Inter-hemispheric asymmetries in the ground magnetic ULF waves response to interplanetary shocks

Interplanetary (IP) shocks drive magnetosphere-ionosphere (MI) current systems that in turn are associated with ground magnetic perturbations. Recent work has shown that IP shock impact angle plays a significant role in controlling the subsequent geomagnetic activity and magnetic perturbations. Despite these numerous efforts, a few questions are still open, such as: How does the IP shock impact the phase and intensity of the ground magnetic perturbations in high latitude regions? Will the hemisphere that the shock strikes first have the most intense ground magnetic response at ULF timescales? Will the hemisphere that the shock strikes first have the first ground magnetic response at ULF timescales? In order to answer these questions, we use data from a chain of Antarctic magnetometers, combined with magnetically conjugate stations on the west coast of Greenland, to investigate the impacts from these inclined and frontal shock conditions modeled by Oliveira and Raeder (2014) and experimentally observed by Oliveira and Raeder (2015). We calculate ULF wave activity in each hemisphere separately. Next, we examine the intensity and the phase differences between the ULF waves in both hemispheres. We order these results according to shock impact angles obtained from a recently published database with over 500 events and discuss how shock impact angles affect north-south hemisphere asymmetries in the ULF waves. A frontal-vs-inclined-shock comparative case study shows that interhemispheric asymmetries of the ground-based observations of ULF waves are strongly related to the IP shocks' impact angles. However, the statistical results suggest that several factors affect the ground magnetic response at ULF timescales, including the IP shock impact angle, local time of the observation, and ionospheric conductivity.