Degree one loading by pressure variations at the CMB
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12583_2013_Article_367.pdf
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Author(s)
Fang, Ming
Kuang, Weijia
Hager, Bradford H
Date Issued
October 2013
Journal
Journal of Earth Science
Publisher
Springer Berlin Heidelberg
Citation
Fang, Ming, Bradford H. Hager, and Weijia Kuang. “Degree One Loading by Pressure Variations at the CMB.” Journal of Earth Science 24, no. 5 (October 2013): 736–749.
Version
Author's final manuscript
Abstract
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 h[subscript 1]=−1.425 for vertical displacement. Further analysis indicates that the negative h[subscript 1] corresponds to thickening above the positive load that defies intuition that pressure inflation pushes overlaying 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>1 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 J[subscript 2], at the observed level.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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DOI of Published Version
https://doi.org/10.1007/s12583-013-0367-5
