Doppler shift oscillations in solar spicules

TL;DR

This study analyzes Doppler shift oscillations in solar spicules using Fourier analysis to detect wave phenomena, estimate magnetic field strength, and suggest granulation as a wave source, contributing to spicule seismology.

Contribution

It provides the first detailed analysis of oscillations in spicules at multiple heights and estimates magnetic field strength using wave observations.

Findings

Detected oscillations with periods of 20-55 and 75-110 seconds.

Identified 3-minute oscillations at observed heights.

Estimated magnetic field strength in spicules as 12-15 G.

Abstract

Consecutive height series of Ha spectra in solar limb spicules taken on the 53 cm coronagraph of Abastumani Astrophysical Observatory at the heights of 3800-8700 km above the photosphere have been analyzed. The aim is to observe oscillatory phenomena in spicules and consequently to trace wave propagations through the chromosphere. The Discrete Fourier Transform analysis of Ha Doppler shift time series constructed from the observed spectra at each height is used. Doppler velocities of solar limb spicules show oscillations with periods of 20-55 and 75-110 s. There is also the clear evidence of 3-min oscillations at the observed heights. The oscillations can be caused by wave propagations in thin magnetic flux tubes anchored in the photosphere. We suggest the granulation as a possible source for the wave excitation. Observed waves can be used as a tool for spicule seismology; the magnetic field strength in spicules at the height of about 6000 km above the photosphere is estimated as 12-15 G.