Halpha Doppler shifts in a tornado in the solar corona

TL;DR

This study investigates the Doppler shifts in a solar tornado observed in Halpha and EUV, revealing that the apparent rotation seen in EUV data is not due to actual plasma rotation, but likely caused by other dynamic processes.

Contribution

The paper provides the first detailed Doppler velocity analysis of a solar tornado in Halpha, challenging the interpretation of observed EUV rotation as true plasma rotation.

Findings

Halpha Doppler maps show alternating red and blueshift patterns with 40-60 min quasi-periodicity.

The observed Doppler pattern does not support the rotation of cool plasma inside the tornado.

Halpha velocity data constrains the interpretation of EUV tornado observations.

Abstract

High resolution movies in 193 A from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory SDO show apparent rotation in the leg of a prominence observed during a coordinated campaign. Such structures are commonly referred to as tornadoes. Time-distance intensity diagrams of the AIA data show the existence of oscillations suggesting that the structure is rotating. The aim of this paper is to understand if the cool plasma at chromospheric temperatures inside the tornado is rotating around its central axis. The tornado was also observed in Halpha with a cadence of 30 seconds by the MSDP spectrograph, operating at the Solar Tower in Meudon. The MSDP provides sequences of simultaneous spectra in a 2D field of view from which a cube of Doppler velocity maps is retrieved. The Halpha Doppler maps show a pattern with alternatively blueshifted and redshifted areas of 5 to 10 arcsec wide. Over time the blueshifted areas become redshifted and vice versa, with a quasi-periodicity of 40 to 60 minutes. Weaker amplitude oscillations with periods of 4 to 6 minutes are superimposed onto these large period oscillations. The Doppler pattern observed in Halpha cannot be interpreted as rotation of the cool plasma inside the tornado. The H$\alpha$ velocity observations give strong constraints on the possible interpretations of the AIA tornado