A Mechanism for Heavy Precipitation over the Kii Peninsula Accompanying Typhoon Meari (2004)

Abstract

An extremely heavy precipitation event occurred in the mountainous Kii Peninsula in Japan, associated with Typhoon Meari in 2004. A marked characteristic of this heavy precipitation was its extreme rainfall rate, more than 100 mm h À1 . Another feature was that the area of precipitation was far from the storm center, more than 500 km. From radar and surface observations, it was found that the heavy rains were composed of a stationary precipitation system and two moving precipitation systems.In order to evince a physical mechanism for the precipitation systems, the event was analyzed in detail using data from cloud-resolving simulations and observations. The results demonstrated that the heavy precipitation was produced in a synergistic manner from the three precipitation systems. The following are identified as the key factors for the formation and maintenance of each precipitation system: a) elimination of vertical convective instability in a low-level warm and moist easterly on the eastern slope of the mountainous region, b) moisture supply due to a low-level confluent flow along the boundary between the low-level easterly and south-easterly flow, and lifting of a slightly warmer south-easterly flow, and c) low-level convergence due to cold pool, running nearly parallel to the rainband axis and located slightly to the southwest of the band, acting as an obstacle to the low-level inflow into the system. Precipitation e‰ciency revealed that precipitation was enhanced when moving precipitation systems merged with the stationary precipitation system. The enhancement was attributed to the greater rate of conversion of cloud water to rainwater via accretion of cloud water by rain, under the condition of intense water vapor flux convergence. The moving precipitation systems provided raindrops for the accretion of cloud droplets in the stationary precipitation system. Based on our findings, extremely heavy precipitation in the present case is caused by the enhancement of the accretion process due to the merger of precipitation systems in addition to precipitation in each system.

Precipitation microphysics characteristics of a Typhoon Matmo (2014) rainband after landfall over eastern China based on polarimetric radar observations

“…Previous studies have shown that warm rain accretion in deep warm clouds tends to produce high precipitation efficiency (PE) and causes heavy rainfall [ Rowe et al ., ; Murata , ]. Murata [] found that the conversion of cloud water to rainwater via accretion dominated the heavy precipitation and produced very high rainfall efficiencies of 50%–60% in numerical simulations of Typhoon Meari (2004). The PE of Typhoon Matmo (2014) is examined here.…”

The JMA Nonhydrostatic Model and Its Applications to Operation and Research

“…Airflow over the Kii Peninsula and its relation to the orographic enhancement of rainfall has been studied by Saito et al (1994) and Murata (2009). Saito et al (1998) compared the Deutscher Wetterdienst nonhydrostatic regional model DWD LM and MRI-NHM for numerical solutions of the 3-dimensional mountain waves, focusing on the computational efficiency of HI-VI and HE-VI schemes.…”

The Kinematic and Microphysical Characteristics and Associated Precipitation Efficiency of Subtropical Convection during SoWMEX/TiMREX

“…Various factors influencing the PE have been studied via numerical simulations (e.g., Weisman and Klemp 1982;Ferrier et al 1996;Li et al 2002;Tao et al 2004;Sui et al 2005Sui et al , 2007. Murata (2009) found that the enhancement of PE in a heavy rainfall event was attributed to the conversion of cloud water to rainwater via accretion of cloud water by rain. Murata (2009) found that the enhancement of PE in a heavy rainfall event was attributed to the conversion of cloud water to rainwater via accretion of cloud water by rain.…”