Analysis of Spectral Nudging Effect on Tropical Cyclone Forecast

Abstract

Most regional limited area models have a chronic problem, the inconsistency between model field and lateral boundary condition, which can lead to distortion and error near the boundary of regional model. The spectral nudging is one of the alternative techniques which can reduce the lateral boundary condition problem. In this study, the spectral nudging technique is applied to tropical cyclone (TC) track and intensity forecast and its effect is investigated using the WRF model.

The result of case study for Typhoon Neoguri and Vongfong shows that the spectral nudging is effective in track forecast by improving large-scale wind and the Western North Pacific subtropical high. However, it also weakens simulated TC intensity because low resolution GFS data is assimilated on WRF forecasting. The sensitivity tests to spectral nudging options are performed to reduce the disadvantage of weakening the TC intensity forecast. The nudging option is optimized through the sensitivity tests to improve the intensity forecast while maintaining improved track forecast by the spectral nudging. 51 experiments about 18 TCs with revised spectral nudging option are accomplished to investigate the general effect of spectral nudging on TC forecast. The results show that the track forecast is generally improved by the spectral nudging especially after 96h and intensity forecast is also improved compared to case studies. In addition, the spectral nudging is especially effective to TC cases which are occurred in the east of WNP and turned near the Northeast Asia.