| dc.description.abstract | This study used the PSU/NCAR MM5 Model to simulate Typhoon Morakot
(2009), and investigated the mechanisms of the torrential rainfall in southwest
Taiwan and the role of the southwest monsoon flow. The results indicated that the
model is able to capture the observed 72-h accumulated rainfall over 2000 mm
after applying bogus vortex data assimilation (BDA) based on 4DVAR that helps
to improve the initial intensity of the typhoon. The simulated track near and after
landfall is close to the best track, resulting in a good agreement of accumulated
rainfall with the observations.
In the sensitivity experiments for monsoon intensity, the 72-h accumulated
rainfall shows only some differences but have significant changes in rainfall
patterns with respect to the intensity of southwest monsoon. For stronger monsoon,
the 72-h accumulated rainfall tends to be enhanced in central Taiwan, while
weaker monsoon induces more rainfall in south Taiwan. In the experiment with the
initial field where Goni vortex is deactivated by BDA, rainfall maximum is
reduced by about one third on 8 August in southwest Taiwan. When the Goni
circulation and strong moisture-laden southwesterly flow converge to the
southwest of Taiwan, it causes extreme rainfall in southwest Taiwan. On the other
hand, as the relative humidity of southwest flow is reduced, the rainfall intensity
also decreases. It appears that the water vapor transmission from southwest flow is
also an important factor for heavy rainfall in this event. Consequently, southwest
monsoon intensity, Goni Typhoon, and southwesterly moisture are integrated to
produce the tremendous rainfall in Taiwan. | en_US |