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Geomagnetic Ultra Low Frequency (ULF) are terrestrial manifestations of the propagation of very low frequency magnetic fluid waves in the magnetosphere, and it is critical to develop near real-time space weather products to monitor these geomagnetic disturbances. A wavelet-based index is described in this paper and applied to study geomagnetic ULF pulsations observed in Antarctica and their magnetically conjugate locations in West Greenland. Results showed that (1) the index is effective for identification of pulsation events in the Pc4–Pc5 frequency range, including transient events, and measures important characteristics of ULF pulsations in both the temporal and frequency domains. (2) Comparison between conjugate locations reveals the similarities and differences between ULF pulsations in northern and southern hemispheres during solstice conditions, when the largest asymmetries are expected. Results also showed that the geomagnetic pulsations at conjugate locations respond differently according to the Interplanetary Magnetic Field condition, magnetic field topology, magnetic latitude of the observation, and other conditions. The actual magnetospheric and ionospheric configurations and driving conditions in the case need to be further studied. 

Abstract A chain of magnetometers has been placed in Antarctica for comparisons with magnetic field measurements taken in the Northern Hemisphere. The locations were chosen to be on magnetic field lines that connect to magnetometers on the western coast of Greenland, despite the difficulty of reaching and working at such remote locations. We report on some basic comparisons of the similarities and differences in the conjugate measurements. Our results presented here confirm that the conjugate sites do have very similar (symmetric) magnetic perturbations in a handful of cases, as expected. Sign reversals are required for two components in order to obtain this agreement, which is not commonly known. More frequently, a strongYcomponent of the Interplanetary Magnetic Field (IMF) breaks the symmetry, as well as the unequal conductivities in the opposite hemispheres, as shown in two examples. In one event the IMFYcomponent reversed signs twice within 2 hours, while the magnetometer chains were approaching local noon. This switch provided an opportunity to observe the effects at the conjugate locations and to measure time lags. It was found that the magnetic fields at the most poleward sites started to respond to the sudden IMF reversals 20 min after the IMF reaches the bow shock, a measure of the time it takes for the electromagnetic signal to travel to the magnetopause, and then along magnetic field lines to the polar ionospheres. An additional 9–14 min is required for the magnetic perturbations to complete their transition. 

Abstract The horizontal currents in the high‐latitude ionosphere are the primary driver of the magnetic field perturbations that are observed at the surface of the Earth. These currents and their ground effects are an important aspect of the magnetosphere‐ionosphere coupling process. This paper discusses the method of inversion that uses spherical harmonic potential function, in which magnetic field measurements on the ground can be used to derive maps of the “ionospheric equivalent currents,” a mathematical representation of the horizontal currents flowing on a thin shell. It is shown that the use of both internal telluric and external current sources is required when fitting the spherical harmonic series; otherwise, the ionospheric currents will be overestimated. Furthermore, the inversion needs to compensate for magnetic effects of the magnetospheric ring current; otherwise, this current is projected onto the ionosphere. The amplification of the surface horizontal magnetic field and the suppression of the vertical magnetic field are demonstrated. The equivalent currents may be useful for estimating the ionospheric conductivity values. Additionally, these currents can be compared with the results from simulation models as a means of validation. 

Abstract 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 ( ) in each hemisphere separately. Next, we examine the ratio of Northern to Southern Hemisphere intensities and the time differences between the maximum 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 and (2) the most intense response in . 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.