The aurora often appears as an approximately oval shape surrounding the magnetic poles, and is a visible manifestation of the intricate coupling between the Earth’s upper atmosphere and the near-Earth space environment. While the average size of the auroral oval increases with geomagnetic activity, the instantaneous shape and size of the aurora is highly dynamic. The identification of auroral boundaries holds significant value in space physics, as it serves to define and differentiate regions within the magnetosphere connected to the aurora by magnetic field lines. In this work, we demonstrate a method to detect and model the poleward and equatorward boundaries in global UV images. Our methodology enables analysis of the spatiotemporal variation in auroral boundaries from 2.5 years of UV imagery from the IMAGE satellite. The resulting dataset reveals a root mean square boundary normal velocity of 149 m/s for the poleward boundary and 96 m/s for the equatorward boundary and the velocities are shown to be stronger on the nightside than on the dayside. Interestingly, our findings demonstrate an absence of correlation between the amount of open magnetic flux and the amount of flux enclosed within the auroral oval. Furthermore, we highlight the inadequacy of a simplistic generalization of the expanding-contracting polar cap paradigm in explaining temporal variations in the auroral oval area, underscoring the imperative for an enhanced understanding of equatorward boundary fluctuations.

The boundaries of the auroral oval and auroral electrojets are an important source of information for understanding the coupling between the solar wind and the near-earth plasma environment. Of these two types of boundaries the auroral electrojet boundaries have received comparatively little attention, and even less attention has been given to the connection between the two. Here we introduce a technique for estimating the electrojet boundaries, and other properties such as total current and peak current, from 1-D latitudinal profiles of the eastward component of equivalent current sheet density. We apply this technique to a preexisting database of such currents along the 105◦ magnetic meridian producing a total of eleven years of 1 minute resolution electrojet boundaries during the period 2000–2020. Using statistics and conjunction events we compare our electrojet boundary dataset with an existing electrojet boundary dataset, based on Swarm satellite measurements, and auroral oval proxies based on particle precipitation and field aligned currents. This allows us to validate our dataset and investigate the feasibility of an auroral oval proxy based on electrojet boundaries. Through this investigation we find the proton precipitation auroral oval is a closer match with the electrojet boundaries. However, the bimodal nature of the electrojet boundaries as we approach the noon and midnight discontinuities makes an average electrojet oval poorly defined. With this and the direct comparisons differing from the statistics, defining the proton auroral oval from electrojet boundaries across all local and universal times is challenging.

The exchange of kinetic and electromagnetic energy by precipitation and/or outflow, and through field-aligned currents are two aspects of the ionosphere-magnetosphere coupling. A thorough investigation of these processes is required to better understand magnetospheric dynamics. Building on our previous study using DMSP spectrometer data, here we use Swarm vector field magnetometer data to describe the auroral oval morphology in terms of east-west magnetic field perturbations. We define a threshold for detecting magnetic fluctuations based on the power spectral density of ΔBEW and derive the disturbed magnetic field occurrence probability (dBOP) at low [0.1–1Hz] and high [2.5–5Hz] frequencies. High-frequency distributions of dBOP reveal a dayside-nightside asymmetry, whereas low-frequency dBOP exhibits a persistent morphological asymmetry between the dawn-to-noon and the dusk-to-midnight sectors, peaking at dawn. Notably, weak solar wind conditions are associated with an increase in the dBOP asymmetric patterns. At low frequency in particular, while the dBOP seems to be primarily constant at dawn, the dusk dBOP decreases during quiet times, inducing a relatively larger dawn-dusk asymmetry in such conditions. We find that the dBOP distributions at low frequencies exhibit features similar to those present in distributions of the auroral electron precipitation occurrence probability, suggesting that the low-frequency dBOP constitutes a reasonable proxy for the large-scale auroral oval. Our interpretation is that the dBOP at low frequencies reflects a quasi-steady state circulation of energy, while the high-frequency dBOP reflects the regions of rapid changes in the magnetosphere. The dBOP is therefore a crucial source of information regarding the magnetosphere-ionosphere coupling.