Auroral Oval Boundary Dynamics on the Nature of Geomagnetic Storm

Abstract

During emergency events, we could significantly depend on the stable operation of radio communication, navigation, and radars. The ionosphere, especially its auroral regions, significantly influences radio systems, which is why scientists and engineers create systems to monitor these regions. Using data from the global GNSS network, we analyzed the 10 strongest magnetic storms of solar cycle 24: five coronal mass ejection-driven (CME-driven) and five high-speed stream-driven (HSS-driven) storms. The analysis was based on the calculation of the standard deviation of the total electron content (TEC) derivative (rate of TEC index, ROTI). Under all the storms, the ROTI featured similar dynamics: the average ROTI reaches the highest values during the main phase, and the higher the intensity is, the more intense and equatorward the average ROTI registered. The highest cross-correlations are observed with a lag of 1 h, between the IMF z-component Bz and the magnetic latitude where the highest ROTI values appear. The auroral electrojet (SME index) shows the highest impact on the ROTI dynamics. An increase in the space weather indices (in absolute value) is accompanied by a decrease in the latitude where the maximal ROTI occurs. We found that the peculiarities of a storm affect the ROTI dynamics: all the CME-driven storms feature a high cross-correlation (>0.75) between the IMF z-component Bz and the magnetic latitude where the highest ROTI appears, while the HSS-driven storms feature a lower cross-correlation (<0.75) between them. The difference in duration of similar (by maximal values of geomagnetic indices) HSS- and CME-driven storms could produce differences in the highest ROTI values. Correlations show that compared to HSS-driven storms, CME-driven ones more directly impact the ROTI values and locations of regions with a high ROTI.

Extreme value theory applied to the auroral electrojet indices

“…Consequently, the strength of geomagnetic storms directly correlates to the level of threat posed to ground communication and satellite operations. The auroral electrojet (AE) index serves as a globally quantifiable measurement that represents the current flow of auroral-induced geomagnetic disturbances below and within the auroral oval (Frey, 2007;Edemskiy and Yasyukevich, 2022). Additionally, the AE index, introduced by Davis and Sugiura (1966), correlates with the physical processes of energy release in the magnetotail resulting from the interaction between the solar wind and the magnetosphere (Kauristie et al, 2017).…”

A Physical Explanation for the Formation of Auroras

“…The geomagnetic activity reaches the maximum around the magnetic latitude of 70 degrees [8]. Auroral oval boundary dynamics is associated with geomagnetic storm intensity [9]. When stronger geomagnetic storms occur, auroras extend frequently equator-ward and increase the appearance of space weather activity [10] [11].…”