Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998geoji.134..527c&link_type=abstract
Geophysical Journal International, Volume 134, Issue 2, pp. 527-544.
Astronomy and Astrophysics
Astronomy
46
Geomagnetic Field, Inverse Problem, Palaeomagnetism, Spherical Harmonics
Scientific paper
A basic tenet of palaeomagnetism is that the Earth's magnetic field behaves on average like that of a central axial dipole (g01 ). Nevertheless, the question of possible persistent second-order features is still open. Recently Johnson & Constable (1995, 1996) performed a regularized non-linear inversion and found evidence for persistent non-zonal features. Formal uncertainties would indicate that there are significant (non-zero) terms at least up to degree and order 4. Using a recent compilation of two different data sets from lavas (0 to 5 Ma) and the Johnson & Constable codes, we test the robustness of this result. The data set has been divided into three subsets: the Brunhes polarity data (B), all normal polarity data (N) and all reverse data (R). In each subset of data, a prominent g02 , of the order of 5 per cent of g01 , is clearly present, as previously established by several authors. In some subsets, smaller terms appear: g22 and g11 in the Brunhes data, h13 and h12 in N, and h12 , g03 and g33 in R. A threshold under which terms resulting from the inversion cannot yet be considered as robust appears to be of the order of 300 nT. Indeed, tests show that many terms, which are different for each epoch (B, N or R), may be artefacts due to aliasing because of poor site distribution, or due to the underestimation of a priori errors in the data; these could result from undetected tectonic rotations, non-horizontal palaeoslopes, or viscous overprints. Because of these limitations in resolution, it may not yet be possible to identify robustly terms other than the axial dipole and quadrupole. The persistence of high-latitude flux concentrations, hemispheric asymmetry or normal versus reversed field asymmetry cannot yet be considered as demonstrated.
Carlut Julie
Courtillot Vincent
No associations
LandOfFree
How complex is the time-averaged geomagnetic field over the past 5 Myr? does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with How complex is the time-averaged geomagnetic field over the past 5 Myr?, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and How complex is the time-averaged geomagnetic field over the past 5 Myr? will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1576872