Radar investigations of June solstice F-region irregularities

Abstract:

We present results of two observation campaigns of pre- and post-midnight equatorial F-region irregularities made during two June solstice, when conditions for development of equatorial spread F are believed to be unfavorable. The first campaign was carried out in June/July 2011 when the solar flux index F10.7 was about 95 SFU and used the FCI 30 MHz coherent backscatter radar interferometer located in the magnetic equatorial site of Sao Luis, Brazil. The second campaign was conducted during June/July 2014, when the solar flux was about 130 SFU (NOAA SPWC). The second campaign was used the Measurements of Equatorial and Low-latitude Ionospheric irregularities over Sao Luis, South America (MELISSA) radar interferometer, which was recently developed and replaced the FCI radar in Sao Luis. We will present new measurements made by MELISSA and a comparison of the 2011 and 2014 observations. We found that, despite a small change in solar flux conditions, a drastic change in the occurrence of meter-scale irregularities is observed. We will present and explain the observations, and discuss the underlying ionospheric and electrodynamic conditions based on auxiliary satellite measurements and modeling.