Impacts of Ice Cloud Radiative Effects on the Simulated Atmospheric Circulation

Ice clouds are commonly believed to perturb the global radiation balance and exert noticeable influences on the atmosphere. But it remains a question as to what extent ice clouds can change the general circulation. In numerical models, ice clouds are normally overlapped with the other types of clouds, and it is difficult to separate the impact of one particular type of cloud. In this study, we follow the methodology of the Clouds On-Off Klima Intercomparison Experiment (COOKIE) but focusing specifically on the ice clouds. AMIP-type simulations using the Community Atmospheric Model (CAM) version 5.3 are conducted for one control simulation and three sensitivity cases with shortwave (SW) and/or longwave (LW) ice cloud radiative effects (ICRE) being turned off. By comparing different sensitivity cases with the controlled simulation, we are able to separate and quantify the impacts of the SW and LW components of the ICRE. It is interesting to find different but both important ICRE impacts in the tropical and extratropical areas. Comparatively, the LW ICRE plays a more important role than the SW ICRE. Especially in the tropics, the structure of the atmospheric circulation and stability experiences much larger variation when LW ICRE is removed than that when SW ICRE is off. Our results imply further needs to improve the representation of ice clouds and ICRE in the GCMS.