WMOD00439

• Title: HIPLEX-1: Experimental Design and Response Variables
• Date: 4/4/1984
• Weather Modification - Doc Type: Report

502

JOURNAL OF CLIMATE AND APPLIED METEOROLOGY

VOLUME 23

TABLE 2: HIPLEX-L physical hypothesis.

For the seeded clouds, the sequence of events leading to the changes
in the precipitation characteristics of the clouds is hypothesized to
be as follows (response variables and final test statistics associated
with each step of the hypothesis are indicated in parentheses and
are defined further in Table 3):

I) An average ice-crystal concentration of about 10 L -I is produced
in the supercooled water cloud at temperatures higher than -100C.
The initial ice-crystal concentration in the unmixed seeding plume
will be considerably higher to allow for the effects of diffusion. The
average ice-crystal concentration produced by seeding in these warmer
cloud regions is higher than found in unseeded clouds at comparable
times after treatment.* (CIC2, CIC5)

2) Ice crystals grow by diffusion to a size where riming occurs,
so that higher concentrations of rimed crystals appear in seeded
clouds at comparable times after treatment. The seeding-produced
crystals tend to develop as columns. Crystals found at these tem-
peratures in unseeded clouds at comparable times after treatment
tend to have habits characteristic of growth at lower temperatures.
(CCR5, FCC5)

3) Rimed ice crystals in the liquid portions of the cloud grow by
accretion to graupel on the order of I mm in diameter and in con-
centrations of about 0.1 L -1, which then fall through the cioud.
Accretional crystal growth is accompanied by a decrease, relative to
the unseeded clouds at comparable times after treatment, in liquid
water concentration. The ice crystals produced by seeding have a
significant advantage over those that occur in unseeded clouds because
they originate earlier, in the lifetime of the cloud. This leads to the
earlier appearance of precipitating ice particles in the seeded clouds,
so, that greater concentrations and larger sizes of such particles are
present at comparable times after treatment. (PIC8, MVD8, A WC8,
TFPI)

4) Radar first echoes develop earlier in seeded clouds than in
unseeded clouds. (TFE)

5) Precipitation falls from cloud base in the form of graupel and/
or rain (melted graupel) earlier in the lifetime of the seeded cloud
and in greater volume than occurs in unseeded clouds. In addition,
a larger proportion of seeded clouds than unseeded clouds will produce
rain. (TlPA, TlPR, TIPB, RERC, AER, A VRA, A VRC, PCPA,
PCPR)

6) Rain at the ground, averaged per experimental unit, is greater
for seeded clouds than for unseeded clouds. (No measurements of
rain at the ground are available for HIPLEX-I.)

* "Treatment" refers to the release of seeding material from the
seeding aircraft (in which case the cloud is seeded) or the activation
of a placebo mechanism (resulting in an unseeded cloud).

crease both the probability and the amount of precip-
itation from the test case clouds.
The statement of the physical hypothesis in Table
2 describes the expected sequence of events with em-
phasis on differences between seeded and nonseeded
clouds. Those differences are expressed in a form com-
patible with the measurement capabilities available for
the experiment. Elements in a hypothesis that are. not
subject to verification in the experiment, like Step 6
of the HIPLEX-I hypothesis, are of little substantive
value in the experimental design. (It was recognized
at the outset that no feasible raingage network would
be able to measure the rainfall from the HIPLEX-I
clouds, because they were so small.) No hypothesis
was spelled out for the Class B clouds, because there

were uncertainties about the possible effects ofic~ mul-
tiplication or dynamic processes. It was expected that
the essential elements of the hypothesis in Table 2
would probably also be valid for Class B clouds.
For each step in the physical hypothesis, one or
more response variable was defined and measured to
monitor the progress of the cloud behavior in com-
parison to that hypothesized. Table 3 contains a list
of the response variables for HIPLEX-l. The defini-
tions of the variables generally indicate when they were
measured; the locations of the measurements are dis-
cussed in the following section and in the Appendix.
Some degree of redundancy exists in the list of re-
sponse variables. For example, CIC2 and CIC5 both
indicate the ice-particle concentrations shortly after
the treatment time. There was some uncertainty about
just when the increased concentrations due to dry-ice

TABLE 3. Primary and secondary response variables and final test
statistics.

I CIC2
2 CIC5
3 CCR5
4 PIC8
5 MVD8
6 AWC8
7 TFPI
8 TFE
9a TIPA
9b TIPR
lOa RERC
lOb AER

Primary response variables:

Cloud ice concentration, 2 min after treatment
Cloud ice concentration, 5 min after treatment
Concentration of crystals rimed, 5 min after
treatment
Precipitating iCe number concentration, 8 min
after treatment
Mean volume diameter of precipitating ice
particles, 8 min after treatment
Average liquid water concentration, 8 min after
treatment
Time to first precipitating ice (particles with
diameters ~ 0.6 mm in concentrations> 0.1
L-')
Time to first SWR-75 radar echo (15 dBz)
Time to initial precipitation at + 100C level,
aircraft measurement
Time to initial precipitation at + 100C level,
SWR-75 radar (15 dBz)
Radar-estimated rainfall at + 100C level, using a
constant Z-R relationship
Aircraft-estimated rainfall at + 100C level

FCC5

Secondary response variables:

2 M2EA
3 M3EA
4 D2EC
5 D3EC
6 MAXZ,
7 TIPB

Final test statistics:

la PCPA

I b PCPR

2a A VRA

2b A VRC

Fraction of crystals which are columnar, 5 min
after treatment
Maximum area of the 20-dBz echo
Maximum area of the 30-dBz echo
Time duration of the 20-dBz echo
Time duration of the 30-dBz echo
Maximum radar reflectivity factor
Time to initial precipitation at cloud base (15-
dBz echo on SWR-75 radar)

Proportion of experimental units that precipitate,
based on TIPA
Proportion of experimental units that precipitate,
based on TIPR
A verage volume of precipitation per experimental
unit, based on AER
A verage volume of precipitation per experimental
unit, based on RERC