Statistical analysis of the total electron content observed at 23°S in the Brazilian sector

The vertical total electron content (VTEC) time series obtained at Sao Jose dos Campos (23.2 degrees S, 45.9 degrees W), Brazil, were statistically analyzed to study the low latitude ionosphere in the Brazilian sector during the year of 2006 (a period of low solar activity). Statistical analysis showed that Probability Density Functions (PDFs) and kurtosis have an intermittent behavior on small-scales (periods from minutes to one day) and presence of two functions on large-scales (periods from 3 to 30 days). The skewness result suggests the presence of some kind of waves due to the action of tropospheric sources (lower atmospheric origin). Results obtained by wavelet transform show strong oscillations with scale-sizes between 3 and 30 days, possibly associated with the planetary oscillations. According to these statistical and wavelet analyses we conjecture that there exist two important factors regarding the ionospheric effects: one factor is due to turbulent states found in small scales and the other factor consists in a more or less deterministic state provided by planetary waves (3-16 days or full solar rotation (27-28 days)). Further, these strong oscillations were also noted in multifractal analysis. We found a decrease of multifractality degree of the same scale-sizes. (C) 2009 COSPAR. Published by Elsevier Ltd. All rights reserved.