Comparison of ERA‐40, ERA‐Interim and NCEP/NCAR reanalysis data with observed surface air temperatures over Ireland

Abstract

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][1990][1991][1992][1993][1994][1995][1996][1997][1998][1999][2000][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][2002][2003][2004][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.

Evaluation of Polar WRF forecasts on the Arctic System Reanalysis domain: Surface and upper air analysis

“…ERA-Interim uses a 4D-Var system to merge short-term model forecasts with conventional and satellite observations from 1989 to the present [Dee and Uppala, 2009]. ERA-Interim has been shown to perform well in modeling near-surface temperatures over Ireland [Mooney et al, 2010] and in depicting tropospheric temperatures over the Arctic [Dee and Uppala, 2009]. Here, the output from ERA-Interim is on a 1.5°× 1.5°latitude/longitude grid and has been projected onto the Polar WRF domain without interpolation in order to provide a qualitative spatial analysis of near surface air temperature and evaporation.…”

The circulation of Icelandic waters – a modelling study

“…The atmospheric forcing of the model consists of the 6-hourly NCEP/NCAR re-analysis fields (Kalnay et al, 1996). This state-of-the-art data set (Hodges at al., 2011;Mooney et al, 2011;Tilinia et al, 2013) was chosen because it stretches back to the year 1948 and therefore allows a greater flexibility in the setup of future hindcast simulations. The model reads in the following seven parameters: precipitation rate, specific humidity (2 m), sea level pressure, air temperature (2 m), total cloud cover, zonal and meridional wind speed (10 m).…”

Elevation correction of ERA-Interim temperature data in complex terrain

“…They can also provide reliable data for decision-makers (e.g. tourism planning) and model developers (Dodson and Marks, 1997;Minder et al, 2010;Maurer et al, 2002;Mooney et al, 2011).…”