Validation of international reference ionosphere models using in situ measurements from GRACE K-band ranging system and CHAMP planar Langmuir probe

Abstract

The in situ measurements of electron contents from GRACE K-band (dual-frequency) ranging system and CHAMP planar Langmuir probe were used to validate the international reference ionosphere (IRI) models. The comparison using measurements from year 2003 to 2007 shows a general agreement between data and the model outputs. The improvement in the newer IRI model (IRI-2007) is evident with the measurements from the GRACE satellites orbiting at the higher altitude. We present the comparison between the models and data comprehensively for various cases in solar activity, local time, season, and latitude. The IRI models do not well predict the electron density in the years 2006 and later, when the solar activity is extremely low. The IRI models generally overestimate the electron density during local winter while they underestimate during local summer. In the equatorial region, the large difference at local sunrise lasts for all years and all seasons. The IRI models do not perform well in predicting the anomaly in the polar region such as the Weddell Sea Anomaly. These discrepancies are likely due to smoothed (12-month averaged) solar activity indices used in the IRI models and due to insufficient spherical harmonic representation not able to capture small spatial scales. In near future, further improvement on the IRI models is expected by assimilating those in situ satellite data by implementing higher resolution (spatial and temporal) parameterizations.