The long-term fluctuation of the Schwabe period (LSP) of sunspots number (SSN) has been found to have high correlation with the variation of the length-of-day (LOD) in low frequency by using the data of smoothed monthly mean SSN during 1818-1999 and the method of wavelet transform. Analyses indicate that the maximum correlation coefficient between the series of LSP and LOD during 1892-1997 is about 0.9, with a time lag of about 5 years for the LOD related to the LSP. Though the maximum correlation coefficients between the LSP and the other two LOD series (1818-1997) reduce to about 0.4, they remain over the thresholds of 95% confidence level. This suggests new evidence for possible impact of solar activity on the long-term fluctuation of the earth rotation.
The relationship between the inter-annual variations of the earth rotation, atmospheric angular momentum (AAM), sunspot number and El Ni(?)o is analyzed. The result shows that the inter-annual variation of the earth rotation responds to the variation of AAM and the preg-nancy of El Ni(?)o timely. Generally, the inter-annual compo-nent of the earth rotation will reach zero in a changing proc-ess that increases from the negative to the positive extreme before El Ni(?)o occurs about half year or more. And the solar activity may have certain influence on the appearance of El Ni(?)o. We consider that El Ni(?)o will possibly appear around the end of 2001.
