Comparison of total electron content predicted using the IRI-2007 model with GPS observations over Lagos, Nigeria

Comparison of total electron content predicted using the IRI-2007 model with GPS observations over Lagos, Nigeria 

A O Adewale1,$,*, E O Oyeyemi1, J O Adeniyi2, A B Adeloye1, O A Oladipo2 

1Department of Physics, University of Lagos, Nigeria. 2Department of Physics, University of Ilorin, Nigeria 

Indian Journal of Radio & Space Physics Vol. 40, February 2011, pp.21-25


Correspondence to:

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Key Points:

•  Total electron content (TEC), IRI-TEC variation, GPS-TEC variation 

Abstract:

The comparison of IRI-2007 (NeQuick option) derived total electron content (TEC) (IRI-TEC) with Global Positioning System observations (GPS TEC) recorded at Lagos, Nigeria (6.5°N, 3.4°E; dip latitude 2°S) has been done. The observations were carried out using a dual frequency Novatel GSV 4004B GPS Ionospheric Scintillation and TEC monitor. The diurnal and seasonal variations of measured TEC were analyzed for 2009, a year of low solar activity. The TEC values were grouped into four seasons, namely March Equinox (February, March and April), June Solstice (May, June and July), September Equinox (August, September and October), and December Solstice (November, December and January). The IRI-2007 predicts reasonably well the observed diurnal and seasonal variation patterns of TEC values during all the seasons. However, the model gave a relatively poor prediction during 0200 – 0600 hrs LT, with the TEC percentage deviation (∆TEC) having values greater than 50% during all seasons and ∆TEC never exceeded 50% at any other hour of the day except at 0800 hrs LT during both December Solstice and September Equinox. The early morning deviation between predictions and observed vertical TEC (VTEC) could arise because maximum electron density of the F2 layer (NmF2) or the shape of the electron density profile, or both, is not well predicted by the NeQuick model; and some improvements need to be implemented to obtain better predictions of TEC over Lagos. 

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