Upper mantle electrical conductivity for seven subcontinental regions of the earth.

Abstract

Spherical harmonic analysis coefficients of the external and internal parts of the quiet-day geomagnetic field variations (Sq) separated for the seven continental regions of the observatories have been used to determine conductivity profiles to depths of about 600km by the Schmucker equivalent substitute conductor method. The profiles give evidence of increases in conductivity between about 150 and 350 km depth, then a general increase in conductivity thereafter. For South America we found a high conductivity at shallow depths. The European profile showed a highly conducting layer near 125km. At the greater depths, Europe, Australia and South America had the lowest values of conductivity. North America and east Asia had intermediate values whereas the African and central Asian profiles both showed the conductivities rising rapidly beyond 450km depth. The regional differences indicate that there may be considerable lateral heterogeneity of electrical conductivity in the Earth's upper mantle.

Upper Mantle Electrical Conductivity in the Himalayan Region.

“…Campbell and Anderssen, 1983;Campbell and Schiffmacher, 1988) the cutoff values of Gm were tailored to decrease with increasing m in proportion to the decreasing amplitudes of the Sq field harmonics defined by the (24/m)-hr components. When extensive tests were made on the present data set either making the above m adjustments to GM or by simply assigning it a constant value for all m's, no significant difference was seen.…”

“…Campbell and Anderssen (1983) and Campbell (1989) to the continental Sq systems. Campbell and Schiffmacher(1988), compared the seven continental region upper mantle conductivities using the International Quiet Year 1965 geomagnetic data set.…”

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…Geomagnetic disturbances associated with storms and substorms are typically several hundreds of nano teslas on the surface, which can easily mask underlying Sq signals. Despite the small amplitude, studies on Sq have been important for understanding the ionospheric electrodynamics (Richmond 1979(Richmond , 1995b and its coupling to the magnetosphere and lower atmosphere (Wagner et al 1980;Richmond 1995b); for determining a base level for geomagnetic indices (Mayaud 1980;Love and Gannon 2009;Gjerloev 2012); for monitoring solar radiation activity (Svalgaard and Cliver 2007;Svalgaard 2016); and for estimating electrical conductivity within the Earth (Campbell and Schiffmacher 1988a;Campbell et al 1998;Okeke and Obiora 2016).…”

Effects of the Magnetospheric Currents on the Sq-Field and a New Magnetic Index Characterizing Sq Dynamo Current Intensity.

“…In studying the electric conductivity in the Earth's interior the Sgfield is one of sources of important information (CAMPBELL, 1987(CAMPBELL, ,1988. On the other hand, in magnetic survey, the crustal electricity anomaly study and some magnetospheric-ionospheric phenomena studies the Sq-field should be removed from the records.…”