CLIMATE—THE SYNTHESIS OF WEATHER 
primarily in the “sterile mean.” In this he achieved a 
considerable measure of success as may be judged even 
from the brief summary in Table I. His treatment 
certainly did present the month or season as one of 
change and conflict. More recently the description of 
the climate of Germany has been carried a stage further 
by Flohn [13] who has discussed the regional climatology 
and has pointed out the effects of the major topographic 
features on local weather in the different air masses. 
Dinies’ example has been followed by others, notably 
by Landsberg [21] who examined the air masses of 
central Pennsylvania, by Batschurina and his collabora- 
tors [5] who reviewed the air masses of Western Russia, 
by Schamp [31] who applied a classification to the 
969 
mass properties of America, adopting a somewhat differ- 
ent classification from that of Bergeron in order to 
suit the local circumstances. 
In 1940 Petterssen [29] summarized and reviewed 
the various assessments of the thermal structure of 
different air masses and presented original maps of the 
Northern Hemisphere, setting out the positions of the 
different sources in winter and summer. 
Still more recently Belasco [6] has made elaborate 
assessments of the temperature and humidity structure 
of the air of various types reaching the British Isles 
along a large number of tracks. Perhaps the most in- 
teresting feature of this paper is the comparison which 
he makes of the structure of the air over the Azores 
Tape I. FREQUENCIES AND CHARACTERISTICS OF AIR Masses at FRANKFURT AM Matn 1924 To 1929 
Rabe || Topic | Martine | Soar | Oee | o BOee | oes Con Ill-defined| Mixed 
nenta 
Frequency of air masses 
Winter (1924-30)%.............-.. 4.6 292 30.2 20.6 11.4 2.6 8.2 1.3 7.0 11.9 
Summer (1924-30)%............... 1.8 3.4 34.0 6.6 32.4 0.8 4.6 1.0 8.6 6.8 
February 
Mean temp. (°C).................. 1.8 3.5 5.8 —2.8 0.8 —15.8 8.3 4.5 = = 
Mlesz, em, (A®)\soeaseccsee oon e5s. 6.2 10.4 7.8 4.2 3.6 —10.4 Wii 10.5 — = 
IMbin, eT, (ADescesenoessesscosee|| —Weo3 1.4 2.4 —4.0 —1.3 —19.0 6.2 —0.7 = = 
Vapour pressure (mb)............. 5.1 6.7 7.5 3.5 5.2 1.6 9.1 5.6 = = 
INI@3, fF OGCHSIOME), 5 s0cec55de0ss5500 5 2 41 20 10 4 18 ? — = 
Winter 
Overcast days (%)................- 5 44 72 32 52 8 81 — _ = 
Clear cay (Gps asossasemocunosses 53 22 0 37 5 38 0 — — = 
July 
IWileain tera, (AO) ecocessacooccsebos — 22.5 18.9 23.8 17.3 = 21.4 _ = = 
IMlese ied. (AO)scposcauesboecos coc _— 28.6 23.8 30.4 21.8 — 29.9 — = = 
Mitmaeatemnap (6©@))), sacs sass crase vee _ 16.6 14.4 17.0 13.1 = 15.6 = = = 
Vapour pressure (mb)............. — 18.1 15.5 18.5 12.0 _— 19.5 — — = 
INO; OF @OCAMOMSs sccscenccheessedo 0 2 56 17 29 0 6 0 = = 
Summer 
Overcast days (%)................ 13 13 36 4 39 0 44 = = = 
Cleanidaysi(Y)re. 05.022 -.20- 0-8 13 25 8 23 5 75 6 — — — 
Greek Islands, and by Roy [30] who has more recently 
attempted to apply air-mass analysis to the Indian 
Peninsula. In this careful study Roy has not only classi- 
fied the air masses, using the data of modern synoptic 
charts and aerological ascents, but in addition he has 
described concisely the climatological features of the 
air masses of the various seasons in regard not only to 
their temperatures, humidities, and thermal structure, 
but also in regard to the incidence of fog, and the charac- 
teristics of cloud. Roy suggests that there should be 
compiled in India detailed air-mass climatological tables 
for a number of representative stations as a routine 
to form the basis of the discussion of the air-mass 
climatology of the subcontinent. 
An extension of the examination of air masses was 
made by Palmén [27] by forming mean values of tem- 
perature and humidity in the upper air in the several 
air masses, using data for the British Isles. In this he 
used essentially Bergeron’s classification of air masses 
[7]. Willett [33] at about the same time listed the air- 
and Iceland with that which reaches the British Isles 
after travelling from those directions. In Tables II 
and III are set out the comparisons of mean tempera- 
tures in winter and summer. 
A caution must be given that in Belasco’s work the 
air trajectories were not taken back to the source but 
only for a distance of about 1500 miles from the British 
Isles. Hence there is, for example, no certainty concern- 
ing the actual source region of the trajectories which 
passed over the Denmark Strait on their course to the 
British Isles. Table II however does give some idea of 
the manner in which modification takes place in the 
temperature of the air when it passes over long stretches 
of water and at the same time travels into a latitude 
where the radiation balance is reached at a different 
temperature level. 
All these studies of the upper air in relation to air- 
mass classification were intended primarily to further 
the task of the synoptic forecaster. To a great extent, 
however, they can be made to serve the climatologist in 
