Articles | Volume 10, issue 23
Atmos. Chem. Phys., 10, 11641–11646, 2010
https://doi.org/10.5194/acp-10-11641-2010
Atmos. Chem. Phys., 10, 11641–11646, 2010
https://doi.org/10.5194/acp-10-11641-2010

Research article 08 Dec 2010

Research article | 08 Dec 2010

Impact of different definitions of clear-sky flux on the determination of longwave cloud radiative forcing: NICAM simulation results

B. J. Sohn1, T. Nakajima2, M. Satoh2, and H.-S. Jang1 B. J. Sohn et al.
  • 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 taken account for making model-generated cloud forcing comparable to the satellite measurements.

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