Nelson Jorge Schuch

Solar flare detection sensitivity using the South America VLF Network (SAVNET)

[1]xa0We present recent observations of Sudden Phase Anomalies due to subionospheric propagation anomalies produced by solar X-ray flares. We use the new South America VLF Network (SAVNET) to study 471 ionospheric events produced by solar flares during the period May 2006 to July 2009 which corresponds to the present minimum of solar activity. For this activity level, we find that 100% of the solar flares with a X-ray peak flux above 5 × 10−7 W/m2 in the 0.1–0.8 nm wavelength range produce a significant ionospheric disturbance, while the minimum X-ray flux needed to do so is about 2.7 × 10−7 W/m2. We find that this latter minimum threshold is dependent on the solar cycle, increasing when the Sun is more active, thus confirming that the low ionosphere is more sensitive during periods of low solar activity. Also, our findings are in agreement with the idea that the ionospheric D-region is formed and maintained by the solar Lyman-α radiation outside solar flare periods.

Wave characteristics of geomagnetic pulsations across the dip equator

In order to clarify the wave characteristics of Pi2 and Pc 4–5 magnetic pulsations around the dip equator, we analyzed magnetic data from the latitudinally dense magnetometer array in Brazil. We found that the phase difference between Pi2 pulsations observed at globally separated low-latitude stations is small, whereas Pi2 pulsations observed within the dayside dip equator region of ±2° latitude show phase lags of about 30° ∼ 50° behind those in the off-dip equator region. Pc 4–5 magnetic pulsations at the dip equator also show the same phase character. Pi2 amplitudes are enhanced in the equatorial region, where the phase lags of pulsations must be associated with the enhancement of ionospheric conductivity. The equatorial phase lags can be explained by invoking the induction effect of the equatorial enhanced ionospheric current above the good conductor Earth.

MULTITAPER SPECTRAL ANALYSIS OF COSMIC RAYS S ˜ AO MARTINHO DA SERRA'S MUON TELESCOPE AND NEWARK'S NEUTRON MONITOR DATA

In this work we present an analysis on the correction efficiency of atmospheric effects on cosmic ray S ˜ ao Martinho da Serras muon telescope and Newarks neutron monitor data. We use a Multitaper spectral analysis of cosmic rays time series to show the main periodicities present in the corrected and uncorrected data for the atmospheric effects. This kind of correction is very important when intends to study cosmic rays variations of extra-terrestrial origin.