Features of the F3 layer occurrence over the equatorial location of Trivandrum

Abstract

Abstract. The general features of the F3 layer occurrence over the magnetic equatorial location of Trivandrum (8.5 • N; 77 • E; dip lat ∼ 0.5 • N) in India during the period from 1996-2005 are presented using the ionosonde observations. The study brings out that the F3 layer occurrence over Trivandrum is weak and rare compared to the other equatorial locations. The F3 layer occurrence is relatively more pronounced during the magnetically active conditions, thus indicating the dependence of the layer formation over Trivandrum on magnetic activity. It is also observed that the percentage occurrence of the F3 layer decreases with increasing solar activity.

Stratification of the Low-Latitude and Near-EquatorialF2Layer, Topside Ionization Ledge, andF3Layer: What We Know about This? A Review

“…Raghavarao and Sivaramam [67] concluded that the topside ledges occurred more frequently and lasted longer into the night during sunspot minimum period than at sunspot maximum. The same conclusion was made regarding the appearance of F3 layer according to ground-based sounding data [43].…”

“…Similarly, according to the ground-based data F3 layer is observed rarely at the equator than at low latitudes ±(7∼8 • ) [37,39,41,65]. Recent studies show that the F3 layer near the magnetic equator behaves in a different way than that in the magnetic low-latitude region [41,43,66]. The F3 layer moves rapidly upward near the magnetic equator, while it stays almost at a certain altitude in the magnetic low-latitude region.…”

“…Thus, the F3 layer is not always formed even during strong magnetic storms. However, according to groundbased sounding data, the F3 layer appears more often in the disturbed days [43]. …”

“…It is obvious that the equatorial F2 layer stratification and the occurrence of an additional layer in the equatorial ionosphere is the one phenomenon. [32], the subject of the F3 layer received extensive investigations at low and equatorial latitudes concerning its spatial and temporal distribution based on the ionosonde observations of single or several stations distributed at three longitudinal sectors (American, Indian, and Pacific longitudes) [34][35][36][37][38][39][40][41][42][43][44]. From these investigations, it is known that the F3 layer can be observed under geomagnetically quiet conditions.…”

Features of theF3layer in the low-latitude ionosphere at sunset

“…This additional layer was later renamed the F 3 layer because it has the same chemical composition as the F region . After that, the subject of the F 3 layer received extensive investigations at low and equatorial latitudes concerning its spatial and temporal distribution [Jenkins et al, 1997;Balan et al, 1998;Hsiao et al, 2001;Batista et al, 2002;Rama Rao et al, 2005;Zain et al, 2008;Uemoto et al, 2007;Sreeja et al, 2010;Zhao et al, 2011], and also its storm time characteristics [Zhao et al, 2005;Paznukhov et al, 2007;Balan et al, 2008;Sreeja et al, 2009;Zong et al, 2010]. The mechanism of the storm time F 3 layer resembles that in quiet periods and was caused by a rapid upward E × B drift resulting from an eastward penetration electric field but sometimes can be caused by strong field-aligned diffusion due to the storm time meridional wind surges as proposed by Lin et al [2009aLin et al [ , 2009b.…”