Size spectra of snow particles measured in wintertime precipitation in the Pacific northwest

Particle size spectra collected by the University of Washington's Convair-580 research aircraft at a variety of altitudes and temperatures in winter frontal and orographic precipitation systems during the Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE) are analyzed in this study. The particle size spectra generally appeared to conform to an exponential size distribution, with well-correlated linear fits between the log of the number concentration and particle diameter. When the particle size spectra were grouped according to the habit composition as determined from airborne imagery, significantly improved correlations between the size spectrum parameters and temperature were obtained. This result could potentially be exploited for specifying the size distribution in a single-moment bulk microphysical scheme, if particle habit is predicted by the scheme. Analyses of 'spectral trajectories' suggest that the rime-splintering process was likely responsible for the presence of needle and column habit types and the positive shift in both [N.sub.0s] and [[lambda].sub.s] at temperatures warmer than -10[degrees]C.