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### HORACE ROBERT BYERS, Sc.D. Professor of Meteorology Texas A & M University 

# General Meteorology

FOURTH EDITIONThis book was set in Times New Roman. Theeditors were Robert H. Summersgill,BreteC. Harrison,and Susan Gamer; the cover wasdesigned byJosephGillians; and the production supervisor was ThomasJ. LoPinto. New drawings were done by John Cordes, J & R Technical Services, Inc. The Maple Press Company was printer and binder.

Library ofCongress Cataloging in Publication Data Byers. Horace Robert, date General meteorology. First ed. published in 1937 under title: Synoptic and aeronautical meteorology. I. Meteorology. I. Title. QC861.2.B9 1974 551.5 73-19886 ISBN 0-07-009500-0

GENERAL METEOROLOGY Copyright 

### © 1959, 1974 by McGraw-Hili, Inc. All rights reserved. Copyright 1944by McGraw-Hili,Inc.All rightsreserved. Formerlypublished under the title ofSYNOPTIC AND AERONAUTICAL METEOROLOGY copyright 1937 by McGraw-Hili, Inc. All rightsreserved. Printed in the United States ofAmerica. No part ofthis publication mayberepr<4 stored in a retrieval system, or transmitted, in any form orby any means, electronic, mechanical, photocopying, recording, orotherwise, without the prior written permission ofthe publisher. 4567890 MAMM 7987218 GENERAL METEOROLOGY

CfJ is 

### V", = 

### Or = 

### ORcos CfJ, where 

### r is the radius ofa latitude circle and 

### R is the radius of the earth. The relative west-to-east speed, which would be the 11 component of the wind, is /I = 

### VA

- V"" where 

### VA is the absolute west-to-east component. Conservation ofthe absolute angular momentum means that 

### VA R cos CfJ = const, or 

### VA, R cos CfJ2 = 

### VA,R cos CfJI (9-1) Consider particles displaced from the equator to 30°. Take 110 as - 5 m sec-1 (east wind at equator). Then 

### V

### Ao 

## = V",o

- 5 cos 0 

### VA,o = 

### (V",o

- 5) -30 = 1.155(V",o

- 5) cos 1130 = 

### VA,o

- V""o 1.155(V",o

- 5)

- 

### OR cos 30 

## = 1.155(464.45

- 5)

- (464.45 

### x 0.866)

= 530.7 402.2

= 128.5 m sec- 1 West winds with speeds ofthis magnitude are more than twice the speeds observed in extreme cases in the strongest high-leveljet streams. If the above example were carried to latitude 

### 60°, the wind would be at 686.7 m sec- 1. The speeds that would ! : result from conservation ofangular momentum are so far from the real speeds that one immediately realizes that something must happen to the wind system. The reduction ofthe winds to speeds that we normally observe cannot be accounted for by friction, which at least in the upper air, probably could reduce them by only a few percent. What happens is that the meridional circulation breaks down into smaller circulations. Bergeron1 depicted a system containing a meridional circulation of three cells. This system, considerably modified, is shown in Fig. 9-1. The net

, , meridional circulation is represented in vertical cross section aroundtheprofile ofthe

I earth, and the actual wind directions at the surface of the earth are shown within the circumference. Throughout the atmosphere the meridional components are on the average less than one-tenth ofthe zQnal componentsJExcept for a belt ofdeep easterlies around the equator, the upper winds are prevailingly from the west. At the surface, three wind belts are noted in each hemisphere: the trade winds of low latitudes, the middle-latitude westerli;s, and the polareasterlies.

1 T. Bergeron, ()ber die Dreidimensional Verknilpfende Wetterilnalyse, Geofysiske

Publikasjoner, vol. 5, no. 6, 1928.

# ~~~ -Rjv,£ 

# 1. I

# ---

# ----

-----

__ THE GENERAL CIRCULATION 219



### R is the radius component of Iponent. Con­
= 

### const, or
S «PI rpl (9-1) 

### «P2 

### 5 m sec- 1 

### (east



### )s 30

speeds observed ve example were ?eeds that would

.real speeds that l1d system. The be accounted for :them by only a lwn into smaller ial circulation of g. 9-1. 

### The net lthe profile ofthe are shown within Imponents are on for a belt ofdeep )m the west. At ade winds of low
.teranalyse, Geofysiske --- .. . 

# -**_._~p** QJ.JitL

__**F_~l!J:~l-Q~~J** ___**.~_**

# ~~~ 

# .­

- _---'!J> WesterlIes

__**~** • 

# ZJ**.::':-~=-==-@~~~IDJjQlC==-~.** __.

# r;**~~~** ___ olE

### ~~-=­**~_._-.---** Trade Winds <E .­



### ..

## ~=~.-~----rrl.-C1~==-~ •________**~_QJJ~IQR!~j...** __**~.Q!:'!..~~lt. ~_~**  ___ :.

### ~~~

__ Trade

### Win~

# --====-~-­**=--==--:'=:=~QB":;J'=:I~fi**tJ.LJ:

### ~­ Westerlies

__ 

# --- ------,..**~~~~~~;~~**

# ~ FIGURE 9-1 Schematicrepresentation ofthe general circulation, modified after Bergeron.



### The pressure-wind relationship applied to the surface circulation requires a belt of high pressure at about 300

### N and S of the equator. This belt is called the "horse latitudes."l Low pressure is required between the westerlies and the polar easterlies. Except for the easterlies of the trade-wind belt, the surface wind systems are quite variable. Thecontinents develop thermallyinduced wind and pressure systems, with relatively high pressures over the land areas in winter and lower pressures in summer. The wind systems pictured in Fig. 9-1 

### are best marked over the oceans, particularly in the Southern Hemisphere where the continental areas are small. The low-pressure area around the latitude of600 

### is mostinconstant. It

### is an average made up ofthe effects ofall the moving cyclones ofmiddle and high latitudes. The polar highs are also quite variable, especially in the Northern Hemisphere. It

### is apparent from Fig. 9-1 

### thatlow-level convergence occurs inthe meridional components at the equator between the trade winds ofthe two hemispheres and also

1 It is thought that the name is derived from the numerous bodies of horses seen

floating on the sea in these latitudes in the seventeenth century. It is related that sailing vessels transporting horses to the New World were becalmed in the highpressure center and. running low on feed and water, reduced their cargoes in midocean.Figure 4.19 Path and dally positions ofa (or;utanl-ievel balloon in tlie Southern !!..cllli.lI/!trTf lIj)per lVCJferliesfAifer /aullchmg al ChristcllUrcll,

### 1~rn;;Zcaland, all March 30, 1966, the GHOST balloon drifted at an altitude ofabout 12 km ill IIpj)cr.ielll'l wallesfor 3) days. (NCA,R [National Centerfor Atmospheric Re,earch], Boulder, Colorado) in large-scale Illation systems to retain a constant spin, or angular momenWill. abollt the eartb's axis ofrotation. A stream of air moving toward the

### eqll~ltor adopts a cyclonic cunatllre (collnterclockwise in the Northern Hcmisphere) relatiyc to the surface at the lower latitude as the distance from thc axis of rotation incrcases. Eventllally the curvcd path turns the wind back towanl the polc. Passin?; its origin;ll latitude, the wind takes ;\ll oppositc (tllat is, anticyclonic) curvature relative to the earth as it comes closer to the polar axis, where the rotational yelocity is less. (These effects arc easily dClllollStratcd 011 a /!,Iobc.) The resultiug Rossby 11'1H'(,S llI;IY lJayc lengths of 3,000 to (),OOO kl1l, permitting thrcc to 5i;.; (j)'(ul11­ polar \\,;lyes that correspond to surface paths of depressions and anticyclones in the

### wCSlcrIie~ (see }iiRure ·Ll9). Thcir length, amplitude, amI position are influcnccd by dilfercntial heating at the surface ;tnd by ex91