ENGINEERING

Taiwan Typhoon and Flood Research Institute (TTFRI) conducted an ensemble experiment for quantitative precipitation forecast (QPF) that was designed to provide skillful typhoon predictions to government agencies such as the Central Weather Bureau (CWB), Water Resources Agency (WRA), the Soil and Water Conservation Bureau (SWCB), and the National Science and Technology Center for Disaster Reduction (NCDR). The ensemble QPF experiment included 20 members produced by the TTFRI, CWB, NCDR, National Taiwan University (NTU), National Taiwan Normal University (NTNU), National Central University (NCU) and Chinese Culture University (CCU).

The challenges in developing ensemble prediction include the selection of a good set of ensemble members, improving model physics and the initial/boundary conditions.

The experiment was designed to examine the sensitivities of numerical models to uncertainties in initial conditions and model physical parameterizations. As a result, the ensemble forecasts reduced the typhoon track forecast errors, and also improved the QPFs for five typhoons for which warnings were issued by CWB in 2010.

Although the ensemble forecast performed quite well for the rainfall distribution and typhoon tracks, the extremely heavy rainfall over a very short duration – which was related to mesoscale convective systems (MCS) - could still not be well predicted by the models. However, TTFRI continues to improve the ensemble forecast as the results may contribute to disaster reduction.

To interactively explore the forecast results, TTFRI chose the Avizo Green software as it generates eye-catching pictures and movies with 3D effects that attract audience’s attention and greatly facilitates results presentation. “We generate movies and figures to show special or severe cases to the public, highlighting and explaining heavy precipitations, fierce winds, etc.”, says Chin-Cheng Tsai, researcher at TTFRI. “Besides the presentation aspect, the Avizo software allows researchers at TTFRI to deal with some special cross section along the typhoon center for comparing the typhoon structure forecast with observations.”