Some relationships between snow cover and climate

(1)

Publisher’s version / Version de l'éditeur:

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la

première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

Internal Report (National Research Council of Canada. Division of Building Research), 1956-08-01

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

NRC Publications Archive Record / Notice des Archives des publications du CNRC :

https://nrc-publications.canada.ca/eng/view/object/?id=7d8b66cd-1f07-40d7-8892-d38146e44044 https://publications-cnrc.canada.ca/fra/voir/objet/?id=7d8b66cd-1f07-40d7-8892-d38146e44044

NRC Publications Archive

Archives des publications du CNRC

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.4224/20338060

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Some relationships between snow cover and climate

(2)

NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

SOME RELATIONSHIPS BETWEEN SNOW COVER AND CLIMATE

by

L.W. Gold and G.P. W i l l i a m s

( T h i s r e p o r t has been p r e p a r e d f o r i n f o r m a t i o n and r e c o r d purposes and i s not t o be

r e f e r e n c e d i n any p u b l i c a t i o n ) Report No.

98

of t h e D i v i s i o n of B u i l d i n g Research O t t a w a ~ u g u s t

1956

(3)

The snow and i c e r e s e a r c h program of t h e D i v i s i o n of B u i l d i n g Research i n c l u d e s not o n l y l a b o r a t o r y s t u d i e s but t h e i n v e s t i g a t i o n of snow c h a r a c t e r 1 s t i c s i n t h e f i e l d . T h i s r e s e a r c h work has been g r e a t l y a s s i s t e d by t h e

s t e a d i l y accumulating r e c o r d s from t h e Canadian Snow Survey which i s c a r r i e d out under t h e a u s p i c e s of t h e A s s o c i a t e Committee on S o i l and Snow Mechanics.

Using some of t h e d a t a o b t a i n e d i n t h i s way, t h e a u t h o r s of t h i s r e p o r t ( A s s i s t a n t Research O f f i c e r s i n DBR, M r , Gold being Head of t h e Snow and I c e Research S e c t i o n ) have c o n t i n u e d e a r l i e r s t u d i e s on t h e a n a l y s i s of t h e Snow Survey r e s u l t s w i t h s p e c i a l r e f e r e n c e t o t h e i n t e r - r e l a t i o n of snow cover and c l i m a t e .

The D i v i s i o n w i l l welcome comments on t h i s r e p o r t by t h o s e who s t u d y i t , p a r t i c u l a r l y s i n c e t h i s i s s o new a f i e l d of r e s e a r c h i n which s o much y e t remains t o be done.

O t t awa

,

(4)

ABSTRACT

& e l b i n a r y a n a l y s e s of d a t a c ~ l l e c t ~ e d t o d a t e by

, ; C 8 ~ a ~ ~ d i a n Snow S l l s v e y g i v e encouraging i n d i c a t i o n s of

dug: ~ 0 ~ ~ i b 2 . l i . t ~ of c o s r e l a t % n g snow cover p r o p e r t i e s t o

-;a.;aate. It was f o m d t h a t m o w d e n s i t y I n exposed area@ IF, &pendent on. s combinatfon cf w9nd v e l o c i t y and temper- a t u r e , The s t r e n g t h of t h e snowp as measured by I t s hasdnsss e z ~ l t h e t h e r m a l c o n d u c t i v i t y of t h e snow C O V ~ F ~ ~ L B Q can be

2 x : c s l a t e d t o c l i m a t e pskmarlly t h r ~ u g h I t s dependence

on

(5)

SOME FELATIONSHLPS BETWEEN

SNOW COVER AND CLIMATF

L.W, Gold and G.P, Williams

I n 1946 a snow survey was i n Z t i a t e d by t h e Associate Committee on S n f l and Snow Mechanics of t h e N a t i o n a l Research Council of Canada (1). The purpose s f t h i s survey was t o determine t h e p h y s i c a l c h a s a c t e r S . s t i c s of t h e snow cover i n Canada. With t h e kind co- pera at ion of t h e Meteorological S e r v i c e of Canada and p r i v a t e corn anSes, s e v e r a l o b s e r v a t i o n s t a t i o n s were e s t a b l i s h e d ( ~ i g . 17. A t t h e s e s t a t i o n s ,

c e r t a i n p h y s i c a l p r o p e r t i e s of t h e snow c o v e r and p e r t i n e n t m e t e o r o l o g i c a l d a t a were measured and r e c o r d e d ( 2 ) .

Papers appeared i n 1950 and 1451 g i v i n g summarLes of r e s u l t s based on o b s e r v a t i o n s made i n t h e s u r v e y , but no d e t a i l e d a n a l y s e s were made (3,4,5,6), By 1955 s u f f i c i e n t d a t a had been c o l l e c t e d t o warrant a more complete s t u d y . Then it was p o s s i b l e t o look f o r g e n e r a l c o r r e l a t i o n s between s p e c i f i c snow p r o p e r t i e s and snow p r o p e r t i e s and c l i m a t i c f a c t o r s ,

Each annual snow cover h a s p a r t i c u l a r p r o p e r t i e s which e v e n t u a l l y w i l l e s t a b l i s h t h e average c h a r a c t e r i s t i c s of t h e c o v e r , i n a manner comparable t o t h e establishment of c l i m a t e by weather c y c l e s . It i s n a t u r a l that t h i s s i m i l a r i t y e x i s t s , because t h e cover i s a n e f f e c t of m e t e o r o l o g i c a l

e v e n t s whicn determine weather. If c o r r e l a t i o n s could be e s t a b l i s h e d between snow cover p r o p e r t i e s and m e t e o r o l o g i c a l f a c t o r s , t h e problem of determining snow cover c h a r a c t e r i s t i c s would be g r e a t l y s i m p l i f i e d , Then it would be p o s s i b l e t o determine snow c o n d i t i o n s o r s p e c i f i c p r o p e r t i e s of snow cover from t h e comparative abundance of m e t e o s o l o g i c a l d a t a . T h i s procedure would seduce t h e number of o b s e r v a t i o n s i t e s r e q u i r e d and t h e time element n e c e s s a r y f o r e s t a b l i s h i n g the average snow cover c h a r a c t e r i s t i c s , The Canadian Snow Survey has adopted t h i s p r i n ~ i p l e ,

Except f o r l o c a l f l u r r i e s 9 t h e m o i s t u r e which forms snow cover i s c a r r i e d i n t o a r e g i o n i n l a r g e a i r masses. These a i ~ masses develop o v e r P o l a r , A t l a n t i c o r P a c i f i c

r e g i o n s . Those which develop over P o l a r ~ e g i o n s are c o l d and normally c a r r y l i t t l e m o i s t u r e , P o l a r air masses dominate t h e w i n t e r scene over a l a r g e p a ~ t of Canada and are u s u a l l y a s s o c i a t e d w i t h c o l d , c l e a r weather (71, Masses which c a r r y i n most of t h e moisture develop o v e r t h e A t l a n t i c and Pacif l c a r e a s 9 a f a c t o r which I s r e f l e c t e d i n snowfa21 d i s t r i b u t i o n maps

( 8 8 )

-

(6)

With e a c h p a r t cf t h e a i r mass i s a n a v e r a g e t e m p e r a t u r e , m o i s t u r e c o n t e n t , and wind v e l o c i t y , which v a r y w i t h b o t h t i m e and p o s i t i o n . When t h e a i r mass, o r a p a r t of i t , r e a c h e s a c r i t i c a l s t a t e i n v o l v i n g t e m p e r a t u r e and m o i s t u r e c o n t e n t , p r o c e s s e s occur which r e s u l t i n p r e c i p i t a t i o n r e a c h i n g t h e ground.

The form of snow c r y s t a l s which a r r i v e a t t h e round i s

dependent on t h e h i s t o r y of t h e c r y s t a l i n t h e a i r (107. S i n c e t h e m a j o r p o r t i o n of development of t h e c r y s t a l o c c u r s i n c l o u d s w e l l above t h e ground, t h e r e need be l i t t l e c o r r e l a t i o n between m e t e o r o l o g i c a l c o n d i t i o n s which e x i s t a t t h e ground l e v e l and t h e p r o p e r t i e s of t h e f a l l i n g snow. I n mountainous r e g i o n s , where t h e p r e c i p i t a t i n g c l o u d i s much c l o s e r t o t h e o b s e r v a t i o n

l e v e l , some c o r r e l a t i o n s have been d e t e c t e d ( 1 1 , 1 2 ) . Though m e t e o r o l o g i c a l c o n d i t i o n s a t t h e ground may n c t be r e l a t e d t o t h e p r o p e r t i e s of t h e snow w h i l e i t i s s t i l l i n t h e a i r , t h e y a r e v e r y i m p o r t a n t i n d e t e r m i n i n g how snow p a r t i c l e s a r e d e p o s i t e d

( 1 3 ) .

Of t h e m e t e o r o l o g i c a l v a r i a b l e s t h a t a r e measured, wind v e l o c i t y and a i r t e m p e r a t u r e a p p e a r t o be t h e dominant f a c t o r s a f f e c t i n g t h e f o r m a t i o n of t h e c o v e r ( 1 4 ) .

Once t h e snow i s d e p o s i t e d , t h e thermodynamic p r o c e s s i n v o l v i n g t h e snow p a r t i c l e r e v e r s e s from one of growth t o one of d e c a y , c a l l e d metamorphism ( 1 5 , 1 6 ) . Under t h e i n f l u e n c e of a c o n t i n u o u s l y changing environment, t h e p h y s i c a l p r o p e r t i e s of t h e snow modify. Temperature, g r a d i e n t s of t e m p e r a t u r e , p r e s s u r e , g r a d i e n t s of p r e s s u r e , all a c t on t h e snow t o produce a mass f l o w a p p e a r i n g i n t h e s o l i d , l i q u i d o r vapour phase. The

r e s u l t i n g c o n t i n u o u s change i n t h e p h y s i c a l p r o p e r t i e s of d e n s i t y , c r

e

s t a l shape and s i z e and i n t e r c r y s t a l l i n e bonding i s p a r t i c u l a r l y no iceable ,n t h e upper l a y e r s of t h e c o v e r . A t a d e p t h of 20 cm., s e a s o n a b l e s t a b i l i t y i s a c h i e v e d ( 1 7 ) . The m e t e o r o l o g i c a l f a c t o r s d e t e r m i n e t h e environment i n which t h e metamorphic p r o c e s s i s

o c c u r r i n g .

Dependence of Snow D e n s i t y on Wind V e l o c i t y and Temperature Many d i f f i c u l t i e s oacilr t o c o m p l i c a t e t h e problem of

r e l a t i n g snow c o v e r c h a r a c t e r i s t i c s t o c l i m a t e . I n any one a r e a , t h e w e a t h e r , which e s t a b l i ~ h e s t h e c l i m a t e , undergoes l a r g e v a r i - a t i o n s from y e a r t o yeara o r w i t h i n one y e a r . F u r t h e r v a r i a b i l i t y

i s i n t r o d u c e d by t h e i n f l u e n c e of t o p o g r a p h y , v e g e t a t i o n and o t h e r f a c t o r s i n t i m a t e l y i n v o l v e d i n t h e f o r m a t i o n of t h e c o v e r . T h i s v a r i a b i l i t y makes i t d i f f i c u l t t o a s s i g n a v e r a g e v a l u e s t o t h e p r o p e r t i e s measured. F o r example, wind v e l o c i t y , t ) e m p e r a t u r e , h u m i d i t y , e t c . , measured a t a s i t e may n o t be r e p r e s e n t a t i v e of t h e a v e r a g e wind v e l o c i t y , t e m p e r a t u r e , h u m i d i t y , e t c . , which e x i s t a t t h e time of measurement o v e r t h e o b s e r v a t i o r l a r e a .

(7)

T h i s a p p l i e s a l s o t o measilrement ~ f snow p r o p e r t i e s a t s i t e s where snow o ' b s e r v a t i o n s were t a k e n i n one a r e a o n l y and l o c a l v a r i a t i o n s could not be e v a l u a t e d . Observers were i n s t r u c t e d t o choose a n a r e a t y p i c a l of t h e s u r r o u n d i n g c o u n t r y , but l o c a l c o n d i t i o n s o f t e n made t h i s i m p r a c t i c a l o r i m p o s s i b l e .

A f u r t h e r d i f f i c u l t y i s whether t h e w e a t h e r d a t a , u s u a l l y r e c o r d e d as a v e r a g e s , a r e t r u l y r e p r e s e n t a t i v e of t h e w e a t h e r which i n f l u e n c e d t h e snow c o v e r . For example, i n a

s i n g l e month, one maJor storm w i t h h i g h winds might be t h e dominant f a c t o r a f f e c t i n g t h e snow c o v e r c h a r a c t e r i s t i c s f o r t h a t month. The average wind v e l o c i t y r e c o r d e d f o r t h a t month might n o t be r e p r e s e n t a t i v e of t h e wind v e l o c i t i e s which o c c u r r e d d u r i n g t h e storm. Another example would be t h e e f f e c t of a s i n g l e day of f r e e z i n g r a i n o r thaw which would have an i n f l u e n c e on

t h e snow c o v e r n o t r e f l e c t e d i n t h e monthly a v e r a g e t e m p e r a t u r e v a l u e s . Because of t h e s e d i f f i c u l t i e s , i t was r e a l i z e d t h a t e x a c t r e l a t i o n s h i p s c o u l d n o t be e s t a b l i s h e d .

To overcome some of t h e d i f f i c u l t i e s a s s o c i a t e d w i t h s i t e and c l i m a t i c v a r i a t i o n s , only d a t a c o l l e c t e d d u r i n g

months of continuous c o l d a t s t a t i o n s w i t h exposed s i t e s were used t o determine t h e f i r s t r e l a t i o n s h i p s t o be p r e s e n t e d . S i n c e wind v e l o c i t y and t e m p e r a t u r e a p p e a r t o be t h e dominant f a c t o r s

i n t h e f o r m a t i o n of t h e c o v e r , o n l y t h e s e e l e m e n t s were used t o c a l c u l a t e a n index of t h e c l i m a t e . P r e v i o u s i n v e s t i g a t i o n s

i n d i c a t e d t h a t d e n s i t y i s t h e most i m p o r t a n t p h y s i c a l c h a r a c t e r i s t i c of snow c o v e r , upon which secondary p r o p e r t i e s , such as s t r e n g t h and t h e r m a l c o n d u c t i v i t y depend ( 1 3 , 1 7 , 1 8 ) . T h e r e f o r e , by

c o r r e l a t i n g d e n s i t y t o c l i m a t e i t i s a p p a r e n t t h a t a c o r r e l a t i o n a l s o can be found between c l i m a t e and o t h e r snow p r o p e r t i e s .

The a i r t e m p e r a t u r e and wind v e l o c i t y d a t a were combined i n t o a weather i n d e x . Attempts t o r e l a t e a i r t e m p e r a t u r e o r wind v e l o c i t y , s e p a r a t e l y , t o snow d e n s i t y f a i l e d t o show s i g n i f i c a n t r e s u l t s . The monthly a i r t e m p e r a t u r e s were d i v i d e d i n t o s i x

c l a s s e s : +25OF. t o +15OF,; +15OF. t o +5OF.; +5OF. t o -5OF.; -5OF. t o -15°F.; -15F0. t o -25OF.; -25OF. t o -35OF., which covered t h e range of monthly a i r t e m p e r a t u r e s encountered. The monthly average wind v e l o c i t y was d i v i d e d i n t o s i x c l a s s e s : 0

-

5; 5

-

10; 1 0

-

15; 1 5

-

20 ; 20

-

25; 25

-

30 m.p.h., which covered t h e range of wind v e l o c i t i e s e n c o u n t e r e d . The w e a t h e r index was made by adding

t h e c l a s s numbers of wind v e l o c i t y and t e m p e r a t u r e . F o r example, i f t h e average monthly a i r t e m p e r a t u r e was o°F. i t would f a l l i n c l a s s

3

(+5OF. t o -5OF.). If t h e a v e r a e monthly wind v e l o c i t y was 8 m.p.h. i t would f a l l i n c l a s s 2 75

-

1 0 m.p.h.)

.

The

weather index f o r t h i s month was t h e sum of t h e two c l a s s e s which i n t h i s c a s e , e q u a l s f i v e .

(8)

Every month was a s s i g n e d a w e a t h e r i n d e x , which could be compared t o a n average monthly d e n s i t y . F i g u r e 2 p l o t s t h e average monthly d e n s i t y of t h e l a y e r l y i n g between 4 i n c h e s

and 1 2 i n c h e s from t h e snow s u r f a c e , a g a i n s t t h e monthly weather index f o r exposed s t a t i o n s . It i s s e e n t h a t a g e n e r a l r e l a t i o n - s h i p e x i s t s . I n F i g , 2 , t h e s e i s a c o n s i d e r a b l e s p r e a d i n d e n s i t y v a l u e s f o r any p a r t i c u l a r index. T h i s may be due t o t h s n a t u r e of t h e d a t a , t h e smearing e f f e c t which i s i n h e r e n t i n t h e use of monthly a v e r a g e s and i n d i c e s and t o f a c t o r s which have been

n e g l e c t e d . When t h e m o ~ t h l y a v e r a g e s were c a l c u l a t e d f o r s h e l t e r e d s t a t i o n s and p l o t t e d a g a i n s t t h e weathes index f o r $he month,

l i t t l e c o r r e l a t i o n was foamd. T h i s 1s because most of t h e s h e l t e r e d s t a t i o n s a r e l o c a t e d i n a p a ~ t ~f Canada s u b j e c t t o weather f l u c t u a t i o n a t h a t produce m e l t i r ~ g and r a i n . T h i s f a c t o r p l a y s a major r o l e i n d e t e r m i n i n g t h e c h a r a c t e r i s t i c s of snow

c o v e r .

Both a i r temperature and wind v e l o c i t y i n f l u e n c e snow d e n s i t y , For example, d e n s i t y v a l u e s a t Old Glory Mountain, B r i t i s h Columbia and R e s o l a t e , N,W.T., a r e compasable. Yet i n a t y p i c a l y e a r t h e average w i n t e r t e m p e r a t u r e a t Old Glory Mountain can be 25°F. t o 30°F. h i g h e ~ t h a n t h e a v e r a g e w i n t e r t e m p e r a t u r e a t R e s o l u t e , However, t h e a v e r a g e wind v e l o c i t y a t Old Glory Mountain i s almost double t h a t r e c o r d e d a t R e s o l u t e . When t h e

two f a c t o r s of wicd v e l o c i t y and a i r t e m p e r a t u r e a r e combined i n t o a n i n d e x , t h e t w ~ s t a t i o n s have comparable w e a t h e r i n d i c e s .

It i s n o t c l e a r how t e m p e r a t u r e e n t e r s i n t o t h e r e l a t i o n - s h i p , Boasolasco h a s shown t h a t t h e d e n s i t y of new snow

d e c r e a s e s w i t h d e c r e a s i n g t e m p e r a t u r e from 0°C. to-15°C. and t h e n r e v e r s e s t h i s t r e n d ~ Q Pt e m p e r a t u r e s below l 5 O C . ( 1 2 ) It may be t h a t t h e t e m p e r a t u r e i s n o t t h e r e a l v a r i a b l e i n v o l v e d , but merely a n i n d i c a t o r of o t h e r p r o c e s s e s . F o r example, t h e low t e m p e r a t u r e s , t h a t occur a t R e s o l u t e o r cn t h e P r a i r i e s

,

may be a s s o c i a t e d w i t h many s n o w f a l l s c o n t r i b u t i n g l e s s t h a n 1- i n c h pez s n o w f a l l t o t h e c o v e r . A c o v e r , b u i l t up i n such s m a l l s t e p s , h a s i t s snow

t h o r o u g h l y worked over by t h e wind, S t a t i o n s w i t h h i g h e r a v e r a g e t e m p e r a t u r e s a r e l i k e l y t c have s n o w f a l l s which c o n t r i b u t e a

c o n s i d e r a b l e arno1m.t t o t h e c o v e r . The g e n e r a l r e l a t i o n shown i n F i g . 1, a l t h o u g h n o t s s t l s f a c t o s y , i s t h e most promising o b t a i n e d from t h e d a t a a v a i l a b l e ,

The R e l a t i o n of Snow Hardness t o Climate

The v a l u e of c e r t a i n p h y s i c a l c h a r a c t e r i s t i c s of snow c o v e r such as d e n s i t y , g r a i n s i z e s g r a i n shape and d e g r e e of bondingJ depends p r i m a r i l y on t h e thermodynamkc p r o p e r t i e s of t h e environment, t h a t i s s w e a t h e r o r c l l m a t e . Other p h y s i c a l p r o p e r t i e s such as s t s e ~ g t h p r o p e r t i e s , t h e r m a l c o n d u c t i v i t y and p e r m e a b i l i t y depend on e l l m a t e t h r o u g h t h e i s r e l a t i o n s h i p t c d e n s i t y , g r a i n s i z e , e t e , I n this r e s p e c t t h e y a r e secondary p r o p e r t i e s of t h e snow c o v z . ~ ,

(9)

Fza::~ th e d a t a c o l l 2 c t e d i n t h e survey i t was f o w d t h a t snow hasdnesaa a s measused by t h e N a t i o n a l Research Council h a r d ~ e s s gauge, depends primarily on d e n s i t y and t o a l e s s e r e x t e n t on t e n p e r a t u s e and g r a i n s i z e

(181,

A 40°c. change i n temperature had a p p r o x i m a t e l y t h e same e f f e c t on snow h a r d n e s s a s a corresponding change of 0 . 2 gm/cm3 i n d e n s i t y . F i g u r e 3 shows t h e dependence of t h e mean of t h e l o g a r i t h m s of a random sample of h a r d n e s s e s , on a n index d e r i v e d f ~ o m d e n s i t y and temperature c . o r s e s p o n d l ~ ~ g t o each h a r d n e s s r e a d i n g , The l i n e a s s o c i a t e d w i t h each mean v a l u e , g i v e s t h e s p r e a d t h a t was observed f n t h e d a t a . Due t o d i f f i c u l t i s involved i n m e a s u i n g hasdnesses g ~ e a t e r t h a n

5

1600 grn/cm spy value over 1000 was a r b i t s a ~ i l y g i v e n t h e v a l u e of 2500. The daahed l i n e i s t h e dependence ~ b s e r v e d when v a l u e s over 1000 gm/cm2 a r e i n c l u d e d and t h e s o l i d l i n e

i s t h e dependence when t h e y a r e n o t i n c l u d e d . Each l i n e was t h e b e s t f i t c a l 2 u i a t e d by t h e method of l e a s t s q u a r e s . The lower r i g h t nasd sorrier of F i g . 3 shows how t h e i n d e x i s

d e r i v e d . F o r i ~ s t a n c e , snow w i t h a d e n s i t y of 0.2 gm/cm2 and a temperatuke of - 2 5 O ~ , would be g i v e n a n index number of seven.

Wind and t e m p e r a t u r e p l a y a l a r g e p a r t i n d e t e r m i n i n g t h e c h a r a c t e r i s t i c s of snow c o v e r d u r i n g d e p o s i t i o n . What p a r t t h e s e f a c t o r s p l a y i n d e ~ e l ~ p i n g t h e c h a r a c t e r i s t i c s of t h e snow, e i g h t i n r k e s below t h e s u r f a c e , i s s t i l l not c l e a r . As soon a s snow i s d e p c s l t e d , a mechanism of bonding between

snow g r a i n s i s i n h t i a t e d a s p a r t of t h e metamorphism p r o c e s s . The degree of bonding, which develops between g r a i n s , depends

on t h e thermornech%nical f o r c e s t o which snow i s s u b j e c t . T h i s bonding p l a y s a n a J o s r o l e I n d e t e r m i n i n g t h e s t r e n g t h of t h e snow. I n F i g ,

3,

v a - i a t l o n s i n t h e s t r e n g t h p r o p e r t i e s a t

any one index number probably r e f l e c t v a r i a t i o n s i n t h i s i n t e r - g r a i n bonding whlcb, I n ~ I ; ~ F D , r e f l e c t t h e thesrnomech%nical

c 0 n d i t i o r . s t o wtLPr_kA t h e snow grairas have been s u b j e c t . Climate p l a y s a l a r g e p a r t i n d e t e r m i n i n g t h e t h e r m o c o n d i t i o n s and,

( t h r o u g h wfnd a c t f o n a t l e a s t ) , perhaps even t h e mechanical. Two c o r n o n l y obse-ved extremes i n h a r d n e s s v a l u e a r e hazd snow

c r u s t s , whl ch develop t h s ~ l i g h wind actict.-i, and s u g a r snow,

which i s comaraorz d u r i n g t h e s p r i n g freeze-Dhaw per-lsd. A t , some time i n t h e i r k a i s t o r y , t k e a e two e x t ~ e r n e s m y have t h e same d e n s i t y and t e n p e ~ a t u ~ e .

The E f f e c t of Snow C o v e r or Heat Flow and t h e Subsequent I n f l u e n c e s f Climate

W i l l i a m s , 13 h i s conpa~:son of snow p r o p e r t i e s between Aklavik and R e s o l u t e

,

f ~ 1 m d a c o r k e l a t i o n between t e n p e s a t u ~ e

g r a d i e n t t h s s u g h snow and t h e mean d e n s i t y of snow ( 1 9 ) .

L a b o r a t o r y e x p e p i n e ~ $ s show t h a t t h e r m a l c o n d u c t i v i t y of snow

(10)

and h e a t flow from t h e ground i n t o t h e snow c o v e r , a s measured a t O t t a w a , Canada, d u r i n g t h e w i n t e r 1955

-

56, i n d i c a t e t h e i n f l u e n c e of snow cover on h e a t flow ( F i g . 4 ) . These measure- ments were r e c o r d e d a t n i g h t when t h e h e a t flow was a t a c o n s t a n t v a l u e . The e f f e c t of even a 2 - i n c h snow c o v e r on t h e h e a t flow i s v e r y s t r i k i n g ; under a p p r o x i m a t e l y t h e same t e m p e r a t u r e

c o n d i t i o n s a t t h e a i r i n t e r f a c e , t h e h e a t f l o w , w i t h two i n c h e s of snow c o v e r , i s l e s s t h a n one q u a r t e r of t h a t w i t h no c o v e r . Curve ( 4 ) , showing measured c o n d i t i o n s w i t h a 12 - i n c h snow c o v e r , f u r t h e r emphasizes t h e e f f e c t

.

Under t h e p r o t e c t i v e b l a n k e t of snow, t h e warm up of p r e v i o u s l y cooled ground i s

c l e a r l y n o t i c e a b l e .

S i n c e t h e r m a l c o n d u c t i v i t y depends on d e n s i t y , it must be c o r r e l a t e d t o c l i m a t i c f a c t o r s . The t y p e of c l i m a t e t h a t d e v e l o p s h i g h d e n s i t y snows i s u s u a l l y a s s o c i a t e d w i t h low snow- f a l l , low t e m p e r a t u r e s and medium t o h i g h wind s p e e d s . T h e r e f o r e , a c l i m a t e t h a t produces a h i g h d e n s i t y snow c o v e r , u s u a l l y has extreme weather c o n d i t i o n s t h a t l e a d t o maximum h e a t flow from t h e s u r f a c e , F i g u r e 4 i n d i c a t e s t h a t t h e range i n p o s s i b l e h e a t flow under s i m i l a r weather c o n d i t i o n s i s v e r y g r e a t . T h e r e f o r e , t h e r e should be a s i g n i f i c a n t r e g i o n a l v a r i a t i o n i n t h e a v e r a g e amount of h e a t e x t r a c t e d from t h e ground d u r i n g a w i n t e r season. The d e p t h of f r o s t p e n e t r a t i o n o r t h i c k n e s s of i c e c o v e r developed d u r i n g a w i n t e r , i s a good i n d i c a t o r of t h i s v a r i a t i o n .

(11)

1. Bui idir:-i_g R e a e a r - ~ k La Carbsda, Vo3. 2 , No. 2 , December

1955,

pp 52-54. 2 . KleFn, G . J O 9 $ear:s, DOC. a ~ d Gold, L.W., Method of Measuring t h e

S i g n i f i c a n t Charaste,A.st%cs of a Snow Coves. A s s o c i a t e Committee on S o i l and Me?.hanlcs N a t i o n a l Research Council, D i v i s i o n of B u i l d i n g R e s e a ~ a h , TOM. 1 8 , 0 t t a w a , November, 1950,

3.

K l e i n , G . J . , Canadian Survey of P h y s i c a l C h a r a c t e r i s t i c s of Snow Covers, A s s o c i a t e Committee on S o i l and Snow Nechanics, N a t i o n a l

Research C o u n c i l , Divisiori of B u i l d i n g R e s e a ~ e h

T.M.

15, Ottawa 1950. 4. K l e i n , G.J.

,

P ~ o c e e d i r i g s of t h e Westem Snow C o n f e ~ e n c e , V i c t o r i a ,

B.C, A p ~ 1 1 , 1951,

5.

Pearae, D O C o and Gold, L,W,, The Canadian Snow Survey, 1947-50, A s s o c i a t e Cornmkttec on S o i l ar-d Snow Mechanics, N a t i o n a l Research

Council, D l v l s i c n of BuiZdT~g Research T.M. 2 1 , Ottawa 1951.

6 .

Gold

,

L.W. afid W i l l i a m s , G o P o , Some R e s u l t s s f t h e Canadian Snow Survey. Prepared for p - e s e ~ t a t i o n t o the E a s t e r n Snow Conference, Hanoves, New Hampshire, February 9-10, 19560 N a t i o n a l Research C o u n c i l , D i v i s i o n of B u i l d i n g Research.

7 . Cownor, A , J . , S n o w f a l l Maps i n Canada. Proceedings of C e n t r a l Snow C o n f e r e n c e , December 11-12? 1941,

8.

Thomas, M . K , , C12xza,a+oLogiv~al A t l a s of Canada, N a t i o n a l Research

Council N o .

31519

D f v f e i o n of B u i l d i n g Research Report 41. Ottawap December 1953.

9 . Boughnes, C,C, and P o t t e r , J O G , , Snow Cover I n Canada. Weatherwise, Vol. 6 , No. 6 , De,cember 1953. pp 155-171,

1 0 . Nakaya, U,

,

Snow C~ystals, N a t u r a l and A r t i f i e i a l , Harvakd U n i v e r s i t : ~ P r c a s , 1954.

1 2 . B o a s s l a s c o , N o , Geofiaizs. PUTS e A p p l i c a t a , No. 28, 1954, pp 208-222. 1 3 . R i c h t e r , G . D . , Snow Cover, i t s Formation and P r o p e r t i e s . Academy

Scfence U.S ,S , R . Popular Science S e r i e s , P u b l i s h i n g House of t h e Academy Science U.S,S,R., Moscow, Leningrad, 19450

1 4 . D m i t r i e v a , N O G O , C a l c u l a t i o n of Snow Cover D e n s i t y u s i n g M e t e o s o l o g i c a l Data ( ~ a s c h e t p l s t r A a s t d _{snezAhnogo pokra po rneteorologischeskiw}

damyfi9 M e t e o r o l o g i i a 1 G i d i o l o g 2 i a 9 Ms. 2 ) " S f p r e Translation No. 24, 1954, 4 ~ 0

(12)

15, Ysshf d a , F , and ,:~l.l.eag~xl+s, P h y s i c a l S t u d 1 . e ~ on Deposited S n ~ w , I., T h . e ~ n a l . p y o p s r t l . s s , Conts%bm,t i o n s from I n s t i t a t e Low Tenpesata~se Scfene.e, No,

7,

1.955> pp 3.9-74,

17. Williams, ';;,Po, A Stludy o r Sr11,ow D e ~ s i t y A c ~ o s e Canada,

Unpzab11.;3hed D i v i a S,o:r. of Bu'..l.d?,.ng Re 3i3a~a12k-i R e p m t

.

18.

Gold 1; ,W , !, Th;? SiT;vr='2r3gtk 071' SP.T:/N 3,.7ch :Lnmp,~12 >?!q XC:?~, ,, :Fj~bmit t e d

t o t h e Jnu~nal nf Qla:r,:bokcgyp Decembe~

1955"

N"i.tJ.ona1

R e s e a ~ - . h Cm~~:~r;.:'ll, D:i.vl.sS.c,ri, of B u i l d l : ? ~ g R s s e s ~ c : h . ,

19.

WillIm,s G, P o , AP. _{an alga$^.} _{ob' SZ.C!M}_{C O V ~ F}_{C ~ h a ~ ~ ~ ~ ~ + ~ s ~ i 8 t i c ~}

a t Akl3.vf.k and W e g ~ L ~ t e , N a t i , ~ ~ a l I3eses.r-b ?nn:x~!c:'_?..

D%v .E,B l,sr, oE B l ~ ? _ l d k ~ ? g Re ~-~?,3:.~?,.h R ~ P C P F ~

9

_l. _!!,M+I;Fs _t._2.95b.

20. Kondsatyevs, A . S O r Thesmsl C o z d u c t i v f t g cf t h e 3now Cover, and P h y s i c a l P s o c e s s e s caused by t h , e Temper.atu.t.e G ~ a d l e n t

.

( ~ T f p l o p r o v o d v o s t snegovoqo pokrsva i Rizkcheskie p r a t s e s s y p ~ o $ a k b s d i a s c h $ e w ne.m pod olianiem temperaturflogo g r a d i e n t ) .

Publj.shed ir: ,Ph:y.3j.c2a1. and klle;::herzl.~.al P k o p e r t i e s of _Snow _and

t h e i r TJtl,l.!!zation 2.n .Ai:rf%.isl.d ac.d Road C o n e t ~ u c t i o a s ,

Mogeow, LsnYn.grad, Akadem.l.l.a N@hik9 U . S ,S,Ri 1945, pp 14-28. S % p m Tranalatic,n No, 2 2 ,

2.954,

1.3

p .

(13)

(14)

W E A T H E R I N D E X ( W / V

-

TEMP. C L A S S )

F I G U R E 2

W E A T H E R I N D E X R E L A T E D T O M O N T H L Y

D E N S

I

T Y V A L U E S A T E X P O S E D S T A T

I

O N S

ACROSS C A N A D A

D.B.R. R E P O R T 98

(15)

-

I I I I I I I 1 I I I I

-

_-

-

0 -10 - 2 0 - 3 0 -40 T E M P E R A T U R E O C

-

I I I I I I I I I I I I

DENSITY

-

TEMPERATURE INDEX No.

FIGURE

3 THE DEPENDENCE O F SNOW HARDNESS ON

AN INDEX D E R I V E D FROM A C O M B I N A T I O N

O F SNOW DENSITY AND TEMPERATURE

(16)

t

-

0 0

-

I I

-

I

-

\ GROUND SURFACE 7

-

TEMPERATURE OC LEGEND

a

15/1/56 0300 A M N O S N O W C O V E R , H E A T F L O W 19.5 BTU/HR F T ~ @ 2 2 / 1 / 5 6 0300 A M 2 I N C H E S S N O W COVER, H E A T F L O W 3.93 BTU/HR F T ~ @ 2 2 / 2 / 5 6 0300 A M 1 2 I N C H E S S N O W C O V E R , H E A T F L O W 1 . 5 5 BTU/HR F T ~ F I G U R E 4

TEMPERATURE TAUTOCHROMES AND A S S O C I A T E D HEAT F L O W AS OBSERVED A T OTTAWA