SAN FRANCISCO Steven Nelson Camo Jersey , July 8 (Xinhua) -- New research has identified geomagnetic intensity variations as the cause for a secondary pattern of "wobble" within periods of stable polarity on the Earth.
Centuries of human observation, as well as the geologic record, show that the Earth's magnetic field changes dramatically in its strength and structure over time.
Some 800,000 years ago, a magnetic compass' needle would have pointed south because the Earth's magnetic field was reversed. These reversals typically happen every several hundred thousand years.
Besides the reversals, there is a secondary pattern of geomagnetic "wobble," known as paleomagnetic secular variation, or PSV, that may be a key to understanding why some geomagnetic changes occur.
In a paper published in Earth and Planetary Science Letters, researchers reported identifying the pattern by studying two high-resolution sediment cores from the Gulf of Alaska that allowed them to develop a 17,400-year reconstruction of the PSV in that region, then compared those records with sediment cores from other sites in the Pacific Ocean to capture a magnetic fingerprint, which is based on the orientation of the magnetite in the sediment that acts as a magnetic recorder of the past.
The Earth's magnetic field does not align perfectly with the axis of rotation, which is why "true north" differs from "magnetic north."
In the Northern Hemisphere, this disparity in the modern field is driven by regions of high geomagnetic intensity that are centered beneath North America and Asia.
When the magnetic field is stronger beneath North America, or in the "North American Mode," it drives steep inclinations and high intensities in the North Pacific, and low intensities in Europe with westward declinations in the North Atlantic.