What is Chandler Wobble caused by and how well can it be predicted?


This is the name given to the movement of the earth's pole by 0.7 arcseconds over a period of about 14 months. For more information, visit a site over at the National Radio Astronomy Obserrvatory and check out the IEPS Bulletin at the U.S. Naval Observatory which predicts the earth polar wander based on a mathematical model. Chandler Wobble is a periodic phenomenon which means that it can be modeled by 'simply' fitting a harmonic series of sines or cosines to the past record of deflections, and then using this empirical model to make limited forecasts into the future. From what I understand of the technical literature, the cause of this wobble is believed to reside in the natural resonances in the body of the spinning earth due to the detailed distribution of mass in its surface, interior, oceans and atmosphere. This system has a '14-month' harmonic which can be excited through a complex pattern of forcings by the moon, sun and sudden crustal rearrangements (earthquakes). There are many distinct periodic excitations by the sun and moon and their changing distances and tidal forcings, and these result in distinct monthly, yearly and multi-year periodicities in the polar wander. The Chandler Wobble may be a natural harmonic resonance that is also stimulated by these other constant lunar-solar forcings at the natural resonance frequency of the solid earth.


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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the
NASA IMAGE/POETRY Education and Public Outreach program.