Mooney, P.A. and Mulligan, F.J. and Fealy, R.
Comparison of ERA-40, ERA-Interim and NCEP/NCAR
reanalysis data with observed surface air temperatures
International Journal of Climatology, 31.
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.
||reanalysis data; observed data; surface air temperatures; data assimilation; marine buoys; Ireland; regridding;
||Faculty of Social Sciences > Geography
Dr. Priscilla Mooney
||03 May 2011 09:41
|Journal or Publication Title:
||International Journal of Climatology
||Royal Meteorological Society
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