全球能量收支预算

基于新的观测和分析给出全球年平均能量收支预算,以及陆地、海洋的能量收支贡献及其时间变化。     

Climate sensitivity of the NCAR Community Climate Model (CCM2) to horizontal resolution

The dependence on horizontal resolution of the climate simulated by the National Center for Atmospheric Research Community Climate Model (CCM2) is explored. Simulations employing R15, T21, T31, T42, T63, and T106 horizontal spectral truncations are compared. Parameters associated with the diagnostic cloud scheme are modified for each resolution to provide similar global average cloud radiative forcing at each resolution. Overall, as with earlier studies, there are large differences between the low resolution R15 and T21 simulations and the medium resolution T42 simulation. Many climate statistics show a monotonic signal with increasing resolution, with the largest variation occurring from low to medium resolution. Although the monotonic signal is often from the low resolution simulations toward atmospheric analyses, in some cases it continues beyond the analyses at the highest resolution. Where convergence occurs, it is not always to the atmospheric analyses, and the highest resolution simulations are not the best by all measures. Although many climate statistics converge, the processes that maintain the climate do not, especially when considered on a regional basis. The implication is that the finer scales are required to capture the nonlinear processes that force the medium scales. Overall, it appears that, at a minimum, T42 resolution is required, but higher resolution would be better. Applications at T42 should take into consideration how model errors indicated by these resolution signals might affect any findings.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Interaction of a Masonry Dam and the Rock Foundation

The Urft dam is an old German gravity dam located in the Eifel near Cologne. In order to ensure its stability and for adjustment to today??s technical standards rehabilitation works were required. Two inspection galleries were excavated below the storage level by means of smooth blasting. To reduce the porewater pressure acting on the dam??s base and thus to increase the stability of the dam also the drainage system was reconstructed and improved. Because the Urft dam is curved, its load bearing behavior reveals a certain arching effect. In order to take advantage of this arch action the stability proof was carried out by means of three-dimensional analyses according to the FEM. In these analyses the interaction of dam and the foundation rock was accounted for. Explorations, laboratory and in situ testing of the masonry and the foundation rock were carried out and a monitoring program was established. The monitoring results allowed a calibration of the three-dimensional model for stability analyses by means of back analyses. On this basis the final stability proof could be conducted.     

A comparison of low-latitude cloud properties and their response to climate change in three AGCMs sorted into regimes using mid-tropospheric vertical velocity

Low-latitude cloud distributions and cloud responses to climate perturbations are compared in near-current versions of three leading U.S. AGCMs, the NCAR CAM 3.0, the GFDL AM2.12b, and the NASA GMAO NSIPP-2 model. The analysis technique of Bony et al. (Clim Dyn 22:71–86, 2004) is used to sort cloud variables by dynamical regime using the monthly mean pressure velocity ω at 500 hPa from 30S to 30N. All models simulate the climatological monthly mean top-of-atmosphere longwave and shortwave cloud radiative forcing (CRF) adequately in all ω-regimes. However, they disagree with each other and with ISCCP satellite observations in regime-sorted cloud fraction, condensate amount, and cloud-top height. All models have too little cloud with tops in the middle troposphere and too much thin cirrus in ascent regimes. In subsidence regimes one model simulates cloud condensate to be too near the surface, while another generates condensate over an excessively deep layer of the lower troposphere. Standardized climate perturbation experiments of the three models are also compared, including uniform SST increase, patterned SST increase, and doubled CO₂ over a mixed layer ocean. The regime-sorted cloud and CRF perturbations are very different between models, and show lesser, but still significant, differences between the same model simulating different types of imposed climate perturbation. There is a negative correlation across all general circulation models (GCMs) and climate perturbations between changes in tropical low cloud cover and changes in net CRF, suggesting a dominant role for boundary layer cloud in these changes. For some of the cases presented, upper-level clouds in deep convection regimes are also important, and changes in such regimes can either reinforce or partially cancel the net CRF response from the boundary layer cloud in subsidence regimes. This study highlights the continuing uncertainty in both low and high cloud feedbacks simulated by GCMs.     

A clarification of certain issues related to the CO2—Climate problem

In this paper we examine and clarify several arguments that have been put forth by Dr. S. B. Idso in an article appearing within this issue of Climatic Change.