NORWEGIAN WAVE-THEORY 37 
The Norwegian Wave-Theory of Cyclones’ 
B. HAURWITZ* 
Meteorological Services of Canada, Toronto 
N RECENT YEARS air mass analysis 
has been widely accepted by mete- 
orologists on this continent as a 
basis for the study and forecasting 
of the weather. One of the funda- 
mental assumptions of this method is 
the theory that cyclones form as 
waves at surfaces of discontinuity 
between air masses of different origin 
and history which, consequently, have 
different physical properties, e. g., 
temperature and humidity. 
The practical side of air mass 
analysis is well represented in this 
booklet by Mr. Namias and Prof. 
Willett. The theoretical questions, 
whether waves actually can occur at 
such surfaces of discontinuity and 
whether these waves have any resem- 
blance to the nascent cyclones ob- 
served in the atmosphere, have only 
been touched slightly in their articles. 
They are, naturally, of secondary in- 
terest to the practical meteorologist. 
THE PROBLEM 
Perhaps it might be argued that a 
mathematical study of the possibility 
of cyclonic waves is just a fruitless 
pastime without any practical value. 
Are not cyclones in their earliest 
wave-like stages found on almost 
every weather map? However, before 
the Norwegian school of meteorology 
conceived their idea of the origin of 
cyclones as waves at frontal surfaces, 
no such phenomena were noticed. If 
something appeared on the map which 
today would be interpreted as a 
frontal wave it certainly was formerly 
never recognized as such. And even 
now the wave theory of cyclones is 
not generally accepted. Thus there 
can be no doubt that the theory of 
the origin of cyclones as frontal 
waves can be strengthened and ac- 
cepted only if it is proved that such 
atmospheric oscillations are actually 
possible and do occur more or less 
generally in the atmosphere. 
Furthermore, the quantitative re- 
lations between length and velocity 
of the cyclonic wave and temperature 
and wind discontinuity at frontal sur- 
faces can only be obtained by the 
mathematical theory. The verification 
of such formulae by observations 
would represent the real check on 
the theory. Quantitative relations are 
further necessary since there exists 
sometimes a tendency to interpret 
weather situations without regard to 
the obvious numerical impossibility 
of the proposed explanation. 
Thus the wave theory of cyclones 
presents a definite hydrodynamical 
problem to the theoretical meteorolo- 
gist. He has to show that at frontal 
surfaces such as we observe in the 
atmosphere, waves can originate 
which have the characteristic quali- 
ties of the cyclonic frontal waves 
which are found on the maps; they 
must possess a similar wave-length 
and velocity of propagation, and the 
.motion of the air particles in the 
computed wave must agree with the 
air motion in the observed nascent 
cyclones. Another very important 
point is that these waves must be 
unstable, i. e., their amplitude, at 
first very small, must increase with 
time until the cyclone loses its wave 
character and becomes a vortex. The 
later vortical stages of the life his- 
1This article first appeared in the BULLETIN 
A.M.S., June-July, 1937. 
*Research Associate, Blue Hill Observatory. 
