# PX420 Solar Magnetohydrodynamics

## Weighting: 7.5 CATS

Our knowledge of what is happening in the sun is increasing rapidly, largely as a result of space-based instrumentation. The challenge now is to understand it. The basic process is simple: Heat moves outwards from its source at the centre (nuclear fusion). However, on its way out, this energy drives many processes on many different length scales many of which are not at all well understood. For example, there is still no convincing theory of how the sun's magnetic field is generated and how the atmosphere is heated.

This module starts by stating the basic properties of the sun as deduced from observation and general physical principles, and introduces a hydrodynamic model of the sun. This treats the solar matter as a fluid. There are the usual gravitational and pressure gradient forces governing the fluid motion but, because the constituent particles of the fluid are charged, there are also electromagnetic forces. As a result, we need to worry about Maxwell's equations as well as Newton's laws. The module then discusses applications of this theory, called magnetohydrodynamics, to model and understand phenomena like sunspots, coronal loops, prominences, solar flares, coronal mass ejections and space weather.

Aims:
To review the basic physics underlying the structure and the dynamics of the sun, to provide a background in the description of physical processes in the Sun in terms of magnetohydrodynamics and to show the results of recent observations.

Objectives:
At the end of this module you should:

• Know the structure of the Sun and the main features and phenomena observed on the solar surface and in the solar atmosphere
• Understand the basic physical processes at work in the sun
• Be able to describe the basic dynamic processes operating in the Sun, in terms of MHD

Syllabus:

1. An outline of observational properties ranging from the solar interior ot the Sun's outer atmosphere
2. Theoretical aspects of solar magnetohydrodynamics (MHD)
3. Magnetic equilibria. Stratification. Force-free magnetic fields. Magnetic arcades, prominences, suspots, intense flux tubes.
4. MHD Waves. Helioseismology.
5. Solar flares. Heating of the solar corona. Coronal mass ejections and space weather.

Commitment: 15 Lectures

Assessment: 1.5 hour examination

The module has a website.

Recommended Texts:
ER Priest, Solar Magnetohydrodynamics, Dordrecht ;
L Golub and JM Pasachoff,Nearest Star: The Surprising Science of Our Sun, Harvard Univ. press

Leads from: PX264 Physics of Fluids and PX392 Plasma Electrodynamics