Statistical Analysis of Quasi-Stationary Mesoscale Convective Systems over Complex Terrain in Japan

A quasi-stationary mesoscale convective system(QSMCS) over complex terrain in warm seasons is one of the extreme weather events that cause heavy rainfall in Japan. In spite of the stationary behavior of such MCSs, a number of convective cells develop, move, and dissipate mainly through back-building processes. Although there are case studies that examine the physical processes and environmental conditions related to QSMCSs there are few studies that comprehensively investigate QSMCSs from a statistical point of view. In addition, since the characteristics of complex terrain are different from region to region, the examination of stationary mechanisms for QSMCSs should be conducted at regional-scales. The purpose of this study is to examine the statistical characteristics of rain-producing QSMCSs over complex terrain in Japan by using operational radar observations at 1-km resolution and 10-min intervals during 2005-2011. In order to assess the regional-scale characteristics of QSMCSs, we divide the western part of Japan into 5 areas at scales of about (300 km)². Since it is known that QSMCSs in warm seasons in Japan are organized along the low- and middle-level wind direction, we chose the 850-hPa wind as a representative wind to classify the morphology of QSMCSs in terms of the representative wind direction over each region. By examining the spatial distribution of means and standard deviations of precipitation intensity over each area, it was found that rain-producing QSMCSs are localized on the upwind side of complex terrain when the wind condition is from the sea. Most of QSMCSs along the Pacific Ocean have a line-shaped structure that is perpendicular to the wind direction at the 850-hPa level. However, some QSMCSs have a disorganized cluster, because there is less width of complex terrain perpendicular to the wind direction at the 850-hPa level. The condition of the representative wind and the width of complex terrain perpendicular to the representative wind direction is very important for QSMCSs maintenance and organization over complex terrain.