LOCAL WINDS 
foehn current diminishes and the cold air remnants in 
the valleys are augmented, these remnants may again 
combine into a shallow cold-air layer covering the 
entire valley floor. The foehn current then lifts from 
the valley floor, a fact that shows up in meteorological 
recordings as marked temperature and relative humid- 
ity jumps called foehn pauses. Figure 14 shows a partic- 
ularly good example of the temperature and humidity 
records during the foehn period from February 2-5, 
1904, at four alpine (Inn valley) stations at different 
altitudes. In this figure all features of the individual 
foehn phases, foehn pauses, and the characteristic re- 
sponse of the stations to the south foehn are evident. 
FEB. 2 
2400 
FEB. 3 FEB. 4 
1200 2400 1200 2400 
FEB. 5 
1200 2400 
1200 
ouao 
TEMPERATURE (°C) 
1 
a 
RELATIVE HUMIDITY (%) 
Fig. 14.—Typieal south foehn registrations from the Inns- 
bruck foehn area from February 2 to 5, 1904. Thin solid line— 
Innsbruck (573 m); dashed line—Igls (876 m); dotted line— 
Heiligwasser (1240 m); thick solid line—Patscherkofel (1970 
m). (After ». Ficker (24].) 
According to A. Defant, remnants of cold air in 
valleys form closed systems and may be excited into 
oscillations (similar to waves on lakes) by the passage 
of a foehn current over them. These oscillations show 
up as temperature fluctuations that are not to be 
confused with the short, periodic pressure fluctuations 
that occur during foehn. 
Of special interest is the wave form of the air flow 
in the free atmosphere on the lee side of hill chains, 
mountain ridges, or other extended elevations of the 
ground. When the wave crests of this leeward current 
reach above the condensation level, the stationary wave 
becomes visible as a fixed ‘““Moazagotl cloud” on the 
lee side of the mountains. The Moazagotl cloud con- 
sists of one or more cloud banks parallel to the moun- 
tain barrier; it forms continuously on the windward 
side of the wave and dissipates on the lee side. Sailplanes 
may reach great altitudes in the Moazagotl updraft. 
Prandtl, Kiittner, and recently Lyra [55] have con- 
ducted theoretical investigations of these Moazagotl 
or foehn waves in the lee of mountains. In the develop- 
ment of the theory an increasing number of factors 
have been taken into consideration; Lyra’s recent ex- 
tension of the theory to include any polytropic stratifica- 
tion brought the theory of smusoidal air currents on the 
lee side of barriers to a preliminary conclusion. Figure 
669 
15a shows the theoretically computed streamline pat- 
tern over a mountain barrier. Such foehn waves with 
their attendant cloud systems have been observed over 
numerous mountains. The waves caused by the Rocky 
Mountains in the northwestern United States have 
been investigated in detail by Hess and Wagner [38]. 
A particularly mteresting case, in which the waves on 
the lee side reach an altitude of 40,000 ft, is shown in 
Fig. 15d. 
Ss 
RK MP 
(6) 
Fie. 15.—Stationary waves in the free atmosphere on the 
lee side of mountains. (a) Streamlines across a mountain 
range with Moazagotl clouds on the lee side. (After Lyra [55].) 
(6) Cross section from Tatoosh Island, Wash., (PTA) to 
Minneapolis, Minn., (MP) for 0300Z, January 14, 1945; isolines 
of potential temperature in degrees absolute. Vertical scale: 
units of pressure-altitude (ft) of U. 8. standard atmosphere. 
(After Hess and Wagner [88].) 
During well-developed foehn currents, marked phys- 
iological disturbances in men and animals occur on 
the lee side of mountains. These disturbances are as- 
cribed to the short-period pressure fluctuations during 
foehn [28, pp. 65-105], but their causes have not been 
completely explained as yet. 
The Bora. Hann’s theory, which includes all fall- 
wind phenomena in the mountains, must also explain 
the cold fall-wind phenomenon. If a very cold air mass 
passes over a mountain barrier, or if it blows from the 
interior of a cold land mass over a plateau, the dynamic 
temperature rise during its descent on the lee side may 
not suffice to turn this fall wind into a warm foehn. 
Rather, this wind will be cold upon its arrival in the 
plain and is called bora, after the best-known of these 
local winds, which occurs on the coast of Dalmatia 
[48, 49, 57]. There, the cold, continental outbreaks of 
winter air from Russia find their way through Hungary 
and over the mountains of Dalmatia to drop over a 
