No evidence for solar absorption anomaly by marine water clouds through collocated aircraft radiation measurements

No observational evidence was found for the so-called anomalous solar absor ption by maritime water clouds through collocated aircraft measurements tak en during the Japanese Cloud-Climate Study (JACCS) program. The aircraft ex periment has been carried out by using two aircraft equipped with various i nstruments fur wintertime stratocumulus clouds over an area centered at (29 degrees N, 129 degrees E) in the East China Sea. Here we have carefully an alyzed solar absorption by the water stratocumulus clouds observed on Febru ary 2, 1998. The visible-band net fluxes measured above and below the cloud layer were almost the same within measurement accuracy; this means no subs tantial absorption in the visible spectral region, On the other hand, there were significant differences as between the near-infrared-band net fluxes measured above and much as 50-80 W m(-2) between the near-infrared-band net fluxes measured above and below the cloud layer; this difference correspon ds to absorptance of 6-10% of the total-band solar irradiance above the clo ud layer, Without cloud particles, water vapor absorption was estimated to be about 4% of the total-band irradiance for the layer. Distributions along the night legs of the measured visible-band and near-infrared-band absorpt ance were in phase in their positions with zero mean visible-band absorptan ce. The measured radiation budget averaged over long distances along the fl ight legs for the inhomogeneous cloud layers agreed well with theoretical c ounterparts calculated for plane-parallel, homogeneous cloud models based o n the observed microphysical parameters.