628 
lapse rate is found which terminates at a tropopause 
at 11.2 km, and, in view of the high surface pressure, a 
surprisingly warm tropopause (—58C). This sounding 
unfortunately ends at 13.0 km (—52C). In order to 
obtain an indication of temperatures above the top of 
the Caribou sounding, recourse was made to the closest 
sounding which penetrated significantly above 13 km, 
and was still under the anticyclonic influence. This 
turned out to be the sounding for Portland, Maine 
(225 miles south-southwest of Caribou), taken at 1500 
Z, December 25; this station has a sea-level pressure of 
1052 mb. The Portland sounding shows the presence of 
two well-marked tropopauses, the lower at 11.1 km, 
temperature —59C; this is undoubtedly the same tropo- 
pause as found over Caribou since the potential tem- 
peratures at the bases of the inversions are nearly the 
same, 330K and 332K, respectively. The base of the 
upper tropopause at Portland is found at 15.1 km, 
—64C, and 387K potential temperature. It therefore 
appears reasonable that the Caribou sounding taken 
near the center of the 1054-mb anticyclone would also 
have possessed an upper, high (15 km), cold (—65C) 
tropopause characteristic of warm anticyclones. 
The presence of the relatively high, cold tropopause 
of the polar anticyclone at its source region, although 
unusual, is not so surprising, but the presence of a 
double tropopause in the warm anticyclone was un- 
expected. 
The high potential temperature (387K) of the upper 
tropopause is worthy of special note since it is even 
higher than the potential temperature of the equatorial 
tropopause, 380K, as given in Physikalische Hydro- 
dynamik, [3, p. 671]. The Swan Island (17.4°N, 83.9°W) 
sounding for 1500Z, December 25, has a well-marked 
tropopause inversion at 17 km, a temperature of —78.2C, 
and a potential temperature of 388K. In the Wash- 
ington, D. C., soundings made at twelve hours before 
and twelve hours after 1500Z of December 25, the 
potential temperatures at the bases of the exceedingly 
well-marked upper tropopause inversions are even 
higher, 395K, 403K, and 408K, respectively. The Wash- 
ington sounding for 1500Z, December 25, is also 
shown in Fig. 1. The remarkably high value of the 
tropopause potential temperatures observed at Wash- 
ington, D. C., and Portland, Maine, could not have 
been achieved by adiabatic lifting of the prevailing 
Xropopause at middle latitudes whose potential tem- 
peratures of 320K to 360K [3] are so much lower than 
those observed in the case under discussion. Nor does 
there appear to be present any radiative process which 
would cause the formation of an upper inversion over 
such a large area. It appears certain that in this situa- 
tion there must have been advection northward of the 
tropopause from equatorial latitudes to at least the 
latitude of Portland, Maine, (43.7°N). The complete 
aerological discussion of this interesting case of anti- 
cyclogenesis is outside the scope of this article, but it 
should certainly be studied in detail to see how each 
of the large-scale factors—mechanics of the westerly 
waves and advection from equatorial latitudes—con- 
tributed to the anticyclogenesis. 
MECHANICS OF PRESSURE SYSTEMS 
SOME UNSOLVED PROBLEMS 
The central problem concerning anticyclones is the 
explanation of the warm, deep ‘“‘dynamic”’ anticyclone. 
The “piling-up” of air which is associated with this 
type of anticyclone is of course the counterpart to the 
removal of air which characterizes the cyclone. Com- 
plete explanations of both of these fundamental phe- 
nomena are still lacking. The deep anticyclone may be 
created out of transformation of a shallow polar anti- 
cyclone, or it may arise in its own right. Although some 
promising clues have been uncovered involving con- 
figuration of the westerlies and surface conditions, their 
influence on the cause and location of deep anticyclones 
is not fully known. That dynamic factors are important 
is indicated by semipermanent anticyclones located in 
the subtropics. That surface conditions are important 
is indicated by certain preferential locations of deep 
anticyclones. The role of advection in the upper tropo- 
sphere in instituting or strengthening anticyclogenesis 
requires clarification. Whether changes in the height and 
temperature of the tropopause precede, accompany, or 
follow anticyclogenesis deserves further study. The 
existence and location of the high-level anticyclones 
south of the westerlies should be examined, especially in 
relation to tropical rainfall patterns. 
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