15 Astronomical and Geophysical Factors of the Perturbed Chandler Wobble …
207
geoid of the GFZ model [14]. An example of comparing the δg variations due to
solid-state tides with the measurement data shows that the combined tidal variations
of the Earth’s deformable media determine 98% of the observed oscillations. These
coherent fluctuations in geomedia can be identified with the ones of a viscoelastic
thin layer of the adopted deformable Earth model. Then the differences between the
solution of such a model problem obtained in the first approximation and observed
processes will be in the proportionality coefficients. In turn, these coefficients can be
identified with a sufficient degree of accuracy from astrometric and geodetic observations and measurements data. This approach allows some generalization in the case
of taking into account hydrosphere oscillations. Indeed, if the oceanic oscillations are
taken into account, we can assume that the remaining discrepancy in the oscillations
of the measured signal δg along with the influence of atmospheric pressure [15] will
also be caused by hydrosphere fluctuations from a relatively small (on the scale of the
entire Earth’s surface) neighborhood. Variations in atmospheric pressure are usually
non-stationary and measured directly at the point of observation. The corresponding
fluctuations in the gravitational acceleration can be considered proportional to atmospheric pressure [15, 16]: they can be easily filtered out. However, atmospheric
fluctuations in the high-frequency range like any tidal variations of the atmosphere
are small. Therefore, the remaining 2% of the amplitude of the high-frequency g
oscillations will be due to hydrosphere fluctuations. As an example of the correlation between the variations in the gravitational acceleration and local hydrosphere, a
comparison is made (Fig. 15.3b) between the sea-level fluctuations at the coastline
of Rorvik (Norway) marked on the map without the long-period component and the
corresponding component isolated from δg. Also, in Fig. 15.3a, the gravitational
accelerations and close to diurnal sea level variations are compared. For example, if
the residual between the measurement data and tidal model of the solid-state oscillations of the gravitational acceleration is represented as the sum of the diurnal and
semidiurnal variations δg
ϕ
+ δg
2ϕ , then it correlates with the variation δh
ϕ
− δh
2ϕ
of the sea level.
15.4 Geophysical Factors in the Model of the Earth Pole
Oscillatory Process
It is well-known [1, 17, 18] that the amplitude and phase of the Chandler component
of the Earth pole oscillatory process are very sensitive to various perturbing factors
including those with irregular properties (oceanic, atmospheric, and possibly others).
The magnitude of the amplitude of the steady-state motion is determined by the
frequency difference and dissipation coefficient. Therefore, the Chandler component
of the Earth pole oscillations should be considered the most sensitive to the irregular
impacts. The mechanism of these impacts is naturally related to weak inertia tensor
perturbations.
207
geoid of the GFZ model [14]. An example of comparing the δg variations due to
solid-state tides with the measurement data shows that the combined tidal variations
of the Earth’s deformable media determine 98% of the observed oscillations. These
coherent fluctuations in geomedia can be identified with the ones of a viscoelastic
thin layer of the adopted deformable Earth model. Then the differences between the
solution of such a model problem obtained in the first approximation and observed
processes will be in the proportionality coefficients. In turn, these coefficients can be
identified with a sufficient degree of accuracy from astrometric and geodetic observations and measurements data. This approach allows some generalization in the case
of taking into account hydrosphere oscillations. Indeed, if the oceanic oscillations are
taken into account, we can assume that the remaining discrepancy in the oscillations
of the measured signal δg along with the influence of atmospheric pressure [15] will
also be caused by hydrosphere fluctuations from a relatively small (on the scale of the
entire Earth’s surface) neighborhood. Variations in atmospheric pressure are usually
non-stationary and measured directly at the point of observation. The corresponding
fluctuations in the gravitational acceleration can be considered proportional to atmospheric pressure [15, 16]: they can be easily filtered out. However, atmospheric
fluctuations in the high-frequency range like any tidal variations of the atmosphere
are small. Therefore, the remaining 2% of the amplitude of the high-frequency g
oscillations will be due to hydrosphere fluctuations. As an example of the correlation between the variations in the gravitational acceleration and local hydrosphere, a
comparison is made (Fig. 15.3b) between the sea-level fluctuations at the coastline
of Rorvik (Norway) marked on the map without the long-period component and the
corresponding component isolated from δg. Also, in Fig. 15.3a, the gravitational
accelerations and close to diurnal sea level variations are compared. For example, if
the residual between the measurement data and tidal model of the solid-state oscillations of the gravitational acceleration is represented as the sum of the diurnal and
semidiurnal variations δg
ϕ
+ δg
2ϕ , then it correlates with the variation δh
ϕ
− δh
2ϕ
of the sea level.
15.4 Geophysical Factors in the Model of the Earth Pole
Oscillatory Process
It is well-known [1, 17, 18] that the amplitude and phase of the Chandler component
of the Earth pole oscillatory process are very sensitive to various perturbing factors
including those with irregular properties (oceanic, atmospheric, and possibly others).
The magnitude of the amplitude of the steady-state motion is determined by the
frequency difference and dissipation coefficient. Therefore, the Chandler component
of the Earth pole oscillations should be considered the most sensitive to the irregular
impacts. The mechanism of these impacts is naturally related to weak inertia tensor
perturbations.