44 AIR MASS ANALYSIS 
Fig. 3 
Fic. 1. (9) VERTICAL CROSS SECTION 
THROUGH A SYSTEM OF Two AIR 
MASSES WITH PARALLEL BOUNDARIES 
SEPARATED BY A SURFACE OF DISCON- 
TINUITY, AS CONSIDERED BY THE 
THEORY. THE BOUNDARIES AND THE 
SURFACE OF DISCONTINUITY ARE IN- 
CLINED AGAINST THE SURFACE OF THE 
EARTH. 
Fic. 2. (10) VERTICAL CROSS SECTION 
THROUGH THE ACTUAL POSITION OF 
WARM AND CoLp AIR MASSES RELATIVE 
TO THE SURFACE OF THE EARTH. 
Fic. 8. (11) SAME As Fic. 1 WITH A 
STREAM SURFACE WHICH RUNS PARTLY 
HORIZONTAL OveR THIS APPROXIM- 
ATELY HORIZONTAL AREA (INDICATED 
BY THE RECTANGLE) THE STREAM SUE- 
FACE MAY BE REGARDED AS THE SUR- 
FACE OF THE EARTH. 
warm layer have boundaries parallel 
to the frontal surface (Fig. 9). In 
reality, the frontal surface intersects 
the surface of the earth so that the 
cold mass has the form of a wedge 
(Fig. 10). Solberg*) has given some 
preliminary results but the problem 
is so extremely difficult that until 
now a somewhat round about ap- 
proach has been used. Waves of the 
cyclonic type in the layers parallel 
to the frontal surface and therefore 
inclined to the horizontal according 
to Margules’ formula’), have been 
studied. It was found that some of 
the “stream surfaces” along which the 
motion of the air particles takes place 
are practically horizontal planes for 
an extent of about 2000 km or 
more (Fig. 11). Now a stream sur- 
face can be assumed to be rigid, 
since according to the definition of 
a stream surface the motion is paral- 
lel to it. If we let the stream sur- 
face in Fig. 11 become solid and re- 
gard it as the surface of the earth a 
very close analogy to the atmosphere 
is obtained in the region near the 
intersection between stream surface 
and surface of discontinuity. The 
cold air lies like a wedge under the 
warm air and the wave motion near 
the surface is almost parallel to the 
solid horizontal stream surface, which 
may be identified with the surface of 
the earth. Farther away from the 
frontal surface the agreement with 
reality is of course less satisfactory, 
since the curvature of the solidified 
stream surface will be stronger. But 
the intensity of the wave decreases 
with the distance from the surface 
of discontinuity. The field of motion 
is dynamically most important at the 
front, and loses its significance com- 
paratively rapidly in lateral and ver- 
tical directions. Therefore the method 
of assuming solidification of a hori- 
zontal stream surface is more satis- 
factory than might appear at first. 
8Solberg, H.: Integrationen der atmosph§aris- 
chen Storungsgleichungen (I), Geofys. Publ., 
vol. V, no. 9, 1928, pp. 104-120. 
®Namias, this booklet, p. 25. 
