تعيين رسانش الكتريكي و درجه حرارت گوشته فوقاني با استفاده از تغييرات ميدان Sq

Determination of the electrical conductivity and temperature of the upper mantle using Sq field

A fluctuating electric current flowing in the Earthʹs atmosphere causes corresponding electric currents to flow in the conducting Earth below the source current. The depth of penetration of the induced currents is determined by the characteristics of the source currents as well as the distribution of electrically conducting materials in the Earth. At the Earthʹs surface observatories measure the composite of external (source) and internal (induced) field components from the currents. The quiet daily field variations, called Sq for ʹsolar quiet-time1, provide a natural signal source with frequencies appropriate to upper mantle conductivity studies. This paper is concerned with the quiet-day field variations, their separation into external and internal contributions, and the use of this separation to profile the electrical conductivity of the Earthʹs upper mantle. For the situation in which field measurements are available about a spherical surface that separates the source from the induced currents (and a current doesnʹt flow across this surface), Gauss (1838) devised a special solution of the differential electromagnetic field equations that is separable in the spherical coordinates r,Q and cp In Gaussʹs solution, the •far-WYAYY .-jifc^ :Ja>lj oX> ♦W-YTYYTYT E-mail: bayrami@ut.ac.ir tY