200
S. S. Krylov et al.
parameters are included in the transformation matrix from the geocentric equatorial coordinate system to the Earth geographic coordinate system. One of the main
problems in predicting the Earth pole motion is to take into account the parameters
variability in the main components of the Earth pole oscillation (Chandler wobble
and annual oscillatory process) [7].
Usually, the Chandler wobble is understood as the Earth pole oscillation with the
frequency of free nutation of the Earth’s rotation axis (with the Chandler frequency)
in the Earth-bound coordinate system [8]. It can also be considered in a narrower
sense, as a steady-state oscillation mode at the Chandler frequency and, in a broader
sense, as a multi-frequency oscillatory process with a main frequency being close to
Chandler’s one. However, it is very difficult to give an unambiguous definition that
would fully correspond to the physical process under consideration. Uncertainty in
the interpretation of the Chandler component is due to the lack of a comprehensive
explanation of the excitation mechanism. In some cases, it is convenient to use the
terminology of the perturbation theory. If the steady-state regime of the Chandler
wobble (with a constant frequency and average amplitude) is formally taken as an
“unperturbed” motion, then the perturbations that lead to variations in the Chandler
wobble parameters, which may be considered as perturbations, although it should be
noted that the steady state of the Chandler wobble is also a perturbed motion.
Explaining the excitation mechanism of the Chandler wobble is one of the fundamental problems when studying the Earth pole motion. At least, a part of the perturbations leading to variations in the Chandler wobble parameters are caused by this
mechanism. Therefore, the study of the variability of the main components parameters of the Earth pole oscillation (generally speaking, not only Chandler wobble, but
also annual oscillations) is of considerable interest both for the task of predicting the
Earth pole motion and the study of the excitation mechanism of the Chandler wobble.
First of all, the problem is to identify the celestial–mechanical and geophysical
reasons for such behavior of the Chandler component of the Earth pole oscillations.
Factors affecting the Earth motion relative to the center of mass can be divided
into astronomical and geophysical. The Earth motion in space, as well as, the motion
of the Earth’s moving media occurs under the influence of the bodies in the solar
system, and primarily under the Sun and the Moon. Therefore, when studying the
Earth motion it is natural and necessary to take into account the astronomical and
geophysical factors together. Lunar–solar gravitational perturbing forces lead to the
precession and nutation of the Earth, the refined theory of which taking into account
the internal structure of the Earth is in good agreement with observational data. In
contrast to precession and nutation, the Earth deformability and the mobility of its
various media are determining factors for the motion of the instantaneous axis of
rotation in the Earth’s body. And in this case, it is important to take into account not
only the mobility of the media, but also the astronomical factors that influence them,
since during the evolution of the solar system many processes must be considered as
synchronized processes.
The purpose of this chapter is to study the oscillatory processes of the Earth pole
under the perturbing astronomical and geophysical factors, as well as, the aspects
of their synchronization. In Sect. 15.2, the definition of the unperturbed Earth pole
S. S. Krylov et al.
parameters are included in the transformation matrix from the geocentric equatorial coordinate system to the Earth geographic coordinate system. One of the main
problems in predicting the Earth pole motion is to take into account the parameters
variability in the main components of the Earth pole oscillation (Chandler wobble
and annual oscillatory process) [7].
Usually, the Chandler wobble is understood as the Earth pole oscillation with the
frequency of free nutation of the Earth’s rotation axis (with the Chandler frequency)
in the Earth-bound coordinate system [8]. It can also be considered in a narrower
sense, as a steady-state oscillation mode at the Chandler frequency and, in a broader
sense, as a multi-frequency oscillatory process with a main frequency being close to
Chandler’s one. However, it is very difficult to give an unambiguous definition that
would fully correspond to the physical process under consideration. Uncertainty in
the interpretation of the Chandler component is due to the lack of a comprehensive
explanation of the excitation mechanism. In some cases, it is convenient to use the
terminology of the perturbation theory. If the steady-state regime of the Chandler
wobble (with a constant frequency and average amplitude) is formally taken as an
“unperturbed” motion, then the perturbations that lead to variations in the Chandler
wobble parameters, which may be considered as perturbations, although it should be
noted that the steady state of the Chandler wobble is also a perturbed motion.
Explaining the excitation mechanism of the Chandler wobble is one of the fundamental problems when studying the Earth pole motion. At least, a part of the perturbations leading to variations in the Chandler wobble parameters are caused by this
mechanism. Therefore, the study of the variability of the main components parameters of the Earth pole oscillation (generally speaking, not only Chandler wobble, but
also annual oscillations) is of considerable interest both for the task of predicting the
Earth pole motion and the study of the excitation mechanism of the Chandler wobble.
First of all, the problem is to identify the celestial–mechanical and geophysical
reasons for such behavior of the Chandler component of the Earth pole oscillations.
Factors affecting the Earth motion relative to the center of mass can be divided
into astronomical and geophysical. The Earth motion in space, as well as, the motion
of the Earth’s moving media occurs under the influence of the bodies in the solar
system, and primarily under the Sun and the Moon. Therefore, when studying the
Earth motion it is natural and necessary to take into account the astronomical and
geophysical factors together. Lunar–solar gravitational perturbing forces lead to the
precession and nutation of the Earth, the refined theory of which taking into account
the internal structure of the Earth is in good agreement with observational data. In
contrast to precession and nutation, the Earth deformability and the mobility of its
various media are determining factors for the motion of the instantaneous axis of
rotation in the Earth’s body. And in this case, it is important to take into account not
only the mobility of the media, but also the astronomical factors that influence them,
since during the evolution of the solar system many processes must be considered as
synchronized processes.
The purpose of this chapter is to study the oscillatory processes of the Earth pole
under the perturbing astronomical and geophysical factors, as well as, the aspects
of their synchronization. In Sect. 15.2, the definition of the unperturbed Earth pole