Abstract
The ionospheric total electron content (TEC) in the low-latitude Singapore region (geographic latitude 01.37° N, longitude, 103.67° E, geomagnetic latitude 8.5° S) for 2010 to 2011 was retrieved using the data from global positioning system (GPS)-based measurements. The observed TEC from GPS is compared with those derived from the latest International Reference Ionosphere (IRI)-2012 model with three options, IRI-Nequick (IRI-Neq), IRI-2001, and IRI-01-Corr, for topside electron density. The results showed that the IRI-Neq and IRI-01-Corr models are in good agreement with GPS-TEC values at all times, in all seasons, for the year 2010. For the year 2011, these two models showed agreement at all times with GPS-TEC only for the summer season, and for the period 11:00 to 24:00 UT hours (19:00 to 24:00 LT and 00:00 to 08:00 LT) during the winter and equinox seasons. The IRI-2012 model electron density profile showed agreement with constellation observing system for meteorology, ionosphere, and climate (COSMIC) radio occultation (RO)-based measurements around 250 to 300 km and was found to be independent of the options for topside density profiles. However, above 300 km, the IRI-2012 model electron density profile does not show agreement with COSMIC measurements. The observations (COSMIC and GPS) and IRI-2012-based data of TEC and electron density profiles were also analyzed during quiet and storm periods. The analysis showed that the IRI model does not represent the impact of storms, while observations show the impact of storms on the low-latitude ionosphere. This suggests that significant improvements in the IRI model are required for estimating behavior during storms, particularly in low-latitude regions.
Highlights
The electron density distribution in the low-latitude F-region of the ionosphere is obtained by knowing the combined effect of production by EUV flux, loss exchange between O2 and N2, and transport process by means of E × B plasma drift
This contour diagram shows that total electron content (TEC) is found to be highest during the equinoctial months, which is shown by the International Reference Ionosphere (IRI)-2012 model results
The results showed that the IRI-Neq and IRI-01Corr models are in good agreement with the global positioning system (GPS)-based measurements for all seasons and all times, while the IRI 2001 model overestimated the GPS-TEC
Summary
The electron density distribution in the low-latitude F-region of the ionosphere is obtained by knowing the combined effect of production by EUV flux, loss exchange between O2 and N2, and transport process by means of E × B plasma drift. The daytime eastward electric field in the ionosphere combined with the north-south geomagnetic field produces E × B upward plasma drift and is responsible for initiating the well-known phenomena called the fountain effect at the equator, causing the equatorial ionospheric anomaly (EIA) (Moffett and Hanson 1965; Kumar and Singh 2009). The TEC in the low-latitude/EIA region is subject to day-to-day variability and is a challenging problem for ionospheric modelers (Huang et al 1989; Klobuchar 1986). The validation of the IRI model for equatorial and low-latitude regions is important because of its growing applications in various military and civilian areas with broad objectives
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