Geomagnetic secular acceleration, jerks, and a localized standing wave at the core surface from 2000 to 2010
Abstract
The geomagnetic secular acceleration (SA), defined as the second-order time derivative of the Earth's core magnetic field, is investigated using data from the CHAMP satellite. We present a set of SA spherical harmonic models calculated from 3 year time intervals of CHAMP data, centered on epochs ranging from 2002.19 to 2009.51 with a 30 day step. These models are parameterized as second-order Taylor expansions in time and are not regularized, except for SA degrees larger than 8. We find that the SA underwent two power pulses in 2006 and 2009 at the core-mantle boundary (mostly on degrees 5 and 6) and at the Earth's surface (mostly on degrees 2 to 4). These pulses take the form of intense SA patches at the core surface in the low-latitude Atlantic sector and in the Indian Ocean sector. In the Atlantic sector, the 2006 and 2009 SA patches are markedly anticorrelated. Principal component analysis suggests that the two pulses are part of a standing wave of period about 6 years. At the Earth's surface, this wave results in a succession of geomagnetic jerks, i.e., sudden SA polarity changes, in 2003, 2007, and 2011 near the Atlantic sector. The 2011 jerk is detected using the latest observatory data available, including quasi-definitive data from January to October 2013. The origin of the wave is not clear; we find that it cannot be generated by the zonal toroidal flow of a torsional oscillation. Other possible interpretations are discussed.
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