Relationships between Snowfall Densities and the Main Types of Solid Hydrometeors Deduced from Measured Size and Fall Speed, for snowpack modeling applications

Initial densities of deposited snows mainly depend on hydrometeors types of snowfalls. Some previous researchers qualitatively indicated their relations. However a quantitative relationship between snowfall densities and hydrometeors types had not been established because of difficulty in parameterizing varieties of types of hydrometeors in a 15 snowfall event. Thus in a previous study, we introduced a new variable, CMF (Center of Mass Flux distribution), which described the hydrometeors mainly contributing to a snowfall. The CMF is a set of the averages of the size and the fall speed weighted by the mass flux estimated from all measured hydrometeors in a snowfall. It represents the predominant type of hydrometeors of the snowfall quantitatively. In this study, we examined the relationships between the densities of newly fallen snows and their predominant snow types as indicated by the CMFs. We measured the snowfall densities, 20 simultaneously observing the size and the fall speed of the hydrometeors of the snowfalls and deduced the predominant hydrometeor types of each snowfall event from their CMFs. The measurements of snow densities were carried out for short periods, 1 or 2 h, during which the densification of the deposited snows was negligible. We also selected cases when snowfalls contained basically the same type of hydrometeors.As a result, we could obtain the relationships between the main snow types and the snowfall densities not only qualitatively reported by previous researchers but also the quantitative 25 relationships between snowfall densities and the CMF-densities, which were a presumed density derived from the size and mass components of the CMFs. This suggests the possibility of estimating snowfall densities, which reflected snow types (the main types of hydrometeors), directly from the measured size and the fall speed data, and using them as the initial densities for a snow pack in a numerical model, even though difficult issues remain in parameterization for a plactical use. Our results might be applicable only to temperate snow at our observation site, Nagaoka, 37 o N, where riming and 30 aggregation are predominant. However the methodology in this study would be useful for other kinds of snow.