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Atmos. Chem. Phys. Discuss., 10, 22093-22107, 2010
www.atmos-chem-phys-discuss.net/10/22093/2010/ doi:10.5194/acpd-10-22093-2010 © Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. |
Impact of different definitions of clear-sky flux on the determination of longwave cloud radiative forcing: NICAM simulation results
1School of Earth and Environmental Sciences, Seoul National University, Seoul, 151-747, Korea
2Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8568, Japan
Abstract. Using one month of the cloud-resolving Nonhydrostatic Icosahedral Atmospheric Model (NICAM) simulations, we examined the impact of different definitions of clear-sky flux on the determination of longwave cloud radiative forcing (CRF). Because the satellite-like cloud-free composite preferentially samples drier conditions relative to the all-sky mean state, the conventional clear-sky flux calculation using the all-sky mean state in the model may represent a more humid atmospheric state in comparison to the cloud-free state. The drier bias is evident for the cloud-free composite in the NICAM simulations, causing an overestimation of the longwave CRF by about 10% compared to the NICAM simulated longwave CRF. Overall, water vapor contributions of up to 10% of the total longwave CRF should be added to make the NICAM-generated cloud forcing comparable to the satellite measurements.
Citation: Sohn, B. J., Nakajima, T., Satoh, M., and Jang, H.-S.: Impact of different definitions of clear-sky flux on the determination of longwave cloud radiative forcing: NICAM simulation results, Atmos. Chem. Phys. Discuss., 10, 22093-22107, doi:10.5194/acpd-10-22093-2010, 2010.