B l o w i n g

S n o w

DISCUSSION

Thederivationofequation(13)depends ontwocritical
assumption.(a) Particles fall at terminal velocity, and (b)
the shape factor (drag coefficient) is the same in all direc-
tions.Very consistent vertical distances between dots on
each trace strongly support both assumptions.Measured
variations in fall velocitywere random forall traces, and
withinthe uncertaintyofthe measurement.We sawno
trace oscillations characteristic of particles falling with a
preferred orientations(as reported for plate snow crystals,
forexample).The ratiooflongest axistoperpendicular
axisaveraged1.49forsaltatingsnowphotographedby
Schmidt(1981).Saltationimpactsandnon-uniform
instantaneous drag on such particles will cause rotations
that continue afterparticle's enterourapparatus.These
rotationsshouldyieldanaverage shapefactorapproxi-
mately constant with respect to direction.

ticles with negativechargesaltating on asnow surfacewith
net positive charge, theelectrostatic force(attraction) short-
ens trajectories.On the other hand,particles with positive
charge, eroded from the surface during wind gust,should
havelongertrajectorieswithhigherrebounds.These
particles will have increased probability of suspension by
turbulence.Based on the results reported here, questions
of charge distribution with height,and charge decay rate
for particlesfreshlydetachedfrom thesurface,becomecriti-
cal next steps in our research.

CONCLUSIONS

Although the apparatus is necessarily large, modification
of Millikan's (1910) technique can provide charge-to-mass
ratios forindividual saltating particles.

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