Special issue  

In the terrestrial ionosphere, sporadic (metallic) layers are formed. The formation of these layers are related to the action of atmospheric waves. These waves, also named tides, are due to the absorption of solar radiation in the atmosphere. We investigated the role of the tides with 8 h period in the formation of the sporadic layers. The study was conducted using ionosonde and meteor radar data, as well as computing simulations. The 8 h tides intensified the density of the sporadic layers.

We study how the polar regions of the Earth connect to space along magnetic field lines. While the Earth's magnetic field is mostly the shape of a dipole, at high latitudes the field lines tend to be open and connect to interplanetary space. This area of open field line is called the polar cap, and it is highly dynamic. Through data analysis and computer simulations, we find that the shape of the polar cap is closely controlled by the magnetic field embedded in the solar wind.

We observed two different wave propagations in the earth’s upper atmosphere: a gravity wave in the mesosphere and the ionospheric disturbances. We investigated the wave propagations by using airglow imaging techniques. It is found that there was a gravity wave generation from the tropospheric convection spot, and it propagated upward in the ionosphere. This reports observational evidence of gravity wave propagation from the troposphere to ionosphere.

This paper brings analysis of spread-F echoes along the years of 2003 to 2012 from Christmas Island radar. We organize our data with the objective of observing the peak time and altitude distribution. Our results indicate the peak time occurrence of echoes to be distributed closer to local sunset during solar maximum and around midnight during solar minimum; meanwhile, the peak altitude echoes show higher altitude occurrences during solar maxima and lower altitudes during solar minima.

In this work, we use the Disturbance Ionosphere indeX (DIX) to study equatorial plasma bubble (EPB) events over the Brazilian equatorial and low latitudes. Our results showed that the DIX detected EPB disturbances in terms of their intensity and occurrence times. Therefore, these responses agreed with the ionosphere behavior before, during, and after the studied EPBs. Finally, these disturbances tended to be higher (lower) in high (low) solar activity.

Using the Digisonde data this paper shows that the small variation in the geomagnetic activity during low solar activity can affect both the parameter of height and the frequency of the intermediate layer (ILs) over the low-latitude Brazilian sector. The most expressive responses of the ILs to geomagnetic activity were observed during the summer when the height of the ILs suffered a significant decrease with the increase of the magnetic activity magnetic in the first hours of the day.

This study showed the ionospheric response over low-latitude regions in Brazil predicted by Martínez-Ledesma et al. (2020) for the solar eclipse event on 14 December 2020. We used a multi-instrumental and modeling analysis to observe the modifications in the E and F regions and the Es layers over Campo Grande and Cachoeira Paulista. The results showed that solar eclipses can cause significant ionosphere modifications even though they only partially reach the Brazilian low-latitude regions.

In the present work, the lunar semidiurnal tide (M₂) was investigated in the equatorial plasma bubble (EPB) zonal drifts over Brazil from 2000 to 2007. On average, the M₂ contributes 5.6 % to the variability of the EPB zonal drifts. A strong seasonal and solar cycle dependency was also observed, the amplitudes of the M₂ being stronger during the summer and high solar activity periods.