Videosonde is one of strong tools to measure hydrometeors in clouds directly. It is a balloon-borne radiosonde that acquires images of precipitation particles via a CCD camera. The system has a stroboscopic illumination that provides information on particle size and shape. One of the advantages for the videosonde is to capture images of precipitation particles as they are in the air. Because the videosonde can obtain particle images without contact, it can measure particles neither bouncing nor destroyed, which is different from a film-capture-type sonde. In the previous studies, several hundred videosondes have been launched into clouds in climatologically different areas and have contributed to better understanding of the precipitation mechanisms. However, it was impossible to launch videosondes continuously into the same rain systems in a short time because we had only one expensive receiver. Suzuki et al. (2012) developed a new videosonde receiving system, and we have succeeded in the continuous launching of the videosonde for the first time. Videosonde observations of Baui Monsoon clouds were conducted as part of the in-situ campaign observation by a C-band polarimetric radar synchronized with videosonde (Nakakita et al., 2009), which were carried out at Okinawa Electromagnetic Technology Center of National Institute of Information and Communications Technology (26∫292 N, 127∫502 E).
On 20 May 2012, a Baiu stationary front was located over the East China Sea, and we experienced heavy rain of 71.1 mm from 09 JST to 13 JST at our videosonde launching site. Six videosondes were launched into the different developing stages of the rainband. In the cases of the developing stage, frozen drops were observed from 0∫C to -15∫C. Graupel were also detected in the same altitude. On the other hand, in the mature stage, we observed them between 5∫C and 0∫C layer, and graupel were dominant in between 0∫C and -5∫C. It was supposed that freezing processes and graupel formation processes near the 0∫C was different in the different developing stages.