The Secondary Low and Heavy Rainfall Associated with Typhoon Mindulle (2004)

Abstract

This paper presents an observational and numerical study of Typhoon Mindulle (2004) as it affected Taiwan. Mindulle made landfall on the east coast of Taiwan at 1500 UTC 1 July 2004, and after 13 h, it exited Taiwan from the north coast. Severe rainfall (with a maximum amount of 787 mm) occurred over central-southwestern Taiwan on 2 July 2004. During the landfall of Mindulle's main circulation, a secondary low formed over the Taiwan Strait. However, the secondary low, after it developed significantly (vorticity exceeded 5 ϫ 10 Ϫ4 s Ϫ1 over a 30-km radius), did not replace the original center as was observed in many other storms. Instead, it moved inland and dissipated after the original center redeveloped near the north coast of Taiwan. In this study, the evolution of the secondary low, the redevelopment of the primary center, and the processes leading to the severe rainfall were examined. Results showed that the processes leading to the formation and the development of the secondary low were similar to those described in previous studies. These processes include the leeside subsidence warming, the horizontal transport of vorticity around the northern tip of the Central Mountain Range (CMR), and the overmountain upper-level vorticity remnant. However, because of the northward track, Mindulle preserved some strong vorticity on the eastern slope of the CMR. This strong vorticity remnant was steered northward over the ocean offshore from the north coast where the redevelopment of the primary center occurred. This "quasi-continuous track" of Mindulle has not been documented in previous studies. The vortex interaction between the redeveloped primary center and the secondary low resulted in the northeastward movement of the secondary low, which then dissipated after making landfall. Analyses also showed that even though heavy rainfall would occur over the mountain area when only the southwesterly flow prevailed, as on 3 July 2004, Typhoon Mindulle and the secondary low provided extra convergence that resulted in the west-east-oriented convective bands. These convective bands and the orographic lifting of the circulation associated with the secondary low resulted in the heavy rainfall over the central-western plains area.

High-Resolution Modeling of Typhoon Morakot (2009): Vortex Rossby Waves and Their Role in Extreme Precipitation over Taiwan

“…5). The development of zonally oriented convective bands over the Taiwan Strait is similar to the case of Typhoon Mindulle (2004) as documented in Lee et al (2008) and Chien et al (2008), although here we attribute the enhanced convergence to VRW activity, rather than a secondary circulation center in the case of Mindulle.…”

“…The interaction of a typhoon with northeasterly monsoon in the vicinity of Taiwan and topography was investigated by Wu et al (2009b), who found that the spatial distribution of the heavy rainfall was sensitive to topographic forcing and changes in the simulated vortex, both of which affected the interaction with the northeast monsoon flow. In a similar fashion, Chien et al (2008) and Lee et al (2008) studied the rainfall distribution over Taiwan associated with the interaction between Typhoon Mindulle (2004) and the southwest monsoon. They found that a secondary low, which formed off the western coast of Taiwan as the typhoon made landfall over the northeast of the island, played an important role in the development of deep convective banding in the convergent flow between the secondary low and the southwesterly monsoon off the western coast of Taiwan.…”

Mesoscale processes for super heavy rainfall of Typhoon Morakot (2009) over Southern Taiwan

“…3, over the Southern Taiwan Strait and southwestern Taiwan, the northerly flow as a part of the typhoon evolved to the westerly, and then southwesterly, flow as the typhoon slowly moved northward in these 3 days. The movement and strengthening of the southwesterly flow into this region is not uncommon when a typhoon departs from Taiwan, and the accompanying moisture provides the source for heavy rainfall as the southwesterly flow impinging the local topography Lee et al, 2008).…”

Extreme Rainfall Mechanisms Exhibited by Typhoon Morakot (2009)

“…Warm ocean eddies in Morakot's path also provide certain favorable conditions for enhancing Morakot's convection . After the typhoon's passage over Taiwan, such intense southwesterly flow may be an important factor in enhancing the total accumulated rainfall in Taiwan which has also been exhibited by other typhoons, such as the northbound Typhoon Mindulle (2004) Lee et al 2008). Using the WRF model (Skamarock et al 2005), Ge et al (2010) highlighted the importance of the steep CMR in producing the extreme rainfall in south Taiwan.…”