WMOD00439

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

Reprinted from JOURNAL OF CLIMATE AND ApPLIED METEOROLOGY, Vol. 23, No.4, April 1984
American Meteorological Society
Printed in U.S,A.

HIPLEX~l: Experimental Design and Response Variables

PAUL L. SMITH

Institute of Atmospheric Sciences, South Dakota School of Mines and Technology, Rapid City, SD 57701

ARNETT S. DENNIS AND BERNARD A. SIL YERMAN

Division of Atmospheric Resources Research, U.s. Bureau of Reclamation, Denver, CO 80225

ARLIN B. SUPER AND EDMOND W. HOLROYD, III
u.s. Bureau of Reclamation, Montrose, CO 81401

WILLIAM A. COOPER
,

University of Wyoming. Laramie, WY 82070

PAUL W. MIELKE, JR. AND KENNETH J. BERRY
Colorado State University, Ft. Collins, CO 80523

HAROLD D. ORVILLE AND JAMES R. MILLER, JR.
Institute of Atmospheric Sciences, South Dakota School of Mines and Technology, Rapid City, SD 57701
(Manuscript received 23 December 1982, in final form 21 October 1983)

. ABSTRACT

The design and conduct of HIPLEX-I, a randomized seeding experiment carried out on small cumulus
congestus clouds in eastern Montana, are outlined. The seeding agent was dry ice, introduced in an effort to
produce microphysical effects, especially the earlier formation of precipitation in the seeded clouds. The earlier
formation was expected to increase both the probability and the amount of precipitation from those small
clouds with short lifetimes. The experimental unit selection procedure, treatment and randomization procedures,
the physical hypothesis, measurement procedures and the response variables defined for the experiment are
discussed. Procedures used to calculate the response variables from aircraft and radar measurements are sum-
marized and the values of those variables for the 20 HlPLEX-1 test cases from 1979 and 1980 are tabulated.

1. Introduction

The main purpose of the HIPLEX program con-
ducted by the U.S. Bureau of Reclamation was to re-
duce the scientific uncertainties concerning both nat-
ural and artificially modified precipitation processes
in warm season convective clouds of the High Plains
regionloftheUnited States. This objective evolved out
of some earlier convective cloud seeding experiments
in the Dakotas (Dennis et al., 1975a,b) and elsewhere
that yielded evidence of rainfall increases, but did not
achieve an acceptable level of scientific confirmation.
The HIPLEX program began in 1973, and an overall
experimental approach was dcvelopeQ by the Illinois
State Water Survey (ISWS, 1976). The ISWS report
advocated a three-phase approach beginning with ex-
ploratory studies in the geographical region of interest
(Phase 1), continuing on to experiments on single
clouds or cloud systems (Phase 2), and then to an area

@ 1984 American Meteorological Society

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experiment (Phase 3). The proposed approach was
similar in many respects to that adop,ted by Braham
et al. (1957). The ISWS report emphasized the design
of Phase 2, the single-cloud experiment. While exper-
iments of that sort had been conducted previously in
the High Plains region and elsewhere, it was anticipated
that increased scientific knowledge and improved air-
craft and radar measurement capabilities would pro-
vide a basis for increased understanding of the pre-
cipitation processes.
Exploratory studies were initiated under HIPLEX
in Montana, Kansas, and Texas in the mid-l 970s. The
studies in Montana were carried far enough by late
1977 to establish that the predominant precipitation-
forming mechanism in that area is an ice process
(Cooper, 1978b; Hobbs et al., 1980). In numerous
clouds, concentrations of ice crystals less than 1 L-}
were observed in the presence of supercooled liquid
water in concentrations of the order of 1 g m-3 at

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