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 Atmospheric De-aliasing

Atmospheric De-aliasing Products

A new series of 6-hourly atmospheric de-aliasing products based on reanalysis (ITG3D-ERA-Interim) - coverage: 2003-2011.5

Temporal aliasing caused by incomplete reducing of background models is still a factor that affects the quality of the gravity field solutions. To improve the atmospheric part of the de-aliasing products, a new set of 6-hourly total-atmospheric mass fields based on the ECMWF's reanalysis data (ERA-Interim, Dee et al., 2011) was computed. The new set (ITG3D-ERA-Interim) has been improved over the atmospheric part of GRACE-AOD1B in terms of (a) the computational process, i.e. a modified 3D integral approach, that considers a more realistic physical and geometrical Earth's shape as well as a better approach for numerical integration (ITG3D approach in Forootan et al., 2013), is used to compute the products; (b) the input parameters, i.e. the ERA-Interim reanalysis atmospheric fields are used as the input of our 3D integration. Note that the ERA-Interim atmospheric fields are computed based on the same operational cycles as ECMWFop, while assimilating several in-situ and satellite observations. Therefore, the ''jumps'' of 2006 and 2010 do not exist in ITG3D-ERA-Interim time series. ITG3D-ERA-Interim is available via:

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Computational Notes:

The main changes within the new 3D integration with respect to the atmospheric part of GRACE-AOD1B are threefold (Forootan et al., 2013):

  • geometrical modification i.e., including ellipsoidal radius instead of a constant radius, incorporating geoid heights from the ITGGRACE2010s static solution instead of using the surface geopotential from ECMWF, as well as using a more accurate transformation for computing radial coordinates according to the Office of the Federal Coordinator for Meteorological Services and Supporting Research, 1997;
  • physical modification i.e., including the more accurate latitude- and altitude- dependent gravity acceleration within the vertical integration instead of a simple linear approximation of the latitude-dependent gravity acceleration; and
  • numerical improvements, i.e., considering sub-intervals between each model level for better performing the vertical integration, as well as using the Gauss-Legendre Quadrature (GLQ) method for improving the computation of the desired atmospheric de-aliasing spherical harmonics by horizontal integration.

A mean field of 2001+2002 has been removed within the computation of ITG3D-ERA-Interim, making them comparable to those of GRACE-AOD1B (for details see: Flechtner, 2007 and Forootan et al., 2013).

Computations by: Olga Engels (Didova) and Ehsan Forootan.

When using these data please cite:

  • Forootan, E., Didova, O., Kusche, J., Löcher, A. (2013) Comparisons of Atmospheric Data and Reduction Methods for the Analysis of Satellite Gravimetry Observations. Journal of Geophysical Research - Solid Earth, 118(5), pp. 2382–2396, doi:10.1002/jgrb.50160.

For assessing the potential impact of the new products on the computations of linear trends as well as the amplitude of annual and semi-annual GRACE-derived mass changes, we refer to:

  • Forootan, E., Didova, O., Schumacher, M., Kusche, J., Elsaka, B. (2014) Comparisons of atmospheric mass variations derived from ECMWF reanalysis and operational fields, over 2003 to 2011. Journal of Geodesy, 88(5), pp. 503–514, doi.org/10.1007/s00190-014-0696-x.
  • Forootan, E., Didova, O., Schumacher, M., Kusche, J., Brockmeyer, C. (2013) On computation of atmospheric de-aliasing products and its impact on GRACE-derived mass estimation. AGU Fall Meeting, online, San Francisco.


References:

  • D.P. Dee et. al. (2011) The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q. J. R. Meteorol. Soc., 137, 553-597, doi:10.1002/qj.828.
  • F. Flechtner (2007) AOD1B product description document for product releases 01 to 04. Technical Report, Geoforschungszentrum, Potsdam.