Solar Physics

The subsurface structure of a sunspot as derived from SOHO/MDI data (credit: SOHO/ MDI consortium).

The Sun's atmosphere is a violent, chaotic place, threaded with ropes of twisted magnetic field that build up stress and cause vast explosions more powerful than any man-made bomb. Direct measurements of the magnetic field are impossible, so scientists resort to complex computer models to explore it. Atoms as we know them cannot survive in the Sun’s atmosphere, called the corona, where temperatures can exceed 2 million degrees Celsius. Instead they are stripped of their electrons to become plasma.

The positively and negatively-charged particles of the plasma spiral along the magnetic field and move with it, like children on a helter-skelter. But large-scale movements of the plasma can also move the magnetic field, equivalent to the children moving the helter-skelter whilst sliding down it. Emerging from the Sun’s surface, called the photosphere, are many ropes of magnetic field that turn into and away from the Sun. Large clumps of plasma move about on the surface, dragging and stretching the magnetic field as plasma travels from the equator towards the poles.

Helioseismology is the study of the structure and dynamics of the Sun’s interior through the observation of oscillations on the visible solar surface (the photosphere). Such oscillations are produced by acoustic (p-mode) waves generated at the top of the solar convection zone. By analyzing the spectrum of these oscillations, helioseismologists are able to measure the sound speed, density, and bulk velocity in the interior of the Sun as a function of depth and can determine the departures of these quantities from spherical symmetry. The sound speed is now known to about one part in 104 through most of the solar interior.

Observation: 
Theory & Computation: