The role of the traveling planetary wave ionospheric disturbances on the equatorial F region post-sunset height rise during the last extreme low solar activity and comparison with high solar activity

This investigation studies traveling planetary wave ionospheric disturbance (TPWID) type oscillations on the modulation of the F region post-sunset height rise during the electric field pre-reversal enhancement (PRE). The studied period, from January 2009 to April 2010, occurred during the extremely low solar activity, when the averaged F10.7 was 73 {[}W/m(2) Hz]. In addition, the results are compared with those for a high solar activity period of 2003. We present ionospheric sounding observations carried out near equatorial region (Palmas 10.2 degrees S, 48.2 degrees W, dip latitude 5.5 degrees S) and low latitude region (Sao Jose dos Campos 23.2 degrees S, 45.9 degrees W, dip latitude 17.6 degrees S; located under the southern crest of the equatorial ionospheric anomaly) in the Brazilian sector. The studies found that the magnitude of the electric field during PRE time and consequently the day-to-day variations of the F region virtual height at equatorial region and low latitude are modulated by waves with periods of around 3-4, 5-6, 10-15, and 24-35 days. The observations show that during low solar activity, the TPWID oscillations are lower than during high solar activity, but with the same amplitude around 200 km. The TPWID long period oscillations of around 27 days present very distinct characteristics at the equatorial region and low latitude, indicating that these regions are not directly connected. Our study also shows that the response to the TPWID short period of around 3-4, 5-6, and 10-15 days at the equatorial region and low latitude present very clear coupling during January-February, 2009, possibly due to the sudden stratospheric warming and TPWID mechanisms. (C) 2014 Elsevier Ltd. All rights reserved. (AU)