Solar Cycle Variations in the Elemental Abundance of Helium and Fractionation of Iron in the Fast Solar Wind - Indicators of an Evolving Energetic Release of Mass from the Lower Solar Atmosphere

TL;DR

This study links solar minimum changes in the lower solar atmosphere to variations in the elemental composition of the fast solar wind, revealing evolving mass release processes over multiple solar cycles.

Contribution

It demonstrates a correlation between the emission length scale in the lower transition region and in situ measurements of solar wind composition during recent solar minimums, highlighting changes in solar wind source processes.

Findings

Decreased Helium abundance in fast solar wind during recent minimum.

Iron fractionation approaching photospheric values.

Long-term decay of Helium input into the heliosphere over solar cycles.

Abstract

We present and discuss the strong correspondence between evolution of the emission length scale in the lower transition region and in situ measurements of the fast solar wind composition during this most recent solar minimum. We combine recent analyses demonstrating the variance in the (supergranular) network emission length scale measured by SOHO (and STEREO) with that of the Helium abundance (from WIND) and the degree of Iron fractionation in the solar wind (from the ACE and Ulysses). The net picture developing is one where a decrease in the Helium abundance and the degree of Iron fractionation (approaching values expected of the photosphere) in the fast wind indicate a significant change in the process loading material into the fast solar wind during the recent solar minimum. This result is compounded by a study of the Helium abundance during the space age using the NASA OMNI database which shows a slowly decaying amount of Helium being driven into the heliosphere over the course of the several solar cycles.