Research ArticleCLIMATOLOGY

Climate-driven polar motion: 2003–2015

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Science Advances  08 Apr 2016:
Vol. 2, no. 4, e1501693
DOI: 10.1126/sciadv.1501693
  • Fig. 1 Observed pole position data.

    Mean monthly polar motion excitations (black lines) derived from the observed daily values after removing semiannual, annual, and Chandler wobbles. Smoothed solutions (blue lines) reveal quasi-decadal variability in the corresponding component of the 20th-century linear trend (dashed red lines). Cyan shadows in the background cover our study period, over which the drift direction deviates (solid red lines) from the long-term linear trend.

  • Fig. 2 Climate-induced mass redistribution on Earth’s surface.

    (A) Linear rate of change in mass (in WEH per year) during April 2002 to March 2015, derived from monthly GRACE observations and associated sea-level computations. Solutions are reproduced with different color scales for (B) the GIS, (C) the AIS, and (D) the oceans.

  • Fig. 3 Climate-induced polar motion.

    (A) Polar motion excitations caused by four climate-related sources. (B) Total reconstructed (REC) and observed (OBS) excitations. We add global (nontidal) AOM-associated excitations (Embedded Image and Embedded Image mas/year) to the reconstructed solutions and remove the 20th century linear trends from the observations (see Materials and Methods). (For ease of comparison, minor smoothing is applied to the observed data.) Large positive gradients during 2005–2012 (cyan shadow), followed by negative trends, are apparent for χ2(t), and it may be explained by analogous trends associated with TWS [see (A)].

  • Fig. 4 Spatiotemporal variability in TWS.

    Linear trends in TWS mass redistribution (in WEH per year) during two periods (from January 2005 to December 2011 and from January 2012 to December 2014) derived from monthly GRACE observations.

  • Fig. 5 Origins of observed polar motion.

    (A) Reconstruction and partition of polar motion during 2003–2015. Observed data have the 20th-century linear trends removed. Semimajor and semiminor axes of error ellipses are defined by the uncertainties in the magnitude and direction of the corresponding polar motion vector. For clarity, we do not show error ellipses for GICs, which have large uncertainties but very small amplitudes (see Materials and Methods) and AOM. (B) Observed (including the long-term linear trend) and reconstructed mean annual pole positions, in the excitation domain, with respect to the 2003–2015 mean position. Blue error band is associated with the reconstructed solution; red signifies additional errors that are related to uncertainty in the long-term linear trend.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/4/e1501693/DC1

    Fig. S1. SHs of degree 2 order 1.

    Fig. S2. GIS and polar motion excitations.

    Fig. S3. AIS and polar motion excitations.

    Fig. S4. Global GICs and polar motion excitations.

    Fig. S5. Mass evolution of regional GICs.

    Fig. S6. TWS and polar motion excitations.

    Fig. S7. Polar motion excitations due to nontidal AOM variability.

    Table S1. Polar motion excitation rates for different time periods.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. SHs of degree 2 order 1.
    • Fig. S2. GIS and polar motion excitations.
    • Fig. S3. AIS and polar motion excitations.
    • Fig. S4. Global GICs and polar motion excitations.
    • Fig. S5. Mass evolution of regional GICs.
    • Fig. S6. TWS and polar motion excitations.
    • Fig. S7. Polar motion excitations due to nontidal AOM variability.
    • Table S1. Polar motion excitation rates for different time periods.

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