Ground surface energy exchange studies at Norman Wells, N. W.T.

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NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

GROUND SURFACE ENERGY EXCHANGE STUDIES AT NORMAN WELLS, N.W.T. by R.

J.

E. Brown /:!:ti f . y z ~ ~ I n t e r n a l Report No. 2 5 9 o f t h e D i v i s i o n o f B u i l d i n g R e s e a r c h O t t a w a December 1 9 6 2

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PREFACE

Information on permafrost in Canada is being gathered continuously from a variety of sources including technical literature, reports from others operating in permafrost areas, circulation of a questionnaire to appro- priate groups in the North, and from direct field observations. Accompanying the collection of permafrost information by these means is the continuing study of the basic factors affecting its distribution and continued existence in order to improve the ability to predict its occurrence, Such work involves investigations of the basic climatic and terrain components of the energy exchange at the earthts surface that affect the occurrence of permafrost,

This report records the results of field studies of some of the components conducted by the author at the Division's Northern Research Station at Norman Wells, N.W.T. during the summers of

1959

and 1960. Difficulties were encountered in instrumentation and some of the results are inconclusive, Nevertheless, the Division hopes that the information obtained will contribute to a better under- standing of some aspects of the energy exchange regime ifi permafrost regions.

The author is a research officer in the Northern Research Group of the Division of Building Research, National Research Council where he is doing research on the distribution of permafrost in Canada.

Ottawa

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TABLE OF CONTENTS

-

APPARATUS AND OBSERVATION METHODS

1. P o t e n t i a l Evapotranspiration and Evaporation

( a ) P o t e n t i a l e v a p o t r a n s p i r a t i o n a t Thornthwaite s i t e ( b ) P o t e n t i a l e v a p o t r a n s p i r a t i o n a t o t h e r v e g e t a t i o n

s i t e s

( c ) Latent e v a p o r a b i l i t y of t h e a i r

( d ) Evaporation from open water s u r f a c e 2. Radiation

( a ) Incoming short-wave r a d i a t i o n ( b ) Net r a d i a t i o n

3. Ground Thermal Regime ( a ) Depth of thaw

( b ) Ground temperatures i n thawed l a y e r ( c ) Ground temperatures i n permafrost

( d ) S o i l moisture c o n t e n t RESULTS OF OBSERVATIONS

1. P o t e n t i a l Evapotranspiration and Evaporation

( a ) P o t e n t i a l e v a p o t r a n s p i r a t i o n a t Thornthwaite s i t e

( b ) P o t e n t i a l e v a p o t r a n s p i r a t i o n a t o t h e r v e g e t a t i o n s i t e s

2. Radiation

(a) Incoming short-wave r a d i a t i o n ( b ) Net r a d i a t i o n

3. Ground Temperatures and Depth of Thaw ( a ) Depth of thaw

( b ) Ground temperatures i n thawed l a y e r

( c ) Ground temperatures i n permafrost

( d ) S o i l moisture c o n t e n t

CONCLUSION

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GROUND SURFACE ENERGY EXCHANGE STUDIES

A T NORMAN WELLS, N.W.T.

R. J. E. Brown

For t h e p a s t few y e a r s , i n v e s t i g a t i o n s have been conducted by t h e DBR Northern Research Group ( f o r m e r l y t h e

_-

Northern ~ u i l d i n ~ S e c t i o n ) on t h e occurrence and d i s t r i b u - t i o n of permafrost i n Canada. I n f o r m a t i o n h a s been g a t h e r e d from a v a r i e t y of s o u r c e s i n c l u d i n g t e c h n i c a l l i t e r a t u r e , r e p o r t s from o t h e r s o p e r a t i n g i n permafrost a r e a s , and from d i r e c t f i e l d o b s e r v a t i o n s . Emphasis h a s been placed on t h e d e t e r m i n a t i o n of t h e s o u t h e r n l i m i t of permafrost b u t observa- t i o n s from t h e e n t i r e permafrost r e g i o n a r e b e i n g recorded

a l s o . T h i s c o l l e c t i o n of i n f o r m a t i o n i s c o n t i n u i n g , f a c i l i t a t e d by a permafrost q u e s t i o n n a i r e , which was prepared by t h e D i v i s i o n of B u i l d i n g Research and c i r c u l a t e d t o a p p r o p r i a t e groups

throughout n o r t h e r n Canada.

Obtaining a p i c t u r e of permafrost d i s t r i b u t i o n s o l e l y by such means i s i n e v i t a b l y a long-term p r o j e c t b u t t h e need was recognized f o r s t u d y i n g t h e b a s i c f a c t o r s a f f e c t i n g i t s d i s t r i b u t i o n and continued e x i s t e n c e t o

improve t h e a b i l i t y t o p r e d i c t i t s occurrence. I n t h e f a l l of 1958, t h e D i v i s i o n i n i t i a t e d s t u d i e s of t h e b a s i c c l i m a t i c and t e r r a i n components of t h e energy exchange a t t h e e a r t h ' s s u r f a c e a f f e c t i n g t h e occurrence of permafrost. During t h e summers of 1959 and 1960, f i e l d o b s e r v a t i o n s were c a r r i e d o u t a t t h e D i v i s i o n ' s Northern Research S t a t i o n a t Norman Wells, N.W.T. Norman Wells i s l o c a t e d on t h e r i g h t bank of t h e Mackenzie R i v e r , 90 m i l e s s o u t h of t h e A r c t i c C i r c l e 'and about 300 m i l e s n o r t h of t h e s o u t h e r n l i m i t of permafrost

( F i g u r e 1). The d e p t h t o permafrost a t Norman Wells v a r i e s from a few i n c h e s t o s e v e r a l f e e t depending on t h e s u r f a c e c o v e r and d i s t u r b a n c e by c o n s t r u c t i o n . Permafrost o c c u r s everywhere under t h e ground s u r f a c e and i s about 200 f t t h i c k .

The o b j e c t i v e s of t h e f i e l d s t u d i e s a t Norman Wells were twofold: t o develop i n s t r u m e n t a t i o n t e c h n i q u e s and t o

o b t a i n q u a n t i t a t i v e v a l u e s of some of t h e energy components a t t h e ground s u r f a c e . P o t e n t i a l e v a p o t r a n s p i r a t i o n , l a t e n t e v a p o r a t i o n , and n e t r a d i a t i o n of v a r i o u s t y p e s of v e g e t a t i v e cover and incoming short-wave r a d i a t i o n were measured. Ground t e m p e r a t u r e s were measured i n b o t h t h e s e a s o n a l l y thawed and p e r e n n i a l l y f r o z e n ground under t h e s e v e g e t a t i v e t y p e s . The l o c a t i o n s of t h e s i t e s i n t h e Norman \Veils a r e a a t which t h e s e o b s e r v a t i o n s were made a r e shown i n P i g u r e 1.

The o b j e c t of t h i s r e p o r t i s t o d e s c r i b e t h e

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f i e l d s t u d i e s and t o p r e s e n t t h e r e s u l t s of t h e s e s t u d i e s . APPARIITUS AND OBSERVATION METHODS

1, P o t e n t i a l E v a p o t r a n s p i r a t i o n and Evaporation

The t r a n s f e r of w a t e r , i n t h e form of vapour, from t h e s o i l t o t h e a i r by e v a p o r a t i o n , and from v e g e t a t i o n t o t h e a i r by t r a n s p i r a t i o n , i s a s i g n i f i c a n t p r o c e s s i n t h e energy exchange regime o p e r a t i n g a t t h e ground s u r f a c e . For e v e r y c u b i c c e n t i m e t r e of l i q u i d w a t e r i n t h e ground t h a t i s t r a n s f e r r e d t o t h e atmosphere, 540 c a l of h e a t a r e consumed t o change t h i s l i q u i d t o vapour, This r e p r e s e n t s a s i g n i f i c a n t p r o p o r t i o n of t h e t o t a l h e a t budget and a f f e c t s t h e t h e r m a l l e v e l of t h e ground i n which t h e p e r e n n i a l l y f r o z e n c o n d i t i o n e x i s t s , I t i s s u s p e c t e d t h a t c o n s i d e r a b l e h e a t t r a n s f e r may be involved a l s o i n t h e condensation of w a t e r vapour a s evidenced by t h e presence of a s u p e r s a t u r a t e d l a y e r a t t h e

bottom of l i c h e n even when i t s s u r f a c e i s completely d e s i c c a t e d

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The o b j e c t i v e s of t h e Norman Wells p o t e n t i a l evapo- t r a n s p i r a t i o n and e v a p o r a t i o n s t u d i e s were t h r e e f o l d ( l ) , The f i r s t one was t o c o n t i n u e o b s e r v a t i o n s of p o t e n t i a l e v a p o t r a n s - p i r a t i o n a t t h e c l i p p e d g r a s s (Kentucky b l u e g r a s s ) p l o t

i n s t a l l e d by t h e O n t a r i o Research Foundation i n 1949 ( 9 ) . The o r i g i n a l purpose of t h i s i n s t a l l a t i o n was t o t e s t t h e v a l i d i t y of t h e Thornthwaite world c l i m a t i c c l a s s i f i c a t i o n system, which i s based on p o t e n t i a l e v a p o t r a n s p i r a t i o n , f o r n o r t h e r n a r e a s t h a t have l o n g days d u r i n g t h e v e g e t a t i v e

growing season, Accompanying t h i s was t h e a t t e m p t t o determine q u a n t i t a t i v e d i f f e r e n c e s i n p o t e n t i a l e v a p o t r a n s p i r a t i o n from d i f f e r e n t v e g e t a t i o n t y p e s ( i . e . s e d g e , moss, l i c h e n ) beneath which permafrost e x i s t s , and t o compare t h e s e w i t h measurements obtained from t h e Thornthwaite s i t e . The second

o b j e c t i v e was t o measure t h e l a t e n t e v a p o r a b i l i t y of t h e a i r . The t h i r d one was t o measure e v a p o r a t i o n from a n open v ~ a t e r s u r f a c e . The l a s t t w o measurements have been compared w i t h t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n ,

( a ) P o t e n t i a l e v a p o t r a n s p i r a t i o n a t Thornthwaite s i t e

I n 1949, a Thornthwaite t y p e e v a p o t r a n s p i r o m e t e r ( 5 - f t s q pans) f o r measuring p o t e n t i a l e v a p o t r a n s p i r a t i o n was i n s t a l l e d by t h e O n t a r i o Research Foundation b e s i d e t h e a i r s t r i p , 1 1/2 m i l e s e a s t of Norman Wells ( 9 ) . D a i l y

measurements were t a k e n each surnmer u n t i l 1953 when t h e

i n s t a l l a t i o n was moved t o a n exposed s i t e i n t h e town a t t h e t o p of t h e bank of t h e EIackenzie R i v e r , a b o u t 250 yd west of t h e Northern Hesearch S t a t i o n ( F i g u r e s 2 , 3 ) . Personnel of

DB~?/NXC took d a i l y p o t e n t i . a l e v a p o t r a n s p i r a t i o n measurements f o r t h e O n t a r i o Research Poundation cach summer from 1355 t o 1360 i n c l u s i v e .

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During t h e summers of 1359 and 1960, Pan "Au was r e p l e n i s h e d by a c o n s t a n t w a t e r s u p p l y system. Pan "B" was s u p p l i e d d a i l y w i t h w a t e r . A f t e r t h e o v e r f l o w had been r e c o r d e d , a measured q u a n t i t y of w a t e r i n e x c e s s of t h e a n t i c i p a t e d p o t e n t i a l e v a p o t r a n s p i r a t i o n was s p r i n k l e d u n i f o r m l y o v e r t h e s u r f a c e . The g r a s s was c u t weekly and f e r t i l i z e r s p r i n k l e d on t h e g r a s s s e v e r a l t i m e s d u r i n g t h e summer, A i r t e m p e r a t u r e and r a i n f a l l were measured d a i l y . Dew p o i n t and wind s p e e d s were o b t a i n e d from t h e D,O,T. M e t e o r o l o g i c a l S t a t i o n a t Norman Wells.

( b ) l a t o t h e r v e g e t a t i o n s i t e s During t h e summers of 1359 and 1 9 6 0 , d a i l y p o t e n t i a l - e v a p o t r a n s p i r a t i o n measurements were e x t e n d e d t o s e d g e , moss and l i c h e n , which a r e n a t i v e t o t h e p e r m a f r o s t r e g i o n s , u s i n g v a r i o u s s i z e s of e v a p o t r a n s p i r o m e t e r s ( 5 , 6 ) . S e v e r a l were i n s t a l l e d a t t h e T h o r n t h w a i t e s i t e t o compare p o t e n t i a l e v a p o t r a n s p i r a t i o n r a t e s w i t h t h o s e o b t a i n e d from t h e l a r g e pans. O t h e r s i m i l a r d e v i c e s were i n s t a l l e d i n s e d g e , moss and l i c h e n a r e a s t o compare p o t e n t i a l e v a p o t r a n s p i r a t i o n r a t e s t h r o u g h t h e s e v e g e t a t i o n c o v e r t y p e s .

The l a r g e s t e v a p o t r a n s p i r o m e t e r s c o n s i s t e d of h a l f a 4 5 - g a l o i l drum a b o u t 56 cm i n d i a m e t e r , On t h e bottom of e a c h drum was welded a t h r e a d e d o u t l e t from which a p i p e l e d t o a n overflow c o n t a i n e r a b o u t

3

f t away ( F i g u r e 4 ) . The s m a l l e s t e v a p o t r a n s p i r o m e t e r s c o n s i s t e d of f r u i t j u i c e c a n s of 1 5 and 1 0 cm i n d i a m e t e r r e s p e c t i v e l y , Overflow was h e l d i n t h e bottom of t h e s e c o n t a i n e r s u n t i l r e l e a s e d f o r measure- ment by removing a s t o p p e r ,

E v a p o t r a n s p i r o m e t e r s were i n s t a l - l e d a t f i v e l o c a t i o n s ( d e s i g n a t e d a s S i t e s One t o Five r e s p e c t i v e l y ( F i g u r e

5 ) ) .

S i t e One was t h e T h o r n t h w a i t e s i t e where one o i l drum, t h r e e l a r g e and t h r e e s m a l l f r u i t j u i c e c a n s were i n s t a l l e d i n 1959, I n 1 9 6 0 , no r e a d i n g s were t a k e n on two of t h e l a r g e and two of t h e s m a l l c a n s , b u t r e a d i n g s were t a k e n t h r o u g h o u t t h e summer on t h e o t h e r s i n s t a l l e d i n 1959 ( F i g u r e 2 ) .

S i t e Two was a t r e e l e s s a r e a w i t h no moss o r l i c h e n , where sedge grew t o a h e i g h t of a b o u t 1 f t w i t h s c a t t e r e d . dwarf w i l l o w and ground b i r c h ( F i g u r e 6 ) . One o i l drum,

t h r e e l a r g e and t h r e e s m a l l f r u i t j u i c e c a n e v a p o t r a n s p i r o r n e t e r s were i n s t a l l e d h e r e i n 1959. I n 1960, t h e s e were r e p l a c e d by t h r e e o i l drums,

S i t e Three was a moss-covered a r e a w i t h s c a t t e r e d s p r u c e and tamarack up t o 6 f t h i g h , dwarf w i l l o w and b i r c h 2 f t h i g h w i t h a ground c o v e r of Labrador t e a and moss. One o i l drum, t h r e e l a r g e and t h r e e s m a l l f r u i t j u i c e c a n evapo- t r a n s p i r o r n e t e r s were i n s t a l l e d . h e r e i n 1959. T h i s s i t e was r e p l a c e d i n 1960 by a sphagnum moss-covered a r e a

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m i l e

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west of D.O.T. Lake, about 4 m i l e s e a s t of Norman Wells where t h r e e o i l drums were i n s t a l l e d .

S i t e Four was a d e n s e l y f o r e s t e d moss-covered a r e a w i t h spruce and tamarack up t o 20 f t h i g h , willow and a l d e r undergrowth up t o

4

f t h i g h and ground cover of Labrador t e a and moss ( F i g u r e s 4 , 7 ) . I n 1959, s i x l a r g e and s i x s m a l l f r u i t j u i c e cans were i n s t a l l e d . From a c l o s e examination of t h e ground, it appeared t h a t t h r e e d i s t i n c t s p e c i e s of moss covered t h e a r e a i n a mosaic. (Samples of t h e t h r e e t y p e s were brought t o Ottawa f o r examination a t t h e N a t i o n a l Herbarium and were i d e n t i f i e d a s Thuidium a b i e t i n u m , Thuidium abietinum and Fleuroziurn sp. i n a s s o c i a t i o n , and Sphagnum s p . ) I n a n a t t e m p t t o d e t e c t p o s s i b l e d i f f e r e n c e s of p o t e n t i a l

e v a p o t r a n s p i r a t i o n through t h e s e d i f f e r e n t moss s p e c i e s , two l a r g e and two s m a l l f r u i t j u i c e cans were i n s t a l l e d . i n each of t h e t h r e e t y p e s of moss. Three o i l drums were added i n 1960.

S i t e Five was covered w i t h l i c h e n (Cladonia a l p e s t r i s , C e t r a r i a n i v a l i s and C e t r a r i a c u c u l l a t a i n c l o s e a s s o c i a t i o n ) t o g e t h e r w i t h s c a t t e r e d s p r u c e , tamarack and b i r c h up t o 1 0 f t

h i g h and Labrador t e a . This s i t e i s 1 / 4 mile west of D.O.T. Lake and about

4

m i l e s e a s t of Norman Wells ( F i g u r e 8 ) . Three l a r g e and t h r e e s m a l l f r u i t j u i c e cans were i n s t a l l e d a t t h i s s i t e i n 1359. These were r e p l a c e d by t h r e e o i l drums i n 1960.

Measurements were t a k e n e v e r y morning on each evapo- t r a n s p i r o m e t e r from t h e d a t e of i n s t a l l a t i o n u n t i l t h e f i r s t autumn f r o s t . A f t e r t h e overflow had been r e c o r d e d , a measured q u a n t i t y of w a t e r i n e x c e s s of t h e a n t i c i p a t e d p o t e n t i a l

e v a p o t r a n s p i r a t i o n was s p r i n k l e d uniformly o v e r t h e s u r f a c e . I n 1959, t h e p e r i o d of o b s e r v a t i o n was v e r y s h o r t . The drum and cans a t t h e Thornthwaite s i t e were i n s t a l l e d between

5

and 1 0 August and r e a d i n g s were completed a b o u t 1 0 September. The remaining e v a p o t r a n s p i r o m e t e r s were n o t i n s t a l l e d u n t i l t h e l a s t week i n August and r e a d i n g s on t h e s e were a l s o completed about 1 0 September.

I n 1960, r e a d i n g s began i n June and were completed on 1 7 September. A i r t e m p e r a t u r e s an.d r a i n f a l l were measured d a i l y a t each s i t e . A t S i t e s Two t o F i v e , some p e r e n n i a l l y f r o z e n s o i l had t o be excavated t o accommodate t h e o i l drums and overflow a p p a r a t u s b u t t h e low s o i l t e m p e r a t u r e s d i d n o t a p p e a r t o i n t e r f e r e w i t h t h e e v a p o t r a n s p i r a t i o n o r overflow.

( c ) L a t e n t e v a p o r a b i l i t y of t h e a i r

An Alumdum d i s c atmometer was borrowed from t h e F e d e r a l Department of A g r i c u l t u r e t o measure t h e l a t e n t

e v a p o r a b i l i t y of t h e a i r a t Norman ' ; J e l l s , a s p a r t of a c o u n t r y - wide program of e v a p o r a t i o n measurements b e i n g conducted by

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t h e M e t e o r o l o g i c a l Branch, Depar.trnent of T r a n s p o r t ( F i g u r e 9 ( 8 ) ) .

T h i s atmometer was i n s t a l l e d i n t h e s o u t h w e s t c o m e r of t h e T h o r n t h w a i t e p o t e n t i a l e v a p o t r a n s p i r a t i o n s i t e . I n 1953, d a i l y r e a d i n g s were t a k e n from t h e b e g i n n i n g of A u g u s t - u n t i l e a r l y September. I n 1960, d a i l y r e a d i n g s were t a k e n from

11 June u n t i l 1 7 September. The r e s u l t s of b o t h summers were compared w i t h o b s e r v a t i o n s from t h e T h o r n t h w a i t e s i t e .

( d ) E v a ~ o r a t i o n from oDen w a t e r s u r f a c e

I n 1360, a Class "A" E v a p o r a t i o n Pan was s u p p l i e d by t h e M e t e o r o l o g i c a l Branch, Department of T r a n s p o r t t o measure t h e e v a p o r a t i o n from t h e s u r f a c e of w a t e r i n a n open pan, a s p a r t of a country-wide program of e v a p o r a t i o n measurements ( F i g u r e 1 0 ) . T h i s i n s t a l l a t i o n was l o c a t e d 1 5 f t w e s t of t h e T h o r n t h w a i t e s i t e . D a i l y r e a d i n g s were t a k e n from

11 June t o

17

September and t h e r e s u l t s compared w i t h t h e o b s e r v a t i o n s from t h e T h o r n t h w a i t e s i t e .

2. R a d i a t i o n

The main s o u r c e of e n e r g y c o n t r i b u t i n g t o t h e e n e r g y exchange a t t h e ground s u r f a c e and t o t h e ground t h e r m a l regime

i s t h e sun. Some of t h e incoming r a d i a t i o n i s a b s o r b e d i n t h e atmosphere, some i s r e f l e c t e d a t t h e ground s u r f a c e back i n t o t h e a t m o s p h e r e , and t h e r e m a i n d e r e n t e r s t h e ground. Two i n s t r u m e n t s were u s e d t o measure t h e r a d i a t i o n component of t h e e n e r g y exchange a t Norman W e l l s : a Gunn-Bellani r a d i a t i o n i n t e g r a t o r and a n economic n e t r a d i o m e t e r .

( a ) Incoming short-wave r a d i a t i o n

The Gunn-Bellani r a d i a t i o n i n t e g r a t o r ( 2 ) g i v e s a measure of t h e t o t a l incoming short-wave s o l a r and s k y

r a d i a t i o n r e a c h i n g a blackened c o p p e r s p h e r e c o n t a i n i n g a l c o h o l ( F i g u r e 11). The i n t e g r a t e d r a d i a t i o n r e c e i v e d by t h e c o p p e r s p h e r e v a p o u r i z e s t h e a l c o h o l w i t h i n

it

which condenses i n t h e g r a d u a t e d g l a s s r e c e i v e r .

Three of t h e s e i n s t r u m e n t s were o b t a i n e d f o r u s e a t Norman Wells. P r i o r t o t h i s , t h e y had been i n s t a l l e d i n t h e DBR T e s t Area i n Ottawa and r e a d i n g s compared w i t h t h e

Eppley p y r h e l i o m e t e r t h e r e t o o b t a i n c a l i b r a t i o n c o n s t a n t s . I n 1959, two of t h e s e i n s t r u m e n t s were i n s t a l l e d a b o u t 4 f t

a p a r t i n t h e n o r t h w e s t c o m e r o f t h e T h o r n t h w a i t e s i t e and d a i l y r e a d i n g s were t a k e n from 8 August t o 1 2 September

( F i g u r e 1 2 ) . I n 1960, two of t h e s e i n s t r u m e n t s were i n s t a l l e d a g a i n i n t h e n o r t h w e s t c o m e r of t h e T h o r n t h w a i t e s i t e . On

23 J u n e , t h e t h i r d i n s t r u m e n t was i n s t a l l e d a t S i t e F i v e ( l i c h e n a r e a ) a t D.O.T. Lake. D a i l y r e a d i n g s were t a k e n on t h e t h r e e i n s t r u m e n t s u n t i l 1 7 September.

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( b ) Net r a d i a t i o n

The n e t r a d i a t i o n normal t o t h e e a r t h ' s s u r f a c e i s

t h e d i f f e r e n c e between t h e t o t a l upward r a d i a t i o n f l u x and t h e t o t a l downward r a d i a t i o n f l u x . Net r a d i a t i o n i s i m p o r t a n t t o many m e t e o r o l o g i c a l problems b e c a u s e

it

i s a measure of t h e e n e r g y a v a i l a b l e a t t h e e a r t h - a t m o s p h e r e i n t e r f a c e ; it i s

s i g n i f i c a n t i n p e r m a f r o s t a r e a s a s

it

i n d i c a t e s t h e amount o f e n e r g y p u t i n t o t h e ground i n which p e r m a f r o s t e x i s t s .

An economic n e t r a d i o m e t e r ( 1 0 ) was used a t Norman W e l l s i n 1959 t o measure t h e n e t r a d i a t i o n of t h e v a r i o u s

v e g e t a t i v e s u r f a c e s a t which p o t e n t i a l e v a p o t r a n s p i r a t i o n measurements were b e i n g made ( F i g u r e s 1 3 , 1 4 ) . Weekly

r e a d i n g s were t a k e n a t e a c h of t h e s e s i t e s when t h e d e p t h o f thaw and ground t e m p e r a t u r e measurements were t a k e n .

A r e c o r d of t h e s u n s h i n e d u r a t i o n f o r e a c h h o u r was o b t a i n e d from t h e m e t e o r o l o g i c a l s t a t i o n a t Norman Wells. U n f o r t u n a t e l y , no r a d i a t i o n measurements were t a k e n a t Norman Wells by t h e Department of T r a n s p o r t s o t h a t t h e r e were no o b s e r v a t i o n s w i t h which t h e r e s u l t s of t h e economic n e t r a d i o m e t e r c o u l d be compared. T h i s i n s t r u m e n t was n o t u s e d i n 1960.

Ground Thermal Regime

O b s e r v a t i o n s were made a t t h e p o t e n t i a l e v a p o t r a n s - p i r a t i o n s i t e s t o compare t h e ground t h e r m a l regime u n d e r d i f f e r e n t t y p e s of v e g e t a t i v e c o v e r . These c o n s i s t e d of

d e p t h of thaw measurements and ground t e m p e r a t u r e o b s e r v a t i o n s on thermocouples i n t h e s e a s o n a l l y thawed and p e r e r n i a l l y

f r o z e n ground. ( a ) Depth of thaw

I n 1957 and 1 9 5 8 , d e p t h of thaw measurements were t a k e n a t f i v e s i t e s of which some were used a s p o t e n t i a l e v a p o t r a n s p i r a t i o n s i t e s i n 1959 a n d 1960. I n 1359 o n l y

f o u r of t h e s e s i t e s were k e p t u n d e r o b s e r v a t i o n . The purpose o f t h e s e measurements was t o d e t e r m i n e q u a n t i t a t i v e v a r i a t i o n s i n t h e d e p t h o f thaw u n d e r d i f f e r e n t t y p e s of v e g e t a t i v e

c o v e r and t o a s s e s s t h e r e l a t i v e i m p o r t a n c e of t h e i n d i v i d u a l components c o m p r i s i n g t h e v e g e t a t i v e c o v e r , i . e . t r e e s ,

undergrowth, s e d g e , moss, and l i c h e n .

Weekly o b s e r v a t i o n s were made w i t h a H o f f e r probe when t h e d e p t h of thaw was l e s s t h a n

3

f t , and w i t h a 1 1/2-

i n . d i a m e t e r s o i l a u g e r when t h e d e p t h of thaw exceeded

3

f t . Three o r f o u r measurements were made weekly a t e a c h s i t e and a n a v e r a g e v a l u e was t a k e n . These o b s e r v a t i o n s were n o t c a r r i e d o u t i n 1960 b e c a u s e

it

was t h o u g h t t h a t 3 y e a r s o f o b s e r v a t i o n s was s u f f i c i e n t t o i n d i c a t e s i g n i f i c a n t d e p t h o f thaw v a r i a t i o n s .

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( b ) Ground t e m p e r a t u r e s i n thawed l a y e r

I n 1959, 20-gauge c o p p e r - c o n s t a n t a n thermocouples were i n s t a l l e d a t t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n s i t e s a t t h e f o l l o w i n g d e p t h s :

T h o r n t h w a i t e s i t e on 11 August a t d e p t h s of 0 , 3 , 6 , 9 , 1 2 , 36 and 60 i n . On 9 September, a thermocouple was i n s t a l l e d a t t h e 7 0 - i n . d e p t h .

Sedge a r e a ( S i t e Two) on 1 3 August a t d e p t h s of 0 ,

3 , 6 , 9 , 1 2 , 18, 24, 30, 36 and 60 i n .

S p a r s e l y t r e e d moss a r e a ( S i t e T h r e e ) on 1 3 August, a t d e p t h s of 0 , 3 , 6 , 9 , 1 2 and 18 i n . On 25 September, a thermocouple was i n s t a l l e d a t t h e 22-in. d e p t h .

Wooded a r e a ( S i t e F o u r ) on 1 3 August, a t d e p t h s of

0 , 3 , 6 , 9 and 1 2 i n . On 22 September, a thermocouple was i n s t a l l e d a t t h e 1 4 - i n . d e p t h .

B e s i d e s t h e above i n s t a l l a t i o n s , thermocouples were i n s t a l l e d a t d e p t h s of 0 , 3 , 6 , 9 , 1 2 , 18 and 24 i n . on

1 3 August i n a moss-covered sedge a r e a i n which d e p t h of thaw measurements were t a k e n . I t had been i n t e n d e d t o i n s t a l l e v a p o t r a n s p i r o m e t e r s h e r e , b u t w a t e r l o g g e d c o n d i t i o n s p r e v e n t e d t h i s .

Two s p e c i a l s e t s of thermocouple s t r i n g s were

f a b r i c a t e d t o o b t a i n a d e t a i l e d t e m p e r a t u r e g r a d i e n t t h r o u g h moss and l i c h e n . I n e a c h c a s e , 1 3 thermocouples were s p a c e d a t 1 - i n . i n t e r v a l s from t h e ground s u r f a c e t o t h e 1 - f t d e p t h and r e a d w i t h a 2 0 - p o i n t s e l e c t o r s w i t c h . These were i n s t a l l e d on 24 August 1 9 5 9 , one i n t h e wooded a r e a ( S i t e F o u r ) where t h e sphagnum moss exceeds 1 2 i n . i n t h i c k n e s s , and t h e o t h e r i n t h e l i c h e n ( S i t e F i v e ) which i s a b o u t 2 i n . t h i c k a t D.O.T.

Lake

.

The s e v e n s e t s o f thermocouples were r e a d weekly when t h e d e p t h of thaw o b s e r v a t j - o n s were t a k e n . I n a d d i t i o n ,

27 c o n s e c u t i v e h o u r l y r e a d i n g s from 9.00 a.m. 1 4 August t o

11.00 a.m. 1 5 August were t a k e n a t t h e T h o r n t h w a i t e s i t e . The o b s e r v a t i o n program of ground t e m p e r a t u r e r e a d i n g s was c o n t i n u e d i n 1960 w i t h a few changes. Weekly r e a d i n g s were t a k e n b e g i n n i n g on 9 June and e n d i n g on

23 September. A t t h e T h o m t h w a i t e s i t e , r e a d i n g s were t a k e n on t h e thermocouples i n s t a l l e d i n 1959. I n a d d i t i o n , thermo- c o u p l e s were i n s t a l l e d a t d e p t h s o f 24 and 48 i n . on 5 J u l y . Thermocouples were a l s o i n s t a l l e d i n Pan B a t d e p t h s of 6 , 1 2 and 26 i n . on 11 June t o compare ground t e m p e r a t u r e s i n s i d e t h e pans w i t h t h o s e o u t s i d e .

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I n t h e sedge a r e a ( S i t e Two), r e a d i n g s on t h e thermocouples i n s t a l l e d i n 1959 were n o t t a k e n i n 1960. New thermocouples were i n s t a l l e d a t d e p t h s of 6 , 12 and 18 i n . on 15 June, a t a depth of 4 8 i n . on 12 J u l y and a t 60 i n . on 1 0 August. The l a s t two thermocouples were i n s t a l l e d s h o r t l y a f t e r t h e s o i l had thawed t o t h e d e p t h s i n d i c a t e d .

I n t h e wooded a r e a ( S i t e F o u r ) , r e a d i n g s were t a k e n on t h e thermocouples i n s t a l l e d i n 1959. I n a d d i t i o n , thermocouples were i n s t a l l e d b e s i d e t h e o i l drums a t d e p t h s of 6 and 12 i n . on

5

J u l y .

Readings were n o t t a k e n i n 1960 on t h e thermocouples i n s t a l l e d i n 1959 i n t h e moss-covered sedge a r e a , which was t o o wet f o r t h e i n s t a l l a t i o n of e v a p o t r a n s p i r o m e t e r s .

The two s p e c i a l thermocouple s t r i n g s w i t h s e l e c t o r s w i t c h e s were i n s t a l l e d i n t h i c k moss and l i c h e n r e s p e c t i v e l y a t t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n s i t e s a t D.O.T. Lake.

Ground temperatures i n permafrost

V a r i a t i o n s i n mean annual ground t e m p e r a t u r e s i n permafrost a r e of p a r t i c u l a r i n t e r e s t i n energy exchange

s t u d i e s . The temperature of t h e permafrost marks t h e thermal l e v e l of t h e ground and i s t h e sum t o t a l of t h e h e a t g a i n s and h e a t l o s s e s c o n t r i b u t e d by t h e v a r i o u s f a c t o r s comprising t h e environment i n which permafrost e x i s t s . Vegetation i s one of t h e s e f a c t o r s , and i n 1960, a device was developed

and i n s t a l l e d t o measure v a r i a t i o n s i n mean ground t e m p e r a t u r e s i n permafrost caused by d i f f e r e n t t y p e s of cover. The d e v i c e c o n s i s t e d of a maximum-minimum r e c o r d i n g d i a l thermometer

3

_{i n .}

i n diameter w i t h a 2 1 / 2 - i n . stem. This was housed i n a 1 0 - f t p l a s t i c pipe i n a d r i l l h o l e i n t h e ground ( F i g u r e

5 ) .

Ten d i a l thermometers were i n s t a l l e d a t Norman Vlells i n 1960. The p l a s t i c p i p e s were i n s t a l l e d i n August t o a l l o w them t o f r e e z e s o l i d l y i n t h e d r i l l h o l e s i n t h e permafrost by September. Three were l o c a t e d i n t h e sedge a r e a ( S i t e Two). Three were l o c a t e d i n a moss-covered a r e a ( s i m i l a r t o S i t e Four) b e s i d e t h e road t o t h e a i r p o r t , and f o u r were l o c a t e d

i n t h e l i c h e n a r e a ( S i t e F i v e ) . A t t h e end of September t h e thermometers were placed i n t h e p i p e s . The i n t e n t i o n was t o r e t r i e v e them a y e a r l a t e r , i n September 1961, and r e c o r d t h e maxirnurn and minimum temperatures. It was assumed t h a t t h e average of t h e maximum and minimum t e m p e r a t u r e s would be a

c l o s e approximation of t h e mean ground temperature. The thermoneters were read i n Nay and Septernber 1961.

To check on t h e t e m p e r a t u r e s recorded on t h e d i a l thermometers, thermocouple c a b l e s were i n s t a l l e d a t t h e s i t e s viith thermocouples a t t h e f o l l o n i n g d e p t h s :

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Sedge a r e a

-

1 / 2 , 1 1 / 2 , 2 1 / 2 ,

3

1 / 2 , 4 1 / 2 , 9 1 / 2 , 1 4 1/2 and 1 9 1/2 f t . Moss a r e a

-

1 / 2 , 1 1 / 2 , 2 1 / 2 ,

3

1 / 2 , 8 1 / 2 , 1 3 1 / 2 and 18 1/2 f t . Lichen a r e a

-

1, 2 ,

3 ,

4 ,

5 ,

1 0 and 11 1 / 2 f t ( F i g u r e 8 ) .

Weekly r e a d i n g s were t a k e n on t h e s e

u n t i l

l a t e September. Arrangements were made t o have monthly r e a d i n g s t a k e n on

t h e s e c a b l e s t h r o u g h o u t t h e w i n t e r b y l o c a l p e r s o n n e l , b u t u n f o r e s e e n c i r c u m s t a n c e s p r e v e n t e d t h i s .

( d ) S o i l m o i s t u r e c o n t e n t

I n 1959, m o i s t u r e c o n t e n t samples were t a k e n i n l a t e August and l a t e September a t t h e s i t e s , a t t h e d e p t h s where

thermocouples were l o c a t e d i n t h e t h a l ~ e d l a y e r . These samples were t a k e n immediately a f t e r measuring t h e ground t e m p e r a t u r e s t o d i s c o v e r what e f f e c t s t h e d i f f e r e n c e s i n m o i s t u r e c o n t e n t m i g h t have on ground t e m p e r a t u r e s . IiESULTS OF OBSERVATIONS 1. P o t e n t i a l E v a p o t r a n s p i r a t i o n and E v a p o r a t i o n ( a ) P o t e n t i a l e v a p o t r a n s p i r a t i o n a t T h o r n t h w a i t e s i t e I n 1959, t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n ( P.E. ) of t h e l a r g e g r a s s - c o v e r e d pans a t t h e Thornthcvaite s i t e was measured d a i l y from 1 A u s s t t o 7 September i n c l u s i v e . The P.E. f o r Pan "B" f o r August was 5.44 cm. The P.E. f o r Pan A from 1 5 - 3 1 August was 3.13 cm and 3.28 cm f o r Pan B ( T a b l e I ) . I t a p p e a r s t h a t t h e two pans had s i m i l a r P.E. r a t e s d u r i n g t h e 1959 o p e r a t i n g s e a s o n .

I n 1960, c a l c u l a t i o n s of P.E. f o r t h e T h o r n t h w a i t e s i t e were made f o r t h e 80-day p e r i o d of 30 June t o

17

September i n c l u s i v e ( T a b l e I ) . During t h i s p e r i o d , T)an A , equipped w i t h t h e c o n s t a n t w a t e r s u p p l y s y s t e m , gave a l o w e r P.E. (16.73 cm) t h a n Pan B ( 1 9 . 4 1 cm) b e c a u s e of o c c a s i o n a l s t i c k i n g of t h e f l o a t pan v a l v e which r e d u c e d t h e s u p p l y of w a t e r from t h e r e s e r v o i r t a n k . It i s s u g g e s t e d t h a t Pan B gave a more r e a l i s t i c measure of t h e P.E. t h a n Pan A .

These observed P.E. r a t e s were compared w i t h f o u r t h e o r e t i c a l f o r m u l a e used t o compute P.E., and w i t h t h e e v a p o r a t i o n of w a t e r from t h e C l a s s A Fan.

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The f i r s t f orrnula s u g ~ e s t e d by t h e E x p e r i m e n t a l Farm, Canada Department of A g r i c u l t u r e , d e r i v e s

P.E.

from l a t e n t e v a p o r a t i o n measurements o b t a i n e d from t h e Alumdum d i s c atmometer ( 8 ) . From 5 t o 11. August 1 3 5 9 , t h i s a p p a r a t u s was n o t f u n c t i o n i n g because t h e porous p l a t e was b r o k e n and a new one had t o be o r d e r e d from Ottawa. Near f r e e z i n g tempera-tures and snow i n e a r l y September made t h e v a l i d i t y of t h e September o b s e r v a t i o n s q u e s t i o n a b l e . Comparison was made, t h e r e f o r e , w i t h t h e e v a p o r a t i o n t o t a l of 1 5 t o 31 August, The f o r m u l a i s :

E.E. x 0.0034 x 2.54 =

P.E.

(cm) ( R e f . 6 )

.

. .

.

(1) where

L.E. i s l a t e n t e v a p o r a t i o n .

Applying t h i s formula g i v e s a

P.F.

of 4.19 crn compared w i t h 3.19 and 3.28 c m measured i n t h e T h o r n t h w a i t e pans ( T a b l e I ) . I n 1960, a good c o r r e l a t i o n was o b t a i n e d between t h e P.E.

measured from Pan R and t h e l a t e n t e v a p o r a t i o n measured on t h e Alurndum d i s c atmorneter f o r t h e p e r i o d of 30 June t o 1 7 September, The t o t a l P.E. f o r Pan

B

was 1 9 . 4 1 cm compared t o 19.47 cm f o r t h e atrnometer ( T a b l e I ) .

The second formula i s T h o r n - t h w a i t e ' s (11) i n which h e d e r i v e d P.E. by c o n s i d e r i n g t h e l e n ~ t h of day and a h e a t i n d e x r e l a t e d t o t h e number of d e g r e e s t h a t t h e mean d a i l y t e m p e r a t u r e i s above 32OF. The amount of p r e c i p i t a t i o n i s n o t c o n s i d e r e d because i t i s assumed t h a t t h e amount of w a t e r e v a p o r a t e d and t r a n s p i r e d i s d e t e r m i n e d by t e m p e r a t i l r e and l e n g t h of day. Without go in^ e x h a u s t i v e l y i n t o t h e d e r i v a t i o n of T h o r n t h w a i t e l s f a c t o r s , it i s s u f f i c i e n t t o s a y t h a t t h e P.E. a t Norman Wells u s i n g a h e a t i n d e x of 1 7 . 3 v a r i e s almos-t l i n e a r l y from 0.02 cm a t 33OF t o 0.30 cm a t GOOF. The

a p p l i c a b l e

P.E.,

depending on t h e mean d a i l y t e m p e r a t u r e , i s m u l t i p l i e d by t h e d u r a t i o n of s u n l i c h t f o r t h a t day i n u n i t s of 1 2 h o u r s . Using t h i s f o r m u l a , t h e computed

P.Z.

f o r

August 1959 was 7 . 9 1 cm. F o r 1 5 t o 3 1 A u ~ u s t 1 9 5 9 , it was

4.47

cm ( T a b l e I ) , I n 1960, t h e T h o r n t h w a i t e computed P.E. was a l s o h i g h e r t h a n t h e measured P.E. f o r t h e 80-day p e r i o d b e i n g 24.75 cm ( T a b l e I ) .

The u s e of t h e T h o m t h w a i t e formula i n h i g h l a t i t u d e s h a s been c r i t i c i z e d because (1) t h e h e a t i n d e x h a s been computed o n l y n o r t h t o 50° and Norman Well-s, f o r example, l i e s a t 66ON;

( 2 ) t h e l e n g t h of day f a c t o r s useci t o compute P.E. a t Norman Wells have a l s o been computed f o r 50°N. F u r t h e r n o r t h t h e d a y s a r e l o n g e r d u r i n g t h e e v a p o t r a n s p i r a t i o n p e r i o d b u t t h e amount of incoming s o l a r r a d i a t i o n i s l e s s b e c a u s e of t h e l o w e r a n g l e o r t h e sun and t h e low a n g l e of i n c i d e n c e . I t

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The t h i r d formula i s H o l d r i d g e t s which i s ( 4 ) : Unit p e r i o d of P.E.(mm) = 58.93

_N~~~~~

_of _units _of

. . .

( 2 ) time i n 1 y e a r

(

t e m p e r a t u r e ,

oc

The s o l v e d v a l u e s f o r t h e i t e m s i n f i r s t b r a c k e t f o r p e r i o d s of time normally used f o r d e t e r m i n i n g P.3. a r e :

1 y e a r

-

58.93 1 month ( 3 1 d a y s )

-

5.00

1 month ( 3 0 d a y s )

-

4 . 8 4 1 month ( 3 0 d.ays)

-

4.83 1 month ( 2 8 d a y s )

-

4.52 1 month ( 2 9 d a y s )

-

4.67

1 day

-

0.16

The comparative p l a n t growth mean t e m p e r a t u r e e q u a l s

Sum of average p o s i t i v e t e m p e r a t u r e s i n O ~ / u n i t of t i m e

number of t h e u n l t s of t l m e ~ n t h e p e r i o d of t h e mean

I

For t h e purposes of computing .P.E., t h i s formula can be s i m p l i - f i e d t o a s e l e c t i n g of t h e p e r t i n e n t f a c t o r s f o r t h e l e n g t h of time i n v o l v e d . For August 1959 (31-day month

-

n o t Leap Year) t h e f a c t o r i s 5.00. T h i s i s m u l t i p l i e d by t h e mean monthly t e m p e r a t u r e i n O C

-

10.3OC. T h e r e f o r e t h e computed

P.E. u s i n g Holdridge t s formula was

5.00

x

1 0 . 3 = 51.50 mm = 5.15 cm. For 1 5 t o

31

August i n c l u s i v e , t h e f a c t o r i s number o f 0.16

x

1 7

(

i n t h e p e r i o d mean f o r t h e p e r i o d

which works o u t t o 2.98 cm (Table I ) . I n 1960 t h e Leap Year f a c t o r s were used t o compute t h e Holdridge t o t a l s . F o r t h e 80-day p e r i o d , t h e t o t a l was 16.07 cm which compares more f a v o u r a b l y w i t h t h e 16.73-cm t o t a l f o r Pan A t h a n w i t h t h e 19.41-cm t o t a l f o r Pan B ( T a b l e I ) . Holdridge c l a i m s t h . a t t h e d e t e r m i n a t i o n of P.E. from t e m p e r a t u r e s a l o n e w i t h o u t u s i n g p r e c i p i t a t i o n d a t a o r o t h e r c l i m a t i c f a c t o r s i s p o s s i b l e b e c a u s e , f i r s t , t h e P.E. r a t e a t a g i v e n t e m p e r a t u r e d e c r e a s e s p r o p o r t i o n a t e l y a l o n g a g r a d i e n t of i n c r e a s i n g p r e c i p i t a t i o n from d r y t o wet a r e a s , s o t h a t t h e p r o d u c t of e v a p o r a t i o n r a t e and mean a n n u a l p r e c i p i t a t i o n i s c o n s t a n t a l o n g t h e g r a d i e n t . This i s r e f l e c t e d i n t h e r e g u l a r i t of t h e p a t t e r n of changes i n physiognomy between t h e s i n g

I

e c l i m a t i c p l a n t a s s o c i a t i o n s of each of t h e f o r m a t i o n s a l o n g t h e p r e c i p i t a t i o n g r a d i e n t . Second, l o c a l v a r i a t i o n s i n edaphic and atmospheric f a c t o r s s u f f i c i e n t t o cause a n a p p r e c i a b l e change i n e i t h e r e v a p o r a t i o n o r t r a n s - p i r a t i o n , o r i n b o t h , a r e c o u n t e r b a l a n c e d by d i f f e r e n t

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p a s t through e v o l u t i o n a r y p r o c e s s e s which b r i n g t h e a c t u a l e v a p o t r a n s p i r a t i o n i n t o e q u i l i b r i u m w i t h t h e P.E. r a t e and t h e moisture a v a i l a b l e . These v a r i a t i o n s a r e r e f l e c t e d i n t h e d i v e r s i t y of a s p e c t and l a c k of r e g u l a r i t y o f t h e p a t t e r n of changes of physiognomy of t h e ( u s u a l l y s e v e r a l ) e d a p h i c , atmospheric, and h y d r i c a s s o c i a t i o n s o f t h e same p l a n t forma- t i o n s a l o n g t h e moisture g r a d i e n t .

The f o u r t h formula i s Penman's mass t r a n s f e r formula ( 7 ) :

where

Bo = e v a p o r a t i o n , cm

e

-

ed = vapour p r e s s u r e d i f f e r e n c e between

0

s u r f a c e and a i r , mm of Hg

U2 = mean wind speed, m i l e s p e r day.

It was assumed t h a t t h e mean t e m p e r a t u r e of a s a t u r a t e d s u r f a c e i s approximately e q u a l t o t h e mean a i r temperature. Wind

v e l o c i t y and a i r temperature r e c o r d s were o b t a i n e d f r o m t h e D.O.T. M e t e o r o l o g i c a l S t a t i o n a t Norman Wells. The wind

f a c t o r was a d j u s t e d t o t h e 2-meter l e v e l by assuming t h a t t h e wind v e l o c i t y d e c r e a s e s w i t h h e i g h t a c c o r d i n g t o t h e one-seventh power law. The Penman t o t a l f o r t h e p e r i o d of 15 t o 31 August 1959 was 4.51 cm which i s c o n s i d e r a b l y h i g h e r t h a n t h e t o t a l s observed f o r t h e Thornthwaite pans (Table I ) . The Penman t o t a l f o r t h e 80-day p e r i o d , 30 June t o 17 September 1960, was 19.32 cm compared w i t h 16.73 cm f o r Pan A and 19.41 cm f o r

Pan B (Table I ) . A comparison was made between t h e c a l c u l a t e d Penman formula and measured P. E. from Pan B f o r 10-day and monthly t o t a l s , r e s u l t i n g i n good c o r r e l a t i o n ( F i g u r e

1 5 ) .

F i n a l l y , t h e observed P.E. from Pans A and B were compared w i t h t h e e v a p o r a t i o n o f w a t e r from t h e C l a s s A .Pan

i n 1960. I t was noted t h a t t h e l a t t e r was c o n s i d e r a b l y h i g h e r

-

25.63 cm (Table I ) .

The P.E. computed from t h e Holdridge formula more c l o s e l y resembles t h e observed P.E. f o r 1959 t h a n e i t h e r t h e Thornthwaite o r converted l a t e n t e v a p o r a t i o n f ormulae

.

The P.E. computed by Thorntliwaite

'

s formula f o r p r e v i o u s summers' o p e r a t i o n of t h e Thornthwaite s i t e have shown it t o be n e a r l y twice a s h i g h a s t h e observed P.E. For t h e p e r i o d o f 1 5 t o 31 August 1959, t h e l a t e n t e v a p o r a t i o n formula gave a l m o s t a s h i g h a P.E. a s t h e Thornthwaite formula. T h i s p e r i o d of l a t e n t e v a p o r a t i o n o b s e r v a t i o n s was r e a l l y t o o s h o r t t o draw any u n q u a l i f i e d c o n c l u s i o n s . I n 1960, t h e r e was c o n s i d e r a b l e

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v a r i a t i o n among t h e v a r i o u s formulae and t h e observed P.E. d u r i n g t h e f i r s t h a l f of t h e 80-day p e r i o d , b u t t h e y were q u i t e c l o s e t o e a c h o t h e r d u r i n g t h e second h a l f .

The main o b j e c t i o n t o t h e T h o r n t h w a i t e , H o l d r i d g e and l a t e n t e v a p o r a t i o n formulae seems t o be - t h e i r d i s r e g a r d f o r d i f f e r e n t p l a n t t y p e s . T h i s would perhaps be p a r t i c u l a r l y t r u e f o r n o r t h e r n a r e a s where moss and l i c h e n a r e s o wide- s p r e a d . Moss i s a v a s c u l a r p l a n t a l t h o u ~ h of much s i m p l e r s t r u c t u r e t h a n h i g h e r p l a n t s such a s s e d g e , s h r u b s and t r e e s . I n a d d i t i o n , t h e amount of t r a n s p i r a t i o n s u r f a c e p e r u n i t ground a r e a may be of a d i f f e r e n t o r d e r of magnitude t h a n t h e h i g h e r o r d e r p l a n t s . Lichen i s n o t a v a s c u l - a r p l a n t and does n o t t r a n s p i r e . The mechanism o f w a t e r movement i n moss and l i c h e n i s n o t c l e a r l y u n d e r s t o o d . One o b j e c t i v e of t h e Norman Wells s t u d i e s was t o g a i n a n u n d e r s t a n d i n g of the r o l e played b y moss and l i c h e n i n t h e o v e r - a l l m o i s t u r e t r a n s f e r .

( b ) P o t e n t i a l e v a p o t r a n s p i r a t i o n a t o t h e r v e g e t a t i o n s i t e s Comparisons were made between t h e P.E. from t h e g r a s s - c o v e r e d pans and t h e

P.E.

from t h e v a r i o u s n a t u r a l v e g e t a t i o n c o v e r t j r p c s i n t h e Norman Wells a r e a . A number of d i f f i c u l t i e s were e n c o u n t e r e d i n 1959. The summer was u n u s ~ ~ a l l y c o o l and wet which reduced t h e e v a p o t r a n s p i r a t i o n of a l l t h e v e g e t a t i o n making i t more d i f f i c u l t t h a n u s u a l t o d e t e c t d i f f e r e n c e s between t h e v a r i o u s t y p e s when t h e y a r e s m a l l . The e v a p o t r a n s p i r o r n e t e r s ( o i l drurns

,

l a r g e and s m a l l f r u i t j u i c e c a n s ) were i n s t a l l e d -throughout August. The f i r s t f r o s t o c c u r r e d i n e a r l y September s o t h a t t h e t o t a l l e n g t h of time when a l l i n s t a l l a t i o n s were o p e r a t i n g s i m u l - t a n e o u s l y was v e r y s h o r t . Some o i l drum r e a d i n g s were i n v a l i - d a t e d because of f l o o d i n g of t h e overflow c o n t a i n e r s . This o c c u r r e d a t s i t e s l o c a t e d i n l o w - l y i n g p o o r l y d r a i n e d a r e a s . P e r i o d i c a l l y , some of t h e f r u i t c a n s became c l o g g e d i n t h e bottom and p r e v e n t e d a l l of t h e e x c e s s w a t e r b e i n g c o l l e c t e d

a s overflow. Although t h e o b s e r v a t i o n p e r i o d was v e r y l i m i t e d , e x a m i n a t i o n of t h e r e s u l t s i n d i c a t e d t h a t evapo- t r a n s p i r a t i o n r a t e s were h i g h e r f o r t h e Thornthwaite s i t e and sedge a r e a ( S i t e Two) t h a n f o r t h e moss and l i c h e n .

B e t t e r s u c c e s s was o b t a i n e d i n 1960 because of

improvements i n t h e i n s t a l l a t i o n s , a l o n g e r o p e r a t i n g s e a s o n , and a warmer summer t h a n i n 1959. The i n s t a l l a t i o n s were completed b e f o r e t h e end of June and d a i l y r e a d i n g s were t a k e n u n t i l

1 7

September.

The r e s u l t s f o r 1960 a r e t a b u l a t e d i n Table I. A t t h e Thornthwaite s i t e , t h e o i l drum and t h e 15-cm d i a m e t e r can gave h i g h e r t o t a l s t h a n t h e l a r g e pans. The drums a t t h e o t h e r s i t e s gave somewhat e r r a t i c r e s u l t s ; r e s u l t s f o r t h e

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s m a l l cans a t S i t e Four were p a r t i c u l a r l y s c a t t e r e d . I t i s t h o u g h t t h a t t h e o i l drums probably gave more r e a l i s t i c P.E. v a l u e s t h a n t h e s m a l l e r c o n t a i n e r s because of t h e i r l a r g e r s u r f a c e a r e a , g r e a t e r depth and d e c r e a s e d r i m e f f e c t .

S p r i n k l i n g i s undoubtedly a l e s s r e l i a b l e method of a d d i n g w a t e r t h a n m a i n t a i n i n g a c o n s t a n t w a t e r supply.

Mean d a i l y a i r t e m p e r a t u r e s were recorded a t f o u r of t h e f i v e s i t e s b u t t h e r e was no a p p a r e n t c o r r e l a t i o n w i t h P.E. The Thornthwaite s i t e had t h e h i g h e s t P.E., b u t i t s

mean temperature f o r t h e 80-day p e r i o d of 54.6OF was h i g h e r t h a n t h a t of t h e wooded s i t e (which was shaded) and t h e sedge s i t e and lower t h a n t h e moss and l i c h e n s i t e s n e a r D.O.T. Lake. The h i g h e r degree of exposure t o wind of t h e Thornthwaite s i t e would c o n t r i b u t e t o i t s h a v i n g

a

h i g h e r P.E., b u t t h e moss and l i c h e n s i t e s a t D.O.T. Lake were a l s o f a i r l y exposed. These l a s t two s i t e s had P.E. v a l u e s s i m i l a r t o t h e wooded a r e a which was s h e l t e r e d . I t a p p e a r s , t h e r e f o r e , t h a t P.E. r a t e s a r e s i g n i f i c a n t l y h i g h e r through Kentucky b l u e - g r a s s (which i s n o t n a t i v e t o permafrost r e g i o n s ) t h a n through sedge, moss and l i c h e n which a r e indigenous. The r e s u l t s of 1960 a r e probably more v a l i d t h a n t h o s e of 1959 because of t h e l o n g e r o b s e r v a t i o n p e r i o d . Over s e v e r a l months, -day t o day d i s c r e p a n c i e s can be i r o n e d o u t and a l o n g e r term p a t t e r n emerges.

I t h a s been s t a t e d t h a t m e t e o r o l o g i c a l f a c t o r s p l a y a prominent r o l e i n e v a p o t r a n s p i r a t i o n r a t e s where s o i l moisture i s n o t t h e l i m i t i n g f a c t o r . N e v e r t h e l e s s , it i s p o s s i b l e t h a t t h e p h y s i o l o g i c a l c h a r a c t e r i s t i c s and r a d i a t i o n and t h e r m a l p r o p e r t i e s of p l a n t m a t e r i a l s such a s moss and

l i c h e n , which m a i n t a i n a h i g h permafrost t a b l e , a r e s i g n i f i c a n t f a c t o r s i n d e t e r m i n i n g t h e c o n t r i b u t i o n of e v a p o t r a n s p i r a t i o n t o t h e energy exchange of permafrost. One d i s c r e p a n c y t h a t a r i s e s i s t h e f a c t t h a t sedge does n o t m a i n t a i n a h i g h perma- f r o s t t a b l e , b u t h a s P.E. r a t e s comparable t o moss and l i c h e n . This may be caused by i t s lower i n s u l a t i n g q u a l i t i e s which permit a g r e a t e r d e p t h of thaw d u r i n g t h e summer.

R a d i a t i o n

( a ) Incoming short-wave r a d i a t i o n

Incoming short-wave r a d i a t i o n was measured d a i l y a t t h e Thornthwaite s i t e from 8 August t o 1 2 September 1959 i n c l u s i v e , u s i n g two Gunn-Bellani r a d i a t i o n i n t e g r a t o r s

( d e s i g n a t e d a s A and B ) which were r e a d a t t h e same time each day.

I n t h e s p r i n g of 1959, i n t e g r a t o r A was i n s t a l l e d i n t h e D.B.R. T e s t Area i n Ottawa and r e a d i n g s from it were compared w i t h r a d i a t i o n measurements o b t a i n e d from t h e Eppley

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p y r h e l i o m e t e r a t t h e D i v i s i o n . I n t h e s p r i n g of 1960, i n t e g r a t o r s A and B and a new one ( d e s i g n a t e d a s C ) were i n s t a l l e d i n t h e D.B.R. T e s t Area f o r c a l i b r a t i o n . The c a l i b r a t i o n c o n s t a n t obtained f o r A i n 1959 was

24.39

Langleys p e r m i l l i l i t r e of condensed a l c o h o l . I n 1960, t h e value obtained was 41.5 Langleys. The v a l u e obtained f o r B

was 366 Langleys and f o r C it was 476 I a n g l e y s , which do n o t correspond w i t h t h e manufacturer' s c o n s t a n t of 18.8 Langleys f o r both i n s t r u m e n t s . Shipping t h e i n t e g r a t o r s back and f o r t h between Norman Wells and Ottawa could have caused i n v i s i b l e b u t s u f f i c i e n t damage t o p r e v e n t them from f u n c t i o n i n g

p r o p e r l y . Despite t h i s , t h e t h r e e i n t e g r a t o r s were used. a t Norman Wells d u r i n g t h e summer of 1960. I n t e g r a t o r s A and B were i n s t a l l e d a t t h e Thornthwaite s i t e a s i n 1959 and

i n s t r u m e n t C was i n s t a l l e d i n t h e l i c h e n a r e a ( S i t e 5 ) . The 10-day t o t a l of r a d i a t i o n v a l u e s i s t a b u l a t e d i n Table 11. M i l l i l i t r e s of a l c o h o l condensed i n each

i n t e g r a t o r a r e shown followed by t h e c o n v e r s i o n of t h e s e v a l u e s i n t o Langleys of r a d i a t i o n . I n t h e l a s t two columns a r e shown t h e 10-day t o t a l s of incoming s o l a r r a d i a t i o n a t P o r t Simpson, N.W.T. and Aklavik, N.W.T. recorded by t h e

Department of T r a n s p o r t on Eppley p y r h e l i o m e t e r s . I t a p p e a r s t h a t t h e i n t e g r a t o r s must have been f a u l t y because a l l t h e r a d i a t i o n values from Norman Wells a r e lower t h a n t h o s e from P o r t Simpson and Aklavik whereas t h e y should probably f a l l between t h e two. There i s l i t t l e c o n s i s t e n c y among t h e

i n t e g r a t o r s i n any given 10-day p e r i o d . Because t h e i n s t r u - ments proved t o be s o u n s a t i s f a c t o r y , t h e o n l y way t h a t any v a l u e s of incoming short-wave s o l a r r a d i a t i o n could be

obtained was by t a k i n g a mean of t h e v a l u e s from P o r t Simpson and Aklavik, which a r e l o c a t e d about t h e same d i s t a n c e s o u t h and n o r t h of Norman Wells r e s p e c t i v e l y .

( b ) Net r a d i a t i o n

During t h e summer of 1959, weekly n e t r a d i a t i o n measurements of v a r i o u s v e g e t a t i v e c o v e r t y p e s i n t h e

Norman Wells a r e a were t a k e n u s i n g an economic n e t r a d i o m e t e r .

To o b t a i n n e t r a d i a t i o n w i t h approximately

3

t o 5 p e r c e n t accuracy, t h e s h o r t e x p r e s s i o n f o r r a d i a t i o n

i n

Langleys p e r minute was used:

where

Rn i s n e t r a d i a t i o n , Langleys p e r minute

6 i s t h e Stefan-Bolz c o n s t a n t Tt = temperature of t o p f a c e , OC

(20)

This e x p r e s s i o n c o n s i d e r s incoming r a d i a t i o n p o s i t i v e and outgoing r a d i a t i o n n e g a t i v e .

The c a l c u l a t e d n e t r a d i a t i o n r e s u l t s and a i r

temperatures a t t h e time of r e a d i n g a r e t a b u l a t e d i n Table 111. This t a b l e a l s o i n c l u d e s t h e e x a c t times a t which o b s e r v a t i o n s were t a k e n and t h e percentage of s u n l i g h t recorded d u r i n g t h e hour i n which each r e a d i n g was made. A s mentioned p r e v i o u s l y , no continuous measurements of incoming s o l a r r a d i a t i o n were made w i t h which t h e observed n e t r a d i a t i o n v a l u e s could be compared. It was t h u s impossible t o compare t h e d i f f e r e n c e s of n e t r a d i a t i o n through d i f f e r e n t t y p e s of v e g e t a t i v e c o v e r w i t h t h e incoming s o l a r r a d i a t i o n a t t h e time of o b s e r v a t i o n .

Despite t h e q u e s t i o n a b l e v a l i d i t y of t h e observa- t i o n s , a g e n e r a l q u a l i t a t i v e p a t t e r n i s e v i d e n t . For example,

it

was a n t i c i p a t e d t h a t t h e n e t r a d i a t i o n v a l u e s f o r l i c h e n would be t h e lowest because of t h i s p l a n t r s l i g h t c o l o u r and consequent h i g h r e f l e c t i v e p r o p e r t i e s . T h i s was t r u e on c l e a r days b u t n o t on p a r t l y cloudy o r o v e r c a s t days when d i f f e r e n c e s i n n e t r a d i a t i o n from one p l a n t type t o a n o t h e r were s m a l l . On t h e o t h e r hand, n e t r a d i a t i o n v a l u e s f o r s e d g e , which i s a l s o a l i g h t - c o l o u r e d p l a n t , were much h i g h e r t h a n f o r l i c h e n

on c l e a r days and indeed h i g h e r t h a n t h e darker-coloured p l a n t s such a s g r a s s and moss. Net r a d i a t i o n v a l u e s a t t h e Thornthwaite s i t e were t h e h i g h e s t on some days b u t n o t on o t h e r s . Net

r a d i a t i o n through moss was h i g h e s t on c l e a r days b u t n o t always on o v e r c a s t days.

From t h e s e crude measurements, i t a p p e a r s t h a t n e t r a d i a t i o n through moss i s h i g h e r t h a n through l i c h e n . Never- t h e l e s s , t h e s e two p l a n t t y p e s maintain t h e permafrost t a b l e a t about t h e same l e v e l i n a given a r e a and n e a r s u r f a c e ground temperatures a r e s i m i l a r under b o t h p l a n t t y p e s . Consequently, i f l i c h e n r e j e c t s a h i g h e r p r o p o r t i o n of t h e r a d i a t i v e f l u x t h a n moss, t h i s may be compensated by t h e moss r e j e c t i n g a h i g h e r p r o p o r t i o n of some o t h e r component of t h e energy exchange t h a n t h e l i c h e n .

3. Ground Temperatures and Dep-kh of Thaw ( a ) Depth of thaw

Depth of thaw measurements i n v a r i o u s t y p e s of v e g e t a t i v e cover were p l o t t e d a g a i n s t F a h r e n h e i t degree days f o r t h e summers of 1957, 1958 and 1959. The use of degree days g i v e s a more r e a l i s t i c comparison t h a n c a l e n d a r d a t e s because of t h e v a r i a t i o n i n a i r temperature from one summer t o a n o t h e r . For example, t h e depth of thaw i n 1959 was c o n s i d e r a b l y l e s s t h a n i n t h e two p r e v i o u s summers because of t h e lower a i r t e m p e r a t u r e s . N e v e r t h e l e s s , a cornparisan

(21)

of d e p t h of thaw w i t 1 1 d e g r e e d a y s o f t h a w i n g i n d i c a t e d a s i m i l a r r e l a t i o ~ l s h i p e x i s t i n g f o r t h e t h r e e s i m n e r s o f o b s e r v a t i o n s

.

Avera i;e v a l u e s of dep-th o f t h a v ~ v s d e g r e e d a y s of t h a w i n g were o b t a i n e d f o r e a c h v e g e t a t i o n c o v e r t y p e and p l o t t e d (I;'i!rl~re 1 6 )

.

I 1 i : f f i c u l t i e s a r e i n h a r e n t i n o b t a i n i n i : d e p t h o f

thaw o b s e r v a t i o n s by p r o b i n g b e c a u s e of s m a l l b11t s i - c n i f i c a n t v a r i a t i o n s i n -the d e p t h . o:P thaw o v e r a h o r i z o n ' t a l d i s t a n c e of o n l y a few f e e t a t a n y s i t e . I n a d d i t i o n , p r o b i n $ i n t h e same a r e a week a f t e r w e r . : l ~ u n a v o i d a b l y d i s t u r b s t h e s u r f a c e c o v e r o f t h e a r e a t o t h e e x t e n t of a f f e c t i n g t h e n a t u r a l thaw p e n e t r a t i o n . N e v e r t h e l e s s , t h e t r e n d s i n d e p t h o f thaw a t t h e vc7ri.ou.s s i - t e s cou1.d be d e t e ~ t e d a f t e r - t h r e e summers and t h e s e o b s e r v a - t i o n r ;

ere

n o t con-tinixed i.n 1';160. P i ~ u r e 5 shows t h e v e g c t a t i o n and s o i l p r o f i l e s a t t h e s i t e s i n t h e Norman We1l.s a r e a a t which d c p t h o f thaw measurements were -talcen.

The g r e a t e s t d e p t h o f t h s w o c c u r r e d i n t h e s e d g e a r e a ( S i t e Two) where t h e r e was n o moss c o v e r . The n e x t g r e a t e s t d e p t h of thaw was o b s e r v e d i n t h e wooded a r e a ( S i t e P o u r ) , probed o n l y i n 1957 and 1950. T h i s s i t e h a d a moss c o v e r 4 i n . t-hiclc o v e r l y i n g 3 i n . of' p e a t . A c t u a l l y t h e 1 3 5 8 d e p t h of thaw was much g r e a t e r t h a n i n 1 9 5 7 w h i c h may b e

e x p l a i n e d by t h e i n a d v e r t e n t d i s t u r b a n c e of t h e s i t e i n 1357

result in^

i n a n u n n a t u r a l l y d e e p thaw t h e f o l l o w i n g y e a r .

The t r e e l e s s s e d g e and moss a r e a w i t h a 3 - i n . moss c o v e r o v e r l y i n g 6 i n . of p e a t had l e s s d e p t h o f thaw t h a n t h e p r e v i o u s l y mentioned a r e a . 'The most s h a l l o w d e p t h o f thaw was o b s e r v e d i n t h e s p a r s e l y t r e e d a r e a t h a t h a s a 5 - i n . moss c o v e r o v e r l y i n g a b o u t 18 i n . of p e a t ( S i t e T h r e e ) a n d t h e wooded a r e a w i t h

4

t o 1 2 i n . of moss o v e r l y i n g s e v e r a l i n c h e s o f p e a t ( S i t e P o u r ) . It a p p e a r s t h e r e f o r e t h a t t h e d e p t h o f thaw i s p r i m a r i l y d e p e n d e n t on t h e t h i c k n e s s o f moss and p e a t . I t i s n o t c e r t a i n t o what d e g r e e t h e d e p t h o f thaw i s i n f l u e n c e d by t h e s h a d e of s h r u b s and tree::. T h i s i s p r o b a b l y a r e l a t i v e l y m i n o r f a c - t o r compared w i t h t h e i n f l u e n c e of moss and pea:.

T h i s i s s u p p o r t e d by t h e a i r t e m p e r a t u r e o b s e r v a t i o n s o b t a i n e d a t t h e v a r i o u s s i t e s d u r i n g t h e summer o f 1960. The mean

d a i l y a i r t e m p e r a t u r e a t t h e t r e e l e s s s e d g e a r e a ( S i t e Two) f o r t h e p e r i o d o f 30 J u n e t o 1 7 S e p t e m b e r 1 9 6 0 , which i n c l u d e s a m a j o r p o r t i o n of t h e t h a w i n g p e r i o d , was 53.2OF. The mean d a i l y a i r t e m p e r a t u r e f o r t h e same p e r i o d i n t h e wooded a r e a

( S i t e F o u r ) was 54.2OP a l t h o u g h t h e d e p t h o f thaw was s e v e r a l f e e t l e s s .

( b ) Ground t e m p e r a t u r e s i n thawed l a y e r

Weekly ground t e m p e r a t u r e s t a k e n d u r i n g t h e summers of 1 9 5 3 and 1 9 6 0 showed t h a t s i g n i f i c a n t d i f f e r e n c e s e x i s t e d