por partes,
si, es normal, las corrientes oceánicas, las variaciones atmosféricas, las mareas gravitacionales,... provocan pequeños desplazamientos,
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ig. 1. The Earth as a clock. (1) Long-term trend. (2) Fluctuations. (3) Seasonal variations. (Ó D. Howse, National Maritime Museum, London.)
¿? ;D no tiene por qué, por la misma razón aumentará su radio de orbitación que compensará esa aceleración rotacional, la nasa ya lo verificó, una contracción atmosférica del 30%, así que si, debemos girar más rápido, además de las variaciones rotacionales inherentes, añado algo al respecto: The Earth does not rotate with perfect uniformity, and the variations have been classified as (1) secular, resulting from tidal friction, (2) irregular, ascribed to motions of the Earth’s core, and (3) periodic, caused by seasonal meteorological phenomena. Separating the first two categories is very difficult. Observations made since 1621, after the introduction of the telescope, show irregular fluctuations about a decade in duration and a long one that began about 1650 and is not yet complete. The large amplitude of this effect makes it impossible to determine the secular variation from data accumulated during an interval of only about four centuries. The record is supplemented, however, by reports—not always reliable—of eclipses that occurred tens of centuries ago. From this extended set of information it is found that, relative to dynamical time, the length of the mean solar day increases secularly about 1.6 milliseconds per century, the rate of the Earth’s rotation decreases about one part per million in 5,000 years, and rotational time loses about 30 seconds per century squared. The annual seasonal term, nearly periodic, has a coefficient of about 25 milliseconds.
Variations in the Earth’s rotation rate (http://www.britannica.com/EBchecked/topic/596034/time/61029/Variations-in-the-Earths-rotation-rate) An overview of the abilities of Very Long Baseline Interferometry (VLBI) to measure the variable Earth rotation and of the international VLBI collaboration is given. The paper concentrates on the short-period, i.e. subseasonal variations of Earth rotation which can be seen in VLBI measurements of length of day (lod) and polar motion between 1981 and 1999. The wavelet transform allows the time localisation of an irregular quasi-harmonic signal within a given data set. The wavelet analysis of lod series yields in the high-frequency range periods of sim28 days, sim14 days down to 6.86 days caused by the lunisolar tides and irregular quasi-periodic variations between 40 and 130 days. These are mainly associated with global zonal wind changes which can be seen when looking on the wavelet cross-scalogram between the lod series and the atmospheric angular momentum (AAM) time series. In polar motion variable periods between two and five months and even down to 7–10 days can be made visible by the wavelet scalograms.Today it is possible by VLBI to determine polar motion and UT1-UTC with a temporal resolution of as short as 3–7 minutes. The results of parallel VLBI sessions which took place since 1998 using two independent VLBI networks were analyzed in the subdiurnal period range and compared by computing the wavelet cross-scalograms, the covariance spectrum and the normed coherency. Periods between 5 and 7 hours can be seen in many of the UT1-UTC data sets besides the well-known diurnal and semi-diurnal periods. The wavelet analyses reveal interesting patterns in the subdiurnal range in polar motion, too.
Short Period Variations In Earth Rotation As Seen By VLBI (http://www.ingentaconnect.com/content/klu/geop/2000/00000021/F0020005/00318432) This paper focuses on atmospheric wind-driven effects on changes in length-of-day (δLOD). A 20th century simulation has been carried out using the ECHAM5 standalone atmosphere general circulation model (GCM). The spectrum of the resulting time series for δLOD shows typical structure patterns which resemble geodetic observations Furthermore a future scenario run for the period 2000–2100 driven by SRES A1B forcing scenario shows a strong increase in the axial atmospheric angular momentum (AAM) which implies a lengthening of the LOD. For the scenario runs the coupled atmosphere ocean GCM ECHO-G has been used. The extent of the simulated changes in axial AAM exceeds results from former studies. By 2100 the model shows an increase in axial AAM of about 10 percent compared to present day conditions. The strongest trends in zonal windspeed are detected in the Southern Hemisphere for mid and higher latitudes in the upper troposphere. The reason for this trend can be found in the thermal wind equation. The westerly winds in high levels are directly related to the magnitude of the horizontal, north-south, gradient in temperature averaged from the Earth’s surface to the height of the level. The future scenario runs show significant strengthening in this gradient at higher levels
Simulation of Historic and Future Atmospheric Angular Momentum Effects on Length-of-day Variations with GCMs (http://www.springerlink.com/content/q02n38573p18448w/) relación AAM y LOD ... The anomalies are sufficiently large and broad that they impact the global atmospheric angular momentum (AAM) and the length of day (LOD) or rotation speed of the solid earth. ...
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The MJO, Atmospheric Angular Momentum and the Length-of-Day (http://www.usclivar.org/Organization/MJO%20WorkingGroup/MJO-AngMoment.html) Abstract. We use wavelet transform to study the time series of the Earth's rotation rate (length-of-day, LOD), the axial components of atmospheric angular momentum (AAM) and oceanic angular momentum (OAM) in the period 1962–2005, and discuss the quasi-biennial oscillations (QBO) of LOD change. The results show that the QBO of LOD change varies remarkably in amplitude and phase. It was weak before 1978, then became much stronger and reached maximum values during the strong El Nino events in around 1983 and 1997. Results from analyzing the axial AAM indicate that the QBO signals in axial AAM are extremely consistent with the QBOs of LOD change. During 1963–2003, the QBO variance in the axial AAM can explain about 99.0% of that of the LOD, in other words, all QBO signals of LOD change are almost excited by the axial AAM, while the weak QBO signals of the axial OAM are quite different from those of the LOD and the axial AAM in both time-dependent characteristics and magnitudes. The combined effects of the axial AAM and OAM can explain about 99.1% of the variance of QBO in LOD change during this period.
Atmospheric and Oceanic Excitations to LOD Change on Quasi-biennial Time Scales (http://www.iop.org/EJ/abstract/1009-9271/6/6/16) ... habrá que esperarse a que alguien lo calcule ¡o lo publique!
si varía la distancia varia la velocidad, (eso si, considerando que no varie la velocidad de rotación de la luna)
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sobre las corrientes oceánicas,
anomalías gravitacionales,
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presión sobre el fondo
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This map shows changes in ocean bottom pressure measured by NASA's Gravity Recovery and Climate Experiment (Grace).
Red shows where pressure varies by large amounts, blue where it changes very little. Just as knowing atmospheric pressure allows meteorologists to predict winds and weather patterns, measurements of ocean bottom pressure provide oceanographers with fundamental information about currents and global circulation. They also hold clues to questions about sea level and climate.
The pressure at the bottom of the ocean is determined by the amount of mass above it.
Gravity data sheds new light on ocean, climate (http://climate.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=152)
(están los programas GRACE (http://www.csr.utexas.edu/grace/) y GOCE (http://www.esa.int/esaLP/LPgoce.html) para más referencias)
otra cosa a tener en cuenta es que en el centro de la tierra la gravedad es nula, por lo que el centro de masas "efectivas" que influyen gravitacionalmente sobre la litosfera estará situado en una esfera concéntrica más cercana a la superficie.
añado un par de estudios:
Seasonal variation of ocean bottom pressure, geoid height, and earthquake occurrences: comparison between GRACE and ECCO (http://wwwsoc.nii.ac.jp/jepsjmo/cd-rom/2007cd-rom/program/pdf/D105/D105-P002_e.pdf)
ABOUT POSSIBLE INFLUENCE OF SOLAR ACTIVITY UPON SEISMIC AND VOLCANIC ACTIVITIES: LONG-TERM FORECAST (http://www.khalilov.biz/pdf/About%20possible%20influence%20of%20solar%20activity%20upon%20seismic%20and%20volcanic%20activities%203.pdf)