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The initial density of deposited snow is mainly controlled by snowfallhydrometeors. The relationship between snowfall density and hydrometeors hasbeen qualitatively examined by previous researchers; however, a quantitativerelationship has not yet been established due to difficulty in parameterizingthe hydrometeor characteristics of a snowfall event. Thus, in an earlierstudy, we developed a new variable, the centre of mass flux distribution (CMF),which we used to describe the main hydrometeors contributing to asnowfall event. The CMF is based on average size and fall speed weighted bythe mass flux estimated from all measured hydrometeors in a snowfall event.It provides a quantitative representation of the predominant hydrometeorcharacteristics of the event. In this study, we examine the relationshipsbetween the density of newly fallen snow and predominant snow type asindicated by the CMFs. We measured snowfall density at Nagaoka, Japan, whereriming and aggregation are predominant, simultaneously observing the size andfall speed of snowfall hydrometeors, and deduced the predominant hydrometeorcharacteristics of each snowfall event from their CMFs. Snow densitymeasurements were carried out for short periods, 1 or 2 h, during which thedensification of the deposited snow was negligible. Also, we grouped snowfallevents based on similar hydrometeor characteristics. As a result, we wereable to obtain not only the qualitative relationships between the main typesof snow and snowfall density as reported by previous researchers, but alsoquantitative relationships between snowfall density and the CMF densityintroduced here. CMF density is defined as the ratio between mass and volume,assuming the diameter of a sphere is equal to the CMF size component. Thisquantitative relationship provides a means for more precise estimation ofsnowfall density based on snow type (hydrometeor characteristics), by usinghydrometeor size and fall speed data to derive initial densities fornumerical snowpack models, and the snow-to-liquid ratio for winter weatherforecasting. In fact, we found that this method can more accurately estimatesnowfall density compared with using meteorological elements, which is themethod generally used in current snowpack models, even though some issuesremain in parameterization for practical use. Transferability of the methoddeveloped in the temperate climate zone, where riming and aggregation arepredominant, to other snowy areas is also an issue. However, themethodology presented in this study would be useful for other kinds of snow

Relationships between snowfall density and solid hydrometeors, based on measured size and fall speed, for snowpack modeling applications