ABSTRACT
The limitation of ionospheric models in describing short-term ionospheric events has led to the development of data assimilative models e.g. the International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model. This paper compares the IRI-Plas derived total electron content (TEC), the peak height (hmF2) and critical frequency (foF2) of the F2-layer with those obtained from Global Positioning System (GPS) receiver's and Digisonde Precision Sounder (DPS-4) measurements over Ilorin (Geog. Lat. 8.50oN; Long. 4.50oE, dip: - 7.9o) during geomagnetic storm days. The model estimation was done by assimilation of Ionosonde foF2 and TEC derived from GPS (GPS-TEC) and Global Ionospheric Map (GIM-TEC) into the model code. In order to study the effect of data assimilation on the model's representation, the "no input" option of the model was used as reference. The result shows that with the exception of the foF2 assimilation mode, all the options generally reproduced TEC quite well for all the storm days considered. Overall, the model adjusted with GPS-TEC gives the best prediction of TEC as it reduced the prediction error of TEC by a multiple of up to three compared to using the GIM-TEC. Also, all the options failed to reproduce the storm induced prominent features in the storm-time features of foF2 and hmF2. In other word, assimilation with the TEC does not generally improve the storm-time predictions of foF2 and hmF2 at the station. Consequently, for storm-time estimation of the F2-layer peak parameters, the 'no input' representation of the model is more valid at this station.
ABSTRACT
In this data article, analysis of the height of the peak electron density (hmF2) data, used to compute the vertical plasma drift (Vz) velocities during year 2010, was reported. The station of focus is Ilorin, a station in the African equatorial region. The hmF2 data used for the Vz computation was obtained from the Global Ionospheric Radio Observatory (GIRO) network of ionosondes, using the Digital Portable Sounder erected at the Equatorial Ionospheric Observatory of the University of Ilorin, Nigeria. Vz velocities were determined from the time rate of change of hmF2. Four categories of hmF2 data intervals for determining the drift were analysed and compared for reliable computation of Vz. This are the measured 15-minute, the calculated 30-minute, the calculated 60-minute, and the directly selected 1-hour interval datasets. The calculated 60-minute interval data was found more reliable than others, satisfying the three significant events that characterized vertical drift observations. These are the evening time pre-reversal enhancement, the daytime pre-noon upward drift, and the nighttime downward reversal periods. The observations from this data will help Space weather scientists and researchers in identifying the best fit of hmF2 data in the computation of drift velocity. The original work which has been published in Adebesin et al. (2013) [1] had made use of this calculated 60-minute interval hmF2 data, but the process/procedures of its selection as the best fit of data interval was not explained in that work.
