Numerical Simulation of a Landfall Typhoon Using a Bogus Data Assimilation Scheme

A typhoon bogus data assimilation scheme （BDA） using dimension-reduced projection four-dimensional variational data assimilation （DRP-4-DVar）, called DRP-BDA for short, is built in the Advanced Regional Eta Model （AREM）. As an adjoint-free approach, DRP- BDA saves time, and only several minutes are taken for the full BDA process. To evaluate its performance, the DRP-BDA is applied to a case study on a landfall typhoon, Fengshen （2008）, from the Northwestern Pacific Ocean to Guangdong province, in which the bogus sea level pressure （SLP） is assimilated as a kind of observation. The results show that a more realistic typhoon with correct center position, stronger warm core vortex, and more reasonable wind fields is reproduced in the analyzed initial condition through the new approach. Compared with the control run （CTRL） initialized with NCEP Final （FNL） Global Tropospheric Analyses, the DRP-BDA leads to an evidently positive impact on typhoon track forecasting and a small positive impact on typhoon intensity forecasting. Furthermore, the forecast landfall time conforms to the observed landfall time, and the forecast track error at the 36thhour is 32 km, which is much less than that of the CTRL （450 km）.