A Preliminary Survey of Clear-Air Echo Appearances over the Kanto Plain in Japan from July to December 1997

Abstract

Abstract A preliminary survey of clear-air echo appearances over the Kanto plain in Japan from July to December 1997 is presented. A distinct contrast was seen between clear-air echoes observed over land and their absence over the ocean. During July to late November, clear-air echoes were observed 40%–80% of the time during days when no precipitation occurred. The clear-air echo was not observed between late November and the end of the study period (December). The drop-off of clear-air echo was associated with daily average surface temperatures dipping below 10°C. During this period, temperatures would often increase above 10°C for short periods but were not associated with clear-air return. The diurnal variation of clear-air echo appearances had two peaks at the periods of the daytime and the twilight. During July to late November, the correlations of clear-air echo appearances with surface temperature, wind direction, and sunshine duration were significantly low. In July and August, there appeared to be...