Precipitation and Airflow Features of a Tropical Cyclone Rainband Associated with Topography Modifications

Presentation Type: 
Chia-Lun Tsai (Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan)
Cheng-Ku Yu (Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan.)

This study used ground-based dual-Doppler observations to document precipitation and airflow features of a tropical cyclone rainband (TCR) associated with Typhoon Longwang (2005) as it passed over the complex topography in the vicinity of northern Taiwan. Before landfall, the precipitation of the TCR was characterized by convective (stratiform) rainfall in its inner (outer) side. The low-level front-to-rear flow was lifted upward in the inner side near the leading edge of the rear-to-front flow and became rear-to-front flow in the mid-to-high levels. Both precipitation and airflow features were nearly two-dimensional at this stage. These structural characteristics were similar to the overturning updraft documented previously in the inner side of the so-called principal band. However, different changes in the structure were observed along the TCR as it passed over northern Taiwan. For the southern segment of the TCR over higher topography, the low-level front-to-rear flow tended to pass through the region of convective precipitation, with some relatively weaker convective precipitation locked in the valley region. These structural changes observed appear related closely to the blocking effect of low-level ambient flow associated with the TCR by high topography, which may in turn decrease the rear-to-front flow on the inner side of the TCR. In contrast, for the northern segment of the TCR over lower topography, overturning updraft features were still maintained well, similar to those observed over the ocean before landfall. The results from the study suggest that both orographically influenced airflow and precipitation play an important role in modulating the structure and intensity of the TCR.