Abstract
In order to investigate the morphology of snow crystals from －4 ℃ to －40 ℃, artificial snow crystal formation experiments using a convection chamber with the “FINDEW” chilled mirror hygrometer were conducted about 200 times. Using the data of relative humidity in the atmospheric phase (RHi) by FINDEW, we made a new diagram of snow crystal types. Our main findings are as follows: 1)Snow crystals mostly generate from ice saturation level to water saturation level from －4 ℃ to －40 ℃. 2)When the humidity is close to the ice saturation level in the same temperature range, only columnar and thick plate types of snow crystals formed. When the humidity increases, snow crystals develop to each particular shape according to the temperature. Below －35 ℃ and over 105 ％ RHi a variety of shapes of snow crystals including poly-crystals formed. 3) Snow crystals sometimes formed below ice saturation level, which is difficult to understand. We postulate that small supercooled droplets, which are floating in the convection chamber, possibly attribute to the growth of snow crystals. 4)The relation between the growth rates and RHi was obtained for the needle type, the dendritic type and the crossed-plate type at temperatures above－30 ℃. On the other hand, no clear relations between the growth rates and RHi were observed for the sector plate type, the hexagonal plate type, and the crossed plates type at temperatures under －30 ℃.
