148 
low the branching. This effect is, of 
course, superimposed upon the pres- 
sure changes due to density advection. 
If the region of divergence is situated 
some distance from the center of the 
surface cyclone, a secondary cyclone 
may form near the peak of the warm 
sector at the ground. 
The effects of the branching upon 
the pressure distribution at the sur- 
AIR MASS ANALYSIS 
face may be roughly estimated by the 
strength of the interacting currents. 
Thus a weak anticyclonic eddy will 
generally yield to an invading strong 
cyclonic flow of polar air, and in this. 
case no secondary will result, while 
two strong currents of different vor- 
ticity will invariably cause large pres- 
sure falls and lead to deepening and 
possibly cyclogenesis. 
§ 5. THE DISPLACEMENT OF FLOW PATTERNS WITH HEIGHT 
Thus far we have concerned our- 
selves with flow patterns observed in 
one isentropic surface. Experience 
has shown (Simmers [16]) that there 
is a relatively small difference in the 
flow pattern from one isentropic sheet 
to another. This, however, does not 
hold true if we choose an isentropic 
surface which is so low that it comes 
under the influence of the surface 
friction. The slight displacement of 
flow pattern with elevation, which oc- 
curs above the friction layer, con- 
forms usually with the displacement 
with elevation of cyclonic and anti- 
cyclonic centers. It should be noted, 
however, that there are exceptions 
and that these are frequently asso- 
ciated with radical changes in 
weather situation (Namias_ [17]). 
The most important exception, per- 
haps, is the case when an anticyclonic 
3456 
654 3q/kg 
Fic. 8. FLow PATTERNS AT DIFFERENT ISENTROPIC SURFACES WHIOH LEAD: 
TO INCREASING INSTABILITY. 
eddy is present below a cyclonic eddy. 
This case is represented schematically 
in fig. 8, where the solid lines repre- 
sent the flow pattern at some isen- 
tropic surface, while the broken lines. 
show the flow pattern along an isen- 
tropic surface ten degrees higher in 
potential temperature. The domes of 
the isentropic surfaces are indicated 
by H and the troughs by L. With 
such a vertical distribution of flow 
patterns it is clear that while the 
lower layers over a region are becom- 
ing progressively warmer and moister, 
the higher layers are becoming colder 
and drier. The advection thus leads. 
to two processes in which the poten- 
tial energy of the air column is in- 
creased: (a) where the lower layers 
are becoming warmer and the upper 
layers are becoming colder, the lapse 
rate is made steeper; (b) since the 
lojig 3 
° 
oO at 8 =300 
wesc at 8 =310° 
ws 
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