WMOD00438

• Title: HIPLEX: A Cooperative Program on Rain Augmentation in the High Plains
• Date: 6/1/1984
• Weather Modification - Doc Type: Report

showed that many of the seeding opportunities there
were associated with severe weather. In order to
avoid even the appearance of contributing to hazard-
ous weather. the HIPLEX managers decided not to
seed clouds in Kansas. These factors. combined with
a need to consolidate the available resources of
equipment and personnel. led to a decision to end
the observational program'in Kansas in the fall of
1978.

The four-station network of rawinsonde stations set
up in 1976 in Texas was expanded to seven stations
in 1979. Cloud physics data were collected byair-
craft and limited seeding trials were conducted in
Texas each summer from 1976 to 1979. but the
trials did not lead toa statistical experiment.

Continued progress at Miles City led to the design
of a statistical experiment on cumulus congestus
clouds called HIPLEX-l. It was started in 1979 and
continued through 1980. It involved the testing of
a detailed physical hypothesis linking dry ice seeding
at cloud top to production of rainfall at cloud base~
Details are given in section 6.

A network of automated surface weather stations
was deployed in eastern Montana in 1 980 following
tests in both Texas and Montana in earlier years. The
primary purpose was to search for covariates (or pre-
dictor variables) which might predict characteristics
of corwective complexes such as location ~nd onset
of the storm. its eventual magnitude. possibilities of
severe weather. etc.

During the summer of 1981. the Miles City field
office was used as the base for CCOPE. CCOPE was
jointly supported by the Bureau and NCAR (National
Center for Atmospheric Research). It involved nu-
merOus other agencies. universities. and private
firms. A total of 14 aircraft and 8 radar sets were
used. and the Montana mesoscale network was
expanded to 123 stations. The CCOPE program was
designed to provide a foundation for continued
experiments on the larger cloud complexes. Details
are given in section 5.7.

HIPLEX-1 was suspended for 1981 to make way for
CCOPE. It had been expected that HIPLEX-l would
resume in 1982. Resumption was precluded by the
Administration's 1981 decision to terminate HIPLEX
as part of a program to cut Government
expenditures.

The planned progression from experiments on indivi-
dual clouds to experiments involving areawide rain-
fall was not completed atany of the three field sites.
Nevertheless. HIPLEX advanced considerably our
knowledge of precipitation processes in cumulus
clouds and the potential for modifying them to

, increase rainfall and the technolog~' necessary to
accomplish such modification.

Early calibration seeding experiments were per-
formed at Big Spring and at Miles City with twin
piston-engine aircraft. which proved sluggish in per-
formance compared to the speed of cloud growth
and decay. The evident need for fast4:}r aircraft with
higher operational altitudes and greslter endurance
in icing conditions led to the procurement of a Lear-
jet for seeding beginning with the 1977 season.
Cloud physics instrumentation was added to the
Learjet prior to the 1 978 season. and the jet was
equipped for dropping Agl flares as well as dry ice
pellets. Following the 1978 season. dry ice was used
exclusively. The more predictable characteristics
and known effects of dry. ice as a seeding agent were
more in line with the intent to reduce the uncertain-
ties of seeding. The use ofasingle seeding agent was
a measure taken to simplify one slspect of the
complex experiments.

Dry ice was manually released from an unpressurized
Aztec during the 1976 season at Miles City. The
Learjet pressurization. and the need for precisely
metered releases. led to the important development
of a reliable dry ice dispensing system carried inside
the pressurized cabin. It initially released the dry ice
at a Jate of about 1.0 kg/km (3.5 lb/nni). Ice crystal
concentrations higher than desired were encoun-
tered with this rate. and the rate was decreased to
aboutO.l kg/km (O.4lb/mi). or only a few pellets per
second. Even this rate may have been a bit high for
some clouds. but a lower uniform seeding rate could
not be practically achieved with the commercially
available 15-mm(0.6-in) diameter cylindrical pellets.

In 1978. a King Air turboprop aircrMt was intro-
duced. The King Air. shown in figure 2.5. was devel-
oped for cloud physics investigations by the
University of Wyoming with HIPLEX funding and
greatly strengthened the capacity of HIPLEX to
generate important cloud physics data. The aircraft
had an excellent navigation system and carried opti-
cal probes to sample cloud and precipitation par-
. ticles up to about 5 mm in diameter.

On numerous occassions throughout the years the
readings of some of the instruments on different air-
craft were compared with each other or with
independent standards. Aircraft were flown past
instrumented towers. beside other aircraft. and
through the same parts of clouds to determine
whether similar instruments were in agreement. The
further comparisons of Johnson~WllIIiams LWC
. meters and similar instruments in a supercooled wind
tunnel by Canadian participants in HIPLEX were an
. especially significant contribution to tho understand-
ing of this important measurement.

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