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 absorption by maritime water clouds through collocated aircraft measurements taken during the Japanese Cloud-Climate Study (JACCS) program. The aircraft experiment has been carried out by using two aircraft equipped with various instruments fur wintertime stratocumulus clouds over an area centered at (29 degrees N, 129 degrees E) in the East China Sea. Here we have carefully analyzed solar absorption by the water stratocumulus clouds observed on February 2, 1998. The visible-band net fluxes measured above and below the cloud layer were almost the same within measurement accuracy; this means no substantial 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 corresponds to absorptance of 6-10% of the total-band solar irradiance above the cloud 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 absorptance were in phase in their positions with zero mean visible-band absorptance. The measured radiation budget averaged over long distances along the flight legs for the inhomogeneous cloud layers agreed well with theoretical counterparts calculated for plane-parallel, homogeneous cloud models based on the observed microphysical parameters.