Evaluation of Different Methods for Calculating the ROTI index over
Brazilian Sector
Abstract
The ROTI index based on the variation of the TEC is used to detect and
characterize the ionospheric irregularities. In the present work, we
present a comparative study of five different methodologies to ROTI
calculation in order to evaluate the most suitable for the Brazilian
region. This was performed over three GNSS stations at different
latitudes: São Luís (SALU, 2°31′ S, 44°16′ W; dip: -6.60°) that is
located near the dip equator; Cachoeira Paulista (CHPI, 22°40’ S, 44°59’
W; dip: -35.99°) which set close to the southern crest of the EIA at low
latitude); and Santa Maria (SMAR, 29° 41′ S, 53° 48′ W, dip: -43.51°) a
low-to-mid latitude station close to center of the SAMA region. The
period of analysis covered January and December 2015. Our results show
that only one out of the five techniques proposed seems to be
appropriated for ROTI construction in the Brazilian sector. Our results
are supported by comparison of the ROTI with TEC maps obtained over
Brazil, ionograms acquired at Fortaleza (FZA0M), SALU, and CHPI
ionosonde stations, and All-Sky imagers collected at the São João do
Cariri, and CHPI. In addition, we were able to observe the typical
irregularities of the Brazilian ionosphere by using the ROTI which we
have classified as EPB.