Stereoscopic measurements of coronal Doppler velocities^⋆

¹ Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland
e-mail: elena.podladchikova@pmodwrc.ch
² ETH-Zürich, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
³ Instituto de Astronomia y Fisica del Espacio, IAFE, UBA-CONICET, Ciudad Universitaria, CC. 67, 1428 Buenos Aires, Argentina
⁴ Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
⁵ Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan-3-Av. Circulaire, 1180 Brussels, Belgium
⁶ Institute of Geodynamics of the Romanian Academy, 19-21 Jean-Louis Calderon, 020032 Bucharest, Romania

Received: 30 January 2021
Accepted: 26 July 2021

Abstract

Context. The Solar Orbiter mission, with an orbit outside the Sun-Earth line and leaving the ecliptic plane, opens up opportunities for the combined analysis of measurements obtained by solar imagers and spectrometers. For the first time different space spectrometers will be located at wide angles to each other, allowing three-dimensional (3D) spectroscopy of the solar atmosphere.

Aims. The aim of this work is to prepare a methodology to facilitate the reconstruction of 3D vector velocities from two stereoscopic line of sight (LOS) Doppler velocity measurements using the Spectral Imaging of the Coronal Environment (SPICE) on board the Solar Orbiter and the near-Earth spectrometers, while widely separated in space.

Methods. We developed the methodology using the libraries designed earlier for the STEREO mission, but applied to spectroscopic data from the Hinode mission and the Solar Dynamics Observatory. We used well-known methods of static and dynamic solar rotation stereoscopy and the methods of extreme ultraviolet (EUV) stereoscopic triangulation for optically thin coronal EUV plasma emissions. We developed new algorithms using analytical geometry in space to determine the 3D velocity in coronal loops.

Results. We demonstrate our approach with the reconstruction of 3D velocity vectors in plasma flows along ‘open’ and ‘closed’ magnetic loops. This technique will be applied to an actual situation of two spacecraft at different separations with spectrometers on board during the Solar Orbiter nominal phase: SPICE versus the Interface Region Imaging Spectrograph (IRIS) and Hinode imaging spectrometer. We summarise how these observations can be coordinated.