MONTHLY WEATHER REVIEW Editor, EDGAR W. WOOLARD
VOL. 70, No. 2
W. B. No. 1350
~ ~~~~
FEBRUARY 1942 CLOSED APRIL 3, 1942
IBSKJED MAY 14, 1942
OBSERVATIONS OF RADIATION PENETRATION THROUGH SNOW
By IRVING F. HAND and ROY E. LUNDQUIST
[U. 8. Weather Bureau Solar Radiation Station, Blue Hill Observatory, and U. 8. Weather Bureau, Salt Lake City, September 19411
The penetration of solar radiation through various thicknesses and qualities of snow is of importance in many
hydrological and other problems. Previous observations 1
of this penetration with pyrheliometric apparatus have in-
cluded little if any work in the United States; and the
authors therefore made some measurements a t Brighton,
Utah, as part of a snow project initiated in the Hydro-
meteorological Section of the Weather Bureau. These
measurements constitute only a preliminary study, but
the results have been sufficient to show the value that further work would have; data should be obtained under
varying conditions of free-air temperature, height above sea-level, wind velocity, humidity, and other meteoro-
logical factors, and especially with snows of different
densities and physical characteristics. For example,
the original loss by reflection from the snow surface nearly
always exceeds the amount remaining for transmission and
absorption. Considerable work has been done on the albedos, or reflection coefficients.a Observations of the
reflection of visible radiation from snow surface,s have
shown that up to 89 percent of the visible radiation is re-
flected from dean white snow, whereas only about one-
half that amount of the red component may be reflected
from the same snow surface. We therefore expect a
larger reflection of the visible than of the total solar radia-
tion; numerous measurements of the latter give albedos
of from 60 to about 87 perc.ent or more under Arctic conditions. Extensive studies have been made of the transmission
of solar radiation through distilled water. We may
assume that fresh snow, when melted, has approximately
the same characteristics as distilled water. We therefore
The phenomena are exceedingly complex.
1 See, e. g.: N. N. Kalitin, Die Strahlungseigenschalten der Schneedecke, Qcrl. Beilr.
Joseph Devaux LBconomie radio-thermique des champs de neige et des glaciers, Qeophys., 34:354-366, 1931.
Anndes de Phyaia& (lo), aO:5-67, 1933.
.... Joseph Devaur, Etude de IAlbedo de la neige dans le spectre infrarouge, C. R., aOo:80, 1H85. F. Steinhauser, Em Beitrag zur Anwendung der beschreibeaden Statistik in der
Hilding Olbson, Radiation measuromenta on Isachsens plateau, Ucografska annaler, Elmatologie Met. Zeit., 52:u)-213, 1935.
l R 9 P d A A 1426 -I.- ___)
F. Sauberer, Venurhe iiber spektrale Messungen der Strahlungseigenschalten von Bchnee und Eis mit Photoelementen M e t . Zeif. 55:%&255 1938. C . Thams, fther die Strahlungseigenschafte~ der Schnkedecke, Qcrl. Bcitr. Qcophys., 63:371&3%3. 1938. N. N. Kalitin Aclinomclria Moscow 1938. A. A. E U Z ~, Penetratiod of tempirature fluctuation into snow, nieteorologia i HV- drolopia Part 1:ll-20 1939. 0. Eikel und C. Thamq, Untersuchungen iiber Dichte-, Temperatur-, und Strahlung- sverhlltnisse der Schneedecke in Davos., Bcitr. z. Uedogie d. Schweir, Oeotechn. Serie. Hydrologie. (Zurich). 1938. 273-340. : N N. Kalitin The measurements of the albedo of a snow cover Mo. WEA. REV. 58:5&1 1930 see also Anders Angstrom Albedo of various surfdes of ground Gco
grafakaannahr, 7:323-342,1925. N. N. Khitin, Lalbedo spectral de la couche de h e , Bull. GI. science8 math. natr.. Sir giogra. gtophys. No. 2-3: 153-163, 1938, Acad. Sciences, Moscow. : H. H. Eimball and I. F. Hand, Reflectivity of diRerent kinds of surfaces, Mo. WEA. REV 57291-275 192 1 dso Mo. WEA. REV 58: 260-282. 1!l30.
4 H: R. James,withcooperation of E. H. Birge. A laboratory study of the absorptlon or light by lake water Trans. Ria. Acad ofSci. Art8 and Lctlera Vol. 31 1938. E. A. Birge andC. Juday. Solar rmdiatiod and inland lak& Fourih Report, T r a m
R ir. Acad. 01 Sd.. Arts and Lcflera. 27:523-562, 1932. C. Juday, The annual energy budget of an lnland lake, Ecologv, 21: 438-450, 1940.
might expect radiation absorption in snow to follow a law
somewhat like that for absorption in distilled water,
where I, is the intensity of the radiation a t the surface of
the snow times the complement of the albedo, and 1 is the
intensity a t depth d, while k is the absorption coefficient;
for snow Eckel gives about 0.083 as the value of k. The instrumental equipment used in the present study
consisted of two Eppley total solar and sky radiation
pyrheliometers,6 a dual recording micromax potentiom-
eter with full-scale deflection of 4 millivolts, a bubble
sextant for obtaining the height of the sun, a portable
potentiometer for checking the action of the recording apparat,us, a Weston precision microammeter, and stand-
ard snow-depth and density apparatus.
A 10-junct)ion Eppley pyrheliometer was mounted on
the roof of the home occupied by Mr. and Mrs. Kenneth
Shsw, cooperative observers of the Weather Bureau at Brighton, Utah, at an elevation of nearly 9,000 feet in the
Wasatch Mountains, 29 miles from the center of Salt Lake
City. The record from this pyrheliometer alternated
every 80 seconds with the record obtained by means of a
50-junction Eppley pyrheliometer placed beneath the
snow. A pit was dug in the snow with a vertical wall on
one side; and in this wall the snow was scooped out, leav-
ing a layer of predetermined thickness above the pyr-
heliometer, which was mounted in a horizontal position
and always at the same distance from the lower side of each layer whose transmission was being studied. A
large sheet of beaverboard was used as a door, with snow packed around the edges to elinhate stray light. The
use of a 50-junction pyrheliometer, which gives about five-
times as great an e. m. f. per gram-calory as the 10- junction, for measuring the greatly diminished intensity
of the radiation after its passage through snow, in con- junction with the 10-junction for measuring the total
radiation, increased the efficiency of record owing to
greater utilization of the record sheet. Just prior to the
readings, the recording potentiometer was checked for
sensitivity by means of the portable potentiometer; and it also was checked a t frequent intervals for galvanometer
swing, and against the standard cell. Preliminary measurements were made on May 14, 15,
and 16, 1941, to develop a satisfactory technique of
measurement; the results have not been tabulated. On
the 17th, a systematic series was made, and the results are
shown in table 1 and in the figure; t5he lower trace shows markedly the effect of lower transmission owing to ice
and slush.
1 = &,e-kd
~~
8 I. F. Hand. Review of Unlted States Weather Bureau solar radiation investigations,
B: B. Woerte A d I. F. Hind, The characteristics of the Eppley pyrheliometer, Mo. MO WEA. REV 65: 415441 1937
WEA. REV., 69: 145148, 1Ml.
ldll2w2-1 23
24 MONTHLY WEATHER REVIEW FEBRUARY 1942
nches of snow pne- trated
Pro- lressiue lhick-
ibe88e8
10
4
2%
1 1 Mechanical
PENETRATION OF SOLAR RADWTON THROUCH SNOW, BRIGHTON, UTAH
Poten- tiom- cter scale readin:
--
0
T
0.6
4.7 4.7
an
The final series of measurements in table 1 differed from
the others in that freshly cut slabs were used by placing
them over a recess made in a 34-inch snow pack from which the top 8 inches had been cleaned off. The recess
was 6jh inches wide, 11 inches long and 8% inches deep,
and was located in a snow-area 40 feet from the Shaw house in full exposure to the sun. Considerable difficulty
was experienced in placing a %-inch slab over the top of the
recess without breakage ; and should additional studies be
made, the use of a glass plate of known transmission would greatly simplify the measurements. The pyrhe-
liometer was set up at level each time for the first series
of measurements and with only one setting during the next and final series. As before, great care was exercised
to keep the same distance between the pyrheliometer and
the lower surface of the snow, in order to minimize errors arising from internal reflections within the snow pit.
The first and greatest loss of incident solar radiation is at the surface of the snow, by reflection. A bright snow
has albedo of about 87 percent, as does also glare ice; the latter seldom occurs on a snow surface. On the other
hand the average reflection coefficients of wet clean and
wet dirty snows are comparatively low, as shown by measurements on May 28 and 29 which gave albedos of 44 percent and 34 percent respectively. Dirty snows in
and near cities have particularly low reflection and high
absorption at the surface. Freshly fallen snow has an
almost perfect mat surface, which results in practically
identical reflection at all angles of incidence. The results of these preliminary observations are
particularly significant because the tests were conducted under conditions contributing to actual run-off. It has
been observed that snow attains an average density of a t
least 30 percent and usually between 40 and 50 percent
before any considerable run-off develops (snow density
Scale wad-
ing
62.3
62.5
63.1
63.3 63.3
is used here to mean percentage of water per unit volume
of snow). Snow density averaged 48 percent at the site; and snow quality for the samples tested averaged 90
percent ic,e grains, with 10 percent water. The fact that average snow densities do not seem to vary greatly in the process of melt,ing during run-off periods adds to the value
of t,hese results.
(tram. calo- ries
____
1.493
1.499
1.513
1.520 1.620
TABLE 1.- Penetration of solar radiation Lhrough snow at Brighton,
Utuh
1.532 1.555 1.553 1.540
1. 518 1.485
Date and lime
May 17 11:52 a. m
11:59 a. m
1205 p. m
12:oi p. n1
12:16 p. m 12:Il p. m
1237 p. m 12:43 p. m 12:46 p. m 12:51 p. m 1255 p. m 1:w p. IIl
22.3 lfi.9 7.8 1.8 1. 2
0
Slab fhick-
MB8CI
% 1
5U 5%
- ~
Gram- calo- ries
13.5 10.4
0.7 ;::
7 0
0
T
0.015
.119 ,119 electr
.342 .263 .121 .OZ8 ,018 0
64.3 64.8
64.7
64. 1
63.2 61. 8
__
Per- cent-
age traps-
m1s-
sion
1.0
7.8 7.8 itiom-
Remarks
%-in. slush !Eyer at 7 In. lar Fine snow. to medium granu-
Fine granular snow %-in. slush layer at bottom. Fine granular snow. Be- fore observation could be made, a f4 in. ice layer formed at 1% in. from top.
Fine granular, but slushy.
Uniform, Bne granular compact snow, average 45 percent density-from 8 to 16 in. below original snow surface-no ice or slush layers detectable.
Densities near the snow surface may vary from as little
as 5 percent to as much as 50 percent under the usual
natural conditions on a watershed. Under the special
conditions at extremely high altitudes or where snow
slides produce pressure that consolidates the snow to nearly ice densities, values outside these limits may occur.
Thus radiation penetration into snow layers at various
seasons, and during changes in density, may be expected
to vary widely. Early in our observations, it became apparent that the transmission varies with the average
quality of the snow and is particularly influenced by
slush or collection of melt-water, and by intermediate ice
layers.
It was noted during one series of measurements that radiation passing through a layer of snow gradually
decreased ; examination revealed the formation of ice and slush at a definite depth. Specifically, from 12:30
to 12:36 p. m. on May 16, using snow 1 inch in thick-
ness, an ice layer gth-inch-thick formed in 6 minutes and
gradually reduced transmission by 15 percent. In another instance, on hlay 17, during. a test using initially identi-
cal snow slabs of 1-inch thickness, the radiation trans-
FEBRUARY 1942 MONTHLY WEATHER REVIEW 25
May 14: 11:45a.m .____.__
5:KIp.m .....-..
May15,5:47p.m ....
May 16; 6 p . m ______ May18,noon ... ___..
mission was reduced during continued exposure of the snow layer to the sun to less than one-half the value
obtained in an earlier observation, due to slush forming
from melt-water. In another comparison on the same
day, where 4 inches of similar fine, granular, compact snow was used for study, transmission through freshly
uncovered snow of uniform texture amounted to 1.8 per-
cent of the total solar and sky radiation, whereas after
exposure to the sun for about 30 minutes the same type
of snow developed a dense %-inch thickness of slush a t
the bottom of the 4-inch layer and reduced transmission
to an unmeasurable value.
It may, therefore, be expected that, as snow melt
increases near the surface of a firm snow pack at a rate faster than it drains away into the snow, thus forming
slush and ice layers, the relative amount of radiation
transmitted to greater depths will decrease.
To determine the radiation absorption effect of ex- traneous matter on snow surfaces, 6 circular plots 18 inches
in diameter were each covered with 1 ounce of standard
paint pigments. Table 2 lists the pigments used, and shows the relative effects of the various colors. The
green showed an absorption nearly equal to that of the
OF. OF. OF. m.p.h. g r .c a l . 0 0 0 0 0 0 0 31 52 40 3.03 __...._
1 1 .9 2.9 2.9 2.5 2 .0 1 .9 ............____._._ 301.0 3 4 .8 5.6 7.8 6.8 6 .9 4 .3 25 48 42 2.85 584.0 7 8.5 10.2 14.0 13.1 11.0 9.1 28 55 51 3.31 __.___.
8.912.0 14.4 20.7 19.5 15.012.1 ....
,
. . - - . - - - - - - -. . . . - -
black, although the blue showed a greater drop during
the first 3 days. One difficulty of this method of test
was the uneven distribution of coloring matter after the
first few hours. We hope to repeat the experiment under conditions which will minimize many of the errors
of this first trial.
TABLE 2.- Differential absorption tests- Standard paint pigments.
I Depth drops in inches
NOTES AND REVIEWS
BERNHARD HAURWITZ. D y n a m i c Meteorology. New York (McGraw-Hill Book Co.), 1941.
It is of interest to recall that the first general treatise on meteorology to present the subject from the dynamical
vieu-point was the Lehrbuch der Meteorologie of A. Sprung, published in 1885; this work remained the only treatise of
the kind until the Dynamische Meteorologie by F. M . Exner, the second edition of which was published in 1925.
Since the appearance of Exners treatise, notable advances
have occurred in theoretical meteorology, and encourag-
ing progress has been made in adapting many of them to daily meteorological practice; and several books on physi-
cal and dynamical meteorology have appeared in recent years, although few are in English.
This book collects into one volume, that may be used
either as a textbook or as a reference work, a compre-
hensive account of theoretical meteorology which includes the results of many recent investigations hitherto avail-
able only in the widely scattered periodical literature.
Numerous references enable the reader to locate further
details on nearly every topic; and for the benefit of the student a large number of problems are included. Insofar
as any previous knowledge of meteorology is necessary, it
is presupposed ; and although for convenience brief recapitulations of the needed principles of physics are
given, it is likewise presupposed that the reader has been
trained in general physics, and in mathematics through
the calculus and elementary differential equations.
After an opening chapter occupied by preliminary
topics, two chapters are devoted to meteorological statics, including the adiabatic equations and theory of atmos-
pheric stability for both dry and saturated air, and a dis-
cussion of surface pressure variations due to advection
aloft. The following chapter discusses the energy of
thermodynamic processes, equivalent and wet-bulb po-
tential temperatures, convective instability and thermo- dynamic charts.
Chapter 5 treats the fundamental actuating factor in
the physical processes of the atmosphere-solar radiation,
365 pp.
its geographical distribution and atmospheric depletion, and the heat balance of the earth; the recent work of
Elsasser and others on atmospheric water vapor absorption
is included. The next two chapters are devoted to the
general dynamical equations of motion of the atmosphere,
the fundamental circulation theorems, and the theory of
geostrophic winds and other simple types of air motion. In chapter 8, surfaces of discontinuity are discussed; and
chapter 9 considers the kinematical analysis of pressure
fields. The next two chapters take up atmospheric turbulence,
with its effects on the variation of wind with height and
the diurnal variation of the wind, and the effect of tur-
bulent transport of heat, water vapor, and momentum.
The following chapter is devoted to the energy of atmos- pheric motions, and its transformation and dissipation.
The final three chapters consider, respectively, the general circulation; the perturbation method of repre-
senting atmospheric motions; and air masses, fronts,
cyclones and anticyclones.
CHARLES P. OLIVIER. Long Enduring Meteor Trains.
Publications of the University of Pennsylvania-The
Flower Astronomical Observatory, Reprint No. 60.
This paper, reprinted from Proc. Amer. Philosophical SOC. 85: 93-135, 1942, is a catalogue of 1,336 meteor
trains which either remained visible for a t least 60 seconds
or, if of shorter duration, showed actual drift; the cata-
logue tabulates the salient facts about all the trains, and a
further table gives detailed data on heights and drifts for
583 of them.
The data were collected both from the immense number
of original records available to the author and from a
search of the published literature. The paper provides a
fundamental and convenient source of existing informa-
tion on the phenomena of meteor trains; and as such, it is
of importance to the meteorologist interested in any
problem involving the motions of the atmosphere a t very
high levels.