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Charles F. Brooks and Eleanor S. Brooks

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SUNSHINE RECORDERS: A COMPARATIVE STUDY OF THE BURNING-GLASS AND THERMOMETRIC SYSTEMS

(Paper presented 28 December 1946 at Annual Meeting, A.M.S., Cambridge, Massachusetts)

Charles F. Brooks and Eleanor S. Brooks

Abstract

Sunshine duration is recorded in most countries by the Campbell-Stokes burning glass (CS) but in the United States by a thermometric type (US).

CS and US instruments were exposed together and compared at Blue Hill Observatory. The average values of insolation at which the CS and US begin and cease to register were estimated from Blue Hill pyrheliometer records to be 0.33 cal cm−2min&minus:1 (CS) and 0.37 cal cm−2min−1 (US) for the two instruments tested. However, the US usually exceeds the CS in summer because it responds to diffuse radiation while the CS does not.

Low-sun corrections are added to the US record by the U. S. Weather Bureau before tabulation. The US corrected record is longer than the CS record, which is not increased by a low-sun correction.

Two sets of conversion values were obtained: (1) from the monthly low-sun corrections at various stations and the direct comparison of the instruments at Blue Hill, (2) from comparison of long CS and US (corrected) records of paired Canadian and United States stations and the Blue Hill and Boston pair.

The value to be added to convert CS to US (corrected) is greatest in summer and least in winter. The annual conversion value is a percentage of sunshine duration increasing from 11 per cent in the northern United States to 14 per cent in the south.

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CHARLES F. BROOKS

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CHARLES F. BROOKS

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Charles F. Brooks and Raymond Wexler
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HERBERT LYMAN and CHARLES F. BROOKS

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SYNOPSIS

After discussing auroral phenomena in general, including types, latitude variation, periodicity, height, and cause, this article describes the principal features of the remarkably brilliant aurora of March 7–8, 1918, and presents a large number or detailed accounts by observers in the United States.

A chart of the United States shows places from which reports of the aurora were received. To facilitate intercomparison the descriptions have been grouped and discussed by latitude belts of 2½° each, for as would be expected, the display was pretty much the same at the same latitudes.

The aurora became visible at dusk, March 7 and attained its greatest brilliance, generally, at 9:30 p. m. (90th Meridian Time). Since no display is homogeneous, however, there are variations in the times of greatest brilliance and in the appearance of details of the display, although there is general unanimity concerning the times, colors, brilliance, and aspect, among widely scattered observers. The descriptions of the positions of arches, particularly of a prominent red one, make it obvious that the actual location of the aurora is the factor which determines its aspect, and the distance to which it can be seen, while the lack of streamers in the display at most southern points show that the clearness of the air limits its visibility.

It seems that the magnetic disturbance accompanying this aurora was a repetition, after three 27-day intervals, of the large magnetic storm of December 16–17, 1917. There was a considerable disturbance on January 12, and a minor one at the end of the next 27-day interval in February. Auroras on April 4, 5, and 6, marked the end of this strong series, which was probably caused by 5 successive presentations of an active area on the sun.

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CHARLES F. BROOKS and HERBERT LYMAN

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CHARLES F. BROOKS and C. LeROY MEISNGER

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CHARLES F. BROOKS and EDITH M. FITTON

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Forecasting Heavy Snowstorms at Blue Hill (Boston), Mass.

I. Tracks of the Cyclones Producing Heavy Snows in the Winters of 1938/9 to 1946/7

Charles F. Brooks and Irving I. Schell

The 16 snowstorms yielding 9 inches or more of snowfall at Blue Hill in the months November to March were all associated with cyclones forming south of Lat. 40° and passing 70 to 265 miles south or southeast of Blue Hill. Half of them were young secondaries.

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