Chromospheric evaporation as the driver of helium enrichment in active region solar wind: A case study

¹ Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, 180 Wenhua Xilu Weihai 264209 Shandong, China
² Korea Astronomy and Space Science Institute 34055 Daejeon, Republic of Korea
³ Max Planck Institute for Solar system Research Justus-von-Liebig-Weg 3 D-37077 Gottingen, Germany
⁴ Space Research and Technology Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Bl. 1 1113 Sofia, Bulgaria

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Received: 27 May 2025
Accepted: 19 December 2025

Abstract

Context. The physical mechanisms of helium abundance (A_He) depletion in the corona and solar wind are closely linked to coronal heating, solar wind origin, and acceleration processes. The relationships between the A_He in the solar wind and the properties and activity of the source regions are crucial for understanding the depletion of A_He.

Aims. We aim to investigate the impact of active region (AR) activity and properties on the A_He in the solar wind.

Methods. First, we established the link between carefully selected ARs and the solar wind. Then, the AR chromospheric activity was quantitatively investigated using observations from the Atmospheric Imaging Assembly and Helioseismic Magnetic Imager on board the Solar Dynamics Observatory. The AR temperatures were derived with the differential emission measure method. We also statistically analyzed the A_He in the solar wind with higher and lower charge states during solar cycles 23 and 24. The parameters of solar wind were measured by the instruments on board ACE and Wind.

Results. We find that an AR with greater chromospheric activity has higher A_He in its associated solar wind. The statistical analysis shows that the median A_He in solar wind with higher charge states is higher than A_He in solar wind with lower charge states.

Conclusions. We conclude that chromospheric activity, primarily chromospheric evaporation processes, is possibly the main heating and transportation mechanism leading to a higher A_He in the corona and solar wind. This could also reasonably explain the variation in A_He in AR solar wind during different solar activity phases and the higher A_He in AR solar wind compared to quiet Sun solar wind.