Ionospheric radio occultation measurements and space weather

GPS radio occultation measurements carried out on board Low Earth Orbiting (LEO) satellites provide a unique opportunity for monitoring the entire electron density distribution from LEO heights down to the bottom of the ionosphere. Furthermore, GPS navigation measurements onboard LEO's may be used to reconstruct the electron density distribution of the topside ionosphere and plasmasphere with high resolution. More than 20000 vertical electron density profiles are obtained since the beginning of ionospheric radio occultation measurements onboard the German CHAMP satellite by using a model assisted retrieval technique. Validation studies reveal RMS deviations of the F2 layer parameters f0F2 and hmF2 of about 1.3 MHz and 47 km, respectively. IRO derived vertical electron density profiles were compared with corresponding profiles derived from vertical sounding measurements obtained at various ionosonde stations and incoherent scatter radar facilities. The absolute deviations from selected European ionosonde data computed as a function of altitude are generally less than 0.5 MHz ( RMS < 1.5 MHz). The topside electron density reconstruction, close to the CHAMP orbit plane, indicates a significant impact of complex space weather events on the shape of the geo-plasma environment. So the 2D electron density distribution in the CHAMP orbit plane reconstructed for the geomagnetic storm on November 6, 2001, indicates very dynamic and severe plasma enhancements near the North Pole.