Statistical Study of the Saturation Effect in Response of GIM TEC to Solar Activity

This study explores the saturation effect in responses of the ionospheric total electron content (TEC) in global ionosphere maps to the solar activity of F10.7 (10.7-cm solar radio noise flux). To find F10.7 value at which TEC values became saturated, the decision tree regression and ensemble learning are built based on the data in the descending solar activity of Cycle 23 during 2002－2009. It is found that saturation features in TEC appear more frequently at the low, especially equatorial ionization anomaly (EIA), latitudes than those at the middle or high latitudes during post-noon period. This indicates that the ionosphere intrinsically has a certain limited capacity, while over the EIA region, the dense ambient electron density has very limited room and tend to become saturated. Detailed results of the saturation features in various local times and seasons will be presented and discussed.