Large Variations of the coefficient $J_2$ of geopotential, and the   dynamical Love number $k_2^d$ from the analysis of laser ranging to LAGEOS~1   and LAGEOS~2
  Secular and seasonal variations of the coefficient $J_2$ of the geopotential are studied from the analysis of laser measurements of distances to the geodetic satellites LAGEOS~1 (1988--2003) and LAGEOS~2 (1992--2003). It is confirmed that beside the well-known annual variations with the amplitude $\approx 2.5 \times 10^{-10}$ there also exist very significant semi-annual variations of a comparable amplitude. Phases of these two modes are such that the total effect may be described as a sharp postive splash of $J_2$ in August and considerably smaller variations in the rest part of year. 
George A. Krasinsky
astro-ph.EP