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<br />Figure 5.3 shows the terminal velocities of un rimed needles, the type of crystals that would <br />grow at -5 "C (UN in diagram). The crystals have the lowest fall speed of any crystal <br />observed up to a dimension of 1 mm. Terminal velocities of less than 0.5 m S.l make these <br />crystals susceptible to the strong upward and downward motions observed to the lee of the <br />main Sierra crest. The diagram shows that columns (e) or plates (P), the type of crystals <br />expected to grow between -1 and -4 ce, have a faster fall speed at smaller sizes, mainly <br />because they are more compact and have less drag. However, the mass of the crystals may <br />be relatively small at these particle sizes. This type of information is programmed into the <br />GLIDE model and allows calculation of particle trajectories. <br /> <br />1.5 <br /> <br /> <br /> <br />- <br />";' <br />In <br />E <br />- <br />c 1 <br />w <br />w ~ <br />D- <br />en <br />..J <br />~ <br />z <br />:E " <br />a: 0.5 <br />w <br />to- <br /> <br />o <br />0.1 <br /> <br /> <br />1 <br />MAXIMUM DIMENSION (mm) <br /> <br />10 <br /> <br />Figure 5.3. - Terminal speeds of ice crystals and snO'.'.1Iakes. Hydrometeor types and sources of information are as <br />follows: LG-Iump graupel of density 0.1 to 0.2 Mg m-5 at the ground (Locatelli and Hobbs. 1974). C-columns at 40 <br />kPa. -20 =C (Heymsfield. 1972)_ P-plates at 40 kPa (Heymsfield, 1972). RA-rimed aggregates at the ground <br />(Locatelli and Hobbs. 1974). UA-unrimed aggregates at the ground (Locatelli and Hobbs. 1974). UN-unrimed <br />needles at 40 kPa (Heymsfield. 1972). PD-piane dendrites at 85 kPa (Heymsfield. 1972). <br /> <br />31 <br />