WMOD00319 ‎(2)‎

• Title: Comparison of Cloud Model Predictions: A Case Study Analysis of One- and Two-Dimensional Models
• Date: 6/11/1975
• Weather Modification - Doc Type: Report

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COMPARISONS OF CLOUD MODEL PREDICTIONS:
A CASE STUDY ANALYSIS OF ONE- AND TWO-DIMENSIONAL MODELS

By

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B. A. Silverman, D. A. Matthews, L. D. Nelson
Bureau of Reclamation
Division of Atmospheric Water Resources Management
Denver, Colorado

And

H. D. Orville, F. J. Kopp, R. D. Farley
South Dakota School of Mines and Technology
Rapid City, South Dakota

1.

INTRODUCTION

One measure of our understanding of
cloud and precipitation processes is our ability
to simulate the essential features of their
behavior through numerical cloud models. Nodel
development will progress most rapidly when
modelers and observationalists interact iteratively
with feedback from one to the other in a mutually
supportive fashion. Unfortunately, this approach
has been only seldom followed.

, A convective cloud modeling workshop
was convened by the Bureau of Reclamation's
Division of Atmospheric Water Resources ~~nagement
in Denver, Colorado, on June 11-13, 1975. The
main objective of this workshop was to design a
specific and continuing effort to close the gap
between models and observations and thereby
maximize the utility of models to contribute to
our understanding of natural and artificially
modified convective clouds. The workshop focused
its discussions on (1) model initialization data
requirements; (2) model verification data require-
ments, including the method or methods by which
model predictions can be bime-synchronized with
observations of cloud development; and (3) objec-
tive model verification criteria.

To lay the foundation for these
discussions, each participating modeler presented
the results of his model for two standard input
data sets, which were sent to him beforehand. The
models were compared first to each other and then
against such verification data as were available,
which were first presented to the modelers at the
workshop.

Twenty-two scientists representing
several universities, Government agencies, and
industrial groups participated in the workshop.
Results from three one-dimensional, steady-state
models (lD, SS), five one-dimensional, time-
dependent models (lD, TD), four two-dimensional,
time-dependent, axi-symmetric models (2D, TD,
Axi), and two two-dimensional, time-dependent,
slab-symmetric models (2D, TD, SLAB) were
presented.

The purpose of this paper is to
summarize the results of this workshop and indicate
what follow-on work is planned or in progress.

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2.

MODEL PREDICTIONS AND OBSERVATIONS

Data used in the workshop were
collected on August 10 and 17, 1973, in the
vicinity of St. Louis as part of Project Metromex.
They were graciously provided by Dr. Bernice
Ackerman of the Illinois State Water Survey, who
also participated in the workshop. Input rawin-
sonde soundings and supporting data that were used
to initialize the models are shown in figures 1
and 2 and table 1, respectively.

It can be seen from figures 1 and 2
that the sounding for August 10 was quite unstable
while that for August 17 was not so unstable.
This resulted, as we shall see later, in the
development of clouds with different growth and
precipitation characteristics, which is the reason
,why these 2 days were selected for the workshop cases.
Since the input and verification data sets were
limited, we were anxious to see if the model
predictions could at least distinguish the nature
of the convective activity on these 2 days.

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STLSt 0
INrTlAL SOUNDING AT 13 HR 0 HIN

Figur>e Z. Skew-T, Log-P thermodynamic d-iagram
showing initial sounding temperature and dewpoint
profiles for st. Louis, Mo., on August ZO, 1973,
at l300 L.S.T.

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