This paper presents a new method for identifying the type of solid hydrometeor mainly contributing to snowfall from the measured size and fall speed data. The main type is determined from the relationship between measured size and fall speed by considering the contributions of various hydrometeor types to precipitation, including graupel, graupel-like snow, aggregates at different riming stages, and small particles such as single snow crystals. The mass flux of each hydrometeor, defined as the product of its mass and fall speed, is needed to evaluate its contribution; however, it is practically difficult to measure. In this study, we estimate mass flux from the empirical relationships between size and mass and between size and fall speed. The mass flux distribution in the size̶fall speed coordinates for all measured hydrometeors is found to accurately reflect the characteristics of types of hydrometeors and their contribution to observed precipitation. Considering these results, we introduce a new variable, the center of mass flux distribution (CMF), in the size̶fall speed coordinates. The CMF, which is the average of size and fall speed weighted by the mass flux, can be obtained in the same way as the center of gravity in mechanics. We believe that it indicates the size and fall speed of the principal hydrometeors among all particles in the observation period. This new method allows the quantitative identification of the main hydrometeor types from the locations of CMFs in the coordinates of size and fall speed. We verify this method by its application to different types of observed snowfall events. Although there is some ambiguity in estimating the mass flux, the method is expected to be useful for identifying the main hydrometeor types in snowfall events and for quantitatively interpreting returned radar power.
Abstract. The initial density of deposited snow is mainly controlled by snowfall hydrometeors. The relationship between snowfall density and hydrometeors has been qualitatively examined by previous researchers; however, a quantitative relationship has not yet been established due to difficulty in parameterizing the hydrometeor characteristics of a snowfall event. Thus, in an earlier study, we developed a new variable, the centre of mass flux distribution (CMF), which we used to describe the main hydrometeors contributing to a snowfall event. The CMF is based on average size and fall speed weighted by the mass flux estimated from all measured hydrometeors in a snowfall event. It provides a quantitative representation of the predominant hydrometeor characteristics of the event. In this study, we examine the relationships between the density of newly fallen snow and predominant snow type as indicated by the CMFs. We measured snowfall density at Nagaoka, Japan, where riming and aggregation are predominant, simultaneously observing the size and fall speed of snowfall hydrometeors, and deduced the predominant hydrometeor characteristics of each snowfall event from their CMFs. Snow density measurements were carried out for short periods, 1 or 2 h, during which the densification of the deposited snow was negligible. Also, we grouped snowfall events based on similar hydrometeor characteristics. As a result, we were able to obtain not only the qualitative relationships between the main types of snow and snowfall density as reported by previous researchers, but also quantitative relationships between snowfall density and the CMF density introduced 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. This quantitative relationship provides a means for more precise estimation of snowfall density based on snow type (hydrometeor characteristics), by using hydrometeor size and fall speed data to derive initial densities for numerical snowpack models, and the snow-to-liquid ratio for winter weather forecasting. In fact, we found that this method can more accurately estimate snowfall density compared with using meteorological elements, which is the method generally used in current snowpack models, even though some issues remain in parameterization for practical use. Transferability of the method developed in the temperate climate zone, where riming and aggregation are predominant, to other snowy areas is also an issue. However, the methodology presented in this study would be useful for other kinds of snow.
Fatigue notch sensitivity of woven fabric composites having a circular hole under tension/torsion biaxial loading was investigated. In-phase (proportional) biaxial stress was applied to tubular specimens. A fatigue notch factor was used to evaluate the fatigue notch sensitivity. The experimental results revealed that the fatigue notch factor was approximately linear with respect to a parameter; cos (tan-' ce) for any fatigue life (a is biaxiality ratio of combined stress). The fatigue notch factor decreased with an increase in fatigue life in the case where the shear stress component was relatively small. However, in the case where the shear stress component was large, it increased with an increase in fatigue life. Under pure torsion loading, fatigue damage did not progress along the principal axis. It grew along both longitudinal and transverse fiber bundles. An empirical equation which can easily predict the fatigue notch factor at any arbitrary fatigue life under biaxial loading was proposed. Unknown variables in this equation are determined by fatigue tests under uniaxial tensile and pure torsion loadings.
It is important to measure the quality of falling snow particles as a help in analyzing radio attenuation during snowfalls. Since the quality of snow particles depends almost entirely on their density (the amount of water they contain), the snow particle density reflects their quality. to permit automatic measurement of the average densities of falling snow particles over long periods of time, the diameters and fall velocities of snow particles are measured by means of image processing. Simultaneously, the weight of all snow particles that have fallen to the ground was measured directly by means of an electronic balance. the density of the falling snow particles is calculated by dividing into this total weight the total volume of snow particles that passed through a unit volume (obtained from the diameter and velocity of snow particles). the diameters, velocities, and number of snow particles are determined by image processing. Snowfall rates calculated from the image processing data are compared with those measured directly and are found to agree.
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