15:30 〜 16:30
[G04-P-02] Revisiting the indirect effect of the triaxiality on the polar motion libration of the non-rigid Earth
The gravitational action of the Moon and Sun acting on the triaxial Earth gives rise to high-frequency forced nutations of diurnal and subdiurnal periods. Accordingly to IAU 2000 Resolution B1.7 this motion must be described as a part of the evolution of the pole with respect to ITRS, usually referred to as libration in polar motion (IERS Conventions 2010).
One part of that libration is due to the indirect effect of the triaxiality. This effect is related with the fact that the response of the Earth to the lunisolar perturbation, even the zonal one, depends on its structure. It was shown by Escapa et al. (2002, 2003) that the triaxiality of the Earth and its core originate diurnal terms due to their crossing with the (2, 0) harmonic of the gravitational potential. Although the magnitude of some of those contributions was greater than the adopted cut-off level (0.5 microarcseconds), they were not considered in the modelling of polar motion libration due to the uncertainty in the value of the triaxiality of the core existing in that epoch.
In the last years, however, there have been published comprehensive investigations by Chen and Shen (2010), and Sun and Shen (2016), among others, providing accurate estimations of the triaxiality of the Earth and its core. Taking advantage of these results, we recalculate the contributions of the indirect effect of the triaxiality on the libration in polar motion. Our preliminary computations show that these updated amplitudes present a noticeable amplification with respect to their earlier values for some of the newly proposed sets of triaxiality parameters.
Chen, W., Shen, W. 2010, J. Geophys. Res., 115, B12419
Escapa, A., Getino, J., Ferrandiz, J. M. 2002, Astron. Astrophys., 389, 1047
Escapa, A., Ferrandiz, J. M., Getino, J. 2003, Proc. of the Journees 2002 Systemes de Reference Spatio-temporels, 152
IERS Conventions 2010, ed. G. Petit and B. Luzum. IERS Technical Note 36
Sun, R., Shen, W. B. 2016, J. Geophys. Res., 121, 7570
One part of that libration is due to the indirect effect of the triaxiality. This effect is related with the fact that the response of the Earth to the lunisolar perturbation, even the zonal one, depends on its structure. It was shown by Escapa et al. (2002, 2003) that the triaxiality of the Earth and its core originate diurnal terms due to their crossing with the (2, 0) harmonic of the gravitational potential. Although the magnitude of some of those contributions was greater than the adopted cut-off level (0.5 microarcseconds), they were not considered in the modelling of polar motion libration due to the uncertainty in the value of the triaxiality of the core existing in that epoch.
In the last years, however, there have been published comprehensive investigations by Chen and Shen (2010), and Sun and Shen (2016), among others, providing accurate estimations of the triaxiality of the Earth and its core. Taking advantage of these results, we recalculate the contributions of the indirect effect of the triaxiality on the libration in polar motion. Our preliminary computations show that these updated amplitudes present a noticeable amplification with respect to their earlier values for some of the newly proposed sets of triaxiality parameters.
Chen, W., Shen, W. 2010, J. Geophys. Res., 115, B12419
Escapa, A., Getino, J., Ferrandiz, J. M. 2002, Astron. Astrophys., 389, 1047
Escapa, A., Ferrandiz, J. M., Getino, J. 2003, Proc. of the Journees 2002 Systemes de Reference Spatio-temporels, 152
IERS Conventions 2010, ed. G. Petit and B. Luzum. IERS Technical Note 36
Sun, R., Shen, W. B. 2016, J. Geophys. Res., 121, 7570