Verification of Typhoon Forecasts for a 20 km-mesh High-Resolution Global Model

In this study, twelve tropical storms between 2002 and 2005 over the western North Pacific Ocean, namely, typhoons, were simulated through medium-range forecast experiments with the 20 km-mesh Japan Meteorological Agency (JMA) and Meteorological Research Institute (MRI) Atmospheric General Circulation Model (JM-AGCM). These simulations were compared with the 60 km-mesh JMA Global Spectral Model (GSM) to evaluate differences in resolution. They are verified with the best-track data as an observation. The verification was conducted in terms of estimating error of position, intensifying tendency, radius of 50 knot, 30 knot, and composite wind profile. This paper addresses the importance of such high resolution to predict typhoon's intensity and inner-core structure. As a result, the JM-AGCM shows slightly smaller position error than the GSM. Moreover, much improvement was seen in the intensity prediction. The JM-AGCM outstandingly can both decrease the central sea level pressure and increase maximum wind velocity while the GSM can not simulate them because of low resolution. The JM-AGCM also shows better intensifying and decaying tendency than the GSM. The verifications of 50 knot and 30 knot radii, and the composite wind profile indicate that the typhoon structure by the JM-AGCM is quite realistic. Moreover, the JM-AGCM expresses the drastic transformation of inner-core wind profile within 100km from the typhoon center more realistically than the GSM. These results indicate that a high resolution global model, such as 20 km-mesh, is vital when discussing the intensity and wind profile of tropical storms.