Interhemispheric Asymmetries in the Ground Magnetic Response to Interplanetary Shocks: The Role of Shock Impact Angle

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; for example, highly inclined shocks drive asymmetric MI responses due to interhemispherical asymmetric magnetospheric compressions, while almost head-on shocks drive more symmetric MI responses. However, there are few observations confirming that inclined shocks drive such asymmetries in the high-latitude ground magnetic response. We use data from a chain of Antarctic magnetometers, combined with magnetically conjugate stations on the west coast of Greenland, to test these model predictions (Oliveira & Raeder, 2015, https://doi.org/10.1002/2015JA021147; Oliveira, 2017, https://doi.org/10.1007/s13538-016-0472-x). We calculate the time derivative of the magnetic field (partial derivative B/partial derivative t) in each hemisphere separately. Next, we examine the ratio of Northern to Southern Hemisphere partial derivative B/partial derivative t intensities and the time differences between the maximum. partial derivative B/partial derivative t immediately following the impact of IP shocks. 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 ground magnetic response. We find that the hemisphere the shock strikes first usually has (1) the first response in partial derivative B/partial derivative t and (2) the most intense response in partial derivative B/partial derivative t. Additionally, we show that highly inclined shocks can generate high-latitude ground magnetic responses that differ significantly from predictions based on models that assume symmetric driving conditions.