Evaluation of IRI-2012 by comparison with JASON-1 TEC and incoherent scatter radar observations during the 2008-2009 solar minimum period

Abstract

he 2008-2009 solar minimum period was unprecedentedly deep and extended and therefore it should be difficult to expect for the data-driven model like the International Reference Ionosphere (IRI) to reasonably well reproduce the ionospheric parameters during this period. In this study, we compare the IRI-2012 with global TEC data from JASON-1 satellite and electron density profiles observed from Millstone Hill Incoherent Scatter Radar (ISR) and EISCAT at middle and high latitudes, respectively. For the global mean ionosphere, daily mean TECs calculated from the model and data are compared with each other during the two-year period and it is found that IRI underestimates TEC by about 34%. Global TEC maps for two TECs are produced in the magnetic latitude and magnetic local time coordinate, which shows the overall underestimation of IRI except for the region around the equatorial anomaly only during the daytime, regardless of season. In the daytime equatorial region, IRI slightly overestimates TEC and this aspect of IRI for low solar activity was also reported in the previous study (e.g. see Jee et al., 2005). In order to further investigate the differences at middle and high latitudes, which are responsible for the overall underestimation in the global mean ionosphere, we compared the electron density profiles between IRI and ISRs at Millstone Hill and EISCAT for the middle and high latitudes. During the daytime, however, it is not very clear that IRI underestimates TEC. In particular, the density profiles show large discrepancy in the topside ionosphere, which requires further investigation since the ISR data may not be reliable in the topside ionosphere for low solar activity.