Work Package Leaders
Anne Sandvik (BCCR) and Jakob J. Stamnes (UiB)
Other Key Investigators
Jón Egill Kristjánsson, Knut Stamnes, Børge Hamre, Nils Gunnar Kvamstø.
International partners
David Mitchell
Background
Unlike any other region on the globe, clouds exert a positive net radiative forcing at the surface (Intrieri et al. 2002). Numerical simulations of the Arctic atmosphere with climate models and NWP models show large model-to-model discrepancies with respect to horizontal distribution, vertical extent, and optical/microphysical properties of clouds, severely limiting their predictive capability (e.g. Randall et al. 1998, Tjernström et al., 2005). The climatic conditions of the Arctic are changing more rapidly than at lower latitudes. Large changes in seaice extent have been observed in recent years, and surface temperatures have risen. Although future projections from global climate models vary, there is wide agreement that the Arctic ice cover will shrink considerably, and the Arctic summers may become ice free by the mid-21st century, or even earlier. These changes will inevitably have a large effect on arctic weather conditions, because the area of stable cold air masses may become greatly reduced. This may have a significant influence on the ubiquitous arctic stratus clouds in the summer. In wintertime, reduced sea ice cover may lead to increased fluxes of latent and sensible heat to the atmosphere, potentially having large implications for extreme weather associated with convective systems.
Research plan
In this work package we will collect data (see WP1 attachment for details), develop adequate models, and perform the data analysis and model simulations required to understand the present Arctic environment and predict how it might be altered in the future. Specifically we will collect field data on cloud particles (liquid and ice phase) as well as properties of snow and sea-ice to establish inherent optical properties of cloud particles, snow, and sea-ice for input to a comprehensive radiative transfer model (CRTM) for the coupled atmosphere-snow-sea-ice-ocean system. The CRTM will then be validated against field data on apparent optical properties (radiances and irradiances). Results from field measurements and the CRTM will then be used to validate parameterizations of cloud microphysics and radiative transfer in the weather prediction models. The new insight gained from this study will be used to improve physical parameterizations in climate models (for model specifications, see table in attachment).