15 Astronomical and Geophysical Factors of the Perturbed Chandler Wobble …
213
in the main components parameters of the Earth pole oscillations may have more
global causes than it is assumed, and the process of their excitation is caused not only
by fluctuations of geophysical media of a stochastic nature. More precisely, these
oscillations can be non-stationary, but be of a natural nature, and not stochastic.
From the result of processing data on the Earth pole motion, it appears [18] that the
oscillations of the Earth’s moving media in the spectral range of the Chandler and
annual harmonics turn out to be ordered in some way. For example, in the observed
Earth pole motion, it is possible to establish the presence of an in-phase oscillatory
process with a precession of the lunar orbit [9, 18].
The spatial motion of the lunar orbit consists of a series of rotations around
intersecting axes. They lead to the cyclical motion of its nodes and perigee [24]. In
addition, the derivatives of the orbit parameters are nonzero and are varying values,
being the subject to small variations. A result of the lunar orbit precession and of
the associated cyclic change in the longitude of the ascending node with a period
of 18.61 years is a change in the orbit plane inclination to the Earth’s equator. The
inclination of the lunar orbit to the Earth’s equator varies from 18.3° to 28.58°. In this
case, the point of intersection of the lunar orbit circle with the equator oscillates along
the equator near its average position, which coincides with the point of the vernal
equinox. Unlike the node (the intersection point of the lunar orbit circles and the
ecliptic in the celestial sphere), which makes a complete revolution, the intersection
point of the orbit and the equator oscillates in the range from –13.2° to 13.2°.
In [25], it was shown that one can find a transformation of the Earth pole coordinates, illustrating in-phase nature of its Earth pole oscillatory process and the lunar
orbit precession. Namely, the oscillatory motion of the pole minus the Chandler (or
annual depending on the amplitudes values of the Chandler and annual harmonics)
and six-year cycles occurs in-phase with oscillations along the equator of the intersection point of the lunar orbit and the equator. This feature requires a more detailed
analysis and study of the causes of such fluctuations. In particular, it is of interest to
establish the contribution of geophysical (atmospheric and oceanic) disturbances to
these oscillations.
As a result of the numerical solution of the differential equations of the Earth
pole motion, the trajectories of the pole are obtained for various perturbations.
The perturbing functions were tabulated according to the IERS published data. For
example, in Fig. 15.7, it is shown a comparison between the fluctuations in the calculated motion of the Earth pole taking into account the combined perturbations from
the atmosphere and the ocean and the fluctuations of its observed motion.
To isolate the oscillatory process with a frequency of 0.05373 cycle/year from
the calculated and observed pole oscillations, the procedure proposed in [25] was
applied. Using transformations of the Earth pole coordinates, the essence of which is
the elimination of two cycles—with the Chandler and six-year periods, it is possible to
obtain a pole oscillation in-phase with the precession of the lunar orbit. In Fig. 15.8a,
a comparison is shown between the variations of the polar angle ϕ isolated from the
observed Earth pole trajectory, its approximation by a two-frequency model with
constant coefficients, and the calculated Earth pole trajectory taking into account
atmospheric and oceanic perturbations. In the lower graph of Fig. 15.8, a graph of
213
in the main components parameters of the Earth pole oscillations may have more
global causes than it is assumed, and the process of their excitation is caused not only
by fluctuations of geophysical media of a stochastic nature. More precisely, these
oscillations can be non-stationary, but be of a natural nature, and not stochastic.
From the result of processing data on the Earth pole motion, it appears [18] that the
oscillations of the Earth’s moving media in the spectral range of the Chandler and
annual harmonics turn out to be ordered in some way. For example, in the observed
Earth pole motion, it is possible to establish the presence of an in-phase oscillatory
process with a precession of the lunar orbit [9, 18].
The spatial motion of the lunar orbit consists of a series of rotations around
intersecting axes. They lead to the cyclical motion of its nodes and perigee [24]. In
addition, the derivatives of the orbit parameters are nonzero and are varying values,
being the subject to small variations. A result of the lunar orbit precession and of
the associated cyclic change in the longitude of the ascending node with a period
of 18.61 years is a change in the orbit plane inclination to the Earth’s equator. The
inclination of the lunar orbit to the Earth’s equator varies from 18.3° to 28.58°. In this
case, the point of intersection of the lunar orbit circle with the equator oscillates along
the equator near its average position, which coincides with the point of the vernal
equinox. Unlike the node (the intersection point of the lunar orbit circles and the
ecliptic in the celestial sphere), which makes a complete revolution, the intersection
point of the orbit and the equator oscillates in the range from –13.2° to 13.2°.
In [25], it was shown that one can find a transformation of the Earth pole coordinates, illustrating in-phase nature of its Earth pole oscillatory process and the lunar
orbit precession. Namely, the oscillatory motion of the pole minus the Chandler (or
annual depending on the amplitudes values of the Chandler and annual harmonics)
and six-year cycles occurs in-phase with oscillations along the equator of the intersection point of the lunar orbit and the equator. This feature requires a more detailed
analysis and study of the causes of such fluctuations. In particular, it is of interest to
establish the contribution of geophysical (atmospheric and oceanic) disturbances to
these oscillations.
As a result of the numerical solution of the differential equations of the Earth
pole motion, the trajectories of the pole are obtained for various perturbations.
The perturbing functions were tabulated according to the IERS published data. For
example, in Fig. 15.7, it is shown a comparison between the fluctuations in the calculated motion of the Earth pole taking into account the combined perturbations from
the atmosphere and the ocean and the fluctuations of its observed motion.
To isolate the oscillatory process with a frequency of 0.05373 cycle/year from
the calculated and observed pole oscillations, the procedure proposed in [25] was
applied. Using transformations of the Earth pole coordinates, the essence of which is
the elimination of two cycles—with the Chandler and six-year periods, it is possible to
obtain a pole oscillation in-phase with the precession of the lunar orbit. In Fig. 15.8a,
a comparison is shown between the variations of the polar angle ϕ isolated from the
observed Earth pole trajectory, its approximation by a two-frequency model with
constant coefficients, and the calculated Earth pole trajectory taking into account
atmospheric and oceanic perturbations. In the lower graph of Fig. 15.8, a graph of