PT - JOURNAL ARTICLE
AU - Love, J. J.
TI - Palaeomagnetic secular variation as a function of intensity
DP - 2000 Mar 15
TA - Philosophical Transactions of the Royal Society of London. Series A:
Mathematical, Physical and Engineering Sciences
PG - 1191--1223
VI - 358
IP - 1768
4099 - http://rsta.royalsocietypublishing.org/content/358/1768/1191.short
4100 - http://rsta.royalsocietypublishing.org/content/358/1768/1191.full
SO - Philos Transact A Math Phys Eng Sci2000 Mar 15; 358
AB - We seek to establish whether or not secular variation, the rate at which the magnetic field is changing in time, is a function of field strength. Towards that end we examine a database consisting of palaeomagnetic directions and absolute intensities from piles of extruded lava flows, many of which record polarity transitions. We find that directions from stratigraphically adjacent lava flows are most (least) correlated when the local field strength is high (low). Since volcanic activity is unrelated to, and therefore uncorrelated with, magnetic secular variation, this relationship between angular correlation and intensity indicates that angular secular variation is quiet (enhanced) when and where the local field strength is high (low). Our conclusion is consistent with some aspects of the recent behaviour of the modern field and is qualitatively consistent with sedimentary data recording reversals. Although we find a simple relationship between angular difference and intensity, a corresponding relationship for relative intensity differences has proved to be more elusive; its possible resolution will benefit from the continued collection of full vectorial palaeomagnetic data from lavas. Statistical models of secular variation need to incorporate the information content of serially correlated stratigraphically ordered data if the lava data are to be fully exploited. We suggest that the apparent inverse relationship between angular secular variation and local field strength could be the result of electromagnetic coupling between the solid inner core and the liquid outer core, with the inner core tending to stabilize core convection, and hence the field, when the intensity is high (as has been hypothesized).