OMCT Simulations for the GRACE De-aliasing Product: AOD1B RL05
This page provides information about characteristics of the simulated bottom pressure fields from the Ocean Model for Circulation and Tides (OMCT, Thomas, 2002) that are used for calculating the GRACE de-aliasing product AOD1B RL05. More information on other aspects of the AOD1B product might be found here:
Statistics for AOD1B RL05 coefficients
Known Issues with AOD1B RL05
OMCT simulations for AOD1B RL04 (outdated, processed until May 2012)
Statistics for AOD1B RL04 coefficients
Known Issues with AOD1B RL04
OMCT model configuration
The OMCT configuration used for AOD1B RL05 has been gradually updated from the OMCT model version that has been in use for the generation of AOD RL04. The spatial resolution was increased to 1.0° on a regular latitude-longitude grid, with now 20 levels in the vertical. Various parametrizations have been modified to adapt to the increased resolution and to align the simulated bottom pressure variability with various observational data-sets.
The initial state of the model was based on temperature and salinity climatologies obtained from the World Ocean Atlas 2001 (WOA01; Conkright, 2002). The model has been subsequently forced by annually varying climatological fields (winds, pressure, 2m-temperatures and freshwater fluxes) for 10 years, followed by 6-hourly real-time forcing from ERA Interim (Dee et al., 2011) covering the period 1989-2000, and finally operational ECMWF data since January 2001.
Bottom pressure variability
The following figures contain information about different characteristics of the simulated bottom pressure fields. Figures are updated daily and represent averages over the most recently simulated 30 days.
Figure 1: Variability of sea surface pressure anomalies (left) and simulated ocean bottom pressure anomalies (right), both relative to mean fields for 2001+2002 and averaged over the last 30 days.
Figure 2: Animation of sea surface pressure anomalies (left) and simulated ocean bottom pressure anomalies (left) relative to mean fields for 2001+2002 for the last 30 days and. Please click on the figures to start the animation.
Figure 3: Water mass transports of the Antarctic Circumpolar Current (ACC) across the Drake Passage as simulated by OMCT.
Figure 4: Area-mean bottom pressure anomalies relative to a mean field for 2001+2002 for the Hudson Bay (middle left), the Baltic Sea (middle right), the Mediterranean Sea (bottom left), and the coastal waters around Antarctica southwards of the Southern ACC front (bottom right). Shape and geographical extent of the averaging regions might be obtained from the upper panel.
Figure 5: Mean amplitudes of diurnal (top) and semidiurnal (bottom) atmospheric tides in atmospheric surface pressure (left), as well as its corresponding response in ocean bottom pressure (right). Note that semidiurnal variability at the S2 frequency has been largely removed by means of an correction model, since S2 bottom pressure variability due to atmospheric pressure forcing is already included in altimetry-based ocean tide models applied in the GRACE gravity field processing. Semidiurnal variability present here merely represents residual amplitudes related to seasonal modulations or (eventually) long-term changes in the atmospheric tides.
Information obtained from this page can be referenced as:
Dobslaw, H., Thomas, M. (2007), Simulation and observation of global ocean mass anomalies, J. Geophys. Res., 112, C05040.
References and further reading:
Conkright, M. E., Locarnini, R. A., Garcia, H. E., O'Brien, T. D., Stephens, C.,
Antonov, J. I. (2002), World Ocean Atlas 2001: Objective Analyses, Data Statistics,
and Figures, CD-ROM Documentation, National Oceanographic Data Center, Silver Spring, MD, 17 pp.
Dee, D. P., Uppala, S. M., Simmons, A. J. et al. (2011), The ERA-Interim reanalysis:
configuration and performance of the data assimilation system, Quaterly Journal of the
Royal Meterological Science, Vol. 137, Issue 656, pp. 553-597
Thomas, M. (2002), Ocean induced variations of Earth's rotation - Results from a
simultaneous model of global circulation and tides, PhD dissertation, University of Hamburg,
Germany, 129pp.
July 16, 2012, Dr. Henryk Dobslaw
