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Mooney, PA;Mulligan, FJ;Fealy, R
International Journal of Climatology
Comparison of ERA-40, ERA-Interim and NCEP/NCAR reanalysis data with observed surface air temperatures over Ireland
133 ()
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Surface air temperatures modelled by ERA-40, ERA-Interim and (NCEP)/(NCAR) reanalysis (NNRP-1) have been compared with observations at 11 synoptic stations in Ireland over the period 1989-2001. The three reanalysis datasets show good agreement with the observed data and with each other. Slopes of the least-squares line to scatter plots of reanalysis data versus observational data show small differences between the three reanalyses, with ERA-40, ERA-Interim and NNRP-1 slopes ranging between (0.79-1.06) +/- 0.01, (0.83-1.01) +/- 0.01 and (0.76-0.98) +/- 0.01, respectively. Summary statistics and the monthly mean temperatures over the 1989-2001 period showed that the reanalyses were significantly warmer in winter than the observations, which resulted in best fit lines with slopes consistently less than unity. ERA-Interim was slightly better than both ERA-40 and NNRP-1 at modelling winter temperatures and it had higher correlation coefficients with the observations. All three reanalyses use different grid sizes and types. Subsequent regridding of the ERA-Interim and NNRP-1 data to the ERA-40 grid showed that the grid difference had no significant influence on the results. Comparison of ERA-Interim and NNRP-1 data with the air temperatures at four marine buoys around the Irish coast for the period 2001-2005 showed that the reanalyses modelled colder winter temperatures than the observations; resulting in best fit lines with slopes consistently greater than unity. The slopes for NNRP-1 and ERA-Interim at the marine buoys, respectively, averaged 1.09 +/- 0.04 and 1.10 +/- 0.05 while the slopes at the four land stations over the same period averaged 0.87 +/- 0.02 and 0.89 +/- 0.02, respectively. We believe that this pattern results from the difference in the treatment of land and sea surfaces in the reanalysis datasets. Copyright (C) 2010 Royal Meteorological Society
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