Improving the Long-term Stability of Geophysical Model Products by Mitigating the Effects of Orography Updates in Operational Weather Forecast Models

Abstract:

The global numerical weather prediction model routinely operated at the European Centre for Medium-Range Weather Forecasts (ECMWF) is typically updated about two times a year to make use of the most recent improvements in the numerical scheme, the physical model or the data assimilation procedures for steadily improving daily weather forecasting. Even though such changes frequently affect the long-term stability of meteorologic quantities, data from the ECMWF deterministic model is frequently preferred over alternative atmospheric re-analyses due to both the availability of the data in near real-time and the substantially higher spatial resolution.

However, global surface pressure time-series, which are crucial for the interpretation of geodetic observables, such as Earth rotation, surface deformation, and the Earth's gravity field, are in particular affected by changes in the surface orography of the model associated with every major improvement in horizontal resolution.

Here, we attempt to harmonize surface pressure time-series from the operational ECMWF model by projecting them onto a common reference topography under consideration of the time-variable atmospheric density structure. The effectiveness of the method will be discussed globally for two major ECMWF upgrades in 2006 and 2010. We will in particular discuss the impact of the method on planned improvements of the GRACE Atmosphere and Ocean De-Aliasing Product AOD1B, and indicate further application opportunities in the context of the Global Geophysical Fluid Center of the International Earth Rotation and Reference Frame Service.