The seasonal cycle of low stratiform clouds is studied using data from surface-based cloud climatologies. The impact of low clouds on the radiation budget is illustrated by comparison of data from the Earth Radiation Budget Experiment with the cloud climatologies. Ten regions of active stratocumulus convection are identified. These regions fall into four categories: subtropical marine, midlatitude marine, Arctic stratus, and Chinese stratus. With the exception of the Chinese region, all the regions with high amounts of stratus clouds are over the oceans. In all regions except the Arctic, the season of maximum stratus corresponds to the season of greatest lower-troposphere static stability. Interannual variations in stratus cloud amount also are related to changes in static stability. A linear analysis indicates that a 6 percent increase in stratus fractional area coverage is associated with each 1 C increase in static stability. Over midlatitude oceans, sky-obscuring fog is a large component of the summertime stratus amount. The amount of fog appears to be related to warm advection across sharp gradients of SST.

The Seasonal Cycle of Low Stratiform Clouds

TERRESTRIAL ecosystems are thought to play an important role in determining regional and global climate1–6; one example of this is in Amazonia, where destruction of the tropical rainforest leads to warmer and drier conditions4–6. Boreal forest ecosystems may also affect climate. As temperatures rise, the amount of continental and oceanic snow and ice is reduced, so the land and ocean surfaces absorb greater amounts of solar radiation, reinforcing the warming in a 'snow/ice/albedo' feedback which results in large climate sensitivity to radiative forcings7–9. This sensitivity is moderated, however, by the presence of trees in northern latitudes, which mask the high reflectance of snow10,11, leading to warmer winter temperatures than if trees were not present12–14. Here we present results from a global climate model which show that the boreal forest warms both winter and summer air temperatures, relative to simulations in which the forest is replaced with bare ground or tundra vegetation. Our results suggest that future redistributions of boreal forest and tundra vegetation (due, for example, to extensive logging, or the influence of global warming) could initiate important climate feedbacks, which could also extend to lower latitudes.

Effects of boreal forest vegetation on global climate

Evolving ideas about the Cretaceous climate and ocean circulation

Use of a land-surface-transfer scheme (LSX) in a global climate model: the response to doubling stomatal resistance

The Planet Simulator is a Model of Intermediate Complexity (MIC) which can be used to run climate and paleo-climate simulations for time scales up to 10 thousand years or more in an acceptable real time. The priorities in development are set to speed, easy handling and portability. Its modular structure allows a problem dependent configuration. Adaptions exist for the atmospheres of Mars and of Saturn’s moon Titan. Common coupling interfaces enable the addition of ocean models, ice models, vegetation and more. An interactive mode with a Model Starter (MoSt) and a Graphical User Interface (GUI) can be used to select a model configuration from the available hierarchy, set its parameters and inspect atmosphericfields while changing model parameters on the fly. This is especially useful for teaching, debugging and tuning of parameterizations. This paper gives an overview of the model’s features. The complete model including sources and documentation is available at (www.mi.uni-hamburg.de/plasim). Zusammenfassung

http://www.dgf.uchile.cl/rene/PLASIM/plasim_mz_1.pdf

The Planet Simulator: Towards a user friendly model

A new parameterization for the shortwave radiative properties of water clouds and the European Centre for Medium-range Weather Forecasts (ECMWF) cloud prediction scheme have both been included in the National Center for Atmospheric Research (NCAR) community climate model. The techniques employed to treat the contribution by water vapor absorption to the cloud radiative properties, the overlaps between cloud layers, and the spectral dependence of the properties are described, and comparisons are made with a more detailed radiation code. Only minor adjustments were necessary to implement the cloud prediction scheme. Results from a suite of integrations are used to examine the effect on model simulations. There are improvements in the model's temperature structure and in the radiation budget and cloud radiative forcing when compared with results from the Earth Radiation Budget Experiment. It is shown that the changes in the cloud distribution over the subtropical oceans induce changes not only in the surface radiative fluxes but also in the surface turbulent fluxes, through modifications to the boundary layer stability. The turbulent fluxes change in such a way as to maintain the cloud. While the cloud distributions in these areas appear realistic, it is argued that important physical processes are ignored by the model and that a more comprehensive formulation of the cloudy boundary layer is required.

Response of the National Center for Atmospheric Research community climate model to improvements in the representation of clouds

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Response of the National Center for Atmospheric Research community climate model to improvements in the representation of clouds