Ionospheric Effects of Sudden Stratospheric Warming During Solar Maximum and Minimum Periods: What Do We See from Puerto Rico?

Some of the main factors that contribute to changes in multiple ionospheric parameters are solar flux, geomagnetic activity, seasonal behavior, and coupling with lower atmosphere, which is particularly strong during sudden stratospheric warming events (SSW). Studying the way that these factors induce changes in the ionosphere is important, since these changes can have a negative effect on different types of communication systems. Multiple case studies have demonstrated large variations in ionospheric electron density in association with SSW in the low-latitude ionosphere, in particular near the crests of the equatorial ionization anomaly. However, the latitudinal extend of these variations was not addressed. In this study, we utilize data obtained in Puerto Rico by three instruments - Ramey digisonde, Arecibo Incoherent Scatter Radar (ISR) and GPS receivers to analyze four winter-time periods: two years with major SSW events (2005-2006, 2012-2013) and two years with minor SSW events (2006-2007, 2013-2014). In addition, selected cases represent two winters with low solar activity and two winters with moderate to high solar activity. The study focuses on the location of Arecibo, Puerto Rico (18.34°N, 66.75°W), ~15° to the north of the northern crest of the equatorial ionization anomaly. We report good agreement in ionospheric parameters between all three instruments. To investigate possible association with SSW events, we remove influences of seasonal behavior, solar flux, and geomagnetic activity by building empirical model and subtracting expected variations from the observational data. The analysis of residuals between the data and the model shows that ionospheric disturbances were observed in Puerto Rico for both minor and major SSW events in the ISR, digisonde and GPS Total Electron Content (TEC) data. We report 20-60% variations in NmF2 and TEC due to SSW effects. Large variations are also observed in electron density, electron temperature and plasma velocity during both daytime and nighttime.