Arctic System Reanalysis Contrasted with the ERA-Interim Reanalysis

Abstract:

The Arctic System Reanalysis (ASR), a high-resolution regional assimilation of model output and observational data across the mid- and high latitudes of the Northern Hemisphere and the global ERA-Interim Reanalysis (ERAI) are compared to atmospheric observations for the period December 2006 – November 2007. ASR performs slightly better than ERAI in terms of annual mean bias for near-surface temperature, dewpoint, pressure, and wind speed, but RMSE and correlations significantly improve over ERAI. These results demonstrate the advantage that the higher resolution ASR provides in the assimilation of additional observations. Upper-level analyses are shown to be well assimilated as biases in temperature, geopotential height, relative humidity, and wind speed are very small compared to radiosonde data. ASR demonstrates lower RMSEs and higher correlations than ERAI throughout most of the free atmosphere, particularly for relative humidity and wind speed. An investigation of the forecast precipitation shows negative biases during cool months similar to ERAI, but positive precipitation biases in ASR during the summer months in the mid-latitudes. A closer look at stations north of 60°N shows that ASR is slightly better than ERAI with smaller biases, except during the summer when too little precipitation falls. Downward shortwave radiation is larger in ASR compared to ERAI and BSRN station observations; however both reanalyses have modest downward longwave radiation deficits during most months.