Statistical investigation of the Auroral oval boundaries using IMAGE WIC

Abstract

The aurora is a visible effect of Earth’s coupling to the Sun, it appears in an approximate oval form over the magnetic poles. The aurora moves to lower latitudes as the geomagnetic activity increases, and the poleward boundary of the aurora marks the open-closed field line boundary (OCB). The location of the OCB is important as it can help determine reconnection rates and predict global-scale space weather. In this thesis I use a dataset created by Ohma et al. (2024a) to investigate how variations in the auroral oval equatorial (EB) and poleward (PB) boundaries are described for different solar wind and magnetic indices. In addition, I conduct a superposed epoch analysis to investigate the boundaries movement during substorms. I focus on the magnetic indices P, open flux content of the polar cap, dP/dt, the rate of change in open flux, A, the closed magnetic flux in the auroral oval, and dA/dt the rate of change in closed flux. In addition Milan et al. (2012)’s solar wind-magnetosphere coupling function ΦD was used as a proxy for dayside reconnection. I find a surprisingly low correlation between P, dP/dt, and ΦD for small values of the nightside reconnection proxy AL and its rate of change dAL/dt. I show that for the region between 0230 and 0500 MLT, the average PB does not move equatorward as Kp increases. I demonstrate how the so-called HeppnerMaynard-Boundary (HMB) and EB are well correlated with a maximum correlation value of 0.67. I find an increased bulge at the onset location during winter, and surprisingly I find the PC to be thinner for all MLTs except between 2100-2300 during the summer. We find that the PB is moderately correlated with ΦD, the EB could be used to find the HMB, and A and P are well explained on average by ΦD during substorms. Characterizing large-scale variations in the auroral oval is crucial for comprehending global geospace dynamics. These findings not only enhance our understanding but also illustrate the potential of future missions with auroral imaging capabilities to further advance this field.