Geodynamics Science Highlight
NASA GSFC Geodynamics 921

SCIENCE HIGHLIGHT

Geodynamics Branch, Code 921

December 2003

Geodynamics Branch Contributions to Special Fall AGU Sessions - 1


Hulot and Langlais Discuss Possible Cause of "The Disappearing Dipole" in session on The Earth's Declining Magnetic Field and Possible Future Reversal

Plot of the Radial magnetic Field at the CMB Decline of the Earth's dipole appears due to formation of a reversed field patch over the South Atlantic, according to the paper by Hulot and Langlais at the Fall AGU Meeting.

Gauthier Hulot and Benoit Langlais, both 921 NRC Resident Research Associates from France, investigated the cause of the current rapid (forced) decrease of the Earth's magnetic field in a paper "Investigating the Nature of the Current Decrease of the Earth's Magnetic Dipole Moment " . By comparing how the core field has behaved at the core-mantle boundary over the past centuries and over the past twenty years, they confirmed that the decrease in dipole strength is mainly due to the growth and southward drift of a "reversed patch" of field located below the Southern Atlantic, and showed this appears to result from both small scale diffusion and advection (but not large scale diffusion) and has been acting in very much the same way over both the past 20 and 150 years.

Investigation of core flow suggests a similar reversed patch could possibly arise below the Northern Atlantic in the near future.

Other papers in the session showed that the present day dipole moment is not lower than it has been during several occasions in the past thousands of year or so. Simulations indicate that during a reversal, a weaker magnetic field would allow more protons to reach the Earth's surface, leading to ozone destruction over wider areas than at present.

A press conference on this session led to an article in the New York Times (December 12, 2003) under the title "Magnetic field is fading, but no dire effects are foreseen" as well as an article in the New Scientist (December 13, 2003) entitled "Our magnetic shield is growing weaker".

Contact: Gauthier Hulot, GSFC, Code 921 (hulot@geomag.gsfc.nasa.gov)

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Responsible NASA official: Dr. Herbert Frey

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