ARCTIC METEOROLOGY 
indicators of moisture content and stability, and are 
easily computed from radiosonde data. The tabulated 
data are not strictly comparable, since the Hurasian 
soundings were selected to include only fresh outbreaks 
of arctic air, while only the average January and July 
TasLe II. Arcric Atk IN SUMMER 
F H T Paw 
Station Gab) | Gm) | @c) |@key| CO 
Eureka Sound 1000 30/+ 6] 3.6 |}+4+ 3 
(all soundings) 900 | 900} +1] 3.6 |)+ 5 
800 | 1800 | — 3} 2.8} +7 
700 | 2800} — 8} 2.0/+8 
600 | 4000 | —14] 1.2 | +10 
500 | 5400 | —22 | 0.8 | +12 
Barents Sea Coast 1000; — |+9|] 5.1 | +6 
(stirred air) 900 |} 850} +2/] 3.7/+4+ 5 
800 | 1750 |} — 2} 3.5 |+ 8 
700 | 2800 | —11 | 1.8 |} +6 
600 | 8850 | —16 |} 0.8 | + 8 
500 | 5150 | —27/} 0.3/+8 
soundings were available for the American Arctic. Even 
so, there was a strong tendency for decreasing 6,»-values 
between 950 and 850 mb above Eureka Sound in July. 
Individual ascents would certainly show convective in- 
stability similar to that observed along the Barents 
Sea Coast. 
TYPICAL ARCTIC CIRCULATION PATTERNS 
Variations in the Average Circulation Patterns. The 
discussion of the midseason average arctic circulation 
patterns, based on maps of average pressure for July, 
October, January, and April, has already indicated the 
major centers of cyclonic and anticyclonic activity and 
traced the frontal zones associated with the develop- 
ment and movement of cyclonic storms. A knowledge 
of the major variations to be expected in the average 
flow patterns is always a valuable aid in the analysis 
and prognosis of daily weather situations, especially 
in the Arctic where observing stations are widely sepa- 
rated and where there is not much past experience to 
draw upon. Much useful information on anomalous 
circulation patterns has been gained from research on 
forecasting by mean circulation methods, but no spe- 
cific studies on the truly arctic regions have been made. 
Since this article is concerned with a region which 
has not entirely ceased to be a “blind spot” on Northern 
Hemisphere charts, a general application of mean circu- 
lation principles will be described for the principal 
seasons. A more detailed application would require ex- 
tensive research along synoptic lines as suggested by 
Willett [24]. 
Summer Variations. The strong thermal control of 
the average summer circulation has been mentioned. 
Thus, as shown by Schell [17], large-scale anomalies 
in the semipermanent ice and snow cover would un- 
doubtedly be locally important, but could hardly 
counteract an opposing anomaly in the general circula- 
tion. A strong summer circulation (high index) might 
at first be considered unfavorable for polar anticyclonic 
developments, but it is thought that summer conditions 
949 
are quite probably the reverse of winter. It is the sub- 
tropical anticyclones, at unusually high latitudes over 
the oceans, that are associated with the periods of weak 
zonal index in summer. At such times, the circumpolar 
cyclones are forced into the Arctic much more per- 
sistently than is normal. 
The fact that summer circulation patterns tend to 
persist and change but slowly should in itself be of con- 
siderable guidance to forecasters in the high latitude 
arctic regions—provided they have at least one daily 
set of surface and upper charts with a reasonable synop- 
tic coverage. 
Late spring and early fall disturbances may be strong, 
but the cyclonic systems of the true summer period are 
relatively weak unless abnormally cool conditions pre- 
vail over the Arctic Ocean area. As suggested by the 
average July chart, disturbances coming from Siberia 
are often reintensified along the Canadian Arctic coast 
line. Their subsequent movement depends mainly on 
the position and intensity of the Baffin Bay upper-level 
cyclonic circulation. Normally no summertime dis- 
turbances approach arctic America from the direction 
of the North Pole, though northern Baffin Bay cyclonic 
systems frequently move poleward up the North Green- 
land-Ellesmere trough. Some part of almost every dis- 
turbance reaching the vicinity of Hudson Bay from the 
west or south will eventually affect the northern Baffin 
Bay section. Summer occurrences of other seasonal 
patterns will be noted. 
Autumn Variations. Early autumn is a season of 
strong thermal contrast between the Arctic, which is 
already producing a winter type of air mass, and the 
more slowly cooling subarctic continental mainland 
areas with their summer-type maritime polar air. The 
average circulation pattern is one of strong zonal wester- 
lies, representing a great increase over average Summer 
conditions, but usually there is an anomalous return to 
a summer type after the first onset of autumn. Con- 
tinental mainland areas warm up again and, with the 
high latitude Arctic cooling rapidly, the stage is set for 
a strong intensification of weak disturbances crossing 
coastal sections of Siberia and/or Canada. With specific 
reference to arctic America, deepening over the Macken- 
zie or Coppermine valleys completes the genesis of 
extreme types of autumn storms, which will curve into 
the Archipelago or northern Baffin Bay and dominate 
the circulation for possibly a week as they slowly fill. 
Weaker variations of the above anomalous type ac- 
count for a high percentage of summer disturbances 
affecting this region. As this is also true for autumn and 
early winter, the so-called “autumn type” is very im- 
portant to northern arctic America. 
Winter Variations. Since the cold season includes 
November and March, minor variations of the average 
January circulation pattern are common throughout the 
winter. Strong zonal westerlies are characteristic of the 
average pattern. Circulation anomalies of the high- 
index type frequently result in a pattern similar to that 
of October, with the required strengthening of pressure 
gradients. Except for occasional high-latitude cyclonic 
eddy systems, northern arctic America is usually cut 
