|
On the Density of Atmospheric Ice Particles |
DRI, 2215 Raggio Parkway, Reno NV 89512
hallett@dri.edu
An approach to measurement of ice particle density may follow a simplistic approach by measurement of particle mass and volume independently: mass obtained by direct weighing or an estimate of the volume of the particle, melted to give a sphere suspended in a near unit density fluid;volume estimated from geometrical approximations of the original ice particle. Both techniques have potential problems with uncertainties of at least +/- 25%.Such and similar approaches have been used to provide size - mass relations for specific types of particles from the viewpoint of mass determination from size and shape.
Direct measurement of particle density may be achieved by following the evaporation of particles collected in flight on a heated forward facing optical flat from the rate of change of area and a knowledge of the ambient conditions.The particle is imaged and video recorded during evaporation; the slope of the area - time plot is related inversely to density.Many particles take a near hemispherical shape on collection and variation in density from the outer surface to the inner core shows density variation with radius.Information on sausage shaped and flat particles may also be obtained.
Results are compared with laboratory and field studies of the density of particles grown under known conditions (temeperature and supersaturation) and results obtained by simplistic assumptions of particles of defined size and shape during aggregation ("haystacking").
