CONSTANTS FOR EMPIRICAL EXPRESSIONS FOR DOWNCOMING ATMOSPHERIC RADIATION UNDER CLOUDLESS SKY

Abstract

Magnitudes of the constants in Brunt's empirical expression for nocturnal radiation were determined from continuous automatic recordings of atmospheric radiation in California under cloudless skies and interpreted for the humidity at 1400 hours on the previous day. With these constants, useful estimates of the average nighttime atmospheric radiation rate can be computed from the local 1400-hours vapor pressure and average nocturnal air temperature as reported by all first-order U. S. Weather Bureau stations. With careful interpretation of weather records, the probable error will be about 3 per cent. Comparisons are made with Loennquist's formula and with calculations by atmospheric radiation charts from known soundings for extreme conditions leading to radiation frosts in southern California. Limited observations of daytime atmospheric radiation indicate that there is little difference in the average value of the radiation ratio between night and day when the character of the overhead air mass is not changing.