WMOD00420

• Title: Corrections of Surface Particle Probe Measurements for the Effects of Aspiration
• Date: 8/4/1988
• Weather Modification - Doc Type: Report

AUGUST 1988

TERR Y DESH LER

559

from 3.7 to 0.8. This is different than previous com-
parisons made with a truck-mounted 2D-C (Holroyd
1986).
To show how surface snowfall measurements change
when corrected for the effects of aspiration, Fig. 12 is
presented displaying time series plots of IPC, average
diameter, and slope, A, of the size distribution. The
uncorrected data are shown in Fig. 12a and the cor-
rected data in Fig. 12b. Correction factors based on
particle size and windspeed, from comparisons with
the truckborne 2D-C, were applied according to Table
3. The IPC in Fig. 12 are presented as a function of
size in a form which has proven useful for analysis.
Each shaded region corresponds to the contribution to
the concentration by particles in a certain size range.
The size scale is shown at the right. The top of each
shaded region is the concentration of particles less than
or equal to the size indicated. For the corrected data
the total concentration is reduced, as are the relative

a.
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b.
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contributions of particles in the smaller size ranges,
while the concentration oflarger particles is increased.
Average diameter increases and A decreases.
Although empirical calibrations are seldom com-
plete, it is believed sufficient agreement has been found
from three experiments investigating the effects of as-
piration on measurements ofIPC to apply a correction
factor of 0.3 to 0.4 to past and future field measure-
ments of total IPC using an aspirated 2D-C probe. This
factor is in agreement with results presented by Holroyd
(1986). Considering IPC as a function of particle size
provides less agreement among the various compari-
sons. Until further work is done to more fully explore
the variation of Cm with size and windspeed, the values
of Cm in Table 3 should be applied only to a narrow
range of conditions. Additional calculations like those
of Norment, but for ice particles and with varying
crosswinds, would provide a useful basis for further
comparisons.

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TIME (UTe)

FIG. 12. (a) Time trace of average diameter, 15 (solid line), slope of the sv..e distribution, ^ (dashed line), and ice particle concentration
by size for surface snowfall measurements using an aspirated 2D-C. For the ice particle concentrations, the top of each shaded region is the
concentration of particles less than or equal to the sizes shown at the right. (b) The same data corrected for the effects of aspiration.

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