Coexistence of Longitudinal and Transverse Oscillations in Polar Plumes Observed with Solar Orbiter/Extreme Ultraviolet Imager

Abstract

Magnetohydrodynamic waves play a key role in heating the solar corona and driving the solar wind. Recent observations have shown the presence of slow magnetoacoustic and Alfvénic waves in polar plumes and interplumes. However, a complete understanding of wave dynamics in the polar regions has long been limited by the lack of simultaneous high-resolution observations. In this study, we utilize a high-spatial-resolution (210 km per pixel) and high-cadence (5 s) data set from the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter, acquired on 2021 September 14. Our findings reveal the simultaneous presence of slow magnetoacoustic and Alfvénic waves within the same polar plumes. For the slow magnetoacoustic waves, the amplitudes of the propagating disturbances are 1.4%–3.2% of the background intensity, with periodicities of 9 minutes, and the projected speeds of these disturbances range between 115 and 125 km s−1. The corresponding electron temperatures in plumes range between 0.58 and 0.69 MK. The damping lengths of these propagating disturbances for five plumes are ≈2.4–7.1 Mm. The propagating disturbances are also detected in the fine-scale substructures within the plumes. Alfvénic waves, on the other hand, are detected with average displacement amplitude, periodicity, and velocity amplitude of 165 ± 82 km, 93 ± 39 s, and 12 ± 7 km s−1, respectively. The ranges for the displacement amplitude, period, and velocity amplitude are 50–600 km, 50–250 s, and 3–32 km s−1, respectively. These results mark the first demonstration of the ability of Solar Orbiter/EUI to simultaneously detect both slow magnetoacoustic and Alfvénic wave modes extending up to 20 Mm in polar plumes.