Observation of multiple sausage oscillations in cool postflare loop

TL;DR

This study reports the detection of multiple sausage oscillations in a cool postflare solar loop using high-resolution H-alpha observations, providing insights into the loop's physical parameters and dynamics.

Contribution

It presents the first observation of multiple sausage oscillations in a cool postflare loop and estimates key physical parameters through seismology.

Findings

Oscillation periods of ~587 s and ~349 s near the apex and footpoint.

Density scale height estimated at ~17 Mm, indicating non-hydrostatic equilibrium.

Alfvén speed outside the loop is approximately 300-330 km/s.

Abstract

Using simultaneous high spatial (1.3 arc sec) and temporal (5 and 10 s) resolution H-alpha observations from the 15 cm Solar Tower Telescope at ARIES, we study the oscillations in the relative intensity to explore the possibility of sausage oscillations in the chromospheric cool postflare loop. We use standard wavelet tool, and find the oscillation period of ~ 587 s near the loop apex, and ~ 349 s near the footpoint. We suggest that the oscillations represent the fundamental and the first harmonics of fast sausage waves in the cool postflare loop. Based on the period ratio P1/P2 ~ 1.68, we estimate the density scale height in the loop as ~ 17 Mm. This value is much higher than the equilibrium scale height corresponding to H-alpha temperature, which probably indicates that the cool postflare loop is not in hydrostatic equilibrium. Seismologically estimated Alfv\'en speed outside the loop is ~ 300-330 km/s. The observation of multiple oscillations may play a crucial role in understanding the dynamics of lower solar atmosphere, complementing such oscillations already reported in the upper solar atmosphere (e.g., hot flaring loops).