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Volume 24 Issue 5
Oct 2013
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Journal of Earth Science  > 2013  >  24(5): 736-749.
Ming Fang, Bradford H Hager, Weijia Kuang. Degree One Loading by Pressure Variations at the CMB. Journal of Earth Science, 2013, 24(5): 736-749. doi: 10.1007/s12583-013-0367-5
Citation: Ming Fang, Bradford H Hager, Weijia Kuang. Degree One Loading by Pressure Variations at the CMB. Journal of Earth Science, 2013, 24(5): 736-749. doi: 10.1007/s12583-013-0367-5
shu

Degree One Loading by Pressure Variations at the CMB

doi: 10.1007/s12583-013-0367-5
  • 1.

    Department of Earth, Atmospheric & Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA

  • 2.

    Planetary Geodynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, USA

Funds:

NASA NNX09AK70G

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  • Corresponding author: Ming Fang, fang@chandler.mit.edu
  • Received Date: 23 Mar 2013
  • Accepted Date: 02 Jun 2013
  • Publish Date: 01 Oct 2013
    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 h1=−1.425 for vertical displacement. Further analysis indicates that the negative h1 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 theJ2, at the observed level.

     

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