The data sets explored are an ECHAM5 Special Report on Emissions Scenarios (SRES) A2 simulation (MPI-M Hamburg, Roeckner et al. (2003)) for the 4th Assessment Report of the Intergovernmental Panel of Climate Change (IPCC AR4) for the time period 1961-2064 and the ERA-40 reanalysis data set (obtained from the ECMWF data server, Simmons and Gibson (2000)) for the time period 19612002, respectively. Regarding the ECHAM5 A2 run starting 2001, the ECHAM5 IPCC 20th century run complemented the data before 2001.

The native resolutions were 1.875° x 1.875° on 16 pressure levels for ECHAM5 and 2.5° x 2.5° on 23 pressure levels for ERA-40, respectively. To obtain easy comparability, the data were regridded to a common 2.5° x 2.5° grid in latitude and longitude and to 18 pressure levels ranging from 1000-10 hPa. Due to the limited representation of the 10 hPa level in ECHAM5 (Cordero and de F. Forster 2006), this upper boundary model level is not used in this study, and the highest level effectively interpreted becomes the 20 hPa level for ECHAM5.

In this study we concentrate on seasonal (northern) summer means (JJA), exploring the parameters temperature and refractivity from the ECHAM5 A2 run and geopotential height and temperature from ERA-40, respectively. Decadal averages and trends were generally used, i.e., 1966-2059 effective time span for ECHAM5 and 1966-1997 for ERA-40, respectively.

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