Degree One Loading by Pressure Variations at the CMB

• Published in: Journal of earth science (Wuhan, China) China), 2013-10, Vol.24 (5), p.736-749
• Main Authors: Fang, Ming, Hager, Bradford H., Kuang, Weijia
• Format: Article
• Language: English
• Subjects: Biogeosciences; Boundaries; Covering; Earth; Earth and Environmental Science; Earth science; Earth Sciences; Elastic deformation; Geochemistry; Geology; Geophysics; Geotechnical Engineering & Applied Earth Sciences; Gravity; Harmonics; Load; Love number; Mantle; Overlaying; Pressure; Special Column on East-West Asymmetry of the Inner Core and Earth Rotational Dynamics; 不对称诱导; 压力变化; 垂直位移; 引力扰动; 核幔边界; 装载; 负荷Love数; 质量负载
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-013-0367-5

Hemispherical asymmetry in core dynamics induces degree-1 pressure variations at the core mantle boundary （CMB）, which in turn deforms the overlaying elastic mantle, at the same time keeps center of mass of the whole Earth stationary in space. We develop a systematic procedure to deal with the degree-1 CMB pressure loading. We find by direct calculation a surprisingly negative load Love number h1=-1.425 for vertical displacement. Further analysis indicates that the negative hi corre- sponds to thickening above the positive load that defies intuition that pressure inflation pushes over- laying material up and thins the enveloping shell. We also redefine the pressure load Love numbers in general to enable comparison between the surface mass load and the CMB pressure load for the whole spectrum of harmonic degrees. We find that the gravitational perturbations from the two kinds of loads at degrees n〉l are very similar in amplitude but opposite in sign. In particular, if the CMB pressure variation at degree 2 is at the level of -1 hpa/yr （1 cm water height per year）, it would perturb the variation of Earth＇s oblateness, known as the J2, at the observed level.