Sources of the Solar Wind

Understanding where the solar wind is born

The solar wind originates from different regions on the Sun, each with distinct magnetic topologies. By combining helium abundance and cross helicity measurements, we can trace in situ observations back to their solar source regions.

Helium and wave properties are set at different heights above the Sun

A schematic shows the Sun on the left with its golden photosphere, a green chromosphere, and a cyan transition region above it. Orange loops rooted in the surface represent closed magnetic field lines. Red lines extending outward into space represent open magnetic fields with switchback-like undulations. A purple dashed boundary labeled 'Sonic Surface r_c' separates the lower atmosphere from a lighter purple region, and a second purple dashed boundary farther out marks the Alfven surface r_A. Blue arrows grow larger with distance from the Sun, indicating the solar wind accelerating as it propagates outward.

magnetic_topologysource_regionschromospheretransition_regionsonic_surfaceAlfven_surfacecross_helicityhelium_abundanceopen_fieldclosed_fieldtransition regionsonic surfaceAlfvén surfacehelium ionizationcross helicitymagnetic topologyopen fieldclosed field

Related Figures

A filled contour map shows mean solar wind speed (color scale 300-540 km/s) as a function of wave activity (horizontal axis, 0-1) and helium abundance (vertical axis, 0-10%).

Mean speed in the helium-wave plane reveals two source populations

Two distinct populations emerge in the combined helium-wave activity space.

Quantitative data underlying the classification cartoon

A cartoon diagram divides the wave activity (horizontal axis, 0-1) versus helium abundance (vertical axis, 0-10%) plane into four labeled regions using black contour boundaries.

A new classification maps solar wind to its magnetic source

This classification scheme distills the quantitative contour analysis into a practical map of solar wind source regions.

Shows the operational classification scheme derived from the physics in Figure 2

This contour plot shows how the normalized cross helicity, a measure of Alfvenic wave activity (vertical axis), varies with solar wind speed (horizontal axis).

Alfvenic wave activity concentrates in faster wind

The solar wind becomes increasingly Alfvenic as speed rises.

Establishes the baseline relationship between Alfvenic wave activity and speed, showing that fast wind from continuously open sources is wave-rich while slow wind spans all wave levels, motivating the need for multi-parameter source classification

Source

Cross Helicity and the Helium Abundance as an In Situ Metric of Solar Wind Acceleration

The Astrophysical Journal Letters (2025)

View Paper