hBkUARY, 1932 MONTHLY WEATHER REVIEW 61
clouds always do b the return radiation they themselves
over the ice an insulating sheet of finely Any substance, even a metal, when g e l y divided, is a poor conductor of heat, and snow is one of the poorest. Hence ice covered with a layer of h e snow, even though that layer be very thin, loses heat
to colder air above much more slowly than it would if bare. Obviously, therefore, under otherwise like con- ditions ice increases in thickness much faster when bare than it does when snow covered. Ice of any given thickness grows fastest when its sur- face is coldest; but this temperature depends in part on the condition of the air abov-lear, cloudy, or foggy- and on the condition of its surface, clean or snow covered. And the fog blanket and the h e snow cover are most likely to form in relatively calm and very cold weather, drifted by the entle movement of the air that commonly
the leeward of the remaining open water. It well may be, therefore, as fishermen tell us, that at certain places, a t least, along the shores of the Great Lakes more ice is formed occasionally, perhaps also on the average, when the temperature of the air is around zero Fahrenheit than there is when that temperature is even 20' to 30' lower, owing, as explained, to the greater prevalence of clear air and clean ice in the first case and fo gy air and snowy ice in the second. %ut here also, as everywhere and always, a few appro- priate figures afford a very necessary check on one's general or qualitative reasoning. Let the conditions be:
a. Temperature of the air -1 8 O C., 0' F., approxi- mately. Thickness of ice, 5, 10, 25, 50 centimeters, respectively. Snow covering, none. b. Tem erature of the air - 29' C., - 20' F., roughly. 4iickness of ice, as in cases a. Snow covering,
1 millimeter.
c. Same as b in respect to temperature of air and thickness of ice. Snow covering, 5 millimeters.
Now since the radiations of snow and ice at these low temperatures are small; the reflection of sunlight and sky- light by snow roughly 90 per cent; the amount of such radiation absorbed by ice also small, especially since there is not likely to be much of it to absorb in midwinter at latitude 47' N., say; and the heat conductivity of ice very low; therefore, as a first approximation, we may assume the temperature of the top surface of the snow or bare ice
've out, but ale0 B ecrease it, sometimes very greatly, by
snow.
obtains on suc E occasions over and onto the ice sheet to
to be that of the adjacent air. The temperature of the under surface of the ice is, of course, 0' C. Furthermore, as experiment has shown, the conductivity of very loose snow may be as low as one three-hundredths that of ice. Assume it, in the present, case, to be one one-hundredth that value, so that as a heat insulator, a layer of our h e snow
1 millimeter deep is the equivalent of a sheet of ice 100 times as thick, 10 centimeters; a 5-millimeter covering of snow t,he equivalent of a 50-centimeter sheet of ice; and
so on for other depths and thicknesses. In case a the difference in temperature between the under and upper surfaces of the ice is 18' C., and in cases b and c the difference between the temperature of the un- der surface of the ice and top surfnce of the snow 29' C. Therefore our various temperature gradients, in terms of
centigrade degrees and thicknesses, or equivalent thick- nesses, in centimeters, of ice are as given m the following table :
Temperature gradients
From these gradients it is clear that often bare ice can grow faster when the temperature of the air is 0' E". than can snow-covered ice of the same thickness when the air is much colder, even -20' F. "ken the thickness of the ice is 16.3 centimeters (6.4 inches) it grows just as fast in 0' F. weather, if bare, as it would with a l-milli- meter covering of loose snow (conductivity of snow one one-hundredth that of ice) in weather a t -20' F. If thinner, the bare ice would grow faster than the snow covered at the given temperatures, and if thicker it would grow slower. If the depth of the snow were 5 millimeters the thickness of the ice would need to be 81.8 centimeters (32.2. inches) for the rates of growth under the given conditions to be the same. In the fist of these cases the rate of increase of thick- ness is about 1 centimeter in four hours, the conductivity of ice being 0.005 (transmitting 0.005 calory per second per square centimeter cross section when the temperature gradient is 1' C. per centimeter), and in the second case 1
centimeter in 20 hours. Thus the fisherman's interesting paradox, the colder the air the thinner the ice, has become orthodox and lost its fascination.
BIBLIOGRAPHY
C. FITZHUQH TALYAN, in charge of library
RECENT ADDITIONS Barney. Maginel (Wright.)
Weather signs and rhymes. New York. 1931. [lo31 p. The following have been selected from among the titles of books recently received as representing those most
likely to be useful to Weather Bureau officials in their meteorological work and studies :
Abbot. C. G. Constantin.
col. illus. 19% cm.
Clute, Willard N.
Frost flowers. 12 p. illus. 23 cm. (Amer. botanist, v. 38, no. 1. Jan. 1932.)
Observatoire de Saint-Louis du SBnBgal (6cole secondaire.) Observations mBt6orologiques. Moyennes conclues de 23 ann6ea d'observatiom. p. 437-474. 25% cm. (Bull. du com. d'6tudea hist. et sci. de 1'Afrique Ocoid. franc. t. 13.1108. 3-4. Juil.-dBc. 1930.)
Periodometer: an instrument for finding and evaluating periodicitiee in long series of observatiom. Washington. 1932. 6 p. figs. pl. 2436 cm. (Smith. misc. coll., v. 87, no. 4.) (Pub. 3138.)
Febris. Cesare. Aldrich, L. B.
Clupplementary notes on body radiation. Washington. Teorie moderne BU l'origine e su la struttura dei cicloni. 1932. 12 figs. 24% cm. (Smith. mkc. coll., v. 85, Pisa. 1931. 106 p. figs. 24% cm. (Pubb. com. naa. no. 11.) (h b . 3131.) ital. geod. e la geof. (Consig. naa. delle ricer.) (N. 2.)
e2 MONTHLY WEATHER REVIEW FIIBRUABY, 1982
D'b
France. OBim ~t i d mCtbrologique..
[1929-30.1 26% cm. Climatologie ahronautique. AnnQ 1929-1930. Paris.
Air mass Local 76th mesn
solar
E0 A. M. P. M. time
-
Hoefcr, Kepitin A.
Im Pampero-Sturm. Eine Strandung vor der La Plata- Mandung. Berlin. n. d. 32 p. illus. 23 cm. (Meera- kunde. Bd. 14, Heft 7.)
Koeppe. Clarence E.
Canadian climate. Bloomington. [c1931.] 280 p. illus. 23 cm.
Ne& & Zambra.
Petsow, Georg.
Thermometric lag. London. 1930. 16 p. figs. 22 am.
Herkunft, HBufigkeit und Schicksal der von 1889 bis 1912 tiber dem Schwarzen Meer beobachteten Zyklonen (Teildruck.) Berlin. n. d. 49 p. fip. 23 cm. 1naug.-Dissert. Friedrich-Wilhelms-Univ. iferlin. 1931.)
Rohwer, Carl.
Evaporation from free water surfacea. Washington. 1931. (U. 8. Dept. sgric. in 01. agr. exp. eta. Tech. bull. no. 271. Dec. 96 p. figs. 8lates. 23% cm. cooper. mth 1931.)
Runge. Heinz.
Stationbe warme und kalte Antizyklonen in Europa.
' Wfirzburg-Aumahle. 1931. 57+ p. figs. platee (fold.) 22% cm. (1naug.-Dicaert. Univ. Leipzig.)
Sifontes, Emesto.
La haja del barometro y loa ciclones Antillanos. 1 sheet. illus. 58 cm. El Universal. (Caracas,Ven. Oct. 27,1931.)
5th rev. ed. (corrected to January, 1931.) Rashington. 1931. lxsxvi, 282 p. diagrs. 23 cm. (Smith. misc. coli. v. 88.)
South Seas bureau. Weat Caroline islands. Meteorological obrcrva-
Results of the meteorological observations made at Plrlsu, Weat Caroline islands for the 6 year, 1926-1930. Pnlsu. 1931. 58 p. pl. 31 cm.
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SOLAR OBSERVATIONS
SOLAR RADIATION MEASUREMENTS DURING FEBRUARY, 1932
By HERBERT H. KIMBALL, in charge Solar Radiation Investigations
For a description of.instruments emplo ed and their exposures, the reader is referred to the I- anuary, 1932
REVIEW, page 26.
Table 1 shows that solar radiation intensities averaged above the normal intensity for February at Washington, close to the February normal at Lincoln, and slightly below at Madison. Table 2 shows an excess in the total solar radiation received on a horizontal surface a t Chicago, New York, Fmesno, Pittsburgh, Twin Falls, La Jolla, and Miami, and a deficiency at Washington, Madison, Lincoln, and Gainesville. No skylight polarization measurements were obtained during the month. At Madison the presence of snow in the vicinity of the station made such readings of doubtful value, and at Washington the polarimeter was undergoing repairs.
TABLE 1.-Sokrr radiation intensities during February, 1932
[Gramcalories per minute per square centimeter of normal surfam1
w.shlngton* D. c.
Bun's zenith dlatsnce I
TABLE 1 .-Solar radiation intensities during February, 193t?-
Continued
lGram-ealorlea per minute per square centimeter of normal surface]
M.dbDn. Wb.
I Sun's d t h distance
Feb. 3 __________ Feb. 4 __________ Feb. 5 ._________
Feb. 6 _.._______
Feb. 11 ._______.
Feh. la _________ Feb. 17 _________ Feb. 19 _________ Feb. 22 _________ Feb. 26 _________ Means. .-- - - - - Departures-.. -
0.96 ______ 0.81 __.___
1.36 ______ 3.63 0.81 4.17 ______ 2.87 ___ - - - 1.62 1.03 2.16 ______ 1.w 0.98
4.96 0.84
_____ 0.95
---__ +0.01
0.86 0. mi 3.45 3.45
1.87 1.68 136 287 b.36
3. m
----.