An Observing System Experiment for Typhoon Conson (2004) Using a Singular Vector Method and DOTSTAR Data

An Observing System Experiment (OSE) has been performed to investigate the effectiveness of dropwindsonde observations and a sensitivity analysis technique on a typhoon track forecast. Using dropwindsonde observations for Typhoon Conson at 1200 UTC 8 June 2004, which are derived from Dropwindsonde Observation for Typhoon Surveillance near the Taiwan Region (DOTSTAR), four numerical experiments are conducted, which are different only in terms of the number of dropwindsonde observations used in a data assimilation system: (i) no observation is assimilated; (ii) all observations are assimilated; (iii) observations within a sensitive region as revealed by a singular vector method at the Japan Meteorological Agency (JMA) are assimilated; and (iv) observations outside the sensitive region are assimilated. In the comparison of the four track forecasts, Conson's northeastward movement is expressed in the second and third simulations while in the first and fourth experiments Conson stays at almost the same position as its initial position. Through the OSE, it is found that DOTSTAR observations had a positive impact on the track forecast for Conson, and that observations within the sensitive region are enough to predict the northeastward movement of Conson, indicating that the JMA singular vector method would be useful for the sampling strategy of targeted observations like DOTSTAR.