HR: 0800h
AN: G51C-0097    [Abstracts]
TI: Three algorithms for the computation of tidal loading and their numerical accuracy
AU: * Schrama, E J
EM: e.j.o.schrama@lr.tudelft.nl
AF: DEOS, Delft University of Technology, Kluyverweg 1, Delft, 2629 HS Netherlands
AB: In this paper the efficiency and numerical accuracy of three algorithms to compute tidal loading is reviewed. The interest goes to vertical deformations and the self attraction and loading effect caused by ocean tides. Load calculations require evaluation of convolution integrals over the sphere. In order to assess the numerical accuracy of a load calculation procedure we recall that there exists an almost exact point-wise integration method. This recipe is suitable for computations at individual stations, unfortunately the algorithm is rather expensive for evaluations on a global grid. The other two algorithms are fast implementations of this procedure, the first relies on the use of spherical harmonics and multiplication in the spectral domain of ocean tide spherical harmonic coefficients times the Green function coefficients expanded in a series of zonal Legendre functions. An alternative is a new method that only relies on rotational symmetry on the sphere. The performance of both field methods deteriorates near coastal boundaries where the average error is about 3 mm, while some part of this error is radiating outward into nearby coastal seas and continents. In rare extreme cases there are localized errors reaching 10 mm. The conclusion is that accurate load and SAL tides in coastal area's should be computed with a point-wise method rather than a field method, that the FFT method is compatible to the spherical harmonics method, and that all field methods are capable of tidal dissipation errors in coastal seas as large as 100 $\mbox{mWatt/m} ^2$ whereas open ocean dissipation errors are typically a factor 100 smaller.
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
DE: 1255 Tides--ocean (4560)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting