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Mid‐ocean observations of atmospheric radiation
Author(s) -
Simpson James J.,
Paulson Clayton A.
Publication year - 1979
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49710544412
Subject(s) - longwave , overcast , atmospheric sciences , environmental science , albedo (alchemy) , shortwave , radiometer , altitude (triangle) , cloud cover , flux (metallurgy) , radiative transfer , meteorology , climatology , physics , geology , remote sensing , mathematics , cloud computing , art , geometry , materials science , quantum mechanics , sky , performance art , computer science , metallurgy , art history , operating system
Mid‐ocean (35°N 155°W) observations of the various components of radiative flux were made from the R/P FLIP during the period 2 through 13 February 1974. Cloud cover ranged from clear skies to overcast, and water vapour pressure varied between 9 and 18 mb, with sea surface temperature near 15.0°C. The net longwave radiative fluxes reported here were obtained: (1) by taking the difference between simultaneous measurements of net all‐wave and net solar fluxes; and (2) by direct measurements with a net longwave radiometer designed by G. W. Paltridge. When observations during rain and fog are excluded, the difference between night‐time 15‐minute averages by the two methods is generally less than lmWcm −2 . During day‐time, indirect measurements are often larger than direct by about 5mWcm −2 ; from internal evidence we prefer the direct values. The albedo of the sea surface was calculated from simultaneous measurements of downward and upward solar fluxes. The observations were analysed to represent albedo as a function of solar altitude and atmospheric transmittance, following the work of R. E. Payne; our results suggest that Payne's smoothed representation is suitable for use over the open ocean. Albedo was observed to decrease with increasing wind speed for clear skies with solar altitude between 15 and 30 degrees but no variation was discernible at higher solar altitudes. Empirical formulae for calculating both shortwave and net longwave components of the radiative flux were compared with measurements. A formula due to F. E. Lumb for determining the incident solar flux given solar altitude, cloud amount and cloud type, consistently yields good agreement with the measurements, within about lmWcm −2 . Daily averages of net longwave flux calculated from several empirical formulae using a linear correction for clouds are within 2mWcm −2 of the observations reported in this paper. Since daily radiation balance values were measured as only 5mWcm −2 , the limitations of the best current empirical formulae are evident.