Comparison of the global oceantide models TPXO 7

Comparison of the global ocean-tide models TPXO 7. 2, GOT 00. 2, NAO. 99 b, FES 2004, and EOT 10 a in New Zealand Vladislav Gladkikh, Robert Tenzer National School of Surveying, Division of Sciences, University of Otago, Dunedin, New Zealand Objectives • Accuracy assessment of ocean-tide models using tide-gauge data in New Zealand. • Compilation of the co-tidal maps of ocean-tide loading displacements in New Zealand. OCEAN-TIDE Radial OCEAN-TIDE LOADING North East Input data • The global ocean-tide models TPXO 7. 2, GOT 00. 2, NAO. 99 b, FES 2004, and EOT 10 a. • The tide-gauge records from 7 stations in New Zealand (Wellington, Tauranga, Taranaki, Marsden Point, Jackson Bay, Timaru, and Port Charmers). • • Methodology The accuracy analysis of the global ocean models was done using the tide-gauge data over the study period of 1 year (2005) with 1 hour data sampling interval. The computation of the ocean-tide loading is based on Farrell’s (1972) method which utilizes the integral convolution of the mass loading Green’s functions with tidal data. The 25 25 arc-min TPXO. 7. 2 data (Egbert and Erofeeva 2002) were used to compute the ocean-tide loading. The ocean-tide loading was calculated for the tidal harmonic constituents M 2, S 2, N 2, K 1, O 1, P 1, Q 1, Mf and Mm and the shallow-water tidal components M 4, MS 4 and MN 4. M 2 Results • The comparison of the ocean-tide and tide-gauge data at 7 stations in New Zealand is shown in Fig. 1. The comparison of the accuracy is provided in Table 1 and Fig. 2. • The amplitudes and phases of the generating tide (left panels) and the ocean-tide loading (mid and right panels) in New Zealand using TPXO. 7. 2 model are shown in Fig. 3 (left panels); the ocean-tide loading amplitudes are summarized in Table 2. S 2 K 1 Fig. 1 The comparison of the ocean-tide and tide -gauge data at 7 stations in New Zealand between 1 st and 20 th of January, 2005 (1 hour data sampling interval). Tide Gauge Average Error [cm] TPXO 7. 2 NAO 99 b GOT 00. 2 Port Chalmers 17. 6 17. 8 16. 4 17. 3 17. 2 Timaru 10. 9 10. 7 15. 2 15. 4 Jackson Bay 9. 0 9. 2 Marsden Point 7. 9 13. 7 10. 9 54. 2 11. 2 Taranaki 9. 2 9. 0 9. 2 10. 5 11. 9 Tauranga 11. 1 11. 0 10. 9 11. 2 11. 1 8. 7 11. 3 25. 7 9. 8 Wellington EOT 10 a FES 2004 Table 1 The average errors of the global ocean tide models TPXO 7. 2, GOT 00. 2, NAO. 99 b, FES 2004, and EOT 10 a at 7 tide-gauge stations in New Zealand. The average errors were computed from (absolute) Fig. 2 Accuracy comparison of ocean-tide models. differences between ocean-tide and tide-gauge data. O 1 Table 2 The ocean-tide loading amplitudes in New Zealand computed for the tidal harmonic constituents M 2, S 2, N 2, K 1, O 1, P 1, Q 1, Mf and Mm, and for the shallow-water tidal components M 4, MS 4 and MN 4. Tidal harmonic constituents Period M 2 Principal lunar semi-diurnal S 2 Amplitude [mm] Radial North East 12. 4206 h 0. 16 - 32. 5 4. 68 - 8. 13 5. 64 - 9. 46 Principal solar semi-diurnal 12. 0000 h 2. 23 - 7. 90 0. 98 - 1. 82 0. 55 - 1. 45 N 2 Larger lunar elliptic semi-diurnal 12. 6583 h 0. 02 - 5. 79 1. 03 - 1. 59 1. 31 - 2. 10 K 2 Luni-solar declinational semi-diurnal 11. 9672 h 0. 83 - 2. 27 0. 30 - 0. 52 0. 12 - 0. 39 K 1 Luni-solar declinational diurnal 23. 9345 h 2. 06 - 5. 55 1. 38 - 1. 80 0. 62 - 0. 88 O 1 Principal lunar declinational diurnal 25. 8193 h 0. 36 - 3. 85 1. 11 - 1. 35 0. 59 - 0. 83 P 1 Principal solar declinational diurnal 24. 0659 h 0. 67 - 1. 58 0. 43 - 0. 56 0. 18 - 0. 27 Q 1 Lunar elliptic diurnal 26. 8684 h 0. 21 - 1. 08 0. 25 - 0. 30 0. 14 - 0. 20 Mf Lunar declinational fortnightly 13. 6608 d 0. 22 - 1. 08 0. 15 - 0. 20 0. 00 - 0. 06 Mm Lunar elliptic monthly 27. 5545 d 0. 07 - 0. 56 0. 09 - 0. 11 0. 00 - 0. 02 Mf Shallow-water tidal components M 4 2 × M 2 6. 2103 h 0. 00 - 0. 21 0. 00 - 0. 05 0. 00 - 0. 07 MS 4 M 2 + S 2 6. 1033 h 0. 00 - 0. 18 0. 00 - 0. 04 MN 4 M 2 + N 2 6. 2692 h 0. 00 - 0. 12 0. 01 - 0. 04 0. 01 - 0. 03 Conclusions • The TPXO 7. 2 global ocean-tide model provides the best solution for modelling the ocean-tide loading in New Zealand. • The maximum ocean-tide loading vertical displacements were found in the upper part of the North Island where they reach 46 mm. The maxima of horizontal and vertical displacements are of the same order of magnitude. The displacements due to shallowwater tidal components are below 0. 2 mm. Reference Egbert GD, Erofeeva SY (2002) Efficient inverse modeling of barotropic ocean tides. J Atmos Ocean Technol 19: 183– 204 Farrell WE (1972) Deformation of the Earth by surface loads. Rev Geophys 10(3): 761– 797 M 4 Fig. 3 The amplitudes (upper panels) and phases (lower panels) of the ocean-tide and of the ocean-tide loading computed for the principal lunar semi-diurnal M 2, principal solar semi-diurnal S 2, luni-solar declinational diurnal K 1, principal lunar declinational diurnal O 1 and lunar elliptic monthly Mf harmonic tidal constituents and for the nonlinear shallow-water tidal component M 4. Units: the amplitudes are provided in millimeters, and phases in arc-degrees.