Concurrent kink and sausage waves in a crescent-shaped structure over a limb prominence

Abstract

A Crescent-shaped prominence Structure (CS) over the solar west limb is studied using Extreme Ultra-Violet (EUV) Imaging Spectrometer/Hinode and Atmospheric Imaging Assembly (AIA)/Solar Dynamics Observatory (SDO). First, the time-varying positions of the top and bottom borders of the CS, along with its central axis, are derived. Time evolutions of the Doppler shifts and line width of Fe XII 195.119 line are studied over the CS borders. Transverse kink oscillations are observed both in the solar-Y direction and in the Doppler shifts over the observers' line of sight (LOS). One explanation could be that the oscillatory direction of the main kink wave build an angle with the observers' LOS. This angle is calculated to be equal to 27° for the CS top border. The main kink amplitude velocity and periods are obtained to be 5.3 $\rm km\, s^{-1}$ and 33.4 min, respectively. The anticorrelation observed between the brightness and thickness of the CS (with -178.1°) suggests the presence of sausage modes with periods of 20.8 min. Based on the AIA imaging, it is suggested that the occurred jets and their afterwards dimming are responsible to trigger the sausage mode. The average electron densities of the CS over the time of the study are obtained to be log($n_\mathrm{ e}$) = 9.3 $\mathrm{ cm}^{-3}$. The Alfvén velocity, magnetic field, and energy flux of the observed fast kink mode over the CS are estimated to be 16.7 $\rm km\, s^{-1}$, 2.79 $\rm G$, and 41.93 $\rm W\,m^{-2}$, respectively. Considering the magnetic flux conservation inside the CS, expanding the CS cross-section causes the magnetic field to decay with the rate of $\rm 4.95 \times 10^{-4} \ G\,s^{-1}$.