Ocean loading globally in grid files.


Instead of having the Automatic and Free Ocean Loading Service choking under the load of  4,147,200 site requests (divide by 100 to get the necessary minimum number of submissions), you may obtain the loading effects in gridded files. It does not provide the same accuracy, since the process that generates the grids stays within the resolution of the respective ocean tide models, meaning that a stage of coastline refinement is not taken. There is a slight improvement in the integration beyond a point-wise summation (discrete and regular spherical harmonic analysis, to be precise). I do use Greens functions and weight quadrangular load cells with their areal integral value instead of a simple cosine of latitude.
The process is sped up using the Fast Fourier transform on a pair of latitude rings.

The tangential displacement is not computed explicitly but rather the scalar field, the lateral gradient of which delivers the 2-D displacements. The radial component is of course treated as a scalar field. By that trick only two instances of load computation are required, not three.

I provide the files (ascii --- one nice day I might be able to provide you with netCDF files) and the routines to interpolate on the grids, so you can obtain the 3-D displacement at random locations. Note that the ascii data is gridded in a special way.

Here you can learn about how to use the data.

[ ] FES2004-bin.tar 697M
  binary files (Fortran - never mind)  
[ ] FES2004-maps.tar 572M
[ ] GOT00-maps.tar 37M
[ ] NAO99-maps.tar 80M
[ ] TPX7.2-header.blq 1.0K
[ ] TPX7.2-maps.tar 149M
[ ] TPX7.2-ptanSS.daf.gz 6.5M
[ ] TPX7.2-radiSS.daf.gz 6.2M
[ ] cmc.tar 50K  Collection of frame-centre tide parameters
[ ] mzfu.tar.gz 23K  Formatted-to-unformatted (bin-to-ascii), Fortran77
[ ] mzuf.f 4.6K  Unformatted-to-formatted (ascii-to-bin), Fortran77
[ ] olcmc.tar 160K  Compute frame-centre tides; Fortran77
[ ] olmg.tar.gz 430K  Compute BLQ files from grids; Fortran77
[ ] sites.tar 60K  Files with sites
[DIR] upd/ -  Updates for files olmg.tar.gz (items of discussion eventually)

File name suffix  .dat  signifies Fortran binary (complex*16) data, .daf ascii data.
The *-maps files above will almost certainly not feature your favourite ocean tide model. Please contact me by email:
hgs kanelbulle chalmers dot se
and I'll see to that the list of maps is extended.

The figure below shows the "displacement potential" in a part of the North Atlantic

Isolines show phase, black 0°, purple 30° and white 60° etc. in steps of 30°.
Amplitudes see legend. The gradient operation is by differentiation with respect to angles in degrees (!), so the unit should read [m °] rather than [m].

Gothenburg, July 27, 2011
Hans-Georg Scherneck