Investigation of Mechanisms Analysis in the Transition from Single-cell to Multicell Thunderstorms Using X-band Polarimetric Radar Observation

Abstract

The localized heavy rainfall induced by the single-cell could be more hazardous if the single-cell merged into the multicell thunderstorms. Flash floods and landslides are common disasters with a lifespan of multicell more than one hour and a scale of an area larger than a single-cell. To mitigate the flood risk, the short-term precipitation forecast is suggested as one of the observation tools to disseminate early warnings for the flood forecasting systems. Therefore, the study of the transition from single-cell to multicell was proposed by utilizing vertical vorticity. The mechanisms studied using dual-Doppler analysis (DDA) were further reviewed to quantify their relationships with vertical vorticity. The characteristics of single-cell could be characterized using vertical vorticity, where the formation height of the peak of core pair vorticity occurred at 4.4 km, and their peak of vortices developed at the same time of occurrence using pseudo-vorticity. Meanwhile, dual-Doppler vorticity analysis observed its formation height at 3.8 km and 3.7 km for positive and negative vorticity, respectively, which occurred in the same period. It was assumed that the period of peak intensity occurred at a similar time for single-cell, which was related to the initial formation of the updraft. The results of mechanisms analysis from the evolution of cell development were mainly affected on the increment of core vorticity intensity. The convergence, updraft, and stretching of the vortex tube were influenced on the increment of core vorticity intensity, especially at the lower level, and the tilting of the vortex tube was mostly affected at the middle-level height. At the later stage of multicell formation, the mature vortex was discovered with the core vorticity maxima boundary remaining due to the existence of updraft and convergence in the development of multicell.