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

Abstract

AbstractThe 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 the Defense Meteorological Satellite Program spectrometer data, here we use Swarm vector field magnetometer data to describe the auroral zone 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 [0.1–1 Hz] and high [2.5–5 Hz] 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. Furthermore, based on a comparison analysis between low‐frequency dBOP and auroral electron precipitation occurrence probability, we suggest that both types of distribution offer a more comprehensive understanding of the large‐scale auroral zone when considered concurrently. 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.