Statistical Temporal Variations in the Auroral Electrojet Estimated With Ground Magnetometers in Fennoscandia

Abstract

The link between the Sun and geomagnetic field disturbances has been reported for a long time. In 1852 Sabine identified a link between the number of sunspots, which is an indicator of solar activity, and geomagnetic field disturbances. He found that during a minimum in the sunspot number we experience a reduction in geomagnetic field disturbances (Cliver & Cliver, 1994). Historical reports have shown that for centuries large scale features on the photosphere have coincided with observations of significant, intense geomagnetic activity in the form of low latitude aurora (Schove, 1983), however the mechanisms behind this were not understood. With the arrival of work by Chapman and Birkeland in the late 19th and early 20th century, the description of the Earth's magnetosphere immersed within the solar wind came into focus. Birkeland's early work introduced a current system, which bears his name, flowing in and out of the polar ionosphere. Despite his initial theories involving a stream of high velocity electrons being emitted from the Sun, he moved to the realization of a neutral solar wind made up of both electrons and positively charged ions (Birkeland, 1908;Chapman & Ferraro, 1931). Although a different current system and theory outlined by Chapman prevailed for some time, with the arrival of space based magnetometers Birkeland's theory proved fruitful as it explained the magnetic field perturbations observed (Zmuda et al., 1966). Chapman and Ferraro's work transformed the field of space physics when they described how magnetic storms are manifested through introduction of the magnetosphere and how it interacts with the solar wind (Chapman & Ferraro, 1931;Siscoe, 2001).

The Ionospheric Leg of the Substorm Current Wedge: Combining Iridium and Ground Magnetometers

“…In prior studies, Walker et al. (2023); Laundal et al. (2021), regularized least‐squares has been used to guide the solution to a more physical result using prior information such as the expected structure.…”

“…As discussed by Walker et al. (2023), the choice of grid in a SECS‐based approach is important. As we want to resolve the DF and CF currents in a similar manner we use the same grid for both the DF and CF SECS.…”

“…Following previous studies such as Walker et al. (2023) and Laundal et al. (2021), we use a cubed sphere grid (Ronchi et al., 1996; Sadourny, 1972).…”

“…As we want to resolve the DF and CF currents in a similar manner we use the same grid for both the DF and CF SECS. Following previous studies such as Walker et al (2023) and Laundal et al (2021), we use a cubed sphere grid (Ronchi et al, 1996;Sadourny, 1972). Our grid, shown in Figure 1, is centered at 258°geographic longitude (glon) and 61°g eographic latitude (glat) with an average grid spacing of 100 km, and orientated approximately along magnetic meridians.…”

Occurrence Probability of Magnetic Field Disturbances Measured With Swarm: Mapping the Dynamic Magnetosphere‐Ionosphere Coupling

“…This is an alternative to deriving the auroral boundaries directly, which can be ambiguous as it has been shown that the relation between optical observations, ground and space magnetic field measurements, FACs, etc. is complex (Walker et al., 2023). Further, when derived from Sun‐synchronous satellite observations, modeled boundaries are subject to a local time bias that is bypassed when looking at occurrence probability instead (Decotte et al., 2023).…”