Xiaoqing Xu, Haidong Pan, Fei Teng, Zexun Wei. Accuracy assessment of global vertical displacement loading tide models for the equatorial and Indian Ocean[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-024-2358-z
Citation:
Xiaoqing Xu, Haidong Pan, Fei Teng, Zexun Wei. Accuracy assessment of global vertical displacement loading tide models for the equatorial and Indian Ocean[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-024-2358-z
Xiaoqing Xu, Haidong Pan, Fei Teng, Zexun Wei. Accuracy assessment of global vertical displacement loading tide models for the equatorial and Indian Ocean[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-024-2358-z
Citation:
Xiaoqing Xu, Haidong Pan, Fei Teng, Zexun Wei. Accuracy assessment of global vertical displacement loading tide models for the equatorial and Indian Ocean[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-024-2358-z
First Institute of Oceanography, and Key Laboratory of Marine Science and Numerical Modeling, Ministry of Natural Resources, Qingdao 266061, China
2.
Laboratory for Regional Oceanography and Numerical Modeling, Qingdao Marine Science and Technology Center, Qingdao 266237, China
3.
Shandong Key Laboratory of Marine Science and Numerical Modeling, Qingdao 266061, China
Funds:
The Shandong Provincial Natural Science Foundation under contract No. ZR2023QD045; the National Natural Science Foundation of China (NSFC) under contract Nos 42076024 and 42106032.
The three-dimensional displacements caused by ocean loading effects are significant enough to impact spatial geodetic measurements on sub-daily or longer timescales, particularly in the vertical direction. Currently, most tide models incorporate the distribution of vertical displacement loading tides; however, their accuracy has not been assessed for the equatorial and Indian Ocean regions. Global Positioning System (GPS) observations provide high-precision data on sea-level changes, enabling the assessment of the accuracy and reliability of vertical displacement tide models. However, because the tidal period of the K2 constituent is almost identical to the orbital period of GPS constellations, the estimation of the K2 tidal constituent from GPS observations is not satisfactory. In this study, the principle of smoothness is employed to correct the systematic error in K2 estimates in GPS observations through quadratic fitting. Using the adjusted harmonic constants from 31 GPS stations for the equatorial and Indian Ocean, the accuracy of eight major constituents from five global vertical displacement tide models (FES2014, EOT11a, GOT4.10c, GOT4.8, and NAO.99b) is evaluated for the equatorial and Indian Ocean. The results indicate that the EOT11a and FES2014 models exhibit higher accuracy in the vertical displacement tide models for the equatorial and Indian Ocean, with root sum squares (RSS) errors of 2.29 mm and 2.34 mm, respectively. Furthermore, a brief analysis of the vertical displacement tide distribution characteristics of the eight major constituents for the equatorial and Indian Ocean was conducted using the EOT11a model.
Figure 1. Distribution of GPS stations in the equatorial and Indian Ocean regions. The triangles denote the 31 GPS stations. The yellow triangle denotes the “mald” GPS station, and the green triangle denotes the “pre2” GPS station.
Figure 2. Tidal admittances of the semi-diurnal VDL tide at Mald station in the CM frame. a. The distribution between normalized amplitudes and the frequency of semi-diurnal constituents. b. The distribution between Phase lags and the frequency of semi-diurnal constituents. Black dots signify the observed tidal admittances while the dashed lines indicate the interpolated curves. Red dots denote the extended K2 values based on the interpolated curves.
Figure 3. Same as Fig. 2, Similar Semi-diurnal tidal admittance at Mald station in the CF frame.
Figure 4. The vectorial composition of the K2 constituent of VDL tide. a. The observed K2 tide (represented by the black arrow) is the vectorial composition of the astronomical K2 tide (represented by the red arrow) and non-astronomical K2 tide (represented by the blue arrow) at Mald station. The green arrow represents the modeled K2 tidal vector (using the FES2014 tide model) in the CM frame. b. Similar distribution in the CF frame, but we use the EOT11a tide model to represent the modeled K2 tidal vector.
Figure 5. Tidal admittances of the Semi-diurnal VDL tide at Pre2 station in the CM frame. a. The distribution between normalized amplitudes and the frequency of semi-diurnal constituents. b. The distribution between Phase lags and the frequency of semi-diurnal constituents. Black dots signify the observed tidal admittances while the dashed lines indicate the interpolated curves. Red dots denote the extended K2 values based on the interpolated curves.
Figure 6. Same as Fig. 5, Similar Semi-diurnal tidal admittance at Pre2 station in the CF frame.
Figure 7. The vectorial composition of K2 constituent of VDL tide. a. The observed K2 tide (represented by the black arrow) is the vectorial composition of the astronomical K2 tide (represented by the red arrow) and non-astronomical K2 tide (represented by the blue arrow) at Pre2 station. The green arrow represents the modeled K2 tidal vector (using the FES2014 tide model) in the CM frame. b. Similar distribution in the CF frame, but we use the EOT11a tide model to represent the modeled K2 tidal vector.
Figure 8. Co-tidal charts of eight major constituents from EOT11a VDL tide model for the equatorial and Indian Ocean. Dashed lines represent amplitude (mm), solid lines represent Greenwich phase-lag (°).
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