CATS2008a_opt: Circum-Antarctic Tidal Simulation, Inverse Model Version 2008a

Laurence Padman, ESR

Map of M2 sea surface height amplitude (m) from CATS2008a. Magenta line shows ice shelf front from MODIS imagery. Click on image for clearer figure.
Phone: +1 (541) 753-6695

Lana Erofeeva, OSU
Phone: +1 (541) 737-3964

Helen Fricker, Scripps
Phone: +1 (858) 534-6145

Susan Howard , ESR
Phone: +1 (206) 726-0501

   
Funded by NASA
 

Model and Software Summary

CATS2008a_opt is a high-resolution regional model of the entire circum-Antarctic ocean, built on a polar stereographic grid at 4 km node spacing, with standard latitude and longitude of 71oS and 70oW (see above figure). The model domain includes ocean cavities under the floating ice shelves. The model coastline is based on the MODIS MOA [Scambos et al., 2007] feature identification files, adjusted to match ICESat-derived grounding lines for the Ross and Filchner-Ronne ice shelves and Interferometeric Synthetic Aperture Radar (InSAR) grounding lines for the Larsen-C Ice Shelf (data courtesy of Eric Rignot, JPL). The water depth map for open water is based on the 2007 release update to Smith and Sandwell [1997], which uses marine gravity from TOPEX/Poseidon and ERS satellites to interpolate between available ship-track depth data. Adjustments to this map have been made in various regions, including the open shelf in front of the Larsen-C Ice Shelf which has been blended with GEBCO bathymetry.

Water column thickness ("wct") under ice shelves follows the data sets described by Padman et al. [2002]. We are aware of problems with wct for Larsen-C Ice Shelf: these will be amended in CATS2008b_opt, due later in 2008.

The model development follows two primary steps. We first develop an optimized forward model used direct factorization of the linearized shallow water equations, forced at the open boundary by tide heights from the global inverse model TPXO7.1 and by the astronomical potentials. The model is tuned to data by the use of a linear benthic drag coefficient rather than the more usual quadratic drag formulation. Each of ten primary tidal harmonics (M2, S2, N2, K2, K1, O1, P1, Q1, Mf, Mm) is tuned separately. While the optimized forward model is not as accurate as could be obtained with more sophisticated tidal physics, it creates a relatively accurate "prior" model for use in the next step of data assimilation.

The second step is to assimilate available data sets. We assimilate (i) TOPEX/Poseidon radar altimetry from the open ocean when no sea ice is present, (ii) a set of ~50 "high quality" tide records (including bottom pressure recorders, coastal tide gauges, and a few long-duration GPS records on ice shelves), and (iii) ICESat laser altimetry data at crossovers on the Ross and Filchner-Ronne ice shelves (see Padman and Fricker [2005]). The set of assimilated tide records is drawn from the larger set described at our Antarctic Tide Gauge Database web page.

CATS2008a_opt is distributed with a Matlab Graphical User Interface ("GUI") and access scripts, collectively referred to as the "TMD" (the Tide Model Driver) toolbox. TMD can be used to quickly access and browse the model, and to make tide height and current (velocity component) predictions. For an overview of the GUI and scripts, view or download the README PDF file. For FORTRAN access routines, please go to the Oregon State "OTIS" web page.

Please reference "pers. comm., L. Padman, 2008" for use of CATS2008a_opt. A paper describing the model in more detail will be submitted to J. Geophys. Res. later in 2008.

While CATS2008a_opt is intended to replace most of our other Antarctic tidal models, each model still on this web site has merits for specific applications. Please contact Laurie Padman for advice on which model to use for a particular application, to be added to an update notification list, or for further information on the tide models.

Download Instructions

The Matlab-based version of CATS2008a_opt, plus the TMD Toolbox, can be downloaded by clicking on the links below. The CATS2008a_opt file size is ~553 MB. If you prefer to receive the model by CD, please contact us. Circum-Antarctic tide models will continue to be developed through the life of ESR's Antarctic research programs. We will also occasionally make updates to TMD.

Download CATS2008a_opt model (~553 MB)

Download TMD Matlab Toolbox

Download TMD Readme PDF

If you prefer, the model and TMD toolbox can be downloaded from our FTP site, as follows:

  1. ftp ftp.esr.org
  2. login: anonymous
  3. password: email address
  4. cd pub/datasets/tmd
  5. binary
  6. get cats2008a_opt_tmd.zip (~553 MB)
  7. get tmd_toolbox.zip (~0.3 MB)

References