U41A-0001
Selection of Super-Ensembles for Regional Climate Projections
Increased confidence in climate projections comes from removal or weighting of outlier models by comparing historical simulations against observations, and from developing multi-model statistics (super-ensembles) to accounting for structural uncertainty. The CMIP3 provides a platform for testing these hypotheses. We have used a selection criterion based on variance for 20th century Arctic surface temperatures and North Pacific sea surface temperature (SST), and mean ice area for regional sea ice. For Alaska, we considered a multivariate criterion based on the seasonal cycles of temperature, pressure and precipitation. Applying model selection criteria, we have some confidence that the SST trend in the North Pacific will emerge from natural variability and that sea ice area will be reduced by 40 percent in most Arctic marginal seas by 2050. Regionally, the models that best capture the seasonal cycles of present-day Alaskan climate project larger Arctic changes than the all-model composite. For northern Eurasia projected differences in temperatures with and without model discrimination were negligible. No one model or group of models appears to be "best" for multiple criteria or multiple regions, a remaining philosophical difficulty.
U41A-0002
Investigating the Feedbacks of Large Wind Farms on the Local Weather and Climate
Wind energy is quickly growing in popularity worldwide as a good alternative source of energy to help mitigate global warming. As its use becomes more widespread, however, the feedback between large wind farms and the atmosphere needs to be investigated. Establishing the effects of large wind farms on local meteorology and wind farm efficiency is important to determine any negative and positive impacts on climate and weather. It is also important for site selection and for determining the optimum array efficiency for maximum power performance. In order to determine these effects, flow around turbine blades need to be resolved. A basic aerodynamic model based on the Blade Element Momentum (BEM) theory is used to simulate the forces associated with the spinning turbine blades. Results are verified against turbine blade data. Power curves from the model and the data match very well at low to medium wind speeds (5-13 m/s). Although there is less agreement at high wind speeds, this improves as the power curve is weighted with a Rayleigh distribution function that is typical of a wind site. Since wind speeds at a site are typically mostly in the 7-13 m/s speed range, these results are sufficient for the purpose of characterizing the forces between the turbine blades and the atmosphere. This aerodynamic model is then integrated into a high-resolution atmospheric model to quantify the effects of these forces on the local flow.
U41A-0003
Sea level research beyond the IPCC Fourth Assessment Report
The chapter on Oceanic Climate and Sea Level of the fourth assessement report written by the IPCC Working Group I summarized a number of recent results about sea level change (e.g.: recent observations based on satellite altimetry indicate that sea level is rising faster since the early 1990s than during the previous decades, but it is yet unclear whether the recent increased rate indicates an accelerating trend or whether it is associated with decadal; Owing to progress realized in the recent years in understanding the causes of present-day sea level rise, we can now almost close the sea level budget for the 1993-2003 decade : about fifty percent of the rate of sea level rise is due to thermal expansion of sea waters in response to ocean warming; Recent estimates of the mass balance of mountain glaciers and ice sheets appear able to explain another forty per cent; Sea level change is highly non-uniform spatially, as revealed by satellite altimetry. In some regions, rates are up several times the global mean rise, while in other regions sea level is falling. The spatial patterns of observed sea level changes are highly correlated to regional change in global heat content and ocean thermal expansion and appear consistent with known characteristics of the large scale ocean circulation). As lead authors of this chapter, having contributed to the writing of the sea level section, we discuss here the degree of confidence we have in observations and in understanding present day sea level rise (i.e. in climate-related and anthropogenic contributions), try to identify current gaps and suggest a number of recommendations for future sea level research.