Microphysical and Kinematical Characteristics of Merged and Isolated Convective Cells Over the Complex Terrain of the Taipei Basin

This study investigates the microphysical and kinematic characteristics in extreme afternoon thunderstorm rainfall during Taiwan-Area Heavy rain Observation and Prediction Experiment/Prediction of Rainfall Extremes Campaign In the Pacific IOP 2. The high-quality S-Pol radar observations and multi-Doppler winds provided valuable information about the convective organization over complex terrain. There were two episodes of heavy rainfall in this event. Episode 1 (1200–1400 LST, Local Standard Time) featured multiple cell merger (MCM) favored by terrain-induced circulation. Around the time of MCM, the enhanced ZDR region (>1 dB) broadened horizontally to ∼8 km in width at 5.5 km above mean sea level (AMSL). Afterward, maximum vertical velocity increased dramatically to ∼20 m s⁻¹ and graupel reached up to 12 km AMSL. In contrast, Episode 2 (1500–1700 LST) exhibited isolated cells with weak updrafts (<10 m s⁻¹) and more snow aloft. The merged ZDR columns coincided with MCM occurrence, preceding peaks in both vertical velocity and rainfall intensity. Building on emerging research investigating the relationship between ZDR column size and severe weather in the US, this study suggests that wide merged ZDR columns may be relevant to severe storms over complex terrain in Taiwan, highlighting their potential utility as indicators of storm intensification.