A6 AIR MASS ANALYSIS 
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“Tabilititsenergie” in the ter- 
minology of Refsdal.7 
It is shown that the lability en- 
ergy’ though smaller than the cur- 
rent and frontal energy, probably 
plays a great role in cyclogenesis, be- 
cause it may get stored up a long 
time beforehand over a rather great 
area, and only released at the most 
favourable moment and in the very 
center of the cyclogenesis, without 
much frictional loss of energy. 
The author has tried to form a 
more concrete idea of the mechanism 
of cyclogenesis, i.e., of the fall of 
pressure around the “warm tongue” 
of a frontal wave cf increasing am- 
plitude. 
This mechanism should consist in a 
sinking of the centre of gravity of 
the whole system under considera- 
tion, conditioned by that ascent and 
convergence of warm air at the 
“warm tongue” of a frontal wave of 
increasing amplitude. This conver- 
gence implies in its turn an increase 
of cyclonic circulation within this 
area, which again involves a fall of 
pressure in the middle of it, com- 
pensated by a slighter general rise 
of pressure in the outskirts of the 
disturbance.” (Bull. Amer. Met. Soc., 
Sept. 1937, p. 269.) 
;According to REFSsDAL (‘‘Der feuchtlabile 
Niederschlag’’, Geofy. Publ., Vol. 5, No. 12, 
1930, p. 9) the “lability energy’ of an air 
mass is defined as the maximum amount of 
energy which could be set free by an over- 
turning or an upward motion of this air mass. 
The “lability energy per unit mass’ between 
two heights is the algebraic sum of the work 
produced when a particle of unit mass is 
raised from the lower to the higher level (the 
compensating downward motion of the sur- 
rounding air being spread out over an in- 
finitely great area). This is conditional in- 
stability, including the instability realizable by 
condensation of water vapor. Compare with 
discussion of energy in Articles on the Tephi- 
gram and Thunderstorm. 
A Note on Dynamic Anticyclones and Cyclones 
In the discussion of American air masses 
it is pointed out that cold Pec air is character- 
istically shallow. In fact the majority of 
moving anticyclones on American weather 
maps are of the shallow so-called cold (or 
polar) type, having warmer PM or TM air 
(with often even low pressure and cy- 
clonie winds) aloft.* Wexlery has shown why 
the radiational cooling in the polar regions 
does not succeed in building up a very deep 
jJayer of Pc air before it is released to lower 
latitudes; the upper warm layers that may 
move south bodily with the Pc are thus PM or 
Tw air still unmodified to Pc. Subsidence? 
usually greatly accentuates the upper warm- 
ness of these cold-type highs as they move 
southward. Figs 3-6 herewith, from Haurwitz 
and Noble, show a case of a cold surface high 
replaced by low pressure aloft. Note, how- 
ever, that this is in part due to the backward 
slope in the free air of the axes of the lows, 
since the lowest pressure is always at the 
eold front at any level and the front itself 
‘slopes backward. 
However, there are also so-called warm anti- 
eyelones which in most cases seem to have 
developed from cold ones after the latter have 
‘slowed down and _ suffered heating from 
below in middle latitudes. Since these highs 
are warmer than cyclones from the surface 
up to high levels (8 km or more) the main- 
tainance of their anticyclonic winds and the 
high surface pressure cannot be explained 
thermally. It must be due either to some dy- 
namic process which piles up air in the upper 
or middle troposphere or to a norihward 
advection of cold (tropical) air in the strato- 
sphere over the anticyclone, sufficient to 
overcompensate the lowering of pressure from 
warming in the troposphere. The warm 
highs are common in western Europe, where 
the cold-stratosphere advection theory for 
their maintenance has been generally ad- 
vocated in recent years. Indeed, some Euro- 
pean cases** have been studied (from sound- 
ings) where apparently a tremendous rise in 
stratospheric pressure caused a marked day 
to day rise in the surface pressure of a cold 
anticyclone while it was becoming warm (a 
common phenomenon); but it has not yet 
been proven that this was more than a coin- 
cidence rather than some necessary conse- 
quence of the effect of tropospheric pressure 
changes in inducing stratospheric advection 
or vice versa. In an American case studied by 
*Haurwitz and Noble, Bull. Amer. Met. 
Soc., March, 1988, pp. 107-111.—A good exam- 
ple; J. Namias, Structure of a Wedge of 
Continental Polar Air, M. I. T. Met. Course, 
Prof. Notes No. 6, 1934. 
+H. Wexler, Mon. Wea. Rev., April 1936, p. 
122-135. and June 1937, pp. 229-236. 
+J. Namias, Subsidence in the Atmosphere 
Harvard Met. Studies No. 2, 1934. 
** H. Thomas, Sitzber. Preuss, Akad. Wiss., 
Phys. Math. Kl. vol. 17, 1934; Khanewsky. 
Met. Zecit., 1929, p. 81; Runge, Met. Zeitt.. 
1932, p. 131; Schmiedel, Veroff. Geophys. Inst. 
Univ. Leivzig, vol. 9, no. 1. 
