WMOD00531

• Title: Raingage Network Requirements from a Simulated Convective Complex Weather Modification Experiment
• Date: 7/14/1980
• Weather Modification - Doc Type: Report

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1176

JOURNAL OF APPLIED METEOROLOGY

VOLUME 19

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Raingage Network Requirements from a Simulated Convective Complex
Weather Modification Experiment

JAMES A. HEIMBACH, JR.!
University of North Dakota. Grand Forks. ND 58202

ARLIN B. SUPER

Water and.Power Resources Service. U.S. Department of the Interior, Miles City, M:r 59301
(Manuscript received 18 March 1980. in final form 14 July 1980)

ABSTRACT

A convective complex weather modification experiment was simulated using Monte Carlo techniques.
The purpose was to estimate the optimum raingage density for evaluation of a possible future experiment.
The data base consisted of radar volume scans made within 150 k:m of Miles City. Montana. during
. May-July 1977. A total of 103 convective complex.:s were identified and tracked from radar data.
Raingage networks of various densities were simulated under the lowest-tilt radar scans to estimate
total rainfall accumulation from each complex. Randomly chosen rainfall amounts were increased by
given percentages to simulate assumed seeding treatments. A Monte Carlo scheme yielded estimates of
the number of experimental units required for various combinations of a- and {3-probability levels. treat-
ment effects (percentage of increases) and raingage densities. Applying these results to the numbers of
operationally available convective complexes as a function of area gave estimates of the optimal spacing
and seasons required to detect a treatment. The results suggest that an unacceptably long field experi-
ment would be necessary to detect treatment effects of 50% or less without some stratification of pre-
cipitation data.

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1. Introduction

The High Plains Cooperative Program (HIPLEX)
is tasked with rcmovingcritical scientific uncer-
tainties from summer convective weather modifica-
tion aimed at precipitation enhancement on the
High Plains of the United States. Toward that end,
a randomized experiment, known as HIPLEX-l,
is currently being conducted with cumulus con-
gestus clouds. If this experiment is successful, it
is anticipated that future work will concentrate on
larger, more complicated cloud systems referred to
as convective complexes. This paper presents a
preliminary attempt to estimate the raingage net-
work requirements for a possiblc future weather
modification experiment dealing with convective
complexes.
Schickedanz and Changnon (1970) investigated
optimal techniques for detecting cloud seeding ef-
fects for hail suppression. Their primary concern
was the specification of the best statistical design,
e.g., random crossover. The issue of experimental
duration was addressed by Schickcdanz and Huff
(1971) who considered experimental design as re-
lated to several stratifications. In both of these

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I Present affiliation: Institute of Natural Resources, Montana
State University. Bozeman. MT 59717.

0021-8952/80/101176-08$06.00
<t'> 1980 American Meteorological Society

papers, data bases were generated from distribution
fits to gage network storm samples or haiJ pad!
observer estimates of hail streaks. This precluded
the examination of sampling variance.
Silverman (1979)2 examined the effects of sam-
pling variance in a simulation of a convective com-
plex experiment. Hypothetical raingage networks
were repeatedly placed over simulated rainfall ac-
cumulation patterns. The number of storms required
to reach specified a- and {3-probability levels in-
creased with gage spacing.
This paper considers the combined magnitudes of
the sampling variance due to the gage network and
the natural or "among-storms" variance. The work
was based on rainfall patterns, estimated by radar,
in the vicinity of Miles City, Montana.

2. Design and evaluation considerations

a. t::Xperimt'ntal design

The intent was to simulate a convective complex
(CC) weather modification experiment. Such an

% Silverman. B. A.. 1979: On the sampling variance of pre-
cipita:ion gage networks and its effect on the evaluation of pre-
cipitation augmen:ation experiments. Extended Abs/ raClJ:
Sn'etuh C()llj~'rl!nct? un lnad~'ertenl and Pi<.lnneJ W.:tJther
Modification, Banff, Alberta, Amer. Meteor. Soc.. 116-1l7.

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