Poor simulation of clouds may be the main reason why current climate models show sea-surface temperature biases over the Southern Ocean. This in turn could have implications for assessing the plausibility of modelled cloud feedbacks in this region under climate change. A new paper led by my colleague Alejandro Bodas-Salcedo – which has just been published as an early online release in the Journal of Climate – looks at the simulation of clouds over the Southern Ocean in the current generation of climate models. The abstract and citation are below, the paper can be accessed here.
Current climate models generally reflect too little solar radiation over the Southern Ocean, which may be the leading cause of the prevalent sea-surface temperature biases in climate models. We study the role of clouds the radiation biases in atmosphere-only simulations of the Cloud Feedback Model Intercomparison Project phase 2 (CFMIP2), as clouds have a leading role in controlling the solar radiation absorbed at those latitudes. We composite daily data around cyclone centres in the latitude band between 40°S and 70°S during the summer. We use cloud property estimates from satellite to classify clouds into different regimes, which allows us to relate the cloud regimes and their associated radiative biases to the meteorological conditions in which they occur. The cloud regimes are defined using cloud properties retrieved using passive sensors, and may suffer from the errors associated with this type of retrievals. We use information from the CALIPSO lidar to investigate in more detail the properties of the ‘mid-level’ cloud regime. Most of the model biases occur in the cold air side of the cyclone composite, and the cyclone composite accounts for most of the climatological error in that latitudinal band. The ‘mid-level’ regime is the main contributor to reflected shortwave radiation biases. CALIPSO data show that the ‘mid-level’ cloud regime is dominated by two main cloud types; cloud with tops actually at mid-level, and low-level cloud. Improving the simulation of these cloud types should help reduce the biases in the simulation of the solar radiation budget in the Southern Ocean in climate models.
Bodas-Salcedo, A., K.D. Williams, M.A. Ringer et al., 2013, Origins of the solar radiation biases over the Southern Ocean in CFMIP2 models, J. Climate, doi: http://dx.doi.org/10.1175/JCLI-D-13-00169.1
Mark Ringer 