New Data Set of Hydrological Angular Momentum With its Associated 6 Days-Long Forecasts

Since more than 15 years, GFZ routinely provides daily updated hydrological effective angular momentum functions (HAM) and its 6 days-long forecasts for the study of Earth orientation parameter variability and for improving polar motion and UT1-UTC predictions. GFZ’s HAM time series are part of a consistent set of effective angular momentum functions (EAM) covering the Earth’s major subsystems atmosphere, oceans, and the terrestrial hydrosphere. In addition, all EAM products are consistent with the GRACE/GRACE-FO atmosphere-ocean dealiasing product AOD1B release 06 which is used for gravity field processing and precise orbit determination.

For the new HAM data set we switch our hydrological model setup from the Land Surface Discharge Model (LSDM) to the open source, high-resolution hydrological rainfall-runoff-routing model LISFLOOD (https://ec-jrc.github.io/lisflood/). We slightly adapted the latest LISFLOOD 0.05° version for geodetic applications by modifying the snow melting parameterization, the soil depth parameterization, and implementing a seasonal snow storage model for Antarctica to optimize the agreement of simulated terrestrial water storage with mass anomalies from the satellite gravimetry missions GRACE and GRACE-FO on different spatial and temporal scales. Due to (I) up-to-date surface parameter maps; (ii) increased temporal resolution of 3 hours; (iii) enhanced parameterization of hydrological processes such as evapotranspiration, soil infiltration, snow accumulation and dynamic river routing; and (iv) a much more extensive set of atmospheric forcing parameters from ECMWF’s latest global atmospheric reanalysis ERA5, the derived HAM time series could be substantially improved in terms of long-term stability, seasonal amplitudes, sub-seasonal and episodic variations, and short-term forecasts. Furthermore, the new HAM data set is consistent with the new AOD1B release 07.