Magnetic variations measured a t three stations across the strike of the anomaly in electrical conductivitv of the earth's mantle suerested bv Whitham and Andersen (1962) near Alert, Elles~nere Island, havelbeen analyzed by simple potential theory. T h e anomalous internal contributions to the magnetic variation 1-ector show striking confinement consistent with an underground current in a northeast-southwest direction a t a depth between 50 and 70 km, a few kilometers southeast of Alert. If the anomalous c o n d~~c t o r is approxin~ated by a uniform infinite cylinder, the horizontal field response as a function of frequency can then be explained with a conductivity of ~3 X 1 0 -'~ e.m.u. and a cylindrical radius of about 50 km. T h e vertical field response is, however, an unsatisfactory fit to this model. A possible asymmetry is noted based on the hourly range data: this could be explained by the dipping of the real conductor under Ellesmere T~l a n r lPreliminary earth potential measurements show that, a s expected, the electric field variations are abnormally low a t Alert.The gravitational consequences of the cylindrical model are discussed and compared with two profiles from the same region. A Bougucr anomaly is found in the predicted region if certain regional gradients are assumed, but its magnitude is snlaller than that predicted from the cylindrical model in hydrostatic equilibriunl. I t is clear that approximate agreement can be obtained with crustal thinning of some 20 km.The significance of the thermal ano~naly thought t o be responsible for the electrical conductivity anomaly is discussed briefly.
Standard-run magnetograms obtained from Mould Bay, Prince Patrick Island, demonstrate a striking absence of vertical magnetic field variations corresponding to an anomalous steepening of the vertical field power spectrum. Assuming the presence of a sheet conductor at depth, it is estimated from the frequency dependence of the spectrum that a 20 km thick layer with a conductivity aboyt 10-11 e.m.u. is required near the bottom of the crust. There appears to be no evidence for such a highly conducting crust. Anomalous temperatures difficult to reconcile with a stable region are required to explain the anomaly by semiconduction processes. The extent of the Mould Bay anomaly is as yet unexplored.Russian results (Zhigalov 1960), and a search of Arctic magnetograms available here, show that severe attenuation of the vertical field fluctuations occurs over the deep ocean basins. It is concluded that the magnitude of the attenuation found on drifting stations can be explained by the presence of the conducting ocean, with reasonable estimates of the wavelength of the inducing field. However, it appears unlikely that the Mould Bay results can be so explained.
Hourly ranges in the principal horizontal field component have been measured for sixteen Canadian IGY magnetic observatories and variation stations. The latitudinal variation of disturbance measured by this index has been determined seasonally and as a function of disturbance. One station, Alert, at the northern end of Ellesmere Island, confirms the existence in these longitudes of an apparently narrow zone or area of enhanced magnetic activity, as defined by this measure of disturbance. Semipersistent structure is also apparent in the principal auroral zone in the meridian sections of magnetic activity.
Diurnal occurrence patterns, amplitude‐frequency plots, the diurnal variation of the mean disturbance field, and the physical significance of this range index have been investigated in an attempt to explain this apparent inner maximum of magnetic activity. More homogeneous very high latitude data are required to determine the morphology of the anomalous region found.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.