ANTICYCLONES 
By H. WEXLER 
U. S. Weather Bureau, Washington, D. C. 
It is the purpose of this article to summarize briefly 
what is known of the origin, structure, and trans- 
formation of anticyclones and to describe their role 
in the general circulation and some aspects of their 
control of weather and climate. 
It is natural for the division of subject matter for this 
Compendium to be made in terms of cyclones, anti- 
cyclones, general circulation, and so on. However, this 
breakdown, while very convenient for the editor and 
the reader, imposes certain difficulties on the author 
since it is quite impossible to discuss the anticyclone as 
a separate entity, with respect to either its origin or its 
role in the general circulation. For that reason, although 
much of the discussion here will deal directly with anti- 
cyclones, there will be occasional and unavoidable di- 
gressions into broader problems. 
The writing of this article was made much easier by 
reference to the excellent review of anticyclones by C. 
E. P. Brooks [4] in Some Problems of Modern Meteor- 
ology, the famous British progenitor of this Compen- 
dium. 
DEFINITION AND THERMAL STRUCTURE 
OF ANTICYCLONES 
An anticyclone is a large atmospheric eddy which 
rotates clockwise in the Northern Hemisphere about a 
center at which barometric pressure is higher than that 
of the surrounding air. Since barometric pressure is a 
very close measure of the mass of overlying air, an 
anticyclone is characterized by an excess of air aloft. 
Thus, over an anticyclone either the effective height 
of the atmosphere is greater or the air is on the average 
denser over the same height. Since there exists no 
evidence to indicate a greater height of the atmosphere, 
it was once thought that the air over an anticyclone 
must be colder and denser at all levels than the air 
over a cyclone. However, from a study of mountain 
observations in Hurope and western United States, 
Hann in 1876 [14] showed that up to the height of the 
mountains (3 to 4 km) anticyclones averaged warmer 
than cyclones except in a shallow surface layer. Fur- 
thermore, Hann stated the abnormal warmth and dry- 
ness was caused by subsidence. From recent aerological 
data more has been learned of the general thermal 
structure of anticyclones as distinguished from that of 
cyclones. For example, values compiled by W. H. 
Dines [7] and Palmén [22], based on soundings in 
England, showed that cyclones are characterized by a 
cold troposphere, a low (8.5 km),! warm (—50C) tro- 
popause, and a warm stratosphere, while anticyclones 
have a warm troposphere (over a cold, shallow surface 
1. Values are taken from Palmén. 
layer), a high (11.5 km), cold (—65C) tropopause, and 
a cold stratosphere. 
In 1908, Hanzlik [15] demonstrated the existence of 
two types of EHuropean anticyclones, the shallow cold 
(polar) anticyclone moving rapidly, usually in the rear 
of a cyclone, and the deep warm anticyclone moving 
very slowly or not at all. Quite often the shallow cold 
anticyclone changes into a deep warm anticyclone, and 
in so doing slows down and sometimes becomes station- 
ary. 
So far as is known there is no statistical study avail- 
able on the vertical temperature structure of the polar 
and warm type of anticyclones although it is likely that 
Palmén’s statistics on anticyclones refer mostly to the 
warm type of anticyclone, since the true polar anti- 
cyclone is rare in England. As a rough generalization 
it may be said that in North America the polar anti- 
cyclone is characterized by a troposphere colder than 
its environment, especially in the lower portion, and a 
low (5 to 8 km), warm (—50C to —65C) tropopause 
and warm, lower stratosphere, while the warm anti- 
cyclone may have a thin, cold layer at the surface, a 
warm troposphere, a high (12 to 17 km), cold (—65C 
to —80C) tropopause, and a cold, lower stratosphere. 
Quite often, however, anticyclones exist which have 
the deep surface layer of cold air characteristic of 
polar anticyclones and the high cold tropopause of 
warm anticyclones. Such anticyclones, combining the 
high-pressure producing qualities of both anticyclonic 
types, are usually extremely intense and would prob- 
ably never be observed at low latitudes because of 
absence of cold tropospheric air. For example, in the 
nineteen unusually intense anticyclones in the North 
Atlantic and Eurasian regions listed by Scherhag [30], 
where central pressures ranged from 1047 to 1079 mb, 
the lowest latitude of location was 50°N. 
ORIGIN OF ANTICYCLONES AND THEIR ROLE 
IN THE GENERAL CIRCULATION 
Polar Anticyclone. The polar anticyclone is created 
by cooling of the surface layer of air, which loses its 
heat to an underlying cold surface by radiation [35] 
or by eddy conductivity. The lower temperature of the 
surface itself is caused by the nocturnal radiational 
cooling of snow and ice fields, such as those in polar 
regions, or by bodies of large thermal inertia (heat 
capacity), such as oceans and large lakes. The cooling 
and vertical shrinking of the surface layer of air de- 
presses the isobaric surfaces aloft, creating an intensi- 
fying “polar cyclone” which causes an inflow of air 
across the isobars, thus creating a larger barometric 
pressure at the surface. This process was studied by 
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