Operational global reanalysis: progress, future directions and synergies with NWP

Within the Copernicus Climate Change Service (C3S), ECMWF is currently producing the ERA5 reanalysis which embodies a detailed record of the global atmosphere, land surface and ocean waves from 1950 onwards. This new reanalysis will replace the highly successful ERA-Interim reanalysis that was started in 2006 (spanning 1979 onwards), and will also encompass the period covered by ERA-40. ERA5 is based on the Integrated Forecasting System (IFS) Cycle 41r2 which was operational in 2016. Therefore, ERA5 benefits from a decade of developments in model physics, numerics and data assimilation. In addition to a significantly enhanced horizontal resolution of 31km, compared to 80kmfor ERA-Interim, ERA5 has a number of innovative features. These include hourly output throughout, and an uncertainty estimate (3-hourly at half the horizontal resolution). The step forward regarding quality and level of detail is evident. Forecasts from ERA5 analyses show a gain of up to one day in skill with respect to ERA-Interim.

One important novelty of ERA5 is the availability within 5 days of real time which will serve users that need recent meteorological information in combination with a long and consistent climate record. Such guaranteed timeliness requires that the ERA5 reanalysis is generated as an operational product.

The operational services in the Copernicus Programme build upon the massive European investments in mature science and technology. For climate reanalysis, this is a two-way interaction for ECMWF. On the one hand, ERA5 benefits greatly from the leverage of the developments in the IFS. On the other hand, the operational model development at ECMWF benefits from reanalysis. One excellent example of this is the Research and Development work performed within the European-Commission funded research projects ERA-CLIM and ERA-CLIM2.

This paper provides an overview of ECMWF’s atmospheric, ocean and land reanalysis activities. In particular, it presents the ERA5 reanalysis system and its performance. It also describes challenges that were encountered and their practical solutions. The outcomes of the ERA-CLIM and ERACLIM2 projects will be summarized. Subsequent developments in, and plans for, the IFS in support of future reanalyses, aligned with the ECMWF strategy, are described.