| Abstract: | 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, DRPBDA
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 36th hour is 32 km, which is much less
than that of the CTRL (450 km). |
