Text this: Spherical coordinates system representation by (3) where continuous increase in azimuth angle <i>ϕ</i> with period 2<i>π</i> depicts spin of Earth around <i>Z</i>-axis (north and south pole), and continuous increase in elevation angle <i>θ</i> with period <i>π</i> depicts flow of magnetic flux along longitudes with source at south pole (<i>θ</i> = −<i>π</i>/2) and sink at north pole (<i>θ</i> = <i>π</i>/2).