Random and long periodic variations in the earth's motion

Abstract

Abstract Observations of the Earth's rotation exhibit random, secular and periodic variations in rate (changes in the length of the day l.o.d.) and in direction (polar motion). These variations are of great significance, because they are probably associated with geophysical phenomena. A matter of particular interest is the question of whether these fluctuations in the l.o.d. and in polar motion can arise from a common geophysical cause. Comparison of the values of l.o.d. with the amplitude of Chandler wobble for the last 80 years indicates that this hypothesis cannot be disregarded; however the data on long period fluctuations are difficult to interpret and the evidence is too poor to permit any conclusion. Also the nature of these fluctuations is not at all clear, because apparent periodic variations can also arise from a random process. Periods of about 4 and 7 years found by us and other authors, however, should be real and associated with meteorological effects.