Effects of the terdiurnal tide on the Sporadic-E layers (Es) development at low latitudes over the Brazilian sector

Abstract

Abstract. Sporadic-E (Es) layers are patches of high ionization observed at around 100–140 km height in the E region. Their formation at low latitudes are primarily associated with the diurnal and semidiurnal components of the tidal winds via the ion convergence driven by the wind shear mechanism. However, recent studies have shown the influence of other tidal modes, such as the terdiurnal tide. Therefore, this work investigates the effect of terdiurnal tide-like oscillations on the occurrence/formation of the Es layers observed over Palmas (10.17° S; 48.33° W; dip lat. -8.3°), a low latitude station in Brazil. The analysis was conducted from December/2008 to November/2009 by using data collected from a CADI (Canadian Advanced Digital Ionosonde) ionosonde. Additionally, the E Region Ionospheric Model (MIRE) was used to simulate the terdiurnal tidal component in the Es layer development. The results show modulations of 8-hour periods on the occurrence rates of the Es layers during all seasonal periods. In summer and autumn, we see three well-defined peaks in a superimposed summation of the Es layer types per hour. We also observed that the modulation of the terdiurnal tide on the Es occurrence rates minimizes in December, the beginning of the summer season.

Analysis of Blanketing Sporadic‐E Layer and Associated Tidal Periodicities Over a Brazilian Station Undergoing a Transition From Low Latitude to Midlatitude

“…Fontes et al. (2023) investigated the terdiurnal tide‐like oscillations on the Es occurrences over Palmas and found a modulation of 8‐hr in all seasons of the year. However, the authors noted that this effect was observed to be at a minimum during December.…”

“…This classification is based on the observation that during nighttime the ftEs/fbEs parameters tend to be generally lower than during daytime (see Figure 1), primarily due to reduced ionization levels. As both Es f and Es l types present similar signatures in the ionograms, some studies (Conceição‐Santos et al., 2019; Fontes et al., 2023) group them into a single type (Es f/l ). It is noteworthy that both “f” and “l” types persist throughout the day, which indicates that they may be formed by metallic ions that have longer lifetimes compared to molecular ions (Plane et al., 2015).…”

“…Recently, Fontes et al. (2023) investigated Es b occurrences in Palmas (10.2°S, 48.3°W, dip lat. : −7.31°), Brazil, and observed elevated Es b occurrence rates during the summer and spring seasons.…”