AEROLOGY OF EXTRATROPICAL DISTURBANCES 
(1000 FT)(KM) 
603 
50 
15 
40 
10 
30 
20 
iKe) 
0-0 
(1000 FT) (Km) 
50 
40 
30 
20 
OM SEC™ 
KILOMETERS 
Fre. 2.—Mean cross section through northwesterly flow over Europe. Constructed from all European observations on morning 
of November 29, 1942 (observations from Wetterber. Disch. Seewarte). Legend as in Fig. 1 (winds in meters per second). Dash-dotted 
lines indicate intermediate isovels. 
side of equation (6) is greater than zero. Thus, the in- 
equalities 
_gtany [ie ee e ) | 5 dw’ (cyclonic) (7) 
20T sn dL\ ay /> \ay/p_| ~ dy (anticyclonic) 
express the condition for cyclonic or anticyclonic shear 
in a frontal zone. Hence, the result above can be ex- 
pressed in the following way: If there is strong anti- 
cyclonic shear in the upper warm air, and this anti- 
cyclonic shear is greater than the negative value of the 
second term on the right in (6), the west. wind increases 
toward the north in the frontal zone. 
This result concerning the horizontal wind shear in a 
frontal zone is of considerable importance for the cy- 
