Mesoscale Convective Systems along the Mei-Yu Front Over South China Sea and Taiwan

During the Mei-Yu season, Mesoscale Convective Systems (MCSs) occur frequently along a quasi-stationary subtropical front over South China, South China Sea (SCS) and Taiwan, resulting in heavy rainfall and flash floods. To improve the predictive capability of heavy-rain-bearing systems requires better understanding of their storm properties, life cycle, and physical processes.

The larger MCSs are on the meso-α scale (>200-300 km across) and are initiated over the SCS and move toward Taiwan along the front. This study will first document the observed properties of MCSs based on the 10 year TRMM measurements. MCSs in the TRMM database are selected along Mei-Yu fronts over SCS and Taiwan. A MCS is defined using the TRMM precipitation radar as contiguous near-surface reflectivity >20 dBZ with area >1000 km2 including at least 4 convective pixels. Radar reflectivity characteristics, ice scattering signature, and lightning flash rates of these two groups of MCSs are investigated.

But on the meso-β scale (typically 50-200 km across), convection embedded in the longer-lived meso-α-system often redevelops, matures, and decays in the vicinity of Taiwan. This behavior warrants attention because it is very different from the usual concept that growth of new convection avoids pre-existing rain areas of the system. During the IOP on June 16 of TiMREX (Terrain-influenced Monsoon Rainfall Experiment), a meso-α-system stayed over Southern Taiwan for more than 12 hours with frequent convective lines moving through, producing more than 500 mm rainfall.

A case study of the MCS both on the meso-α scale and meso-β scale is explored. First, the life cycle of the meso-α-system and intense meso-β convective systems are tracked. Then the storm properties, microphysics and rainfall contribution of the intense meso-β convective systems will be presented. Finally, potential mechanisms of the initiation and maintenance of the intense meso-β convection inside the meso-α rain area will be investigated.