For the first time, the climatology of intermediate descending layers (~150 km) over Brazilian equatorial and low-latitude regions during the extreme solar minimum period of 2009 was investigated. The results are interesting and innovative. For this analysis we used data of height and top frequency of intermediate layers collected from a digisonde located at São Luis and Cachoreira Paulista.

This study concerns postmidnight ionospheric irregularities observed during low solar activity conditions. We analyze data from digisondes and optical imaging systems located in an equatorial region over Brazil. The results show that they occur under unfavorable and unexpected conditions. This work can be useful for space weather forecasting during low solar activity.

We present new results on the behavior of sporadic E layers (Es layers) using GPS (global positioning system) radio occultation (RO) measurements obtained from the FORMOSAT-3/COSMIC satellites and digisonde data over Cachoeira Paulista, a low-latitude station in Brazil.

This work presents an analysis of the scintillation onset over the southern Brazil based on data from two solar maximum periods and simulation of the ionospheric conditions before the scintillation onset. The results shows some patterns which may help to prevent several satellite-based technological applications suffering disruptions due to scintillation issues.

Global coverage measurements made by satellites have provided observational studies which have shown the presence of four peaks in global longitudinal structures from global local time observations of equatorial ionization anomalies. The structures seen in the ionosphere are related to the diurnal non-migrating wave that comes from the troposphere and can be noticed in periods of low and high solar activity in the low-latitude ionosphere regions, mainly at altitudes from ~ 250 km up to ~ 800 km.

The relationship between the tropospheric convection and the ionospheric phenomenology have been investigated in recent decades. In this work a relation between the lightning strike activity and the characteristics of the equatorial spread-F events is analyzed over the Brazilian region, and the results seem to support the hypothesis of some indirect interrelationship between both distinct phenomena.

We have analyzed the low-latitude ionospheric responses to solar flares. In particular we show for the first time that 5 to 8 min of time delay is present in the peak effect in the EEJ, with respect that of S_q current outside the magnetic equator, in response to the flare radiation enhancement. We propose that the flare induced enhancement in neutral wind occurring with a time delay could be responsible for a delayed zonal electric field disturbance driving the EEJ.

This paper analyzes the influence of the recent deep and prolonged solar minimum on the daytime zonal and vertical plasma drift velocities during quiet time over Jicamarca, Peru. Our results show that an anomalously low zonal wind was mainly responsible for the observed anomalous behavior in the zonal drift followed by a decrease in the E-region conductivity and the dynamo electric field during 2008.

In this work the response of the Brazilian equatorial ionosphere is studied during three HILDCAA events that occurred in the year of 2006 using the digisonde data. Geomagnetic indices and interplanetary parameters were used to calculate a cross-correlation coefficient between the E_y and the hmF2. The results showed that the pumping action of particle precipitation into the auroral zone has moderately modified the equatorial hmF2, being more sensitive during PRE time.

Periodic waves have been observed over São João do Cariri during almost one solar cycle. Similarities between the characteristics of these events with observations at other places around the world were noted, primarily the spectral parameters. Most observed waves have appeared during magnetically quiet nights, and the occurrence of those waves followed the solar activity. Due to their characteristics, most of them must have had different generation mechanisms from the Perkins instability.