Abstract
A comparison of model estimates of ocean-tide loading displacements in New Zealand We analyze the regional accuracy of the global ocean tide models TPXO7.2, GOT00.2, NAO. 99b, FES2004, and EOT10a using the tide-gauge records from 7 stations along the coastline of New Zealand. The comparison reveals that TPXO7.2 provides the bestfit with the tide-gauge data in this part of the world. The TPXO. 7.2 ocean tide model is then used for computing and analysis of the vertical and horizontal ocean-tide loading displacements in New Zealand. The ocean-tide loading is calculated for the semi-diurnal and diurnal tidal harmonic constituents M 2 , S 2 , N 2 , K 2 , K 1 , O 1 , P 1 , and Q 1 , the long-period tidal components M f and M m , and for the shallow-water (nonlinear) components M 4 , MS 4 , and MN 4 . The charts of the ocean tide (offshore) and the ocean-tide loading (onshore) are compiled on a 5×5 arc-min geographical grid at the study area of New Zealand. The results reveal that the major contribution to the ocean-tide loading displacements up to a few centimeters is attributed to the semi-diurnal and diurnal harmonic constituents. The contribution of the long-period tidal components is to about 1 mm, and the effect of the shallow-water components is less than 0.2 mm. The maxima of vertical and horizontal displacements are typically of the same order of magnitude with larger amplitudes of vertical motions. The maximum amplitudes of vertical motions up to 5.6 cm are found in the upper north region of the North Island. The maximum horizontal motions up to 2.1 cm are in the northwest part of the South Island The ocean-tide loading displacements in New Zealand are finally compared with the crustal deformations due to geodynamic, atmospheric and other phenomena.
Highlights
The Earth tide is the crust displacement as a direct response to the gravitational attraction of the Moon and Sun
We analyze the regional accuracy of the global ocean tide models TPXO7.2, GOT00.2, NAO.99b, FES2004, and EOT10a using the tide-gauge records from 7 stations along the coastline of New Zealand
The presence of large errors of EOT10a and GOT00.2 are evident from Figure 2, where we shown the accuracy of the GOT00.2, NAO99b, FES2004, and EOT10a models relative to TPXO7.2
Summary
Several global ocean tide models are currently available, among them the models of Schwiderski (1980), NAO.99b (Matsumoto et al 2000), FES94.1, FES95 (Le Provost et al 1998), FES99 (Lefevre et al 2002), and FES2004 (Letellier 2004), CSR3.0 and CSR4.0 (Eanes 1994), GOT99.2b (Ray 1999), GOT00.2, TPXO. through TPXO.7.2 (Egbert and Erofeeva 2002), EOT08a (Savcenko and Bosch 2008), EOT10a (Savcenko and Bosch 2010), AG95.1 (Andersen 1995), and AG06a (Andersen et al 2006a, b) Majority of these models were compiled using the shallow water hydrodynamic equations. The comparison of these software packages can be found in Bos and Baker (2005) and Penna et al (2008)
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