On developing a new ionospheric plasma index for the Brazilian equatorial F region irregularities

Abstract. F region vertical drifts ( V z ) are the result of the interaction between the ionospheric plasma with the zonal electric field and the Earth's magnetic field. Abrupt variations in V z are strongly associated with the occurrence of plasma irregularities (spread-F) during the nighttime periods. These irregularities are manifestations of the space weather in the ionosphere environment without necessarily require a solar burst. In this context, the Brazilian Space Weather Study and Monitoring Program (Embrace) of the National Institute for Space Research (INPE) has been developing different indexes to analyze these ionospheric irregularities in the Brazilian sector. Therefore, the main purpose of this work was to produce a new ionospheric scale based on the analysis of the ionospheric plasma drift velocity, named AV. It is based in the maximum value of V z ( V zp ), which in turn is calculated through its relationship with the virtual height parameter, h ’F, measured by the Digisonde Portable Sounder (DPS-4D) installed in Sao Luis (2° S, 44° O, dip: −2,3°). This index quantifies the time relation between the V z peak and the irregularity observed in the ionogramas. Thus, in this study, we analyzed 8 years of data, between 2009 and 2015, divided by season in order to construct a standardized scale. The results show there is a delay of at least 15 minutes between V zp observation and the irregularity occurrence. Finally, we believe that this proposed index allow evaluating the impacts of ionospheric phenomena in the Space Weather environment recently.