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Abstract:
Geomagnetic storms lead to a decrease in the horizontal (H) component of the geomagnetic field at the equator, and we measure the magnitude of this variation with the Magnetic Disturbance index (Dst). This index is an indirect measure of the magnitude axisymmetric ring current (RC).
In this study, we calculate several Dst-index proxies to investigate the RC local time dependence. To do so, we established 4 pairs of observatories distributed in different Local Times: 1) Honolulu - Isla de Pascua (UTC 8.5); 2) San Juan - Fúquene (UTC 4.5); 3) Hermanus - Tamanrasset (UTC +1.5); and 4) Kakioka - Learmonth (UTC +8.5).
Initially, we use a set of the Dst-proxies and compared it to the Dst index during varying geomagnetic activity levels (from Quiet to Severe Storm). The proxies exhibit a strong correlation with the Dst index (>0.8) during active periods (moderate to severe storms), and a more modest correlation (0.5 to 0.7) during quiet time. These proxies can be used to study geomagnetic storms and the data series exhibit the main features observed on the Dst index.
For the 4 local time pairs of observatories, we study 5 events between 2013 and 2014. The results show a clear local time dependence. Geomagnetic storms are more intense at dusk, and weaker at dawn. Geomagnetic storms have a greater impact on the night side. As reported in the literature, we find a measurable asymmetry in the RC during geomagnetic storms.
