Massentransporte und Massenverteilungen im System Erde  
    GEO-TOPGEO-TOP  
 

 

GEOTOP: Sea Surface Topography and Mass Transport of the Antarctic Circumpolar Current

Objectives:

  • Determine the absolute, but temporally changing ocean circulation flow field and associated mass and heat transports by means of a state-of-the-art circulation model assimilating a geodetic dynamic ocean topography (DOT) and oceanographic in-situ data.
  • The ocean model focuses on the Atlantic sector of the Antarctic Circumpolar Current and the Weddell Sea, areas with strong impact of circumpolar bottom water production on global deep sea circulation
  • The geodetic focus is on maximum spatial resolution and accuracy in DOT, including thorough error estimation, rigorous error propagation and adaptation to the ocean model finite element grid.
Left: Geodetic Estimate of a 2004 mean Dynamic Ocean Topography (DOT) Right: Difference between "observed" DOT and DOT from analysis (first panel). Difference between "observed"
and predicted DOT (most right panel).
Summary of the transport results for WOCE SR3 section and four different data assimilation experiments. Observational values are taken from (Rintoul and Sokolov 2001).

Achievements:

The most important experiences of the past two years of GEO-TOP are as follows:

  • The combination and consistent filtering of geodetic data in particular in coastal regions is difficult: geoid is represented in global harmonics, while altimetry data are given along profiles.
  • There exist significant discrepancies between satellite based geoid models and geoid models based on surface data in the area of the ACC.
  • Ocean altimetry in the Antarctic ocean is limited to the sea-ice free seasons. This causes problems in the determination of DOT and of time series of the ocean surface.
  • Geodetic DOT could be successfully assimilated into the ocean model employing the Kalman Filtering approach. Exceptions are the Weddell Sea area and costal areas. 
  • Problems remain in the representation of deep ocean temperature and salinity, which may require assimilation of temperature and salinity data. 
  • Finally, only now high resolution GOCE geoid models become available.

References:

Janjic T., L. Nerger, A. Albertella,J. Schröter, S. Skachko: “On domain localization in ensemble based Kalman filter algorithms”, submitted to Monthly Weather Review, Special collection - Intercomparisons of 4D-Variational Assimilation and the Ensemble Kalman Filter, 2010.

 

Scheinert, M. (2010): Progress and prospects of the Antarctic Geoid Project. In: Pacino, M., Kenyon. S, Marti. U (eds.), Geodesy for Planet Earth, Proc. IAG Scientific Assembly, Buenos Aires, 31.08.-04.09.2009. (accepted for publication)

 

Bosch W. and R. Savcenko (2010): On estimating the dynamic ocean topography – a profile approach. In: Mertikas (Ed.) Gravity, Geoid and Earth Observation. IAG Symposia, Springer, Vol. 135. Accepted, in press

 

Janjic T., A. Albertella, S. Skachko, J. Schröter, R. Rummel: “Observational error covariance specification in ensemble based Kalman filter algorithms”, Proceedings of 5th WMO Symposium on the Assimilation of Observations for Meteorology, Oceanography and Hydrology Melbourne 5-9 October 2009.

 

Albertella, A.; Rummel, R.: On the spectral consistency of the altimetric ocean and geoid surface: a one-dimensional example; Journal of Geodesy, Vol. 83, Nr. 9, pp 805 - 815, Springer, ISSN 0949-7714, DOI: 10.1007/s00190-008-0299-5, 2009.

 

Albertella A., R. Savcenko, R. Rummel and W. Bosch: “Dynamic Ocean Topography – The geodetic Approach” DGFI/IAPG Report No.82/ Deutsches Geodätisches Forschungsinstitut (DGFI)/Institut für Astronomische und Physikalische Geodäsie (IAPG), München

 

Skachko S., Danilov S., Janjic T., Schröter J., Sidorenko D., Savcenko R., and W. Bosch: Sequential assimilation of multi-mission dynamical topography into a global finite-element ocean model. Ocean Science, 4, 307–318, 2008