GGOS Atmosphere

Numerical Weather Models for the Global Geodetic Observing System

In modern geodesy and in particular in space geodetic techniques various effects of the atmosphere have to be considered. The atmosphere delays or advances radio signals emitted by GNSS (Global Navigation Satellite Systems) spacecrafts or by distant radio sources observed by VLBI (Very Long Baseline Interferometry). Atmosphere pressure loading causes deformations of the Earth's surface of up to more than one centimeter, gravity observations from dedicated satellite missions have to be reduced for atmospheric influences, and a considerable part of changes in Earth's rotation (polar motion, length of day) is due to dynamical processes in the atmosphere. Thus, the atmosphere plays an important role for the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) with its central theme 'Global deformation and mass exchange processes in the System Earth'.

The theoretical and practical background related to project GGOS Atmosphere has been documented in the book Atmospheric Effects in Space Geodesy edited by Johannes Böhm and Harald Schuh.

In recent years, models for all these atmosphere-related phenomena have been developed which are based on data from numerical weather models. However, the parameters describing each of these effects have been determined at various institutions, using different weather models with different resolutions, and applying varying geophysical models and hypotheses. The overall goal of project GGOS Atmosphere, conducted at the research group of Advanced Geodesy of TU Vienna under support by the FWF (Austrian Science Fund) for the period 03/2009—09/2013, is to determine consistent and homogenous estimates for

  1. atmosphere angular momentum (functions),
  2. atmosphere delays,
  3. gravity field coefficients for the atmosphere and
  4. atmosphere loading corrections

based on a common data stream with predominantly the same underlying meteorological parameters like pressure, temperature, humidity, and wind velocity. Main tasks of the project were to sift and download state-of-the-art meteorological data sets from the European Centre for Medium-Range Weather Forecasts (ECMWF), extracting high-quality data classes with optimal spatial and temporal resolution (e.g. 3-hourly), and thereupon determine all four target quantities as mentioned above in a consistent manner. Pressure loading corrections, angular momentum functions, and gravity field coefficients for the atmosphere were computed for the whole history of space geodetic observations and these products of GGOS Atmosphere have been supplied to the Special Bureau of the Atmosphere as part of the reorganized Global Geophysical Fluid Center (GGFC) of the International Earth Rotation and Reference Systems Service (IERS). GGOS Atmosphere parameters that have been approved as operational or provisional GGFC product are signified on this website. The gain of providing such a consistent stream of all atmospheric prime quantities in geodesy is to contribute to a better understanding of the Earth system, based on a detailed knowledge of the interactions between geometry, kinematics, and the gravity field of our planet.