The authors have detected a cirrus cloud near the tropopause by using a lidar system located at Chung-Li, Taiwan (25 degrees N, 121 degrees E). The cloud usually appeared between the month of May and September. In 1993-95, the cloud was observed almost 50% of the time that the lidar operated. The cloud was detected in the heights between 15 and 17 km; the region of the atmosphere had a temperature ranging between -70 degrees and -83 degrees C. It was never detected above the tropopause. The cloud was characterized by its very thin structure. The geometrical and optical thicknesses are about 0.6 km and 0.008, respectively, which can be considered as a subvisual cloud. This paper reports more than 20 cloud events observed in the years between 1993 and 1995. Some properties of the clouds are listed and compared with other references.
