The Earth exhibits an equatorial flattening specified by the ellipticity and the east longitude (or orientation) of the equatorial major axis, which is uniquely determined by the degree 2 and order 2 gravitational coefficients, C₂₂ and S₂₂. The 31-year SLR (satellite laser ranging) and 22-year GRACE/GRACE-FO (gravity recovery and climate experiment) data are analyzed to study the climate-related secular and 5.7 years to decadal variations in C₂₂ and S₂₂, in turn, the drift and decadal variation in the Earth’s equatorial ellipticity and orientation of the principal axis of the least moment of inertia. The effects of the surface floating mass changes (including atmosphere, ocean and surface water redistribution and the melting of the mountain and polar glaciers) and the interior fluid convective (Earth’s core flows) were evaluated. Results reveal that the equatorial ellipticity of the Earth is linearly increasing along with a remarkable decadal variation and the Earth’s equator is flattening by ~ 0.16 mm/yr.

地球表现出由椭圆率和赤道长轴东经（或方向）指定的赤道扁平化，赤道长轴由 2 阶和 2 阶引力系数C ₂₂和S ₂₂唯一确定。分析31年的SLR（卫星激光测距）和22年的GRACE/GRACE-FO（重力恢复和气候实验）数据，研究C ₂₂和S ₂₂与气候相关的长期和5.7年至十年的变化，转、地球赤道椭圆度的漂移和年代际变化以及最小转动惯量主轴的方向。评估了表面漂浮质量变化（包括大气、海洋和地表水的重新分配以及山脉和极地冰川的融化）和内部流体对流（地球核心流）的影响。结果表明，地球赤道椭圆率呈线性增加，并伴随着显着的年代际变化，地球赤道正在以约0.16毫米/年的速度变平。