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<br />6
<br />
<br />temperature structure, and source region vary (Rhea, et a1., 1969;
<br />
<br />Chappell, 1970; Orgill, 1971; Grant, et a1., 1974; Marwitz, et a1.,
<br />
<br />~
<br />
<br />1976; Walsh, 1977).
<br />
<br />The convective component of the orographic cloud system is impor-
<br />
<br />.
<br />~
<br />
<br />tant because it can physically alter the shape, size, depth, dynamics,
<br />
<br />water contents, and microphysics of an otherwise stable system (Furman,
<br />
<br />1967; Smith, 1970; Walsh, 1977). The presence of convective motions
<br />
<br />can directly alter the cloud microphysical processes. Imbedded convec-
<br />
<br />tive elements can generate secondary ice crystals by transporting
<br />
<br />crystals from higher levels, accumulating ice nuclei or crystals at a
<br />
<br />given cloud level, multiplying ice crystals, or by generating seed
<br />
<br />crystals which grow by aggregation as they fall through lower cloud
<br />
<br />layers (Chappell, 1970; Grant and Elliott, 1974; Hobbs, et a1., 1976;
<br />
<br />~
<br />
<br />Marwitz, et a1., 1976, Walsh, 1977). Previous research suggests that
<br />
<br />accretional, as well as diffusional, crystal growth are important during
<br />
<br />unstable cloud conditions while only diffusional growth may be important
<br />
<br />in many absolutely stable orographic clouds (Marwitz, et a1., 1976).
<br />
<br />Convective elements can penetrate to higher, colder levels where more
<br />
<br />ice nuclei can be activated and produce many more natural ice crystals
<br />
<br />(Grant, et a1., 1968; Rhea, et a1., 1969; Smith, 1970; Grant and Elliott,
<br />
<br />1974; Grant, et al., 1974; Brown, et a1., 1976). Ice crystal mu1tipli-
<br />
<br />cation processes such as; 1) fragmentation of individual cloud droplets
<br />
<br />during freezing, 2) fragmentation of freezing droplets fo1lo,ring their
<br />
<br />collision with ice particles, 3) mechanical breakup of delicate ice
<br />
<br />crystals due to thermal shock they receive when they collide with and
<br />
<br />~
<br />
<br />nucleate supercooled droplets, 4) Ha11ett-Mossop multiplication mecha-
<br />
<br />nisms, 5) mechanical fracturing of fragile crystals due to random
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