Sudden Changes in Rotational Acceleration of the Earth and Secular Motion of the Pole

Path of the Mean Rotational Pole From 1899 to 1994

“…With such a data set, it is possible to evaluate the trend in polar motion and to investigate possible low-frequency periodic motions, which have been suggested previously (Hattori 1959;Markowitz 1960Markowitz , 1968Markowitz , 1970. Early investigations, which used optical astronomical data, were plagued by the possibility of systematic errors in the proper motions contained in the star 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000 (1988) concluded that the low-frequency oscillation was caused by systematic effects a t the individual stations.…”

Maximum Entropy Spectrum of Long-Period Polar Motion

“…Before discussing measured parameters of the signal, general comments are needed. The time domain presentation of Figs 1 and 2 are grossly similar to those of Rykhlova (1969), Markowitz (1970) and McCarthy (1972). For X, local maxima occur near 1922 and 1948 while local minima are 1936 and 1968.…”

“…There is a working group of the International Astronomical Union charged with this task (Vicente 1971). (1972) says that it has a longer period than the period derived by Markowitz (1970). However, considering the gross uncertainties in estimating a period from time domain graphs such as Figs 1 and 2 we designate the signal found here as a 30-yr period component of the polar motion.…”

The historical acceleration of the earth

“…Markowitz (1970) has analyzed the data available from the first 15 yr of the comparison. He also finds that there are sudden changes in acceleration, with a root-meansquare change of about 350 in y, in agreement with Brouwer's results.…”

“…This is not intended to deny the reality of variations in the Earth's spin. Direct comparison of Universal time with atomic time (Markowitz, 1970) has shown the reality of spin fluctuations almost beyond question, although there is room for argument about details. Further, most of the investigations mentioned earlier concluded that spin fluctuation accounts for a considerable part of the discrepancies in position.…”