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Relation between mean annual air and ground temperatures in the
permafrost region of Canada
R e p r ~ n t e d from t h e PROCEEDINGS: PERMAFROST INTERNATIONAL CONFERENCE, NAS-NRC, P u b l i c a t i o n 1 2 8 7
A N ~ k ~ ~ E D
SESSION V
THERMAL ASPECTS
RELATION BETWEEN MEAN ANNUAL AIR AND GROUND TEMPERATURES
IN THE PERMAFROST REGION OF CANADA
R . J . E. BROWN, Division of Building Research, National Research Council, Canada
Climate i s b a s i c to permafrost formation and i s a most impor- tant factor influencing the e x i s t e n c e of this phenomenon. Of a l l climatic f a c t o r s , air temperature i s the most readily meas- ured and i s most directly related to ground h e a t l o s s and heat g a i n . Observations in Canada and other countries indicate a broad relation between mean annual a i r and ground tempera- tures in permafrost.
Many investigators have estimated the mean annual air temperature required to produce and maintain permafrost [ I ] . There i s , however, much disagreement on this matter. Terzaghi reported that the southern limit of permafrost coin- c i d e s very roughly with the 32OF mean annual air isotherm [2]. Black reported t h a t , b e c a u s e of local conditions, the mean annual air temperature required t o produce or maintain perma- frost varies many degrees; he suggested that i t i s generally between 24 and 30°F [3]. Nikiforoff in h i s hypothesis of the origin of permafrost suggested that the southern boundary coincides approximately with the 28.4OF isotherm [ 4 ] .
In C a n a d a , the southern limit of permafrost a s presently known l i e s between the 25' and 30°F mean annual air i s o - therms e x c e p t in western Quebec [5] (Fig. 1)
.
W e s t of Manitoba, the known limit of permafrost coincides approxi- mately with the 3 0 ' ~ isotherm. In Manitoba, however, it c u t s eastward from the 30' to the 3S°F isotherm. In Ontario it coincides with the 25OF isotherm. In western Quebec it l i e s north of the 2S°F isotherm from whence it extends s o u t h e a s t - ward into southwestern Labrador (and perhaps even further southward).
Although observations are limited, the southern limit appears to c r o s s the 25OF isotherm in southern Labrador and then extend northeastward between the 25' and 30°F isotherms t o the Atlantic c o a s t .Apparently, the mean annual ground temperature differs from the mean annual air temperature by s e v e r a l d e g r e e s and t h i s difference i s not c o n s t a n t . H e n c e , precise prediction of permafrost distribution cannot be b a s e d solely on t h i s factor.
Attempts have been made t o r e l a t e permafrost distribution in Canada with freezing indexes [ 6 , 7 , 81 and thawing indexes [ 6 , 73. These indexes reflect annual fluctuations of a i r temperature about the freezing point and indicate the amount of h e a t added to and withdrawn from the ground. A station with a mean annual air temperature of 32OF will there- fore have e q u a l freezing and thawing indexes. As with mean annual air temperature, there i s a broad relation between permafrost distribution and t h e s e i n d e x e s , but accurate pre- diction of permafrost occurrence cannot be b a s e d solely on this factor b e c a u s e of the influence of other climatic and terrain factors [ 1
1.
N e v e r t h e l e s s , a review of the literature and examination of the known southern limit of permafrost, shows some general correlation between mean air and ground temperature a s indicated by the correspondence between certain isotherms and the permafrost boundary a s w e l l a s by other evidence [ l , 61.
INFLUENCE OF TERRAIN AND OTHER CLIMATIC FACTORS
The difference between mean annual air and ground tempera- ture, and variations in t h i s difference from place t o place are caused by climatic factors other than air temperature in combination with surface and subsurface terrain f a c t o r s . The complex energy exchange regime a t the ground s u r f a c e , which i s influenced by t h e s e f a c t o r s , i s such that the mean annual
ground temperature i s s e v e r a l d e g r e e s warmer than the mean annual air temperature. Factors which seem particularly
influential are net radiation, vegetation, snow cover, and ground thermal properties that vary with time; other factors include relief slope and orientation and surface and subsurface drainage
.
The difference between mean annual air and ground tempera- ture can be explained in part by the f a c t that the ground surface i s heated by solar radiation during the day to a much higher temperature than the a i r above; this e x c e s s heating more than b a l a n c e s the cooling of the ground surface by radia- tion during the night. Snow cover contributes to t h i s situation by insulating the s o i l from the cold air above [ 9 ] .
It i s suggested that the difference between mean annual air and ground temperature would be greater in interior continental l o c a l i t i e s than in maritime locations b e c a u s e of the greater snowfall and accumulation in the former a r e a s [ l o ] .
Variations in net radiation, vegetation, snow c o v e r , and other factors contribute to observed differences in the thick- n e s s and temperature of permafrost in neighboring a r e a s of the continuous zone having slmilar mean annual air temperature; they a l s o help explain the patchy occurrence of permafrost a t a particular location in the southern fringe of the permafrost region. The mean ground temperature in permafrost c a n vary a t any given depth within a region of only a few square miles due to v a r ~ a t i o n s in surface cover, ground t y p e , moisture content, geological structure, or geothermal gradient. In the discontinuous z o n e , variations in mean ground temperature frequently occur between the middle and edge of an individual body of permafrost
.
Fluctuations in the permafrost boundary generally within confines of the 25 and 30°F mean annual air isotherms a c r o s s C a n a d a , and l o c a l variations in the permafrost within a small a r e a , appear to be influenced by microclimatic and terrain f e a t u r e s . Heavy snowfall in late autumn e a s t of Hudson Bay may be responsible for the a b s e n c e of permafrost a t latitudes similar to those w e s t of Hudson Bay where permafrost i s widespread and late autumn snowfall i s considerably l e s s [6].
GROUND TEMPERATURE REGIME IN PERMAFROST
In permafrost, the temperature d e c r e a s e s steadily from the ground surface to a depth of about 50 to 100 f t [ l l ] . Below this depth, the permafrost temperature i n c r e a s e s steadily under the influence of h e a t from the e a r t h ' s interior. Fluctua- tions in air temperature during the year produce a temperature oscillation in the ground to depths on the order of 50 f t with a time lag increasing with depth. At t h e s e d e p t h s , tempera- ture variation i s extremely s m a l l ( l e s s than O.l°F); this i s ' referred to a s the " l e v e l of zero annual amplitude. " Below t h i s depth, influence of the annual air temperature c y c l e i s not f e l t and ground temperatures change only in r e s p o n s e to long-term c h a n g e s extending over many c e n t u r i e s . U s e of the present mean annual air temperature to predict the mean annual ground temperature a t depths below the l e v e l of zero annual amplitude i s complicated by the latter temperature being a reflection of both present and past climatic regimes (with possibly different mean annual air temperatures).
A change in mean annual air temperature c a n r e s u l t , over a long time, in a significant change in the extent and thick- n e s s of permafrost. Observations from C a n a d a , Alaska, and
t h e USSR s h o w t h a t t h e g e o t h e r m a l g r a d i e n t c a n v a r y within w i d e limlts (1°F/40 f t t o 1°F/300 ft) depending on thermal p r o p a r t i e s of s o i l a n d r o c k , g e c l o g l c a l s t r u c t u r e , a n d o t h e r f a c t o r s . In t h e M a c k e n z i e River d e l t a , C a n a d a , W . G
.
Brown [ 121 found n g e o t h e r m a l g r a d i e n t cf 1°F/53 f t . M i s e n c r [ 131 o b s e r v e d a g e o t h e r m a l g r a d i e n t of 1°F/46 f t a t R e s o l u t e , NWT, in the C a n a d i a n Arctic a r c h i p e l a g o . At Point Barrow, A l a s k a , g e o t h e r m a l g r a d i e n t s of 1°F/42 f t a n d 1°F/53 f t were found in a n o i l w e l l [ 1 4 ] a n d b e n e a t h a s m a l l l a k e [ 1 5 1 , r e s p e c t i v e l y . G e o t h e r m a l g r a d i e n t s ranging from 1°F/72 f t to 1°F/324 f t , d e p e n d i n g o n rock t y p e , were o b s e r v e d In the Lena River b a s i n , Siberia [ 161.
The lower v a l u e s o b s e r v e d in North America may be a t t r i b - u t e d partly to t h e proximity of large b o d i e s of w a t e r in c o n t r a s t to t h o s e in the USSR which w e r e m o s t l y in inland w a t e r s h e d s . S h p o l y a n s k a y a [ 171 reported v a l u e s in the T r a n s b a i k a l r e g i o n o f the USSR which a r e of t h e s a m e order of magnitude a s t h o s e c i t e d from C a n a d a and Alaska: 1°F/37 ft in s e d i m e n t a r y r o c k a n d 1°F/92 f t in d e n s e c r y s t a l l i n e r o c k . T h e r e f o r e , a c h a n g e o f 1°F, for e x a m p l e , in the mean a n n u a l a i r temperature c o u l d r e s u l t o v e r a long time in a c h a n g e of 1°F in the mean a n n u a l ground temperature. This would c a u s e a c h a n g e in permafrost t h i c k n e s s o f a p p r o x i m a t e l y 40 to 300 f t , d e p e n d i n g on t h e g e o t h e r m a l g r a d i e n t .
At some of t h e s e s t a t i o n s the r e c o r d s a r e e i t h e r of s h o r t d u r a t i o n , c o n t a i n g a p s , or a r e of q u e s t i o n a b l e r e l i a b i l i t y d u e to o b s e r v e r error or instrument d i f f i c u l t i e s : t h u s , o n l y approx- imate mean a n n u a l ground temperature v a l u e s c a n b e g i v e n . In s o m e c a s e s , the ground t e m p e r a t u r e s may n o t h a v e h a d time to return to t h e i r o r i g i n a l v a l u e s prior t o d i s t u r b a n c e b y i n s t a l - l a t i o n p r o c e d u r e s . In a d d i t i o n , a n e x c e s s of drilling w a s h w a t e r frozen around a temperature c a b l e in a h o l e would c h a n g e t h e thermal d i f f u s i v i t y of t h e ground b e i n g m e a s u r e d from the surrounding u n d i s t r u b e d ground s u f f i c i e n t l y to a f f e c t ground temperature o b s e r v a t i o n s . DISCUSSION R e s u l t s of O b s e r v a t i o n s M o s t of t h e t e m p e r a t u r e s r e p o r t e d w e r e m e a s u r e d under d i f f i c u l t f i e l d c o n d i t i o n s a n d a r e of q u e s t i o n a b l e p r e c i s i o n s o t h a t o n l y g e n e r a l r e l a t i o n s h i p s c a n b e d e d u c e d . T h e s e ground- temperature m e a s u r e m e n t s s u g g e s t t h a t there i s n o t a c o n s t a n t d i f f e r e n c e b e t w e e n them a n d the mean a n n u a l a i r temperatures. There i s n o i n s t a n c e , h o w e v e r , of the l a t t e r b e i n g h i g h e r than t h e former. Some of the ground temperature o b s e r v a t i o n s a r e e i t h e r s i n g l e o b s e r v a t i o n s or a v e r a g e s for o n l y part of a y e a r . As a r e s u l t , t h e v a l u e s v a r y s l i g h t l y from the mean a n n u a l ground t e m p e r a t u r e s , t h e d i f f e r e n c e d e c r e a s i n g w i t h d e p t h to t h e l e v e l of z e r o a n n u a l amplitude w h e r e t h e d i f f e r e n c e s h o u l d b e n e g l i g i b l e . V a r i a t i o n s in temperature with d e p t h a r e , of c o u r s e , g r e a t l y i n f l u e n c e d b y the g e o t h e r m a l g r a d i e n t , the magnitude of w h i c h v a r i e s from p l a c e to p l a c e . In v i e w of t h e s e f a c t o r s , it i s d i f f i c u l t to o b t a i n a p r e c i s e c o r r e l a t i o n b e t w e e n mean a n n u a l a i r a n d ground t e m p e r a t u r e s . B e c a u s e the problem c o n c e r n s v a r i a t i o n s in t h e ground thermal regime o v e r a y e a r o r m o r e , i t i s b e s t to make m e a s u r e m e n t s a t a d e p t h where t h e i n f l u e n c e of short-term w e a t h e r c y c l e s MEAN ANNUAL AIR AND GROUND TEMPERATURES IN CANADA
At p r e s e n t , ground temperature o b s e r v a t i o n s a r e a v a i l a b l e from 17 l o c a t i o n s in C a n a d a ' s permafrost region ( F i g . 1)
.
The l a t i - t u d e , l o n g i t u d e , h e i g h t a b o v e s e a l e v e l , permafrost d i s t r i b u - tion a n d t h i c k n e s s , a n d mean a n n u a l a i r t e m p e r a t u r e s of t h e s e s t a t i o n s a r e l i s t e d in T a b l e I . Information i s g i v e n a l s o for O t t a w a w h i c h i s s o u t h of the permafrost r e g i o n . Groundtemperature v a l u e s a r e l i s t e d in Table 11.
C O N T l NUOUS
100 0 100 200 300 400 500 800
-
M I L E S
w i l l ndt b e large (below a b o u t 2 ft)
.
None of t h e ground temperature v a l u e s ( e x c e p t O t t a w a [38]) h a s b e e n s u b j e c t e d t o Fourier a n a l y s i s b e c a u s e of t h e s h o r t duration of m o s t of t h e o b s e r v a t i o n s a n d their u n c e r t a i n a c c u r a c y . This type of a n a l y s i s c o u l d b e a p p l i e d probably to the Fort Simpson a n d Fort Vermilion v a l u e s .e x a m p l e , the ground temperature in t h e T a u r c a n i s mine of 29°F a t t h e 325-ft d e p t h i s probably s e v e r a l d e g r e e s higher than the p r o b a b l e temperature a t t h e l e v e l of z e r o a n n u a l a m p l i t u d e .
Mean a n n u a l ground s u r f a c e t e m p e r a t u r e s (1 cm depth) a r e a v a i l a b l e a t t h r e e s t a t i o n s . Comparison w i t h mean a n n u a l a i r t e m p e r a t u r e s s h o w e d d i f f e r e n c e s of 8 . O°F a t O t t a w a , Ont
.
,
10.4'F a t Fort S i m p s o n , NWT, and 11.6'F a t Fort Vermillion, A l t a .
D i f f e r e n c e s b e t w e e n mean a n n u a l a i r a n d ground tempera- t u r e s w e r e e x a m i n e d in r e l a t i o n to t h e r e l a t i v e c o n t i n e n t a l i t y o f their l o c a t i o n . Maritime s t a t i o n s include: A s b e s t o s H i l l , Q u e
.
,
C h u r c h i l l , M a n . , a n d Rankin I n l e t and R e s o l u t e , NWT.
D i f f e r e n c e s a t t h e s e s t a t i o n s d i d n o t a p p e a r to vary s i g n i f i - c a n t l y from t h o s e a t t h e o t h e r s t a t i o n s . Undoubtedly t h i s i s d u e to t h e l a c k of p r e c i s i o n in computing the d i f f e r e n c e s a n d t h e v a r i a b l e d e p t h s a t w h i c h o b s e r v a t i o n s w e r e m a d e . As a l r e a d y n o t e d , the m o s t s o u t h e r l y o c c u r r e n c e s of perma- f r o s t w i t h t e m p e r a t u r e s b e t w e e n 31' a n d 32'G, s e v e r a l t e n s of f e e t t h i c k , a n d n o t r e s t r i c t e d to a p a r t i c u l a r type of te'rrain, a r e found a t s u c h s t a t i o n s a s Thompson, M a n . , K e l s e y , M a n . , a n d Uranium C i t y , Sas)r. All t h e s e l o c a t i o n s h a v e mean Relation Between Air a n d Ground TemperaturesAir a n d ground temperature r e c o r d s s h o w t h a t the l a t t e r a r e warmer than t h e former b y a wide r a n g e varying from a b o u t
1°F a t Keg River, A l t a . , to 12'F a t T a u r c a n i s , NWT. Differ- e n c e s b e t w e e n mean a n n u a l a i r a n d ground t e m p e r a t u r e s a r e summarized in Table 111.
S e v e r a l f a c t o r s c o m p l i c a t e t h i s s i t u a t i o n : (a) Some indi- v i d u a l ground temperature v a l u e s a b o v e t h e l e v e l of z e r o a n n u a l amplitude may b e h i g h e r or lower than t h e a n n u a l mean depending on the time of y e a r a n d t h e d e p t h . (b) M e a n a n n u a l ground t e m p e r a t u r e s in permafrost d e c r e a s e with d e p t h from the ground s u r f a c e to a d e p t h of 5 0 to 100 f t a n d t h e n s t e a d i l y i n c r e a s e under the i n f l u e n c e of the g e o t h e r m a l g r a d i e n t . For
T a b l e I .
Permafrost M e a n 4 n n . Lat. Long. H t , a s l a Permafrost T h i c k n e s s , Air Temp.
,
N W (f t) Zone ( f t l b Source (OF) Location 1 . A i s h i h i k , Y .T
.
D i s c o n t i n u o u s 50 to 100 (Wide s p r e a d ) C o n t i n u o u s >930 C o n t i n u o u s 100 to 200 2. A s b e s t o s H i l l , P . Q . 3 . C h u r c h i l l . M a n . 4 . Fort Simpson, NWT. D i s c o n t i n u o u s a b o u t 40 (Patchy)5 . Fort Smith, NWT
.
None.
. .
6 . Fort Vermilion, Alta
.
(Keg River, Alta .)None
.
. .
D i s c o n t i n u o u s a b o u t 5 7 . I n u v i k , NWT. (Aklavik, NWT .) C o n t i n u o u s C o n t i n u o u s >300 8 . K e l s e y , M a n . D i s c o n t i n u o u s (Patchy) a b o u t 30 C o n t i n u o u s 250 to 3 0 0 [ 2 4 1 1 5 . 6 (Aklavik) 9 . M a c k e n z i e D e l t a L a k e , NWT. 1 0 . Norman W e l l s , NWT. C o n t i n u o u s o r D i s c o n t i n u o u s 150 to 200 (Widespread) 1 1 . Rankin I n l e t , NWT. ( C h e s t e r f i e l d I n l e t , NWT .) C o n t i n u o u s a b o u t 1000 1 2 . R e s o l u t e , NWT. 1 3 . S c h e f f e r v i l l e , P .Q. C o n t i n u o u s 1300 D i s c o n t i n u o u s (Widespread) >250 1 4 . T a u r c a n i s , NWT. 1 5 . Thompson, M a n . C o n t i n u o u s 900 D i s c o n t i n u o u s (Patchy) a b o u t 50 1 6 . Uranium C i t y , Sask: D i s c o n t i n u o u s (Patchy) a b o u t 30 1 7 . Yellowknife, NWT.
D i s c o n t i n u o u s 200 to 300 (Widespread) 1 8 . O t t a w a , O n t . None. . .
a ~ e i g h t a b o v e s e a l e v e l b ~ e r m a f r o s t t h i c k n e s s e s b a s e d on information r e p o r t e d t o 1 9 6 3 CDivision of Building R e s e a r c h , C a n a d aT a b l e 11.
M e a n Ann. Ground
Depth Ground Temp. O b s e r v a t i o n
Location (f t) Temp. (OF) (OF) D a t e s Source 1 . Alshihik, Y.T. . 20 28.3
.
. .
1953-1959 (weekly) DTC a2 . A s b e s t o s H i l l , P . Q . 50
. . .
1 9 . 6 Average of t w o D B R ~ 100. . .
1 9 . 6 r e a d i n g s 200. . .
19.6 1 5 Apr. '62 a n d 8 J u l y ' 6 2 3 . C h u r c h i l l , M a n . J u l y 1955 4 . Fort S i m p s o n , NWT. 1 cm 35.4. . .
1959-1962 (daily) [ 3 4 1 10 cm 34.9. . .
20 cm 3 4 . 1. . .
5 0 cm 34.6.
.
.
100 cm 33.7. . .
150 cm 33.2. . .
5 . Fort Smith, NWT.
a b o u t 1 5 a b o u t 3 2. . .
1 9 5 0 ' s D B R ~6 . Fort Vermilion, Alta. 1 cm 3 9 . 8
. . .
1959-1962 (daily)1 0 cm 3 8 . 9
. . .
134120 cm 38.8
. . .
5 0 cm 38.9. .
.
100 cm 38.9. . .
150 cm 38.9. .
.
Keg River, Alta
.
' a b o u t 5 a f e w t e n t h s.
. .
S e p t . 1963 D B R ~b e l o w 32 7 . I n u v i k , NWT. 47
. .
.
1955-1958 (weekly) [ 3 5 1. . .
1961-1963 (weekly) D B R ~. . .
. . .
t o w n s i t e 23.9 22 S e p t . ' 6 2 D B R ~ 2 4 . 5 25.4 1958-1963 (weekly) D B R ~road t o Hidden Lake 2 2 47 9 7 8 . K e l s e y , M a n . down t o 30 25.4 6 M a y 1 9 6 1 D B R ~ 25.9 26.5 28.0 2 9 . 2
. . .
E l 2 1 9 . M a c k e n z i e D e l t a Lake, 5 0 NWT. 75 100 150 200 s u r f a c e 1 0 . Norman W e l l s , NWT. 900 f t from river 6 0 100 180 200 5 0 100 a b o u t 100 50 100 25 5 0 100 140 190 3 25 down t o 25 down t o 30 2 . 3 4 . 3 6 . 3 8 . 3 100 f t £rom river 1 1 . Rankin I n l e t , NWT.
1 2 . R e s o l u t e , NWT. a b o u t 1 5 t o 1 7 1960 1954-1957 (weekly) 1 3 . S c h e f f e r v i l l e , P . Q . 1962 (weekly) 1 4 . T a u r c a n i s , NWT. 1 5 . Thompson, M a n . 1 6 . Uranium C i t y , S a s k . 1 7 . Yellowknife, NWT.
1 9 6 1 1961-1963 (weekly) 1954-1957 (weekly) 1954-1957 (weekly)Tab16 11. (continued)
M e a n Ann. Ground
Depth Ground Temp. O b s e r v a t i o n
Location (ft) Temp. (OF) (" F) D a t e s Source
1 8 . O t t a w a , Ont
.
1 cm 4 9 . 6 10 cm 49.o
20' crn 4 7 . 9 50 cm 4 8 . 5 100 cm 4 8 . 6 150 cm 4 8 . 6 1959-1962 (daily) 1341 a ~ e p a r t m e n t of T r a n s p o r t , C a n a d a b ~ i v i s i o n of Building R e s e a r c h , C a n a d a ' ~ c G i l 1 S u b a r c t i c Research Laboratory a n n u a l a i r t e m p e r a t u r e s of about 24' t o 25OF. An e x c e p t i o n t o t h i s i s A i s h i h i k , Y . T . , w h o s e mean a n n u a l a i r temperature o f 2 4 . S°F i s c o m p a r a b l e , b u t t h e mean a n n u a l ground temperature of 28.3OF a t t h e 20-ft depth i s s e v e r a l d e g r e e s lower t h a n t h e ground t e m p e r a t u r e s a t t h e o t h e r t h r e e s t a t i o n s . H o w e v e r , a mean a n n u a l a i r temperature o f , s a y 25OF or l e s s , i s a l m o s t c e r t a i n to i n d i c a t e a permafrost c o n d i t i o n in the v i c i n i t y .The q u e s t i o n a r i s e s a g a i n a s t o what i s t h e maximum mean a n n u a l a i r temperature a t which permafrost c a n e x i s t . Perma- f r o s t , a l b e i t o n l y a f e w f e e t t h i c k , i s found a t Keg River, Alta., which h a s a mean a n n u a l a i r temperature of 3 1 ° F . I t d o e s n o t o c c u r in the v i c i n i t y of Fort Vermilion, Alta. (28.2OF), nor a t Fort Smith, NWT (26.2OF), nor e v e n a t t h e Experimental Farm a t Fort S i m p s o n , NWT (25 .O°F). C l e a r l y v e g e t a t i o n p l a y s a dominant r o l e in t h i s s i t u a t i o n . Permafrost a t Keg River i s c o n f i n e d t o a few s m a l l s c a t t e r e d spruce-Sphagnum p e a t b o g s . N o s u c h b o g s o c c u r in the Fort Vermillion a r e a . Permafrost e x i s t s a l s o in s i m i l a r b o g s in t h e fort Smith a n d Fort Simpson a r e a s .
The origin of permafrost in t h e s e b o g s , p a r t i c u l a r l y in Keg River, c o u l d b e a t t r i b u t e d to one or more of t h e following c a u s e s :
( a ) It c o u l d b e a remnant from t h e c o o l e r c l i m a t i c regime of t h e P l e i s t o c e n e ;
(b) It could b e short-lived permafrost of p e r h a p s s e v e r a l d e c a d e s d u r a t i o n which formed a s a r e s u l t of s l i g h t l y lower a i r t e m p e r a t u r e s than t h o s e prevailing a t p r e s e n t ; a n d
( c ) It c o u l d b e s h o r t l i v e d a s in t h e s e c o n d c a s e b u t formed a s t h e r e s u l t of t e r r a i n c h a n g e s s u c h a s s n o w c o v e r or d r a i n a g e which were conducive t o i n i t i a t i o n of permafrost without a c h a n g e in mean a n n u a l a i r temperature.
In a l l three c a s e s t h e permafrost i s p r o t e c t e d b y m o s s a n d p e a t cover; it would probably d i s a p p e a r a n d not re-form if Lhis c o v e r were removed.
Thermal M e c h a n i s m s
M e c h a n i s m s which a l l o w formation of permafrost in t h e s e b o g s a r e a s s o c i a t e d with v a r i a t i o n s in h e a t e x c h a n g e a t t h e s u r f a c e o f t h e m o s s a n d p e a t . When d r y , p e a t h a s a low thermal c o n - d u c t i v i t y , e q u i v a l e n t to t h a t of s n o w . When w e t , i t s thermal c o n d u c t i v i t y i s g r e a t l y i n c r e a s e d ; when frozen i t s thermal c o n - d u c t i v i t y i s many t i m e s t h a t of dry p e a t . During s u m m e r , a thin s u r f a c e l a y e r of d r i e d p e a t h a v i n g a low thermal c o n d u c t i v i t y would p r e v e n t warming of the underlying s o i l . During the c o l d p a r t of y e a r , t h e p e a t i s s a t u r a t e d from t h e s u r f a c e ; when i t f r e e z e s , i t s thermal c o n d u c t i v i t y g r e a t l y i n c r e a s e s . B e c a u s e of t h i s t h e amount of h e a t t r a n s f e r r e d in winter from t h e ground t o t h e a t m o s p h e r e through t h e f r o z e n i c e - s a t u r a t e d p e a t i s g r e a t e r than t h e amount t r a n s m i t t e d in the o p p o s i t e d i r e c t i o n through the s u r f a c e l a y e r of dry p e a t a n d underlying w e t p e a t in summer. A c o n s i d e r a b l e portion of h e a t i s a l s o required during t h e warm period t o melt the i c e and t o
Table 111.
Location
M e a n Approx
.
Ann. Air A i r a r o u n d Temp. D i f f e r e n c e (OF) Ground T e m ~ . (OF) (OF) 1 . A i s h i h i k , Y.T. 24.5 28.3 (20 ft) 4 2 . A s b e s t o s H i l l , 19 t o 20 (50 f t t o P . Q . 1 7 200 ft) 2 - 3 3 . C h u r c h i l l , 27.5 t o 28.9 M a n . 19 (25 f t to 54 ft) 8-
1 0 4 . Fort S i m p s o n , 35.4 ( s u r f a c e ) t o NWT.
25.0 3 3 . 2 (150 cm) 8-
1 0 5 . Fort S m i t h , About 32 ( a b o u t NWT.
26.2 1 5 f t ) 6 6 . Fort Vermilion, 3 9 . 8 ( s u r f a c e ) t o Alta.
2 8 . 2 3 8 . 9 (150 cm) 1 0-
1 1 (Keg River, A f e w t e n t h s d e g r e e Alta .) 3 1 b e l o w 3 2 ( a b o u t 5 f t ) 1 7 . I n u v i k , NWT.. . .
About 26 (25 f t t o 1 0 l o o ft) (Aklavi k,
NWT.) 1 5 . 6 8 . K e l s e y , M a n . 30.5 t o 3 1 . 5 25.5 (down t o 30 ft) 5 - 6 9 . M a c k e n z i e D e l t a 1 5 . 6 23.8 ( s u r f a c e ) t o Lake, NWT. (Aklavik) 26.5 (100 ft) 8-
1 1 1 0 . Norman W e l l s , About 26 to 28.5 NWT. 2 0 . 8 (50 f t t o 100 ft) 5 - 8 1 1 . Rankin I n l e t , About 15 t o 1 7 NWT.. .
.
( a b o u t 1 0 0 ft) 4 - 6 ( C h e s t e r f i e l d I n l e t , N W T . ) 1 1 . 2 1 2 . R e s o l u t e , N W T . 2 . 8 1 0 . 0 ( 5 0 f t ) t o 6-
7 8 . 5 (100 ft) 13.
S c h e f f e r v i l l e , About 30 t o 31.5 P.Q. 23.9 (25 f t t o 190 ft) 6 - 8 1 4 . T a u r c a n i s , NWT. 1 7 29 (325 ft) 1 2 15.
Thompson, M a n . 24.9 3 1 t o 3 2 (down 6 - 7 t o 25 ft) 1 6 . Uranium C i t y , 31 t o 3 2 (down S a s k . 2 4 to 3 0 ft) 7 - 8 1 7 . Yellowknife, 33.0 (2.3 ft) t o NWT. 22.2 3 1 . 4 ( 8 . 3 ft) 9-
1 1 1 8 . O t t a w a , O n t . 4 1 . 6 49.6 ( s u r f a c e ) t o 6-
8 a b o u t 4 8 (150 cm)warm a n d e v a p o r a t e the w a t e r . The n e t r e s u l t i s a n e g a t i v e i m b a l a n c e of h e a t a n d c o n d i t i o n s c o n d u c i v e to the formation of permafrost.
Snow C o v e r
The i n f l u e n c e of s n o w c o v e r on the v a r i a t i o n b e t w e e n mean a n n u a l a i r and ground temperatures w a r r a n t s s e p a r a t e c o n s i d
-
e r a t i o n . T h i s i s i l l u s t r a t e d b y comparing mean a n n u a l a i r a n d ground t e m p e r a t u r e s a t Fort S i m p s o n , NWT; Fort Vermilion, Alta
.
,
and O t t a w a , O n t.
,
a l l l o c a t e d a t Dominion Experimen- t a l Farms of the C a n a d i a n Department of Agriculture. D e s p i t e s i m i l a r i t i e s in v e g e t a t i o n and s o i l s , d i f f e r e n c e s b e t w e e n mean a n n u a l a i r and ground s u r f a c e t e m p e r a t u r e s (1 cm depth) for the period 1959 to 1962 vary among t h e t h r e e stations-FortS i m p s o n , 11.2OF; Fort Vermilion, 9.7OF; a n d O t t a w a , 7 .O°F. S i g n i f i c a n t d i f f e r e n c e s in s n o w c o v e r c o u l d a c c o u n t for t h e s e v a r i a t i o n s . Average monthly s n o w cover d e p t h s for O c t o b e r to December when winter f r o s t p e n e t r a t i o n i s i n i t i a t e d a r e 5 . 9 , 3 . 2 , a n d 1 . 3 i n . for Fort Simpson, Fort Vermilion, a n d O t t a w a , r e s p e c t i v e l y .
Average monthly s n o w cover d e p t h s for April a n d M a y when a i r t e m p e r a t u r e s r i s e a b o v e 32OF a n d i n i t i a t e thawing of the f r o z e n ground a r e 1 1 . 2 , 2 . 9 , a n d 0 . 0 i n . . r e s p e c t i v e l y . Therefore, the s n o w c o v e r would h a v e the g r e a t e s t e f f e c t a t Fort Simpson and the l e a s t a t O t t a w a . I t i s d i f f i c u l t t o e s t i - m a t e , h o w e v e r , the n e t e f f e c t of t h e r e l a t i v e a m o u n t s of s n o w c o v e r during t h e f r e e z i n g a n d thawing p e r i o d s on mean a n n u a l ground t e m p e r a t u r e s .
Snow cover r e d u c e s the amount of s o l a r radiation r e c e i v e d a t the ground s u r f a c e t h u s affecting t h e d i f f e r e n c e s b e t w e e n mean a n n u a l a i r a n d ground t e m p e r a t u r e s . O b s e r v a t i o n s a r e a v a i l a b l e for Fort Simpson a n d O t t a w a , and a n n u a l amounts of radiation r e c e i v e d a t b o t h s t a t i o n s have a b o u t t h e s a m e e f f e c t when c o n s i d e r e d in r e l a t i o n t o s n o w c o v e r . During May t o September (1959 t o 1962) when the ground w a s f r e e of s n o w , the d a i l y a v e r a g e incoming s o l a r r a d i a t i o n w a s a b o u t 470 g c a l / s q cm a t O t t a w a a n d 425 g c a l / s q cm a t Fort Simpson-a difference of o n l y 10%. During October to April (1959 t o 1962) when t h e ground w a s s n o w covered a t Fort Simpson a n d O t t a w a for most of t h e p e r i o d , s o l a r r a d i a t i o n a t O t t a w a w a s a b o u t 225 g c a l / s q cm a n d a t Fort Simpson a b o u t
130 g c a l / s q cm-a difference If 42%. The e f f e c t of t h i s l a r g e difference would b e p r a c t i c a l l y n u l l i f i e d , h o w e v e r , b y t h e s n o w c o v e r a t both s i t e s .
CONCLUSION
It a p p e a r s t h a t a n a c c u r a t e prediction of mean a n n u a l ground temperature and t h e o c c u r r e n c e of permafrost a t a s i t e s o l e l y from t h e mean a n n u a l a i r temperature i s s u b j e c t t o v a r i a t i o n s c a u s e d b y o t h e r c l i m a t i c a n d terrain f a c t o r s a l r e a d y n o t e d . Many more o b s e r v a t i o n s a r e required before anything more than a broad r e l a t i o n c a n b e e s t a b l i s h e d . T h i s i s a formidablc b u t , h o p e f u l l y , n o t i m p o s s i b l e t a s k .
REFERENCES
[ l ] R. F . Legget, H , B. D i c k e n s , R. J . E. Brown. "Perma- f r o s t I n v e s t i g a t i o n s in C a n a d a , " P r o c . , 1 s t I n t l . Symp. Arctic
w.,
Vol. I1 (Geology of t h e Arctic), U n i v . Toronto P r e s s , 1 9 6 1 , p p . 956-969.[ 2 ] K . T e r z a g h i . " P e r m a f r o s t , " J . Boston S o c . C i v i l E n q r s . , Vol. 3 9 , 1 9 5 2 , p p . 1-50.
[ 3 ] R. F
.
Black. " P e r m a f r o s t , " Ann. Ropt. Bd. o f R e g e n t s S m i t h s o n i a n , 1 9 5 0 , W a s h i n g t o n , D . C . , G.P.O., pp. 273-301.[ 4 ] C . Nikiforoff
.
"The P e r p e t u a l l y Frozen S u b s o i l of S i b e r i a , " S o i l S c i . , Vol. 2 6 , 1 9 2 8 , pp. 61-78.[ 5 ] M . K . Thomas. C l i m a t o l o g i c a l A t l a s of C a n a d a , N a t l . R e s . C o u n . , D i v . Bldg. R e s . , a n d D e p t . T r a n s p o r t , Meteorol. D i v . , NRC 3 1 5 1 , 1953.
[ 6 ] R. J . E . Brown. "Distribution of Permafrost a n d I t s Relation t o Air Temperature in C a n a d a a n d the USSR, " Arctic, Vol. 1 3 , 1 9 6 0 , p p . 163-177
[ 7 ] H . A. Thompson. "Freezing a n d Thawing I n d i c e s in Northern C a n a d a , " P r o c . , 1 s t C a n a d i a n C o n f . Permafrost, N a t l . R e s . C o u n . , C a n a d a , A s s o c . Comm. S o i l and S n o w M e c h . , T e c h . M e m o . 7 6 , 1 9 6 3 , p p . 18-36. [ 8 ] E. B. W i l k i n s , W . C . D u j a y . "Freezing Index D a t a Influencing F r o s t Action, " P r o c . , 7th C a n a d i a n S o i l M e c h . C o n f . , N a t l . R e s . C o u n . , C a n a d a , A s s o c . Comm. S o i l a n d Snow M e c h . , T e c h . Memo. 3 3 , 1 9 5 4 , p p . 36-39. [ 9 ] J . E. C a r s o n . S o i l Temperature a n d Weather C o n d i t i o n s , Argonne N a t l . L a b . , Rept. No. 6 4 7 0 , Argonne, I l l . , 1961.
[ l o ] D . W . Boyd. N a t l . R e s . C o u n . , D i v . Bldg. R e s . , O t t a w a , C a n a d a , p e r s o n a l comm
.
,
1 9 6 3 .[ l l ] R. J . E . Brown, G . H . J o h n s t o n . "Permafrost a n d Related Engineering P r o b l e m s , " (in p r e s s ) .
[ 1 2 ] W . G . Brown, G . H . J o h n s t o n , R. J . E. Brown. "Com- p a r i s o n of O b s e r v e d and C a l c u l a t e d Temperature and Perma- f r o s t L o c a t i o n s Under a L a k e , " (in p r e s s )
.
1131 A. D . M i s e n e r . " H e a t Flow and Depth of Permafrost a t Resolute Bay, C o r n w a l l i s I s l a n d , NWT, C a n a d a , " T r a n s . Am. G e o ~ h v s . U n i o n , Vol. 3 6 , 1 9 5 5 , p p . 1055-1060.
[ 1 4 ] M. C
.
Brewer. "Some R e s u l t s of G e o t h e r m a l I n v e s t i g a - t i o n s of Permafrost in Northern A l a s k a , " T r a n s . Am. G e o p h y s.
Union,
Vol. 3 9 , 1 9 5 8 a , p p . 19-26.[ 1 5 ] M . C . Brewer. "The Thermal Regime of a n Arctic Lake," T r a n s , Am. G e o p h y s . U n i o n , Vol. 3 9 , 1 9 5 8 b , p p . 278-284.
[16] P . I . M e l ' n i k o v . " 0 z a k o n o m e r n o s t y a k h
r a s p r o s t r a n e n i y a i r a z v i t i y a merzlykh pochv i gornykh porod v b a s s e y n e R. Leny
,
" M a t e r i a l y Po ObshchemuM e r z l o t o v e d e n i y u , VII Mezhduvedomstvennove S o v e s h c h a n i y e Po M e r z l o t o v e d e n i v u , Ozd-vo Akad. Nauk SSSR, M o s c o w ,
1 9 5 9 , p p . 91-102. [ 1 7 ] N
.
A. S h p o l y a n s k a y a . " 0 v l i y a n i i u s l o v i y teploobmena p o v e r s k h n o s t i p o c h v y s a t m o s f e r o y n a vechnuyu merhlotu v z a b a y k a l ' e , " Vestnik M o s k o v s k o g o U n i v e r s i t e t a , No. 2 , 1 9 6 2 , p p . 37-42. [ 1 8 ] J . L. J e n n e s s . D e p t . M i n e s a n d R e s . , G e o g . B u r . , O t t a w a , C a n a d a (permafrost q u e s t i o n n a i r e , July 22, 1946). [ 1 9 ] J. F . M c Q u a t , E. N e c z k a r , R. D . L a w r e n c e . A s b e s t o s P r o j e c t , A s b e s t o s H i l l , Q u e . , Engr. Field Rept. N o . 2 , Murray Mining C o r p . , Ltd., Toronto, D e c . 1 5 , 1961. [ 2 0 ] W . A. J o h n s t o n . "Frozen Ground in t h e G l a c i a t e d P a r t s of Northern C a n a d a , " T r a n s . ROY. S o c . C a n . , Vol. )(XI', S e r . 3 , S e c . 4 , 1 9 3 0 , p p . 3 1 - 4 0 .[ 2 1 3 J . A. P i h l a i n e n . Fort S i m p s o n , NWT-Engineering S i t e Information; S o i l a n d Permafrost C o n d i t i o n s , N a t l . Res
.
Coun.,
C a n a d a , Div. Bldg. R e s . , T e c h . Paper No. 1 2 6 , NRC 6 4 5 2 , 1 9 6 1 .[ 2 2 ] C
.
H.
Anderson. Dominion Experimental Farm, C a n a d a D e p t . of A g r . , Fort Vermilion, A l t a . , p e r s o n a l c o m m . , 1962. [ 2 3 ] R. J . E. Brown, "Permafrost I n v e s t i g a t i o n s on t h e M a c k e n z i e Highway" (in p r e s s ) .[ 2 4 ] G . H . J o h n s t o n , R. J . E . Brown. "Effect of a Lake on D i s t r i b u t i o n of Permafrost in t h e M a c k e n z i e River D e l t a , " P r o c . , 1 s t C a n a d i a n C o n f . P e r m a f r o s t , N a t l . R e s . C o u n , , C a n a d a , A s s o c . Comm. S o i l and Snow M e c h
.
,
T e c h . Memo 76,1 9 6 3 , p p . 218-225. [ 2 5 ] G
.
D . G a r l a n d , D . H . Lennox. " H e a t Flow i n W e s t e r n C a n a d a , " G e o p h y s . J . Royal A s t r o n . S o c . , Vol. 6 , 1 9 6 2 , p p . 245-262. [ 2 6 ] R. A. H e m s t o c k . Permafrost a t Norman W e l l s , NWT, Imperial O i l , L t d . , C a l g a r y , 1 9 5 3 .[ 2 7 ] "Permafrost Q u e s t i o n n a i r e , " N a t l . Res
.
Coun.
,
C a n a d a , A s s o c . Comm . ' S o i l a n d Snow M e c h . , Note No. 5 , O t t a w a , D e c . 1 9 5 9 .[ 2 8 ] L. A n n e r s t e n . "Ground Temperature M e a s u r e m e n t s in t h e S c h e f f e r v i l l e Area, P .Q., " Proc
