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A study of subvisual clouds and their radiation effect with a synergy of CERES,...

Sun, W., G. Videen, S. Kato, B. Lin, C. Lukashin, and Y. Hu (2011), A study of subvisual clouds and their radiation effect with a synergy of CERES, MODIS, CALIPSO, and AIRS data, J. Geophys. Res., 116, D22207, doi:10.1029/2011JD016422.

Subvisual cirrus clouds that are defined as those whose optical thickness is less than ∼0.3 are found in ∼50% of global observations. Passive remote‐sensing instruments, such as the Moderate Resolution Imaging Spectroradiometer (MODIS), generally fail to detect these optically thin clouds. The launch of NASA’s Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite provides an unprecedented ability to detect thin cloud layers globally. Also, the Clouds and the Earth’s Radiant Energy System (CERES) provides accurate measurements of top‐of‐atmosphere radiation. By using CERES, MODIS, and CALIPSO measurements in a synergistic manner, a quantitative assessment of the influence of subvisual clouds on the Earth’s shortwave (SW) radiation is accomplished. The difference between clear‐sky radiation flux and the flux obtained with the presence of subvisual clouds clearly shows the cooling effect of subvisual clouds in the SW. The subvisual clouds increase the diurnal mean reflected SW flux by ∼2.5 W m−2. The subvisual clouds’ effect on outgoing longwave radiation is also studied using a radiative‐transfer model. The model results show that a layer of subvisual clouds having optical thickness of 0.1 can have a warming effect of ∼15 W m−2. These clouds can also affect the polarization of the reflected SW radiation and the accuracy of aerosol retrieval with satellite measurements. This work demonstrates that the study of subvisual clouds is necessary for an accurate and detailed understanding of Earth‐atmosphere radiation.

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Radiation Science Program (RSP)