The accuracy rate of rime scheme is 55.2%,but the misses forecast rate is 95.8%and the predication performance is not good.The ice thickness calculation module can accurately simulate the characteristics of the ice thickness of the conductor.Using the original icing model and the WRF model,the ice event of southern China in 2008 was simulated and compared.The simulated values of Guizhou stations are close to the.observed values,but the simulation deviation of Hunan Province is large,and the time points of the occurrence and growth of icing do not correspond with the observed values.The correlation coefficient between the simulated extreme thickness and the observed values is 0.489,which is obviously higher than the observed values.(2)Based on the validation results of observational data,The main causes of errors in each module were analyzed.For the frozen rain prediction module,the rate of ice(If)in the Ramer algorithm can’t effective distinguish frozen rain from snowfall events.we add the relative warm layer ratio to distinguish snow from frozen rain again in this module,and the limiting condition of precipitation<1mm/6h was added.We proved that the optimized algorithm can effectively reduce the misses forecast of freezing rain.For the prediction module of rime,the meteorological conditions of the rime were analyzed,the temperature is:-13～3 ℃.Relative humidity:>85%,wind speed<6 m/s and liquid water content must greater than 0.007 g/m(or visibility less than 1 km).Using this condition to forecast the occurrence of rime,it is found that the prediction accuracy of the modified judgment method is 58.2%,and the misses forecast rate is reduced from 95.8%to 38.6%.(3)According to the statistical results of the ice shape from foreign scholars and Henan Power Grid Company,the possible change of the ice shape was speculated:With the amount of ice increasing,the ice shape gradually changes from the crescent shape to the sector shape to the D shape.On this basis,the calculation method of ice thickness under different icing shapes was predicted.(4)Based on the improved parameterization scheme and WRF model,the icing event of southern China in 2008 was simulated again.Compared with the original scheme,the simulation error of the improved scheme was reduced.And the correlation coefficient between the simulated and observed values was obviously increased.The new scheme can simulate the temporal and spatial variation of ice thickness effective.However,due to the difference between the initial field temperature and the observed value,the simulated temperature from the surface to the height of 900hpa is obviously higher than the observed value,and the ice coating scheme can’t start the growth mechanism,therefore,the simulated ice thickness in Hunan and Jiangxi provinces was still quite different from the actual value.