The Response of Ionospheric Currents to the Sudden Stratospheric Warming Events Over Africa

English Abstract:

The 2009 Sudden Stratospheric Warming (SSW) event is the strongest and the most elongated recorded SSW event. Coincidentally, and rather remarkably, at that same year, the Sun exhibited its solar minimum that resulted to a reduced forcing of the ionosphere from solar ionizing flux, solar wind conditions and geomagnetic activities. As a consequence, these events reminded space physicist researchers how significantly an SSW event can affect the ionosphere and its various parameters, and research in this direction has increased over the last decade, except for the African sector. Motivated by these events and the observed research gap, we began to investigate systematically the response of ionospheric current (S_qH) to the 2009 SSW events over Africa. Nine (9) observatory stations, covering both the northern hemisphere and the southern hemisphere, distributed along 4⁰E and 40⁰E longitude are used for this study. The S_qH variability prior to the SSW, during the ascending, peak and descending phase of the SSW was investigated. From this study, our unique results show that during the non – SSW days, S_qH shows positive peak value of 10nT to 93nT between 0900 & 1500 LT (local time). Positive peak S_qH values of 12nT to 61nT (between 1000 & 1400 LT), 7nT to 51nT (between 0700 & 1400 LT), and 11nT to 98nT(between 0600&1600 LT) was observed during the ascending, peak and descending phase respectively. Also, negative peak values of -19nT(between 1700 & 1800 LT) and –0.4nT to –59nT (between 1500 & 2000 LT) was noticed during the peak and descending phase respectively. A significantly reduced magnitude of S_qH with a value of 57nT was found at Addis Ababa (AAB) during ascending period of SSW. Interestingly, during the SSW peak period, S_qH magnitude around AAB was observed to further deplete such that its magnitude around noon period was 51nT . This depletion of S_qH magnitude during the SSW peak period was more intense in the southern hemisphere compare to northern hemisphere. S_qH maximum value of 98nT was observed at Addis Ababa (AAB) near local noon, with a minimum value of -58nT at the same station around 1600 LT during the descending phase. Our investigations carried out on SSW variability reveal that S_qH exhibits counter – electrojet and longitudinal difference at the African dip – equator during these events.