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

TL;DR

This study analyzes laser ranging data to LAGEOS satellites from 1988 to 2003, revealing significant secular, annual, and semi-annual variations in the Earth's geopotential coefficient $J_2$, and discusses implications for Earth's dynamical Love number.

Contribution

It provides detailed analysis of $J_2$ variations over 15 years, highlighting the presence of semi-annual fluctuations and their phase relationships, which were previously less characterized.

Findings

Significant semi-annual variations of $J_2$ with amplitudes comparable to annual ones.

A sharp positive splash of $J_2$ occurs in August.

Confirmation of complex seasonal behavior of Earth's geopotential coefficients.

Abstract

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.