ИСТИНА

We compared two mapping representations of a quiet ionosphere based on different data processing techniques: COSMIC/FS3 satellites radio occultation measurements and VTEC measurements by ground based GPS-receivers for 21 quietest days in 2008. We calculated differential VTEC between TWIM (radio-occultation-based model) and GIM (VTEC-based model) in geographic coordinates. It was found that the difference can be significant, especially in the low latitude region of both hemispheres (near the EIA crests) and predominately in the afternoon sector. We investigated local time and season dependences of longitudinal variations of the differential in the low-latitude and EIA zones. Amplitude of variations is larger at equinox (with maximum in spring season) and smaller at solstice (with minimum in summer season).