Study of the F3 and StF4 Layers at Tucumán Near the Southern Crest of the Equatorial Ionization Anomaly in Western South America

Abstract

The present investigation reports for the first time seasonal and solar activity variations of F3 and StF4 layers at the low‐latitude station of Tucumán (26.9°S, 65.4°W; dip latitude 13.9°S), Argentina, by considering ionograms recorded from 2007 to 2015 by an Advanced Ionospheric Sounder‐Istituto Nazionale di Geofisica e Vulcanologia (AIS‐INGV) digital ionosonde. Occurrences of F3 and StF4 layers are found to be higher during summer months, while they are almost nil in winter. Moreover, occurrences of F3 and StF4 layers show a solar activity dependence with higher values during high solar activity. The solar activity dependence of F3 over Tucumán is similar to that reported earlier for the low‐latitude station of São José dos Campos, Brazil (dip latitude 14.1°S), but different than that reported for the near‐equatorial station of Palmas (dip latitude 6.6°S), Brazil. On the other hand, the solar cycle dependence of StF4 layer is consistent with the one obtained at Palmas. This highlights the complex nature of electrodynamics characterizing the ionosphere from the magnetic equatorial to low latitudes. Moreover, as shown in previous studies, the StF4 layer is always preceded and followed by the F3 layer, and it shows a shorter lifetime than that of the F3 layer. During the considered period, 1812 days were analyzed and the F3 layer was found in 370 days (20.4%), while the StF4 layer was found in 41 days (2.3%). This means that the StF4 stratification is seen during 11% of F3 layer days.

Comment on “A Study of the F2 Layer Stratification on Ionograms Using a Simple Model of TIDs” by Jiang et al.

“…This is now resolved by simply labeling the apparent layers in the sequence above the F1 as F2, F3, and F4 (when present). Complete time series of ionograms showing the typical development of an F3 layer followed by a period of roughly constant virtual height before fading out during a slow fall has been given (Balan et al, 1997; Rama Rao et al, 2005; Sreeja et al, 2010; Tardelli et al, 2018; Tardelli & Fagundes, 2015). Time series of ionograms from both vertical and oblique ionosondes showing the presence of an F3 layer have been given by Lynn et al (2000), and their relationship was explained (Lynn et al, 2002).…”

A Study of the F2 Layer Stratification on Ionograms Using a Simple Model of TIDs

“…In this study, we studied the F2 layer stratification through a ray tracing method to reconstruct the two types of the F2 layer stratifications mentioned above. Because many studies (Batista et al, 2002;Fagundes et al, 2011;Rama Rao et al, 2005;Tardelli et al, 2018;Uemoto et al, 2011;Zhu et al, 2013) have made a statistical studies of the F2 layer stratification at low latitudes, it is important to specify whether both of these two mechanisms could cause the F2 layer stratification. It might be helpful to explain statistical features of the F2 layer stratification over different locations.…”

Superfountain Effect Linked With 17 March 2015 Geomagnetic Storm Manifesting Distinct F3 Layer

“…This additional layer does not occur at middle and high latitudes. Several research groups have published interesting papers on the formation mechanism and short-and long-term variations of the F 3 layer (Balan et al, 1998(Balan et al, , 2000Batista et al, 2002;Fagundes et al, 2007;Lynn et al, 2000;Rama Rao et al, 2005;Sreeja et al, 2010;Tardelli et al, 2016Tardelli et al, , 2018Thampi et al, 2007;Uemoto et al, 2007Uemoto et al, , 2011Zain et al, 2008;Zhao et al, 2014). As proposed by Balan et al (1998), the F 3 layer occurs because of the combined effects of the upward E × B drift and magnetic meridional neutral wind together with the usual daytime photochemical and dynamical processes.…”