The Jet Stream

108 Pages·1954·22.699 MB·English

by  H. Riehl, M. A. Alaka, C. L. Jordan, R. J. Renard (auth.)

METEOROLOGICAL MONOGRAPHS
BOARD OF EDITORS
Editor
E. WENDELL HEWSON
University of Michigan
Associate Editors
J. J. GEORGE H. E. LANDSBERG
Eastern Air Lines United States Weather Bureau
A. H. GLENN R. B. MoNTGOMERY
A. H. Glenn and Associates Woods Hole Oceanographic Institution
Ross GuNN H. A. p ANOFSKY
United States Weather Bureau Pennsylvania State University
W. C. jACOBS c. M. PENNER
Air Weather Service Meteorological Service of Canada
J. KAPLAN H. RIEHL
University of California, Los Angeles University of Chicago
•
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METEOROLOGICAL MONOGRAPHS.
Volume 2 August 1954 Number 7
THE JET STREAM
by
H. Riehl,
M. A. Alaka,
C. L. Jordan, and
R. J. Renard
with a
FOREWORD
by
F. A. Berry
PUBLISHED BY THE AMERICAN METEOROLOGICAL SOCIETY
3 JOY ST., BOSTON 8, MASS.
ISBN 978-1-940033-09-9 ((e Book)
DOI 10.1007/978-1-940033-09-9
PREFACE
The first seven chapters of this publication were given limited distribution as
NAVAER Report 50-1R-249, 1 June 1953, of the Navy Department. Much new
material on the jet stream has appeared since these chapters were prepared. A new
chapter has accordingly been written which serves to bring up to date the jet stream
account as of 1 April1954. Each subsection of chapter VIII reviews recent research on
the topics covered in the corresponding chapters of the NAVAER Report. For example,
subsection 3 of chapter VIII entitled "Climatology" extends the discussion in chapter
III entitled "Climatology of the jet stream."
We are indebted to the Bureau of Aeronautics of the Department of the Navy for
permission to publish Report 50-lR-249 in this augmented form, and for their coopera
tion in facilitating publication.
In the FOREWORD that follows, Captain F. A. Berry outlines the considerations
which led to the preparation of the Report. The present publication presents the
Report with additions to a wider audience.
HERBERT RIEHL
1 June 1954
111
FOREWORD
It is true in many fields of science that the requisite data for the revision of an
antiquated hypothesis or the development of a new theory are available long before
the actual formulation of a neoteric concept. Such has been the case of the Jet Stream
in the science of Meteorology.
As early as 1933, a cross-section depicting a relatively narrow, high-speed stream
of air in the upper westerlies was published in the text, Physikalische Hydrodynamik.
The implications of this cross-section were disregarded by the authors themselves,
possibly in view of the inadequacy of the observational material upon which it was
based. Eleven years later, in 1944, Dr. Hurd C. Willett published mean cross-sections
pertaining to the North American continent which also substantiated the existence of a
meandering, high-velocity stream of air particles in the upper tropospheric regions.
It wasn't until the year 1946, however, that this latest meteorological phenomenon
became the object of rather intensive research at a Navy-sponsored research project at
the University of Chicago and that its numerous potentialities were gradually being
recognized.
Subsequent to that time, considerable research on the subject has been conducted
by various individuals and institutions at different geographical locations, with the
result that a great deal of uncoordinated and sometimes controversial material has
been presented. This material has appeared in divers professional journals, bulletins
and periodicals, not readily available to the Naval Aerologist in the field or afloat.
Because of the tremendous import and the numerous potentialities of this newly
discovered phenomenon, it was deemed imperative that an evaluation and summary
of existing research and data on the Jet Stream be compiled under a single cover and
distributed to the Naval Aerological Service as soon as possible. Accordingly, Task 6
(TED-UNL-MA-501.6), JET STREAM ANALYSIS, was assigned to Project AROWA
by Bureau of Aeronautics letter Aer-MA-5 serial 24803 dated 14 March, 1951, for
prosecution and/ or coordination.
This document is the coordinated effort in the fulfillment of this purpose. Much of
the material ·presented herein is based on lectures by Dr. Herbert Riehl of the
Department of Meteorology, University of Chicago, who also edited the manuscript.
Intimately associated with the entire project, also, were Messrs. M. A. Alaka, C. L.
Jordan, and R. J. Renard of the Department of Meteorology, University of Chicago.
This publication encompasses the synoptic structure of the Jet Stream, as well as
its climatology and relation to middle latitude cyclones and extended forecasting. In
addition, one chapter is devoted to the techniques and procedures of high-level wind
analysis. The dynamic principles relating to Jet Stream formation and maintenance
are also incorporated.
Much of the information presented herein has been derived from a great variety
of source material, with the result that several different units of wind speed are ex
pressed throughout. It is regretted that time did not permit the conversion of the
various units to one system.
F. A. BERRY
Captain, U.S. Navy
Officer in Charge .
Bureau of Aeronautics Project AROWA
iv
TABLE OF CONTENTS
Page
PREFACE by H. Riehl. ............................................................................. iii
FoREWORD by F. A. Berry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
CHAPTER I. INTRODUCTION .......................... ' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Discovery of the Jet Stream ........................................................... 0. .. 0... 1
2. Some Consequences of the Discovery of the Jet Stream ...... 3
0 •••• 0 •••• 0 ••••••••••• 0 ••••••• 0 ••• 0...
CHAPTER II. SYNOPTIC STRUCTURE OF THE JET STREAM. , ... 4
o • o •••••• o ••••• o •••• o • o ••••• o • • • • • • • • • • • • •
1. The Wind Field ............ 4
0 ••••• 0 0 •••••• 0 • 0 ••••• 0 • 0 • 0 0 •••••• 0 • 0 0 •••••• 0 •••• 0 •• 0 • • • • • • • • • • • • •
2. The Field of Temperature 18
0 •• 0 ••••••• 0 •••••••••• 0 • 0 •••••••••••• 0 • 0 ••• 0 • 0 0 0 0 •••• 0 • • • • • • • • • • • • • • •
CHAPTER III. CLIMATOLOGY OF THE JET STREAM .................. 23
o. o •••••••• 0 ••••••••••••••••••••• o.
1. Seasonal Variations 23
0 •••••••••••••••• 0 •••• 0 0 •••••••• 0 0 •••••••• 0 • o, ••••• 0 • 0 0 •••••• 0 0 •••••••• 0. 0 ••
2. Influence of Large-Scale Thermal and Physical Features .............. 30
0 ••••••••••••••••••••••••••••
3. Influence of the Jet on Surface Climates ......................................... 34
0 •••••••••••••••
CHAPTER IV. THE JET STREAM IN RELATION TO MIDDLE LATITUDE CYCLONES ........................... 38
1. The Jet Stream as a Factor in the Development of Extratropical Cyclones ........... 38
0 •••••••••••••••
2. The Problem of Precipitation ........................... 44
0 ••••••••••••••••••••••••••••••••••••••
3. Appendix A .............................. 45
0 •••••••••••••••••••••••••••••••••••••••••••••••••••
CHAPTER V. THE JET STREAM IN RELATION TO EXTENDED FORECASTING ................................ 48
1. The Problem of Extended Forecasting 48
0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
2. Hemispheric Circulation as a Factor in Extended Forecasting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
CHAPTER VI. HIGH LEVEL WIND ANALYSIS ........ 55
0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
1. Introduction ................... 55
0 • 0 ••••••••• 0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
2. Appendix A.-Gradient Wind Nomograms ..... 64
0 ••••••••••••••••••••••••••••••••••••••••••••••••••
3. Appendix B.-Estimating Wind Speeds in the Jet Stream ......................................... 65
CHAPTER VII. DYNAMIC PRINCIPLES RELATING TO JET STREAM FORMATION AND MAINTENANCE ......... 67
o • • •
1. Formulation of the Problem ......................... 67
0 ••••••••••••• 0 •••••••••••••••••••••••••••
2. The Similarity Between the Jet Stream and Ocean Currents ..... , ................................. 68
3. Lateral Mixing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4. Balance of Momentum .......... 74
0 •••••••••••••••••• 0 •••••••••••• 0 ••••••••••••••• 0 •••• 0 •••• 0 •••
5. On the Formation of Regional Jets ... 78
0 •••••••••••••••••••••••••••••••••••••••••••••••••••••••••
6. Experiniental Analogues to Atmospheric Motions 78
0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
REFERENCES. . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
INDEX ........................................................................................... 84
CHAPTER VIII. JET STREAM RESEARCH, 1952-54 ...................................................... 86
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
2. Synoptic Structure .......................... 86
0 •••••••••••••••••••••••••••• • • • • • • • • • • • • • • • • • • • • • •
3. Climatology ................... 90
0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
4. Middle Latitude Cyclones and Weather ............................................... 91
0 ••••• 0 •••
5. The Jet Stream on the Hemispheric Scale. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6. High Level Wind Analysis ..... , ............. 95
0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
REFERENCES (continued) ................................................... , ...................... 100
v
CHAPTER I. INTRODUCTION
1. Discovery of the Jet Stream
During World War II, American pilots flying high but increases upward when the isotherms slope ver
altitude bombers over Japan with air speeds exceeding tically. The currents move with constant speed at all
250 mph, at times, encountered head winds so strong heights when the isotherms are level. A wind discon
that they found themselves in the unenviable predica tinuity marks the front where the temperature gradient
ment of remaining stationary over their target areas. is concentrated.
Such surprisingly strong winds had not been visual· The essential features of this model enjoyed accept
ized for the upper troposphere by atmospheric models ance in most meteorological circles during the interval
then in vogue. These models were based on the concept between the two world wars. Observations verified them
of air masses of broad horizontal extent, with proper to a satisfactory extent up to 10,000 feet beyond which
ties depending on their source and their history, and the atmosphere was not systematically explored. In the
separated by a surface of discontinuity or a finite low levels, it is an observed fact that wind speed varies
transition zone-a front (fig. l.l). Within the indi little with latitude. To the extent that the classical mod
vidual air masses, the isotherms are level or have a els discuss the currents in the upper troposphere, they
uniform slope. The wind speed is uniform at any level largely extrapolate from the lower levels. They do not
visualize a concentration of high velocities in narrow
Frontal Surface regions. Thus, the very strong winds encountered by
the bombers introduced a feature of the circulation in
T the westerlies that was not allowed for by existing
T Homoveneous T+l models.
T+l
T+2 The earliest intimation of the existence of a narrow,
T+2
T+3 T+3 high velocity region in the upper westerlies appeared
T+4 T+4 in a cross-section published in Physikalische Hydro
T+5
dynamik [12] (fig. 1.2). It revealed that the kinetic
N s energy of the westerlies in the upper troposphere was
(a)
not evenly distributed with latitude, in marked con
trast with the lower layers. This initial indication of
the modification which our concepts of atmospheric
structure were to sustain later on, did not attract much
attention at the time of its publication.
In 1944, Willett [108] published mean cross-sections
over North America (fig. 1.3) which again featured
U+2-T- - a localized high velocity stream in the upper westerlies.
U+I!~ Together with the analyses of upper-air data compiled
T+2
u _.I±~- during the war, these sections made it clear that a
revision of the concepts regarding the structure of the
N s upper westerlies was in order.
(b)
Simultaneously with these synoptic developments,
:F;c. 1.1: Schematic representation of the wind and tempera· and to a great extent stimulated by them, theoretical
ture fields in the vicinity of a frontal surface according to classi· investigations [82, 102] sought to discover the dyna
cal concepts: (a) level isotherms and a uniform current in each mic principles responsible for these high winds the im
air mass; (b) sloping isotherms and currents (u, u') increas
ing uniformly with height. portance of which, at least from the point of view of
I
2 THE JET STREAM
air navigation, was easy to appreciate. Rossby [82]
suggested that thermally driven lateral mixing asso·
ciated with a tendency toward equalization of the verti·
cal component of the absolute vorticity with latitude
brought about, from time to time, an accu~ulation of
the kinetic energy of the westerlies at the tropopause
level equatorward of lat. 50°. His theory ( cf. chap.
VII) required that these maxima should increase in
intensity as they were displaced equatorward toward
lat. 30°. A paper published in the same year by Staff
Members of the Department of Meterorology, Univer·
sity of Chicago [102], showed that the zonal winds
observed at the tropopause during periods of straight
west wind circulations appeared to agree fairly well with
profiles computed on the basis of equalization of the·ver·
tical component of the absolute vorticity. The same
paper also furnished synoptic evidence corroborating
Rossby's statement that the flow configuration aloft in
middle latitudes is suggestive of a broad stream me
andering eastward around the hemisphere in wavelike
patterns. The kinetic energy of this stream is concen
trated in a narrow band of high wind speed embedded
in a relatively quiescent surrounding atmosphere. This
FlG. 1.2: Mean vertical distribution of zonal component of
geostrophic wind in northern hemisphere for February [12]. narrow band was named the JET STREAM.
Dl¥ofiOA t
21 kloo --------~~~----~--------~~~=-----~-----r-----t--~~~~~~~~--~,.~----IIKM
20
"
•
17
16
~s
14
13 w
12
II
10
9
T
•
7
6
~
4
0
3
2
i
.i.;. JI ~i•i i .SI. I~ ~I
Fie. 1.3: Vertical cross-section of pressure (mb), temperature (°C) and wind (knots) for North Amenca during winter [108].
INTRODUCTION 3
2. Some Consequences of the Discovery of the Jet Stream
The discovery of the jet stream was destined to have nence as an important feature of the general atmospheric
far-reaching consequences. It revealed, for instance, a circulation, it has become known as a significant factor
striking similarity between the structure of the atmos in diverse weather phenomena ranging from cyclogene
phere and that of major oceanic currents like the Gulf sis in middle latitudes [68] to the "hurst of the
Stream. The establishment of this similarity is of much monsoon" over India [115] and rainfall over the Ha
importance, since features known to exist in one fluid waiian Islands [114]. Of particular importance is the
give a clue as to what to look for in the other. This role it plays in the problems of short- and long-range
leads to a better understanding of both. Further, in forecasting (chaps. IV and V), and in understanding
the few years since the jet stream came into promi- the climate of middle latitudes (chap. III).