Report

A New Global Mode of Earth Deformation: Seasonal Cycle Detected

Science  14 Dec 2001:
Vol. 294, Issue 5550, pp. 2342-2345
DOI: 10.1126/science.1065328

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Abstract

We have detected a global mode of Earth deformation that is predicted by theory. Precise positioning of Global Positioning System sites distributed worldwide reveals that during February to March, the Northern Hemisphere compresses (and the Southern Hemisphere expands), such that sites near the North Pole move downward by 3.0 millimeters, and sites near the equator are pulled northward by 1.5 millimeters. The opposite pattern of deformation occurs during August to September. We identify this pattern as the degree-one spherical harmonic response of an elastic Earth to increased winter loading of soil moisture, snow cover, and atmosphere. Data inversion shows the load moment's trajectory as a great circle traversing the continents, peaking at 6.9 × 1022 kilogram meters near the North Pole in winter, indicating interhemispheric mass exchange of 1.0 × 1016 ± 0.2 × 1016 kilograms.

  • * To whom correspondence should be addressed. E-mail: gblewitt{at}unr.edu

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