Table Of ContentYih-Ho Pao
Arnold Goldburg E ditors
Clear air turbulence
and its detection
Proceedings of a symposium on
Clear Air Turbulence and Its Detection,
Organized and Sponsored by the
Flight Sciences Laboratories, Office
of the Vice Precident – Research
and Development, The Boeing
Company, Seattle, Washington,
August 14–16, 1968
CLEAR AIR
TURBULENCE
AND ITS DETECTION
CLEAR AIR
TURBULENCE
AND ITS DETECTION
Proceed1ngs of a Sympos1um on Clear Air Turbulence and Its Detection,
Organ1zed and Sponsored by the Flight Sciences Laboratory, Boeing Scientific
Research Laboratories, Office of the Vice President - Research and Develop-
ment. The Boeing Company, Seattle, Washington, August 14-16, 1968
Edited by
Yih-Ho Pao and Arnold 6oldburg
Boeing Scientific Research Laboratories
Seattle, Washington, U.S.A
SPRINGER SCIENCE+B USINESS MEDIA, LLC 1969
Library of Congress Catalog Card Number 73-76507
© 1969 Springer Science+Business Media New York
Originally published by Plenum Press in 1969
Softcover reprint of the hardcover 1st edition 1969
ISBN 978-1-4899-5617-0 ISBN 978-1-4899-5615-6 (eBook)
DOI 10.1007/978-1-4899-5615-6
All rights reserved
No part of this publication may be reproduced in any
form without written permission from the publisher
PREFACE
Clear air turbulence is a part of the atmospheric
environment in which aircraft and aerospace vehicles func
tion and hence is of interest to The Boeing Company. The
characteristics of clear air turbulence can be important
in the design for structural strength and for stability and
control characteristics of airplanes and aerospace vehicles.
The detection and avoidance of clear air turbulence can be
important to airfleet operation for passenger safety and
comfort as well as for economic and mission performance.
This Symposium brought together for meaningful dis
cussion three different groups of research workers in clear
air turbulence: those interested in fundamental aspects
of clear air turbulence; those measuring clear air turbu
lence; and those attempting to detect clear air turbulence
at remote distance.
The success of the Symposium is due in direct measure
to the quality of the papers and the seriousness of purpose
of those participating. We wish to thank the invited
speakers, the session chairmen, and the participants for
their efforts towards this goal.
George S. Schairer
Vice President
Research and Development
Guilford L. Hollingsworth
Director
Boeing Scientific Research Laboratories
FOREWORD
Clear air turbulence and the related atmospheric motions
have attracted much attention in recent years. The clear
air turbulence problem becomes more acute with the advent
of high-speed, high-flying and large (thus, more flexible)
jet airplanes which interact with clear air turbulence in
terms of structure, stability, and control across an
increasing range of wavelength scales. Clear air turbulence
also presents a problem in communication since it scatters
signals transmitted by electro-magnetic waves. Clear air
turbulence studies have become an integral part of the Glo
bal Atmospheric Research Program because energy dissipated
at the small scale by clear air turbulence influences global
weather phenomena.
Important as the problem is, however, the term "clear
air turbulence" is not universally agreed upon. The pheno
menon is also often referred to as "critical atmospheric
turbulence" and as "internal (to the atmospheric layer)
turbulence." In the published literature it seems to en
compass a variety of irregular fluctuating motions in a
clear atmosphere at high altitude. Some of these motions
are undulant rather than truly turbulent. For simplicity,
we use the popular term "clear air turbulence" to represent
undulant and turbulent motions in a clear atmosphere.
It has been three years since the 1965 Boeing Scienti
fic Research Laboratories "Lecture Series on Atmospheric
Turbulence and Its Detection (Seattle, Washington, June
October 1965)". It has been two-and-a-half years since the
"National Conference on Clear Air Turbulence (Washington,
D. C., February 1966)". Since these meetings, considerable
research has been accomplished contributing to a better
knowledge of clear air turbulence (CAT). It was the purpose
of this Symposium to present a comprehensive picture of and
to review the recent developments in CAT, especially:
(i) theories and measurements concerning the origin and the
structure of CAT, (ii) methods for forecasting CAT, and
(iii) methods for the remote detection of CAT. Special
emphasis was placed on clear air turbulence in the upper
troposphere and in the stratosphere.
We believe that the principal conclusions reached at the
Symposium on the nature of CAT and its detection methods
were:
vi
FOREWORD vii
(i) The energy dissipated at small-scale by clear air
turbulence influences the large-scale atmospheric motion.
(ii) The vigorous mixing caused by clear air turbulence
changes the meso-scale structure of the atmosphere.
(iii) Clear air turbulence derive~ from the ordered
meso-scale motion of the atmosphere. The larger and faster
airplanes tend to interact with the longer wavelengths of
the clear air turbulence which is strongly influenced by
the meso-scale motion. The relation between CAT and this
ordered motion must be better understood.
(iv) Severe clear air turbulence at high altitude often
occurs in sloping flows. How disturbances amplify in these
sloping flows is crucial to the understanding of the origin
of clear air turbulence.
(v) Clear air turbulence at high altitude is often
sporadic and patchy, and often occurs in a strongly stable
region.
(vi) It is believed that the severe clear air turbu
lence is essentially non-stationary and inhomogeneous.
Fundamental understanding of these stochastic processes is
lacking.
(vii) From the airborne measurements of severe CAT,
gaps occur in the low wavenumber portion of the turbulent
velocity spectra, while the spectra at high wavenumbers,
where CAT is expectea to be locally homogeneous and tem
porally stationary, follows the Kolmogorov -5/3 law. It
is believed that the gaps in the spectra are caused by the
presence of internal waves.
(viii) There appears to be some correlation between
CAT and certain meteorological patterns. Synaptical analyses
of these relations results in CAT forecasting techniques.
However, CAT also occurs in situations with no apparent
significant meteorological pattern. There is an urgent
need to understand the origin of CAT in relation to the
meso-scale and macro-scale atmospheric structure.
viii FOREWORD
(ix) Very sensitive radars which are capable of sensing
refractive index fluctuations in the atmosphere appear to be
a promising method for detecting clear air turbulence. How
ever, the correlation between the intensity spectrum of the
clear air turbulence and the radar return signature remains
to be investigated and synthesized in detail. At present,
it is too expensive to have a network of such radars for
CAT detection for routine operational airline use.
(x) IR detection methods may have promise, but present
IR detectors for CAT sense the overall temperature variation
in a relatively large volume of air, and do not measure the
local temperature fluctuations.
(xi) Coordinated simultaneous measurements of CAT with
sensitive radars, IR detection equipment, ~n ~~u measure
ments with airplanes, radiosondes, and Jimspheres at a
given spatial region, should be encouraged in the future.
These investigations, when carried out, will yield perti
nent information as to: the origin and the structure of
CAT, its relation to the meteorological conditions, and
the relation between the intensity spectrum of CAT and the
signaLs from remote detection.
The Symposium was organized and sponsored by the Flight
Sciences Laboratory, Boeing Scientific Research Laboratories.
All papers were by invitation only. This Symposium Proceed
ings contains 27 papers, with discussions at the end of each
paper, and the Panel Discussion. Since the field of clear
air turbulence is a rapidly evolving one, the editors felt
it was important at this time to include all three types
of papers: the review article presenting introduction to
the subject; the report on finished research presenting
phenomena now understood; and the report on research in
progress presenting phenomena which are not yet explained.
The Symposium Proceedings is divided into five parts:
Part I is concerned with the origin and the structure of
CAT; Part II contains the recent observational results
and data analyses of CAT; Part III is devoted to methods
for forecasting CAT; Part IV is concerned with the methods
for the remote detection of CAT; Part V is the log of Panel
and Floor Discussions and the Conclusion.
FOREWORD ix
The editors wish to thank Miss Edna R. Holmes for com
piling the Authors' Index and Mr. J. Michael Hall for com
piling the Subject Index.
The editors wish to express their appreciation to
Professor Ronald F. Probstein for suggesting that these
Proceedings be collected in permanent form and to Mr. Robert
Ubell and Plenum Press for their aid and cooperation.
Yih-Ho Pao and Arnold Goldburg
Editors
Seattle, Washington
October 1968
ACKNOWLEDGMENTS
I wish to thank the following persons whose suggestions
and comments have helped to form the Symposium program:
Professor Hans A. Panofsky, Professor David Atlas, Mr. Neal
V. Loving, Professor John A. Dutton, and Messrs. William
Moreland and E. M. Hansen.
I particularly appreciate the cooperative response of
the invited speakers in agreeing to participate in the
Symposium and in providing so promptly the summaries of
their papers before the Symposium and the final manuscripts
after the Symposium.
I would like to thank the Session Chairmen, Professor
Robert G. Fleagle, Professor Robert W. Stewart, Professor
Joost A. Businger, Professor Leslie S. G. Kovasznay, and
Professor David Atlas, for the smooth operation of their
sessions.
I am grateful to Mr. Michael E. Callahan for his
superb effort in coordinating the Symposium and for arrang
ing the Symposium social functions, and to Mr. Robert
Carlsen for handling the discussion sessions and arranging
the questions and comments in sequence. I am indebted to
Miss Sarajane Beal for her assistance in distributing the
Symposium programs and for typing the pre-symposium communi
cation, and editing the Summaries of Papers, and to Mr.
Donald Fenton for handling the printing of the Summaries
of Papers and arranging figures for the Proceedings.
The final manuscripts of the Proceedings were retyped
by the secretarial staff of Boeing Scientific Research
Laboratories, in particular, I wish to thank Miss Edna R.
Holmes, Mrs. Pat Easthom, Miss Sarajane Beal and Hiss
Victoria A. Caraway for their typing effort. I would also
like to thank Dr. M. E. Smithmeyer for her help in proof
reading some of the retyped manuscripts.
Finally, I would like to thank Dr. Arnold Goldburg for
his encouragement and support.
Yih-Ho Pao
Symposium Chairman
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