| Based on the CMA-STI datasets during the period from 1972 to 2011 of the typhoon track and intensity.by using the method of the definition of extreme events’threshold values, tropical cyclone abnormal direction changes were calculated.The temporal and spatial distribution characteristic of TC’s anomaly moving direction changes in recent 40 years and the prediction error of typhoon track from the National Meteorological Center of CMA from 2005 to 2010 were analyzed. Dynamic composites of environmental flows in 500hpa including two types of TC’s abnormal path have been examined. The different contribution of three time scale environmental flow,which contains Madden-Julian oscillation(MJO),quasi-biweekly oscillation(QBW),and synoptic scale components,on six tropical cyclones that turned right or left abnormally in the south China sea area were examined in this study, using Lanczos filte method.Results showed that,the tropical cyclone that has a anticlockwise deflection more than 50° or that has a clockwise deflection more than 47° within 12 hours is defined as abnormal direction change;40 years of statistical data indicated that TC abnormal direction changes occurred about 2.68 times a year. The frequency of abnormal path increased integral before 1985. On the contrary,it had been degressive trend after 1985;the probability of abnormal path in September is the largest,about 7%;the abnormal path most commonly occurred in the South China Sea and fell farther to the south in autumn than in summer.During the six years from 2005 to 2010,24h,48h and 72h average distance error was respectively 113.5 km,182 km,274.5 km; the forecast accuracy of TC’s position when the tropical cyclone tured left anomaly was lower than that tured left anomaly;path prediction error caused by the moving direction prediction error is the main reason of abnormal right-turning TC prediction error,but movement speed prediction error is the main cause of abnormal left-turning TC prediction error.Before landing,the moving direction prediction error reaches a maximum. The moving direction prediction error of abnormal right path went for a maximum at Taiwan Strait,and that of abnormal left path went for a maximum in the South China Sea.Results of dynamic composites showed that the subtropical high over the north of the abnormal right-turning TC was much weakened and moved towards east. Besides,there existed a strong SW flow at the southeast of the TC.On the contrary, the subtropical high over the north of the abnormal left-turning TC strengthened and moved towards west,and the strong SW flow at the north of the TC possibly contributes directly to the abnormal turning.TC’s abnormal moving in the South China Sea was closely related with changes of environment steering flow.Both the westward speed of zonal 10-day high-pass and 10-20-day bandpass filtered steering components slowing down and meridional 10-day high-pass filtered steering components speeding up towards north contributed to TC’s abnormal right-turning. On the other side,the zonal 10-day high-pass and 20-day low-pass filtered steering components speeding up towards west and the speed of northward meridional 10-day high-pass filtered steering components slowing down contributed to TC’s abnormal left-turning.The centre of abnormal right-turning TC was located in the branching point where westerly winds and Southeasterly winds southeast to the MJO scale cyclonic vortex intersected,but the MJO scale circulation around abnormal left-turning TC were different,there were no common characteristics.Abnormal right-turning TC mergered with QBW scale cyclonic vortex. However,there were no similar traits when TC turned left abnormally.There existed strong southwester on the southeast of abnormal right-turning TC and strong south wind on the west of abnormal left-turning TC,or winds on the east side of TC weakened when the TC turned left. |
PDF Full Text Request