AAM Version 2.0 as described in the Product Description Document completely follows the model updates of the GRACE/-FO AOD1B release RL07 dealising product. AAM are based on re-analysis and operational data from the ECMWF. For 1960 – 2017, AAM is based on the fifth generation reanalysis of the European Centre for Medium-Range Weather Forecasts (ERA5; Hersbach et al., 2020). Since 2018, AAM is based on the operational ECMWF data product. Operational NWP data-sets are updated daily including related forecasts. They are available for the whole time-period as well, but their quality is drastically improving in particular in the most recent years due to increased spatial resolution, improved representation of physics in the model, and tremendous progress in data assimilation thanks to the computing resources available today.
In contrast to ERA5, the operational analysis data is typically disseminated only every 6 hours. In order to calculate AAM at a higher temporal resolution of 3 hours, we make use of short-term forecasts that are available even at hourly time-steps for the most recent years of the operational ECMWF forecasts.