On the seasonal dependence of intermediate descending layer in low latitudes

Abstract

Understanding the variable behavior of the IDL/Es system contributes significantly to our ability in characterizing and modeling the critical ionospheric dynamics across the globe. In this work we aim to improve the understanding of the IDL/Es system by analyzing the diurnal and seasonal variations in the altitude descent with reference to local time of the day, season, and solar activity. We apply the well-known height-time-intensity analysis method on measurements obtained from the Sharjah ionosonde station, located at the Arabian Peninsula (Sharjah: 25.28°N, 55.46°E) near the northern crest of the equatorial ionization anomaly. The measurements cover three years of the increasing phase of the solar cycle 25 from 2020 to 2022. Considering an oversimplified wind system based on windshear theory, we attempt to establish a relationship between IDL/Es periodicities with diurnal, semidiurnal, and terdiurnal tides without digging into the underlying mechanism. Results suggest a strong relation between semidiurnal and terdiurnal tides and the formation and transport of the IDL, particularly impacting lower E-region and sporadic-E layers during the afternoon and nighttime hours. The results of manual scaling of over eleven thousand ionograms is presented to quantify the behavior of the IDL/Es system's transport. Additionally, a connection between solar activity, descent rate, and initial descending height, with semidiurnal patterns consistently present across seasons and solar activity has been discussed. For different frequency bins used in this work, e.g. 3 MHz, 4 MHz, and 5 MHz, seasonal variations significantly influence descent patterns.