Left panel: typical electron density profile as they can be derived from GPS RO measurements onboard Formosat3/COSMIC, CHAMP, and GRACE satellites. Right panel: ellipse fit to the distribution of ELDI profiles, which show enhanced E-layer ionization (red dots). The yellow stars mark the focal points of the ellipse; the black star marks the center point of the circle fit which coincides with the position of the geomagnetic pole (Mayer & Jakowski 2009).