Accounting for Several Infrared Radiation Processes in Climate Models

AbstractThree aspects of longwave (LW) radiation processes are investigated using numerical experiments with the Canadian Atmospheric Global Climate Model version 4.3 (CanAM4.3). These are the overlapping LW and shortwave (SW) radiation, scattering by clouds and specification of ocean emissivity. For the overlapping of solar and infrared spectra, using a single band scheme was compared against a method directly inputing solar energy. Offline calculations show that for high clouds using the single band can cause an overestimate of the downward LW flux; while a method that accounts for input solar energy in the LW yields results are more accurate. Longwave scattering by cloud traps more infrared energy in the atmosphere and reduces the outgoing radiation to space. Simulations with CanAM4.3 show that cloud LW scattering can enhance the LW cooling rate above the tropopause and reduce it inside the troposphere, resulting in warmer temperatures, especially in the tropics and low latitudes. This implies a larger...