
Key Takeaways:
- The Sun's radiative zone, extending to approximately two-thirds of its radius, drives its rotation and heat transfer via photons and particles, fueling convection in the overlying region.
- The interaction between convection and rotation in the Sun's upper third generates strong magnetic fields, which manifest as sunspots and prominences on the solar surface.
- High-speed plasma jets, originating in or near the chromosphere, are observed, likely driven by convective magnetic field fluctuations, contributing to coronal heating.
- Alfvén waves, generated by convective motions, also propagate into the corona, potentially contributing to coronal heating, although the precise mechanism remains under investigation.
The Solar Dynamics Observatory and Hinode have given us clearer-than-ever observations that show rapid heating events like fast jets of hot material triggered in or just above the chromosphere. The convection within the Sun generates small but violent changes to the magnetic field, which then create these jets. We see in these jets some portion of the hot plasma that fills the coronal loops — one component of the coronal heater.
Another likely component of the heater comes in the form of magnetic (or Alfvén) waves. The convective motions also generate these waves, which “ride” on the same hot jets and roar into the corona at even higher speeds. The Alfvén waves likely dump their energy in the corona, too, but the means by which that happens is a topic of great debate. So, we still don’t know exactly why the Sun’s corona is hot, but we are finding some of the components of the system. This helps us considerably in trying to understand how the complete coronal heater works.
National Center for Atmospheric Research,
Boulder, Colorado