CHAPTER }
SPECIAL OBSERVATIONS
A series of special gummed film collections were made on
Ponape, in the Caroline Islands. In additim to the regular gummed
film observations, (which were made at 0030 GCT daily at Poriape),
a gummed film stand was vlaced near the windward shore of the
island to attempt to sample air unaffected by local dust sources,
No significant differences were found, Another gummed film stand
was placed near the regular stands, but the film was changed at
12-hour intervals, in the morning and evening, On 11 days with
heavy fallout, the film exposed during the daytime hours collected
[
about 50% more activity than did the film exposed during the night
hours, despite the fact that precipitation was about equally
distributed in the two periods. This my be a result of the
nocturnal stabilization of the very lowest layers of the atmosphere
which inhibited the deposition of debris from turbulent eddies,
although dimnal variations in the vertical temperature lapse rate
E
are small on a 13h-square-mile island in the trade wind belt.
(4.9 £t*) coincident with the exoosure of the 2h-hour films.
The
collected water was filtered at the end of each observation period
and the filter sent to New York, for analysis.
On the nine days
with the heaviest fallout at Ponape, the total collection on the
roa
To investigate the devosition of debris due te rainfall,
rainwater samles were collected by a 30-inch diameter funnel
rain filters averaged 56% as much activity as on the one-squire-foot
gummed film, During the month of June, when fallout was relatively
light, the rain filters collected twice as much activity as the
gummed film. This is again indicative of the importance of the
wey
wa
rainout process in bringing old debris (and presumably smaller
particles) to the ground.
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