Active Region Contributions to the Solar Wind over Multiple Solar Cycles

Abstract

Both coronal holes and active regions are source regions of the solar wind. The distribution of these coronal structures across both space and time is well known, but it is unclear how much each source contributes to the solar wind. In this study we use photospheric magnetic field maps observed over the past four solar cycles to estimate what fraction of magnetic open solar flux is rooted in active regions, a proxy for the fraction of all solar wind originating in active regions. We find that the fractional contribution of active regions to the solar wind varies between 30% to 80% at any one time during solar maximum and is negligible at solar minimum, showing a strong correlation with sunspot number. While active regions are typically confined to latitudes ±30∘ in the corona, the solar wind they produce can reach latitudes up to ±60∘. Their fractional contribution to the solar wind also correlates with coronal mass ejection rate, and is highly variable, changing by ±20% on monthly timescales within individual solar maxima. We speculate that these variations could be driven by coronal mass ejections causing reconfigurations of the coronal magnetic field on sub-monthly timescales.

COCONUT, a Novel Fast-converging MHD Model for Solar Corona Simulations: I. Benchmarking and Optimization of Polytropic Solutions

“…The input magnetogram is preprocessed by a projection on spherical harmonics and a selection of a maximum frequency for the reconstruction (noted as ℓ max and fixed to 15 in this case), which is equivalent to a smoothing of the map to remove the small intense structures. These structures are indeed numerically more challenging, while their contribution to the overall structure of the wind at 0.1 au is not clear: for the velocities, they can have a strong impact on the distribution between slow and fast wind (but this is not very relevant for a polytropic wind); for the magnetic field, the dipolar mode is going to become more and more dominant farther away from the star, thus reducing the impact of small-scale magnetic structures (Samara et al 2021;Stansby et al 2021).…”

Stirring the base of the solar wind: On heat transfer and vortex formation

“…In each of these configurations, energy is channelled from the convection into the low-corona. Coronal holes are the dominant source of the solar wind in the Heliosphere (Cranmer et al 2017;Stansby et al 2021), typically producing the fast solar wind (McComas et al 2008;Ebert et al 2009;Macneil et al 2020a;Wang 2020). The magnetic field configuration of a coronal hole is relatively simple, compared with the quiet sun and active regions, given that the field is principally open to the solar wind (Lowder et al 2017;Hofmeister et al 2019).…”

COCONUT, a novel fast-converging MHD model for solar corona simulations: I. Benchmarking and optimization of polytropic solutions

“…The input magnetogram is pre-processed by a projection on spherical harmonics and a selection of a maximum frequency for the reconstruction (noted as max and fixed to 15 in this case), which is equivalent to a smoothing of the map to remove the small intense structures. These structures are indeed numerically more challenging, while their contribution to the overall structure of the wind at 0.1 AU is not clear: for the velocities, they can have a strong impact on the distribution between slow and fast wind (but this is not very relevant for a polytropic wind); for the magnetic field, the dipolar mode is going to become more and more dominant further away from the star, thus reducing the impact of small scale magnetic structures (Samara, E. et al 2021;Stansby et al 2021).…”