Some Differences in the Dynamics of the Intermediate Descending Layers Observed During Periods of Maximum and Minimum Solar Flux

A M Santos,M A Abdu,J R Souza,J H A Sobral,C G M Brum,I S Batista

doi:10.1029/2019ja027682

Abstract

AbstractIn this paper, ionograms from São Luís (SL, 2°S; 44°W, I: −3.8°) and Cachoeira Paulista (CP, 22.42°S; 45°W, I: −34.4°) are analyzed to examine the characteristics of the intermediate descending layers (ILs) over the Brazilian equatorial and low‐latitude regions under different solar flux conditions. The solar flux effects on the ILs are investigated in terms of the rate of occurrence of the IL; the seasonal behavior of some parameters such as the height, frequency, and velocity; and the duration and the number of ILs events observed per day. One of the main results of this work is that unlike over CP, the ILs over SL presented some peculiarities, such as a lower rate of occurrence during a period of solar maximum activity (2003) when compared with a period of solar minimum activity (2009). This apparent variation was likely caused by the magnetic equator moving away from SL during this period. The duration of the ILs was also investigated, and it was found that in 2009, the ILs presented higher life time than in 2003. The descending velocity of the ILs is compatible with the semidiurnal and quarter‐diurnal tides. Over SL, the larger descending rate in some cases (>10 km/hr) may reveal the additional influence of the gravity waves in the IL's dynamics.

Highlights

Intermediate descending layers (ILs) are regions of enhanced electron density located in the ionospheric valley region that extends from the upper E region to the F layer bottomside
This work investigated the behavior of the intermediate descending layers (ILs) over Brazilian regions during solar maximum (2003) and minimum (2009) periods
This was the first study on the morphology of the ILs during different solar activity epochs using exclusively Digisonde data that showed the peculiarities of the ILs including the effects of the magnetic equator displacement

Summary

Introduction

Intermediate descending layers (ILs) are regions of enhanced electron density located in the ionospheric valley region that extends from the upper E region to the F layer bottomside. The ionosonde measurements, for example, can be used to determine the occurrence and location of the ionospheric E‐F valley, but they cannot be used to infer the detailed parameters such as the depth and the height of the valley (Denisenko & Sotsky, 1978; Mahajan et al, 1994), differently from the measurements by an Incoherent Scatter Radar (ISR) that provides electron density with spatial and temporal resolutions at E‐F altitudes, such as the measurements made at the Arecibo Observatory (Raizada et al, 2015, 2018; Trost, 1979) In this context, this work explores the essential features of the ILs observed by two Digisondes operated in Brazil during periods of maximum and minimum solar activity. We will investigate the probability of occurrence of the ILs, as well as the seasonal behavior of the height, frequency, velocity, and the duration and the number of the ILs events observed per day

Experimental Data

Results and Discussion

Conclusions