## 4 Conclusions  
The effects of MOT are sometimes neglected in routine precise long-baseline GPS data processing. In this paper, we first determine the magnitude and spatial distribution of global IGS station's loading displacement caused by MOT. We find that MOT could only cause small variations in the horizontal loading displacement globally, with most of the STD being smaller than 1 mm. The vertical loading displacement caused by MOT is quite large, and becomes smaller with the increasing distance between station and the sea. This is obviously due to the characteristics of ocean tides. The peak-to-peak MOT induced loading displacement variations reaches more than 8 mm at the coastal/island stations, while most of the height variations for inland station are smaller than 1.5 mm, in particular for those in the Eurasia plate, which have almost the same magnitude as that of the E component. Secondly, the OTL modeling method including the MOT correction is implemented in GAMIT. Through reprocessing the GPS data of 109 globally distributed IGS stations based on both the original and the modified GAMIT software, we find that the impact of MOT on the 24-hour GPS solution is slightly larger than the magnitude of MOT loading time series itself, and it also exhibits quite a different spatial pattern. There is no strong correlation between station's MOT induced 3-D displacement and its distance away from the sea. It influences a lot on many coastal/island stations (e.g., REYK) and also on some inland stations (e.g., WTZR), among which the STD and the absolute maximum of the GPS height caused by MOT reaching more than 5 mm and 20 mm respectively, with peak-to-peak displacement change at about 10 mm for the horizontal component and 30 mm for the vertical components. For stations located in North America and Eurasia plates, however, MOT only has a small impact on the GPS time series, with most of the 3-D STD smaller than 1 mm. We think that this may due to the interaction between MOT and the other GPS error sources at each epoch and in different places. We then study the impact of MOT on the long-term velocity of global IGS stations. Our results show that the vertical velocity change caused by MOT is quite big, and also decrease with stations' distance away from the sea. 42% of the selected stations, including most coastal/island stations' vertical velocity change are larger than 10%, and the maximum velocity variation rate reaches more than 50% (e.g., station ASC1, BAHR). Besides, considering the MOT effect could reduce the vertical velocity of all the selected stations in the Southwest Pacific by more than 10%. Thus, we conclude that MOT may also be a potential candidate for the vertical motion of global IGS stations, in particular for those along the coast or in ocean areas, where MOT should be better corrected during high-precision GPS data processing so as to obtain more reliable vertical motion for geodynamic studies, such as PGR, sea level change, _etc_. Moreover, the impact of MOT on the non-linear characteristics of global IGS stations is discussed. We find that in general MOT would only introduce small WRMS variations in the global IGS stations, even for the coastal/island stations, where the maximum variation rate is smaller than 5%. The U component exhibits the smallest impact, the N component ranks the second, while the E component ranks the third, with stations whose WRMS variation rates smaller than 1% account for 84%, 70%, and 62% of the selected stations. 62%, 59%, and 36% of the stations' WRMS reduced for the U, E and N components respectively after considering the MOT effect, among which the maximum reduction with magnitude of 1%-5% gathered mostly along coasts or on the island. Nevertheless, implementing MOTcorrection could also increase the WRMS for some global IGS stations, in particular for the N component (e.g., station NOT1).