Although there have been many observational and modeling
studies of tropical cyclones, our understanding of their intensity and
structural changes after landfall is rather limited. In this study,
several 84-h cloud-resolving simulations of Typhoon Nari (2001), that
produced extremely heavy rainfall over Taiwan, are carried out using a
quadruply nested-grid mesoscale model with the finest grid size of 2
km. After evaluating the model performance in simulating
Nari’s track, intensity and structures, the topographic
effects on the torrential rainfall production are investigated.
It is shown that the model reproduces reasonably well the kinematic and
precipitation features as well as the structural changes of Nari, as
verified against satellite, radar, and rain gauge observations. They
include the storm track, contraction of the eye and eyewall, and the
spiral rainbands; and the minimum central pressure and maximum surface
wind, the rapid pressure rise (~ 1.67 hPa h-1), and the nearly constant
intensity prior to, during and after landfall, respectively. In
addition, the model captures the horizontal rainfall distribution and
some local maxima associated with Taiwan’s orography.
A series of sensitivity experiments of reducing Taiwan topography are
performed to examine the topographic effects on Nari’s track,
intensity, rainfall distribution and amount. Results show that the
impact of island terrain on Nari’s intensity is nearly
linear, with stronger storm intensity in lower-terrain runs. In
contrast, the effects of Taiwan topography on Nari’s track
and accumulated rainfall amount are nonlinear. Thus, we conclude that
Nari’s track is determined by the complex interactions
between the environmental steering flow, Taiwan’s topography,
and the terrain-induced circulations, and that the local rainfall
amount increases with terrain elevation.