The Impact of Dropsonde Data from DOTSTAR on Tropical Cyclone Track Forecasting

DOTSTAR (Dropwindsonde Observations for Typhoon Surveillance near the Taiwan Region) is an international research program conducted by meteorologists in Taiwan partnered with scientists at the Hurricane Research Division (HRD) and the National Centers for Environmental Prediction (NCEP) of the National Oceanic and Atmospheric Administration (NOAA). The DOTSTAR research team initiated the typhoon surveillance in 2003. During 2003 to 2005, 15 missions (19 typhoons and 313 dropwindsondes deployed) had been successfully conducted. Five models (4 operational and 1 research models) were used to evaluate the impact of the dropwindsonde on tropical cyclone track forecasting. Based on 10 cases of model evaluation in year 2004, the statistic results indicate that all models, except the GFDL hurricane model, show positive impact of the dropsonde data on the tropical cyclone track forecasting. In the first 72 hours, the mean track error reduction in three operational global models, NCEP-GFS, FNMOC-NOGAPS and JMA-GSM, is 15, 12, and 20% individually. The track error reduction in WRF regional model is 16%. The Student t-test is applied to examine the significance of above track error reduction. It is found that only NCEP GFS model at 42, 48 h; NOGAPS at 6 h; JMA GSM at 12, 18, 30, 54 h, GFDL at 72 h and WRF model at 12, 18 h reached the statically significant at the 90% level. The 6-72-h averaged track error reductions from the ensemble averages of the three global models are 19%, while 83% of the forecasting times showing error reduction passes the Student-t test at the 90% significance level.