WMOD00372

• Project Name: High Plains Cooperative Program
• Title: The Design of HIPLEX-1
• Date: 4/1/1979
• Weather Modification - Doc Type: Report

is opened, the cloud automatically qualifies as an experimental unit
for the purposes of the a priori evaluation, even though tnere may be
subsequent difficulties in aircraft operations or the clouQ is sub-
sequently determined to be an invalid experimental unit (these clouds
may be deleted as part of the a posteriori evaluation). The seeding
rate with dry ice pellets to achieve the desired ice-crystal concentra-
tion, if the random decision is to seed, will be about 0.1 ,kg/km. A
placebo technique will be used to prevent the crew of the ~eeding
aircraft from knowing the seed/no-seed decision (see secti~n X and
appendixes 0 and E for further details on the seeding strategy, the
placebo technique, randomization procedures, and bias-safeguarding
procedures in general). '

C. First Posttreatment Pass

::.-

The King Air cloud physics aircraft* will penetrate the experimental
unit 2 minutes after treatment**, 300 m (1000 ft) below the treatment
altitude, to document the following response variable:

The average concentration of ice crystals (CIC2) over a 1-km
distance that is within +2 km of the closest distance to the point
of maximum liquid water content on the pretreatment pass (hereafter
referred to as the pointer) and that has an average liquid water
content greater than 0.1 g/m3 and the maximum ice-crystal
concentration. A second pointer***, determined by the maximum
ice-crystal concentration, is also set.

i

* All posttreatment passes for the airborne measurement of response
variables will be made by the King Air cloud physics aircraft.
** For uniformity, the treatment time is assumed to be 30 seconds
after the dry ice dispenser motor is activated~ This allows the
pellets time to reach the desired region of the cloud.
*** The King Air uses three "pointers," one set during the pretreat-
ment pass, a second set during the first posttreatment pass, and a
third set during the first pass through the rain shaft at the +10 oc
level, to guide the aircraft to fixed points for repeated passes
through the cloud and rain shaft. Each pointer is in a floating
frame of reference independent of the ground and consists of a
two-dimensional integration of heading and true airspeed performed by
the onboard computer. Setting the pointer sets the integra~ion to
zero. For the aircraft to return to the pointer, it is flown to the
horizontal position at which the subsequent integration of neading
and true airspeed returns to zero. It is assumed that the ~ircraft
and the cloud drift with the wind equally.

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