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Simple Indices of Climate Variability and Change

PI: David Karoly
Institution: University of Oklahoma
Additional Investigators: Karl Braganza
Five simple indices of large-scale surface temperature variations will be used to assess the performance of a number of climate models in simulating climate variability and change during the 20th century. These indices are based on the spatial fingerprint of greenhouse climate change and include the area-mean surface temperature, the land-ocean temperature contrast, the meridional temperature gradient in the Northern Hemisphere, the magnitude of the annual cycle in temperature over land, and the magnitude of the diurnal temperature range over land. The indices contain information independent of variations in global-mean temperature for unforced climate variations and hence, they are more useful in the attribution of anthropogenic climate change than global mean temperature alone. These indices have been used in recent studies of global climate variability and change simulated by some climate models used in the IPCC Third Assessment (Braganza et al., 2003, 2004a, b) and have also been used in a recent climate change detection and attribution study for the North American region (Karoly et al., 2003).

The indices will be calculated for the global domain and for the North American region from observational data for the period 1880-2003 and compared with data from model simulations for this period. The models to be analysed include simulations from all three US models (NCAR , GFDL and GISS) being made available for the IPCC Fourth Assessment Report, together with several other international models (HadGEM, CGCM, ECHAM5). The variability and correlation structure of the indices will be compared between the observations and the models on three different timescales; interannual variability, decadal variability and trends on 50 year and century timescales. Both control model simulations and runs for the 20th century will be analysed.

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