Extended Abstract

characteristics of a frontal zone, i.e., a strong moisture gradient and a horizontalwind shear line, but with a temperature gradient that is weak over China butsomewhat stronger over Japan. From a large-scale perspective, the Meiyu-Baiurainband represents a zone of convergence between the southwest monsoonflow and northerly flow associated with the passage of midlatitude disturbancesaround the Tibetan Plateau (Fig. 1)Fig. 1. Schematic diagram illustrating the factors that bring Meiyu-Baiu rainfall in earlysummer East Asia (Sampe and Xie 2010).Within the Meiyu-Baiu-Chagma rainband, mesoscale disturbances developaccompanied by intense convection and heavy rainfall (Ninomiya 2004). Thefact that this convergence boundary is often quasi-stationary leads to thefrequent occurrence of extended periods of heavy rain and floods.3. Mesoscale organization of extreme-rain-producing stormsIn a study of extreme 1 rainfall events in the eastern two-thirds of the UnitedStates during a 5-year period, Schumacher and Johnson (2005, 2006) found that66% of the cases were associated with mesoscale convective systems (MCSs).The others were of synoptic or tropical origin. Given that MCSs are dominantfactors in extreme rainfall and flash floods, it is important to understand theorganizational characteristics of MCSs. The most common organizationalpattern for linear MCSs is that found in many squall lines, referred to as trailingstratiform precipitation systems (Smull and Houze 1985; Houze et al. 1989).However, other organizational structures of MCSs have been found to exist. In astudy of 88 linear, warm-sector MCSs over the United States, Parker andJohnson (2000) found three dominant modes of organization of convective linesand attendant stratiform precipitation (Fig. 2). The three modes are convectivelines with trailing (TS), leading (LS), and parallel (PS) stratiform precipitation. TSsystems were the most common, accounting for ∼60% of the cases, with the LS1 Defined as rainfall that surpasses the 50-year recurrence interval.-4-