Electrical conductivity of the Earth's mantle from the first Swarm magnetic field measurements

Abstract

We present a 1‐D electrical conductivity profile of the Earth's mantle down to 2000 km derived from L1b Swarm satellite magnetic field measurements from November 2013 to September 2014. We first derive a model for the main magnetic field, correct the data for a lithospheric field model, and additionally select the data to reduce the contributions of the ionospheric field. We then model the primary and induced magnetospheric fields for periods between 2 and 256 days and perform a Bayesian inversion to obtain the probability density function for the electrical conductivity as function of depth. The conductivity increases by 3 orders of magnitude in the 400–900 km depth range. Assuming a pyrolitic mantle composition, this profile is interpreted in terms of temperature variations leading to a temperature gradient in the lower mantle that is close to adiabatic.

CaSiO3 Perovskite May Cause Electrical Conductivity Jump in the Topmost Lower Mantle

“…Based on the mantle adiabatic geotherm (Katsura et al, ) and assumed linear increase of the volume proportion of CaSiO 3 perovskite from 0% at 600 km to 10% at 800 km depth, the modeled results are given in Figure a. With regards to the effective conductivity by considering the product of mineral conductivity and volume proportion, the relative contribution of CaSiO 3 perovskite to lower mantle conductivity increases by ~1.7 orders of magnitude from ~600 to 800 km depth, which matches well with the geophysically observed electrical conductivity jump at these depths (Civet et al, ; Constable & Constable, ; Olsen, ). In contrast, the relative variations of bridgmanite (with a high volume proportion of more than 70%) at these depths are much smaller (Figure a and Yoshino et al, ).…”

“…Magnetotelluric depth soundings have detected an electrical conductivity jump by 1.5–2 orders of magnitude from ~600 to 800 km depth, corresponding roughly to the topmost lower mantle (e.g., Civet et al, , Constable & Constable, ; Olsen, ). At these depths, minerals that have received wide attention concerning their electrical properties include bridgmanite, majoritic garnet, and ferropericlase.…”

Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents

“…In order to use a realistic conductivity profile for the estimation of the geoelectric field, a new Earth profile was compiled from a shallow (up to 100 km depth) worldwide 3D model (Alekseev et al 2015) for one location and a deep Earth profile compiled from satellite data (Civet et al 2015), and they are used in this study. This composite structure is utilised to compute the line currents of the EEJ in the ionosphere from geomagnetic measurements, which are then used to derive the geoelectric field on the ground that drives GIC.…”

“…The deep-layer conductivity profile was derived from geomagnetic measurements obtained by the Swarm satellite (Civet et al 2015). Table 2 and Fig.…”

An initial ULF wave index derived from 2 years of Swarm observations

“…Additionally, Swarm data are used to study the Sun's influence on the Earth system by analyzing electric currents in the magnetosphere and ionosphere and understanding the impact of solar wind on the dynamics of the upper atmosphere. Swarm currently offers one of the best-ever surveys of the Earth's main and crustal magnetic field (Civet et al, 2015;De Michelis et al, 2015;Hulot et al, 2015;Olsen et al, 2015;Schnepf et al, 2015) as well as the near-Earth electromagnetic environment (Alken et al, 2015;Archer et al, 2015;Buchert et al, 2015;Dunlop et al, 2015;Goodwin et al, 2015;Iyemori et al, 2015;Lühr et al, 2015a, b;Park et al, 2015;Pitout et al, 2015;Spicher et al, 2015). The interested reader is also referred to the special issue "Swarm science results after 2 years in space" (for details, see Olsen et al, 2016).…”