# Earth’s polar flattening

## Change in the zonal harmonic coefficient C20, Earth’s polar flattening, and dynamical ellipticity from SLR data

We examine the change in the Earth’s second degree zonal harmonic coefficient derived from UTCSR SRL time series of  given (a) for the period from 1976 to 2017 as monthly solutions of the zonal coefficient  and (b) for the period from 1992 to 2017 as weekly solutions of the zonal coefficient  obtained via the eigenvalue-eigenvector problem and related to the principal axes system. The mean difference between the coefficients  or  given in various systems consists of the value  which is smaller than time variations in the coefficients  or .