Distinguishing Electromagnetic Ion Cyclotron (EMIC) Waves From Other Pc1 Signatures in Satellite Recordings by Means of the Swarm Satellite Constellation

In this study we make use of the closely spaced Swarm A and C spacecraft to determine the main wave parameters of micro-pulsation in the Pc1 range. Generally, the interpretation of wave events in satellite recordings suffers from the spatial/temporal ambiguity of such data. To resolve that problem, we use for the first time in the 0.2-5 Hz apparent frequency range high-resolution magnetic field data from the Swarm A/C spacecraft pair. Particularly suitable for this analysis is the period of Counter Rotating Orbit Phase in 2021. During that period the along-track distance between the spacecraft was varied from 2 to 40 s. Surprisingly many of the wavy signals at middle latitudes were identified as small-scale (order of 10s km) quasi-static field-aligned current (FAC) structures. Some of the events turned out to be medium-scale (100-200 km) waves oscillating at 1 Hz or less. A number of published electromagnetic ion cyclotron (EMIC) waves were checked on their consistency. One characteristic is their long wavelength (similar to 1,000 km). About half of the cases passed the check, the other did not satisfy the spatial homogeneity. The small-scale FAC structures we believe to be driven by atmospheric gravity waves. While the medium-scale waves we prefer to relate to the effects of the ionospheric Alfven resonator. Resolving for the first time the spatial/temporal ambiguity in satellite wave signals within the Pc1 range by the Swarm constellationSmall-scale (10s km) quasi-static current features are frequently detected, also medium-scale (100s km) waves with less than 1 Hz are foundElectromagnetic ion cyclotron waves exhibit long wavelengths (similar to 1,000 km). This has to be verified for their identification