Comment on “Survey tracks current position of South Magnetic Pole” and “Recent acceleration of the north magnetic pole linked to magnetic jerks”

Abstract

In recent months, two articles have appeared in Eos reporting new positions of the north [Newitt et al., 2002] and south [Barton, 2002] magnetic poles from on‐site measurements of locations for vertical magnetic field dip. Readers should be advised that these reported positions are neither magnetic poles nor geophysically important locations. First let us review some facts about our Earth's field. When a magnetic field can be represented by an axially symmetric dipole pattern similar to the electric field from a pair of equal and opposite electric charges, the axis of this magnetic field is called a pole. For the Earth, Gilbert [1958] first called attention to this dipole feature in his 1600 publication De Magnete. With the magnetic dipole center location corresponding to the Earth's geographic center, and the Earth completely spherical, the exit position of the magnetic dipole corresponded to the location of a fully vertical dip of the field. Global maritime exploration that started around the time of the epic 1492 Columbus voyage greatly depended on the ship compass for navigation and on magnetic declination maps for guidance. It was only natural that considerable interest in special expeditions to locate the mysterious Arctic and Antarctic Earth magnetic poles subsequently arose.

Operational models and drag‐derived density trends in the thermosphere

“…Wave‐particle interactions scatter some of the ring current particles into the loss cone. Many of these particles enter the atmosphere near the South Atlantic Anomaly, where the spiraling ring current particles penetrate deepest into the atmosphere [see Campbell , 2003, Figure 2]. At times of low geomagnetic activity, the operational density models include little of the energy that is contributed by these magnetospheric sources through particle precipitation and Joule heating [ Cole , 1962, 1966; Knipp et al , 2004; Moe and Moe , 2008].…”

Failure of Dst index fields to represent a ring current

“…However, it should always be realized that the geomagnetic coordinates are derived from an Earth‐centered International Geomagnetic Reference Field analysis in which the dipole field (represented by the first three spherical harmonic terms) defines the geomagnetic coordinate system. In fact, the main magnetic dipole field, arising from the flow pattern in the Earth's outer core, is not organized about the Earth's geographic center, but rather its field axis center is sufficiently offset from the Earth's center [ Fraser‐Smith , 1987] to cause the major South Atlantic/South American Anomaly and nonsymmetrical location of magnetic poles, two features not seen in the geomagnetic coordinate representation [ Campbell , 2003c, 2004]. At some low‐latitude Dst stations the disagreement between geomagnetic and eccentric dipole coordinates can become appreciable.…”

The Location of the Earth's Magnetic Poles From Circum‐Terrestrial Observations

“…The time‐space evolution of the dip poles, an independent parameter which reflects the existence of internal processes of our planet, should foster the interest of scientists working on different domains of Earth's science, broadening the knowledge about the Earth's interior. As in the past through the Ørsted (Hulot et al., 2002) satellite mission, which provided an improvement in the knowledge of the Earth magnetic field, nowadays we rely on the ESA's (European Space Agency) three Swarm satellites, coded as Alpha (A), Bravo (B) and Charlie (C), which provide a huge amount of data, allowing us to overcome at once the criticisms of deriving the dip pole positions from ground‐level surveys (Campbell, 2003): From few spot measurements (weak statistics) Inevitably under unpredictable magnetic external conditions during scheduled and time‐limited surveys With contamination by crustal unwanted contributions …”