The ERA5 global atmospheric reanalysis
ERA5 is the latest global atmospheric reanalysis to be produced at the European Centre for Medium Range Weather Forecasting (ECMWF). The period 1979-2018 is complete, and an extension covering 1950-1978 is underway. In terms of key specifications (resolution, uncertainty estimates based on a 10-member ensemble of data assimilations, and hourly output, for example) and in terms of performance ERA5 represents a significant improvement over its predecessor, ERA-Interim. Several challenges have emerged during the production of ERA5 though. A number of these could be addressed at the expense of a delayed completion date. Analyses in the troposphere and lower stratosphere show good consistency with recent reanalyses. There are significant discontinuities in temperature fields in the upper stratosphere. This is also a challenging region for several other global reanalyses. The hybrid formulation of the background error covariance has required ad-hoc adjustments to the climatological component to reflect the variation of background errors during the period spanned by the reanalysis. The treatment of early satellite sounding data (from the Vertical Temperature Profiling Radiometer, VTPR [1972-1978]) has required several developments (in observation error tuning, in quality control, and in the optimisation of radiative transfer modelling). Finally, anomalously high ozone values in the winter polar stratosphere has necessitated developments in the assimilation of ozone observations from the Solar Backscatter Ultra-Violet Radiometer (SBUV) instruments.
Dr. William Bell ECMWF