A global positioning system-based climatology for the total electron content in the ionosphere

The total electron content (TEC) in the ionosphere is an important factor in the propagation of radio waves. Since 1998 the coverage global positioning system (GPS) observations has been sufficient to monitor the TEC globally. We have used the global ionosphere maps provided by the Jet Propulsion Laboratory to devise a new ionosphere climatology (NIC09). The climatology fits the GPS maps to 4.5 TECU, more than twice as well as the IRI2007 climatology. The use of the global mean TEC as the input parameter reduces scaling errors and long-term mean errors in the model. For climatic studies of sea level measured by satellite radar altimeters, it is necessary to go back before 1998. During the earlier years of radar altimetry, we use TOPEX dual-frequency altimeter data to reconstruct the global mean TEC or use the solar radio flux (F-10.7) as a proxy. The comparison of dual-frequency altimeter data with the GPS maps demonstrated that about 8% of the TEC extends above 1350 km and about 14% above 800 km. The root mean square error of the NIC09 climatology was found to be approximately 18% of the TEC, compared to 14% for the GPS TEC maps, and 35% for IRI2007.