The Doppler Radar for Airport Weather (DRAW) system, which started its operation in 1995 as a wind shear detection and warning platform (Ishihara and Hata 1995), has been installed at eight major airports in Japan. During the warm season, the DRAW system's sensitivity and high resolution allowed detection of clear-air echoes that were not generally detectable with conventional weather radars. Whereas the DRAW system has been sensitive enough to observe clear-air echoes, the premise of using this system has been considered phenomena with precipitation. For example, the wind shear detection algorithms have been tuned to recognize the velocity and reflectivity signatures associated with microbursts and gust fronts, which are considered to occur with precipitation in Japan.

In order to assess the utility of these clear-air echoes for use in operational systems, clear-air echo data from the four DRAW sites (Shin-Chitose, Narita, Chubu, Fukuoka) have been analyzed. These sites were selected to represent a range of latitudes (from north to south). In this presentation, we focuses on obtaining quantitative information regarding clear-air echo frequency, area coverage, diurnal structure, the environmental conditions, and there seasonality in the latitude distribution.