Mesoscale Convective Systems (MCS) appeared during the Baiu period are a deep convective system in highly humid environment. MCSs are occasionally maintained and causes heavy rain because the low level airmass has high equivalent potential temperature. In previous studies, mechanisms of maintenance and formation of MCSs have been studied, but there is no research focused on its microphysical and no in-situ observations of ice particles are especially less than 500 μ m. It is absolutely necessary for understanding the process of precipitation formation in a cloud to observe the vertical distributions of sizes, number densities, and ice particle size-distributions (PSDs) because ice particles have various sizes and shapes. In this study, we made an in-situ observations of ice particles in the MCS, using a hydrometeor videosonde (HYVIS) on June 12th, 2008, and we analyzed vertical distributions of ice particles shapes, maximum sizes and reveal ice particles shapes, number densities, mixing ratios and PSDs in the MCS ’s stratiform reagion..

The width of the MCS was about 100 km and the length was about 500 km. It developed around the Baiu front in the East China Sea and its stratiform region covered on Okinawa Island, HYVIS was released at 1426JST. In this region, the bright band was at about 4 km level. From images of various ice particle, they are classified into categories: needle, column, plate, column and plate, aggregate and undefined. We counted the number of ice particles for each category crystal, measured the maximum length (it is the longer one of height and width of the ice particle) by delimiting 10 m, and estimated the vertical distributions of mixing ratios, number densities, and PSDs.

There is no rimed particles in this observation. Plate particles had the largest numbers. It is considered that the degree of ice supersaturation was~10 %. Undefined particles the maximum size range is 10-20 m was predominant and mostly exist around 11.5 km. Therefore, the vertical number densities distribution is less than 100 m at that height became peak.

To get the values of parameters of PSDs indicate a y-intercept(N0) and slope(Λ) quantitatively, we were performed fitting the regression curves assumed Marshall-Plamer distributions. In addition, we considered growths of ice particles from vertical profiles of N0 and Λ. As results, ice particles show aggregation growths in the layer of 12-10 km altitude, deposition in 10-8 km, evaporation in 8-7 km, deposition in 7-6 km, and aggregation in 6-4.6 km. Especially, it suggest that aggregation growths of the 12-10 km layer is due to sticking together small undefined particles is growing to the plate.

For the first time, we successfully observe the stratiform region of MCS using HYVIS and reveal vertical distributions of particles shapes, number densities, mixing ratios and PSDs. It is necessary for accurately understanding the process of ice particle formations to observe MCSs a lot for the future.