Doppler Radar Analysis of Typhoon Otto (1998)-Characteristics of Eyewall and Rainbands with and without the Influence of Taiwan Orography

Abstract

By using the observational data collected by the C-band Doppler radar which was located at the Green Island off the southeast coast of Taiwan, as well as the offshore island airport and ground weather stations, this article focuses on the mesoscale analysis of inner and outer rainband features of Typhoon Otto (1998), before and after affected by the Central Mountain Range (CMR) which exceeds 3000 m in elevation while the storm was approaching Taiwan in the northwestward movement.While the typhoon was over the open ocean and moved north-northwestward in speed of 15 km/h, its eyewall was not well organized. The rainbands, separated from the inner core region and located at the first and second quadrants relative to the moving direction of typhoon, were embedded with active convections. The vertical cross sections along the radial showed that the outer rainbands tilted outward and were more intense than the inner ones. As the typhoon system gradually propagated to the offshore area near the southeast coast of Taiwan, the semi-elliptic eyewall was built up at the second and third quadrants. Moreover, the strength of the eyewall became more intense compared with the outer rainbands, and the maximum wind axis was quite parallel to the vertical orientation of radar reflectivity in the eyewall. After the detailed streamline analysis, it indicated that the eyewall was enhanced by the confluence between the westerly flow, triggered by the farther outer circulation of the storm around the Taiwan Island, and the northwesterly flow near the inner circulation of the storm itself. Also, the left quadrant in the lower portion (below 2 km in altitude) possessed stronger Doppler velocity than that in the right quadrant, and the upper portion (above 2.0 km) had the opposite mode. This reverse phenomenon of Doppler wind in the lower portion of the typhoon became more pronounced while the storm was getting closer to the mountain. The estimated typhoon center below 1.5 km in altitude had a slower

Radar Analysis on the Interaction between Southwesterly Monsoonal Flow and Circulation Associated with Typhoon Morakot (2009)

“…The phenomenon is as important as topographical effect to create the asymmetric distribution of rainbands embedded with in a TC system, which causes extreme difficulty in predicting intense wind and heavy rainfall in Taiwan. The TC-terrain interaction problem has led to plenty of significant studies, including numerical simulations (Wu and Kuo 1999;Wu 2001;Wu et al 2002;Lin et al 2002;Chiao and Lin 2003;Lin et al 2005;Jian and Wu 2008;Ge et al 2010;Chien and Kuo, 2011;Liang et al 2011) and observations (Hor et al 2005;Yu and Cheng 2008;Wei et al, 2011). In contrast, few systematic studies have been done on the TC interaction with the summer monsoon system (Lin et al 2011;Wu et al 2011;Chien and Kuo 2011).…”