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Aircraft measurements of the solar absorption by broken cloud fields: A case study
Author(s) -
Rawlins F.
Publication year - 1989
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.49711548609
Subject(s) - overcast , absorption (acoustics) , albedo (alchemy) , parametrization (atmospheric modeling) , cloud top , cloud computing , solar zenith angle , remote sensing , environmental science , cloud albedo , cloud base , meteorology , cloud height , liquid water content , wavelength , computational physics , atmospheric sciences , optics , cloud cover , physics , radiative transfer , sky , geology , computer science , art , performance art , art history , operating system
Measurements of broad‐band radiation at solar (0.3–3.0 μm) and near‐infrared (0.7–3.0 μm) wavelengths are presented for three flights of the Meteorological Research Flight C130 aircraft in broken cloud fields. The solar absorption is determined from observations made above cloud top and below cloud base, using data in the two spectral bands to minimize errors of cloud sampling between different runs and to reduce the scatter due to cloud edge effects. The method assumes that cloud layer absorption in the visible region is negligible compared with that in the near‐infrared. This allows average absorption to be calculated for small sections of the aircraft track, which will generally include both fully clear and totally overcast cases. The smallest absorption measured is about 2%, in agreement with model results for the clear atmosphere. The largest absorption was found to be 8–12% (for a maximum cloud depth of 1 km), which is similar to measurements reported for layer cloud. An additional finding is that absorption by the broken cloud field varies uniformly with albedo, indicating that the parametrization of absorption in numerical models can be adequately described as a simple function of the albedo in partially cloudy areas.