Dear Shola,

The night-time enhancement in ionospheric parameters (foF2 and TEC) is well established feature - not only at high, but also at middle and low latitudes. The mechanisms for its appearance, however, are different at different latitude. 

At high latitude - the movement of the mid-latitude ionospheric trough and ionization by corpuscular particles seems to be the most important (see the attached article). 

What is interesting in your Figure is that in 20002 and 2003 you have very well pronounced phenomenon known as "winter-time ionospheric anomaly" - i.e. the summer TEC values are equal or less  than the winter TEC values.

Natalya

Dear Andrew,

Thank for your suggestion. I don't think the problem is with the source of my bias values because  it was actually obtained from the Center for Orbit Determination in Europe (CODE), Bern University, Switzerland blog. I later discover that studies such as Perevalova et al., (2010) and Araujo-Pradere et al., (2005) had reported that same feature. Thanks.

Adebiyi

Dear Natalya,

Thank you for that useful contribution. I actually observed that winter anomaly feature but what I don't under before was the mechanism responsible for the observed daytime/nighttime variation. However, I later came across the work of Perevalova et al., (2010) that gave me an insight. I also find this material very useful.

Thanks.

Adebiyi

The diagram presented do not give sufficient information to answer the question.

Pls Prof. What additional info is required so that I can supply them.

Did you find that this TEC  effect is enhannced during periods of geomagnetic storms main phases?  How does it  elvove during recovery phases?