146 
AIR MASS ANALYSIS 
lation weakens, finally dissipating or 
merging into some other circulation. 
Thus the stability of any particular 
eddy may, to some extent, be deduced 
from the distribution of velocity 
around its center, as shown by Namias 
[14]. Stable eddies will have well 
developed circulations with wind ve- 
locities increasing radially outward 
from the center in a nearly symme- 
trical fashion. Such eddies will tend 
to rotate as solids. Once the mother 
current weakens, the symmetry of 
the velocity profile tends to vanish 
and the eddy gradually dissipates. 
Also, for this reason the moisture 
lines may sometime indicate an eddy 
pattern which is the result of some 
already decayed circulation. 
By assuming that the smaller anti- 
cyclonic eddies are frictionally driven, 
it is possible to deduce from the dis- 
tribution of velocity around their cen- 
ters the general direction of migra- 
tion. Suppose we have an eddy with 
a velocity distribution as indicated in 
fig. 6. This eddy obviously derives its 
a direction normal to the isobars. 
In the southeastern quadrant of the 
eddy there is a region of sub-gradient 
winds which thus appears as a region - 
of wind divergence. The converging 
air in the other quadrants (super- 
gradient winds) piling up into the 
center of the eddy will naturally fol- 
low into the divergent region, and the 
eddy will follow a path indicated in 
fig. 6. Applying this rule in the gen- 
eral case, we may say that frictionally 
driven anticyclonic eddies tend to move 
into the region in which the tangential 
winds about them are lightest. This di- 
rection is normally in the direction of 
the mother current. It should be em- 
phasized, however, that this rule ap- 
plies chiefly in the developing stages 
of the eddy and when it is character- 
ized by a symmetry in the velocity 
distribution. The use of the above 
rules for determining the movement 
and stability of anticyclonic eddies 
on the isentropic chart will do much 
to assist in the analysis of the flow 
vatterns and in making forecasts of 
Fic. 6. RELATION OF DIRECTION OF MOVEMENT OF 
ANTICYCLONIC EDDIES TO DISTRIBUTION OF WIND VELOCITY.- 
energy from the westerly and north- 
westerly current, and it may be as- 
sumed that the air motion, being non- 
gradient, has a small component in 
the movement of moist and dry 
tongues. 
To the left of fast-moving streams 
a zone of cyclonic wind shear exists, 
