Two case studies of winter continental-type water and mixed-phase stratocumuli over the sea - 2. Absorption of solar radiation

[1] We have carried out airborne experiments on cloud-radiation interactions for wintertime boundary layer clouds over the East China Sea and the Japan Sea in January 1999 as part of the Japanese Cloud and Climate Study (JACCS) program. By means of collocated and synchronized flights of two instrumented aircraft, flying above and below the cloud layer, respectively, we directly measured the visible and near-infrared (IR) solar absorption for two cases of stratiform clouds: one featuring supercooled water stratocumulus cloud polluted by continental aerosols observed on 21 January and one featuring highly inhomogeneous, mixed-phase stratocumulus clouds observed on 30 January. The former cloud layer, with a geometrical thickness of about 500 m (optical thickness of about 30), absorbed substantial (6%) and significant (21%) amounts of solar radiation in the visible and near-IR bands, respectively. For the latter mixed-phase cloud, on an average over a long flight distance, the visible-band solar absorption was almost zero, while the near-IR-band absorption was about 24% for the cloud layer with a mean thickness of 1.3 km. The results indicate no sign of the so-called anomalous solar absorption for either cloud case. Through radiative transfer simulations for reasonable aerosol-cloud models, along with back trajectory analysis, the visible-band solar absorption by the aerosol-polluted cloud on 21 January was attributed to absorbing aerosols from continental East Asia. The simulation study also suggests that anthropogenic water-soluble aerosols, as well as soil-dust particles, may cause appreciable visible absorption by cloud particles, resulting in an enhanced solar heating in the boundary layer cloud.