A possible correlation between solar activity and Earthʹs oblateness

Recent observations demonstrate that Earthʹs dynamic oblateness ( J 2 ), which has exhibited a decrease since 1979, suddenly increased around 1997 and the increase is still continuing. The decrease is attributed to post-glacial rebound from the mantle, and several causes, all of terrestrial nature, have been suggested to explain the sudden change in the trend. But the observations remain puzzling. On the other hand, close relationships are known to exist between many phenomena on the Earth with solar activity, and unusual behaviours of other planets have also been demonstrated to be correlated with solar activity. We show here that solar activity is significantly correlated with J 2 , and is possibly responsible for the sudden increase in Earthʹs dynamic oblateness around 1997, the latter being due to an enormous increase in the correlation.