Assessment of ionospheric variability from IRI-2016, SPIM-2017, and IGS-GIM using Digisonde and GPS observations over Cyprus

The present study focuses on ionospheric F-layer critical parameters (foF2/hmF2) and Total Electron Content (TEC) by exploiting a long-term data (2009 to 2016) from Digisonde and Global Positioning System (GPS) receiver observations over a lower-middle latitude European location Nicosia, Cyprus (geographic 35° N, 33° E; magnetic dip. 32° N). Also, it adheres to evaluating the performances of global empirical standard International Reference Ionosphere (IRI-2016), Standard Plasmasphere Ionosphere Model (SPIM-2017/IRI-Plas 2017), and interpolated TEC from the IGS-Global Ionospheric Maps (GIMs) by comparing with the Digisonde and GPS observations. Our results confirm a noteworthy departure of estimated foF2/hmF2 and TEC in SPIM-2017, even larger than that of IRI-2016 as regards to the Digisonde and GPS observations, irrespective of season, solar activity, and geomagnetic activity conditions. This contradicts the general perception on an ideal behavior of the empirical climatological model over the middle latitude region, inferring that the transient region between the low and middle latitude does suffer from noticeable uncertainties. Also, we did not notice any convincing response of the storm sub-model in IRI except a rare flipping in its magnitude and absolutely no alteration in SPIM model estimations to the onset of geomagnetic storms over the region despite the storm sub-model was kept 'on'. This suggests a revisit into the underlying storm sub-model database in the models. Interestingly, the ingestion of Digisonde recorded foF2/hmF2 and GPS-TEC into the SPIM-2017 model results in a remarkable convergence of the parameters towards the local observations even during active geomagnetic storm conditions. It ascertains the flexibility in SPIM-2017 towards plausible improvements in the model estimations by ingesting GPS-TEC. Above all, such a scheme is in line with efforts towards reliable ionospheric error mitigations in navigation, communication, and satellite applications.