36 JEROME NAMIAS 
a) 
Tracks of Centers of Cyclones at Sea Level, October 1952. 
Fic. 4—Cyclone tracks for October 1952; upper figures show date, lower figures depth of center 
achieving a more balanced state. The continuity 
(determined with the help of charts not repro- 
duced) was that the trough found near the Azores 
during the last half of January is the one formerly 
present at 60°W during the first half of the 
month. It is interesting to note that the break- 
down (formation of the new trough) was not 
simultaneous with the drop in zonal index but 
required some time (about two weeks). This de- 
layed response appears to find analogy in dishpan 
experiments by Fultz [1953] in which a quasi- 
steady pattern of long waves set up with one 
rate of rotation and of differential heating (be- 
tween rim and center) requires time to break into 
another pattern when these values are altered. 
To sum up, the instability was essentially 
created through the interplay between climato- 
logical (insolation) factors, which cause the fall 
to winter increase in strength of the zonal west- 
erlies, and the initial wave patterns, which are 
the outgrowth of earlier evolutions and have 
a lifetime of their own. The patterns first ad- 
justed to this increase in westerlies by increasing 
wave length. Later on, the new extended wave- 
length pattern was unable to accommodate to a 
rapid diminution in speed of the westerlies, and 
an increase in planetary wave number took place. 
The time scale of this series of events was about 
2’ months. 
The December flow patterns (roughly similar 
