Directly comparing coronal and solar wind elemental fractionation

¹ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Surrey RH5 6NT, UK
e-mail: d.stansby@ucl.ac.uk
² College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22030, USA

Received: 1 May 2020
Accepted: 10 June 2020

Abstract

Context. As the solar wind propagates through the heliosphere, dynamical processes irreversibly erase the signatures of the near–Sun heating and acceleration processes. The elemental fractionation of the solar wind should not change during transit, however, making it an ideal tracer of these processes.

Aims. We aim to verify directly if the solar wind elemental fractionation is reflective of the coronal source region fractionation, both within and across different solar wind source regions.

Methods. A backmapping scheme was used to predict where solar wind measured by the Advanced Composition Explorer (ACE) originated in the corona. The coronal composition measured by the Hinode Extreme ultraviolet Imaging Spectrometer (EIS) at the source regions was then compared with the in situ solar wind composition.

Results. On hourly timescales, there is no apparent correlation between coronal and solar wind composition. In contrast, the distribution of fractionation values within individual source regions is similar in both the corona and solar wind, but distributions between different sources have a significant overlap.

Conclusions. The matching distributions directly verify that elemental composition is conserved as the plasma travels from the corona to the solar wind, further validating it as a tracer of heating and acceleration processes. The overlap of fractionation values between sources means it is not possible to identify solar wind source regions solely by comparing solar wind and coronal composition measurements, but a comparison can be used to verify consistency with predicted spacecraft-corona connections.