Comparison of NCEP-NCAR and ERA-Interim over Australia

This study compares observations of 22 climate variables [rainfall, minimum and maximum temperature, mean sea level pressure (MSLP), and air temperature, geopotential heights, relative and specific humidity, and u-wind and v-winds at 500, 700 and 850hPa] over Australia with NCEP-NCAR (National Centers for Environmental Prediction-National Center for Atmospheric Research) and ERA-Interim, two most often used reanalysis products. The results indicate that both NCEP-NCAR and ERA-Interim generally reproduce the observed spatial patterns of long-term mean annual rainfall, daily maximum/minimum temperature and MSLP, the monthly distribution (annual cycle) of rainfall and temperature, although temperature is generally better simulated than rainfall and ERA-Interim shows an overall better performance than NCEP-NCAR in term of continental scale. In term of linear trends, both NCEP-NCAR and ERA-Interim simulate observed trend signs in some regions, but not in others, and the spatial distributions of temperature trends are generally not as well simulated as that of annual rainfall for both NCEP-NCAR and ERA-Interim. In addition, NCEP-NCAR and ERA-Interim show similar spatial patterns of annual mean air temperature, geopotential heights, humidity and winds. This implies that studies using NCEP-NCAR data could also make use of ERA-Interim to explore the range of uncertainties for the regions and climate variables where NCEP-NCAR and ERA-Interim show differences. This conclusion may also apply to regions other than Australia. For example, the different trend signs of MSLP between NCEP-NCAR and ERA-Interim could present a scientific challenging for climatic change studies using MSLP trends, and the split between large-scale and convective rainfall would also have merits globally to understand if the differences between the two reanalysis data sets are global or if we see convergence on key areas, such as tropices and frontal systems.