Search for Alfven waves in a bright network element observed in H-alpha

Koza, J.¹, Sutterlin, P.², Gömöry, P.¹, Rybak, J.¹, Kucera, A.¹

¹ Astronomical Institute of the Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovakia
² Institute for Solar Physics, The Royal Swedish Academy of Sciences, Alba Nova University Center, 106 91 Stockholm, Sweden

Abstract:
Alfven waves are considered as potential transporters of energy heating the solar corona. We seek spectroscopic signatures of the Alfven waves in the chromosphere occupied by a bright network element, investigating temporal variations of the spectral width, intensity, Dopplershift, and the asymmetry of the core of the H-alpha spectral line observed by the tunable Lyot filter installed on the Dutch Open Telescope. The spectral characteristics are derived through the fitting of five intensity samples, separated from each other by 0.35 A, by a 4th-order polynomial. The bright network element displays the most pronounced variations of the Dopplershift varying from 0 to 4 km/s about the average of 1.5 km/s. This fact implies a persistent redshift of the H-alpha core with a redward asymmetry of about 0.5 km/s, suggesting an inverse C bisector. The variations of the core intensity up to plus/minus 10% and the core width up to plus/minus 5% about the respective averages are much less pronounced, but still detectable. The core intensity variations lag behind the Dopplershift variations about 2.1 min. The H-alpha core width tends to correlate with the Dopplershift and anticorrelate with the asymmetry, suggesting that more redshifted H-alpha profiles are wider and the broadening of the H-alpha core is accompanied with a change of the core asymmetry from redward to blueward. We also found a striking anticorrelation between the core asymmetry and the Dopplershift, suggesting a change of the core asymmetry from redward to blueward with an increasing redshift of the H-alpha core. The data and the applied analysis do not show meaningful tracks of Alfven waves in the selected network element.