Structure change of Typhoon Nari (2007) in the weakening stage

Abstracts

The structure of Typhoon Nari (11th 2007) was investigated based on the field observations and the numerical simulation with the Weather Research and Forecasting (WRF) model. The observations were carried out using the wind profiler and dual Doppler radar at Haenam Weather Observatory and Jeju Island, which were analyzed along with the Quick Scatterometer (QuikSCAT) dataset. The simulation data were obtained from the 60 hours run of the WRF model to get the detailed structure, intensity, and track of the typhoon during the period from 0000 UTC 14 September 2007 to 1200 UTC 16 September. The TC initialization for the numerical simulation was performed with the use of the 3D balanced bogus vortex and spherical high-order filter proposed by Kwon and Cheong (2010) to provide accurate forecasts of the track and intensity. The horizontal wind fields at the surface, the tangential and radial winds, were analyzed using the QuikSCAT data and the model results. The vertical wind structure was investigated using the dual-Doppler and wind profiler data in combination with the model simulation results. The structure change of Typhoon Nari during the weakening stage was analyzed based on the simulations. Compared to the mature stage, in the weakening stage the Typhoon Nari was found to have stronger asymmetric component, and it exhibited stronger vertical tilt but with reduced vertical extent. It was shown that the strong uppertropospheric outflow loses its strength gradually in the weakening stage, but the height of maximum outflow layer was remained unchanged due to the environmental forcing by the upper-troposphere jet. Comparison of the observation and model simulation revealed that a weak outflow was formed in the mid-troposphere in addition to the primary outflow in the upper troposphere.